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  • The tensile behaviors of vanadium-containing 25Cr-20Ni austenitic stainless steel at temperature between 200 ℃ ℃ and 900 °C
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-20
    Guodong Hu, Pei Wang, Dianzhong Li, Yiyi Li

    The high-temperature tensile behaviors of two 25Cr-20Ni austenitic stainless steels with different V concentration (0 wt. % V and 0.3 wt. % V, respectively), have been studied at temperature between 200 ℃ ℃ and 900 ℃ ℃ . The ultimate tensile strength of both steels is strong temperature dependent, which decreases slowly first at 200–300 ℃ ℃ , keeps platform then at 300–500 ℃ ℃ and decreases rapidly afterwards from 600 ℃ ℃ to 900 ℃ ℃ . It is caused by the decreasing strain hardening ability, dynamic strain aging and dynamic recovery together with dynamic recrystallization at different temperatures. At higher than 800 ℃ ℃ , the elongation of both steels increases markedly due to the dynamic recovery and dynamic recrystallization. However, because of the deteriorated effects of M23C6 precipitates at grain boundary, the elongation of both steels at 700 ℃ ℃ does not increase despite decreasing strength. Additionally, the addition of 0.3 wt. % V decreases the ductility of the material in the temperature range of 800 ℃ ℃ to 900 ℃ ℃ , which is induced by the impeding effects of solute vanadium on dynamic recovery and recrystallization.

    更新日期:2017-11-20
  • Microstructure and mechanical properties of a heat-treatable Al-3.5Cu-1.5Mg-1Si alloy produced by selective laser melting
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-20
    Pei Wang, Christoph Gammer, Florian Brenne, Konda Gokuldoss Prashanth, Rafael Gregorio Mendes, Mark Hermann Rümmeli, Thomas Gemming, Jürgen Eckert, Sergio Scudino

    A heat-treatable Al-3.5Cu-1.5Mg-1Si alloy is successfully fabricated by selective laser melting and is investigated concerning microstructures and mechanical properties. The as-prepared samples show a fine-granular microstructure in the individual melt pool of the tracks and a coarse-granular microstructure in the areas between the tracks. After T6 heat treatment, the grain size of the specimens increases slightly and the Q phase formed in the as-prepared specimens transforms to Al2Cu(Mg), Mg2Si, and AlxMny. All Al-Cu-Mg-Si specimens before and after heat treatment fracture around the defects that were generated during processing and show intergranular fracture along columnar grains upon tensile quasi-static loading. The as-fabricated samples exhibit a yield strength (YS) of 223 ± 4 MPa and an ultimate tensile strength (UTS) of 366 ± 7 MPa with an elongation of 5.3 ± 0.3%. After T6 heat treatment, the YS and UTS increase dramatically to 368 ± 6 MPa and 455 ± 10 MPa due to the formation of nano-sized Al2Cu(Mg) precipitates, respectively, while the ductility remain fairly similar.

    更新日期:2017-11-20
  • Precipitate Strengthening and Thermal Stability in Three Component Metallic Nanolaminate Thin Films
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-20
    R.L. Schoeppner, A.A. Taylor, M.J. Cordill, H.M. Zbib, J. Michler, D.F. Bahr

    Cu/Ni/Nb tri-layer and CuNi/Nb alloy multilayer films were annealed to examine the microstructural evolution and mechanical properties of three component laminated metallic nanostructures. Scanning transmission electron microscopy showed NixNby compounds forming on either side of the Nb layer in both tri-layer and alloy films. Post annealing nanoindentation showed all annealing conditions resulted in increased hardness, indicative of the NixNby intermetallic phase increasing the hardness of the films. The hardness of both films achieves a maximum hardness after annealing for 3 hours at 300 °C. The hardness increase as the annealing temperature increases corresponds to a thicker NixNby layer at the incoherent boundary. This strengthening technique could be implemented in a variety of different multilayer systems to achieve age-hardenable multilayer metallic nanostructures.

    更新日期:2017-11-20
  • Effect of hot cross rolling on the microstructure and mechanical properties of an Fe-14Cr ODS ferritic steel
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-20
    J. Macías-Delgado, T. Leguey, V. de Castro

    Oxide dispersion strengthened (ODS) reduced activation ferritic steels are leading candidates to become part of the structure of the first wall/blanket of future fusion reactors. Their major drawback is their poor toughness, which must be improved. In this work, an ODS ferritic steel having nominal composition Fe–14Cr–2W–0.2Ti–0.55 Fe2Y (wt.%), produced by mechanical alloying of prealloyed powders with Fe2Y intermetallic particles and consolidated by hot isostatic pressing, was subjected to either thermal treatments at high temperature or hot cross rolling in an attempt to investigate the effectiveness of such post-consolidation thermomechanical treatments. Its microstructure, nanoparticle dispersion and mechanical properties were analysed and correlated on each condition. As compared with the annealing treatments hot cross rolling led to a significant decrease in the grain size as well as a slight decrease in the size of some of the secondary phases present in the material. Also, the impact and tensile behaviour was improved over the whole temperature range studied.

    更新日期:2017-11-20
  • Misorientation, grain boundary, texture and recrystallization study in ×90 hot bend related to mechanical properties
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-20
    Liang Wang, Bin Wang, Peishan Zhou

    In the present study, electron backscattering diffraction (EBSD) was used to study the relationship between misorientation, grain boundary, texture, recrystallization and the mechanical properties for API (American Petroleum Institute) ×90 hot induction bend. The experimental results show that the yield strength of the parent pipe is 748 MPa, while it reduced about 40 MPa after hot induction bending. The strength in the inner arc side is similar along the longitudinal and transverse direction, but it is anisotropic in the outer arc side. The texture of {113} <110> components and {112} <110> components are the main reason for anisotropy. After hot induction bending, the deformed and elongated grains exist in the bend zone of ×90 bend, and the sub-grain boundaries exist in the grains. The grains in the neutral axis are equiaxed and without lath-like structure and sub-structure. A large fraction of lath bainite (LB) boundaries and Σ3 boundaries in the outer arc side resulted in a high strength and low impact toughness. Moreover, the deformed region and the recrystallization region have the same tendency for the tested specimens, the neutral axis of ×90 bend has a lower stored energy in the grains that could resist the cracks propagation effectively.

    更新日期:2017-11-20
  • Vacancy effects on the mechanical behavior of B2-FeAl intermetallics
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-20
    M. Zamanzade, G. Hasemann, C. Motz, M. Krüger, A. Barnoush

    The present work addresses the impact of quenched-in thermal vacancies on the mechanical properties of B2 iron aluminides. For this reason different binary Fe-Al alloys with different histories of heat treatment were indented at room temperature. The contributions of mono- and bi-vacancies in addition to triple defects on the elastic, plastic and elastic-plastic transition were evaluated using nanoindentation technique. In the samples containing bi-vacancies, the increase of the hardness was much more pronounced compared to the mono-vacancies.

    更新日期:2017-11-20
  • On the Strain Rate Sensitivity of Aluminum-containing Transformation-Induced Plasticity Steels: Interplay between TRIP and TWIP Effects
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-20
    K. Li, Y.S.Y. Injetti, R.D.K. Misra, Z.H. Cai, H. Ding

    The primary objective of the study is to elucidate the effect of strain rate on the deformation behavior of Al-containing transformation-induced plasticity steels (TRIP) via combination of depth-sensing nanoindentation experiments and post-mortem analyses of deformed steels using transmission electron microscopy (TEM). The strain rate sensitivity decreased with increased Al-content. The activation volume of 2Al-steel was ~ half (6 b3) of 6Al-steel (11 b3), where b is the magnitude of the Burgers vector. The strain rate influenced the evolution of strain-induced martensite (TRIP effect), dislocation slip and deformation twinning (TWIP effect). The interplay between TRIP and TWIP effects as a function of strain rate is analyzed and discussed in terms of the three internal energies, namely γ→α (austenite→martensite) transformation Gibbs free energy, strain energy and stacking fault energy. These were impacted by the Al-content of the steels, which altered the austenite stability and propensity to deformation twinning. The study provides insights into the design of next generation of TRIP steels for the fabrication of automotive components.

    更新日期:2017-11-20
  • Creep properties, creep deformation behavior, and microstructural evolution of 9Cr-3W-3Co-1CuVNbB martensite ferritic steel
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-17
    Bo Xiao, Lianyong Xu, Lei Zhao, Hongyang Jing, Yongdian Han, Yu Zhang

    Creep deformation behavior and microstructure evolution of G115 steel were systematically investigated for temperatures of 625–675 °C under uniaxial tensile stress of 120–220 MPa. The relationship between minimum creep rate and applied stress followed the Bird–Mukherjee–Dorn (BMD) equation. The modified BMD equation was proposed using threshold stress to elucidate the actual creep deformation mechanism. The values of the threshold stress were determined to be 177.8, 91.4 and 87.6 MPa at 625, 650, and 675 °C, respectively. The true creep activation energy and the true stress exponent were 275.76 kJ/mol and 6, respectively. Thus, the dominant creep deformation mechanism was identified as dislocation climb. Three types of precipitates can be revealed after creep deformation: W-rich Laves, Nb-rich MX, and Cu-rich phases. The creep damage of G115 steel after creep deformation was characterized by martensite cracks and martensite fractures owing to the hardness and brittleness of the lath martensite structure. Further, a dense array of deep and equiaxed dimples appeared in the central region of fracture surfaces under the tested creep conditions. Ductile fracturing was the main fracture mechanism during creep deformation.

    更新日期:2017-11-20
  • Microstructure Evolution and Enhanced Mechanical Properties in SUS316LN Steel Processed by High Pressure Torsion at Room Temperature
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-17
    Shouwen Shi, Zhe Zhang, Xiaobin Wang, Gaobin Zhou, Guofu Xie, Da Wang, Xu Chen, Kei Ameyama

    Nowadays, it is of interest to enhance the strength of metals for light-weight design of nuclear reactor, so the objective of the present study is to improve the mechanical properties of SUS316LN steel through grain refinement. The nanostructured SUS316LN steels were produced by high pressure torsion (HPT) at room temperature. The variations of microstructure and strain-induced martensite transformation during HPT were investigated. The homogeneous nanostructured SUS316LN steel with an average grain size of approximately 40 nm was achieved by HPT for 5 revolutions under a pressure of 5 GPa, which demonstrated extremely high tensile strength (1828MPa) and high hardness (530HV). The interstitial nitrogen atoms can reduce the stacking fault energy of the material and also play an important role in interaction with mobile dislocations during HPT. Therefore, compared to SUS316L steel, the formation of the nanograined structure was much faster and the strain-induced martensite transformation was restrained in the HPT-produced SUS316LN steel.

    更新日期:2017-11-20
  • Basic creep modelling of aluminium
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-16
    S. Spigarelli, R. Sandström

    In recent years a basic creep model that does not involve adjustable parameters has been developed. The main feature of this model is that it is fully predictable and the assumptions at its basis can be easily verified once the output is compared with experimental data. This model, initially developed for pure copper, has been here applied to pure aluminium. A critical issue has been identified with the controlling mechanisms during power-law breakdown. The increase in the creep rate at high stresses and low temperatures can be quantitatively explained from the raised climb rate due to the deformation-induced increase in concentration of vacancies. The model can also account for the fairly wide range of stresses where aluminium follows power-law creep with a creep exponent of 4 to 5. At $L̫VxnLE$L̫Vxnhe creep exponent increases somewhat due to the presence of an internal stress. Since no adjustable parameters have been required, the model represents a notable enhancement over the conventional approach, which is based on the use of the power-law equation and requires fitting of experimental data to determine the values of the material parameters.

    更新日期:2017-11-20
  • Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-16
    G.J. Lyu, J.C. Qiao, J.M. Pelletier, Y. Yao

    In the current study, Zr-based metallic glass matrix composites (MGMCs) were prepared by doping high-melting point of tantalum powders and investigated by dynamic mechanical analysis. The results suggest that the relaxation processes are changed by modifying the chemical composition. The influence of crystalline phase on the dynamic mechanical response of Zr-based MGMC has been analyzed. The master curves of loss modulus can be well fitted by the Kholrausch-Williams-Watts (KWW) model, decreasing of the parameter βKWW β KWW implies that the Zr-based MGMC doped with more tantalum powders has higher dynamic heterogeneity. To better understand the dynamic mechanical properties of the MGMCs, quasi-point defects (QPD) theory is adopted, the kinetic characteristics of glass transition of Zr-based MGMCs are analyzed in a quantitative manner. The experimental results provide an insightful information on the complex structural relaxation of the metallic glass matrix composite.

更新日期:2017-11-20
  • High strength, ductility, and electrical conductivity of in-situ consolidated nanocrystalline Cu-1%Nb
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-16
    Khaled M. Youssef, Mohamed A. Abaza, Ronald O. Scattergood, Carl. C. Koch

    Nanocrystalline metals—with grain sizes less than 100 nm— have strengths exceeding those of coarse-grained and even alloyed metals 1 ; 2. A bulk nanocrystalline Cu-1%Nb alloy was synthesized by an in-situ consolidation mechanical alloying technique. The mechanical behavior of this alloy was investigated by hardness and tensile tests. The nanostructure was investigated by X-ray diffraction and transmission electron microscopy and the fracture surface by scanning electron microscopy. Electrical resistivity was measured using a four-point probe technique. The dilute additives of Nb and the processing conditions induced artifact-free bulk nanocrystalline materials that possess extraordinary high strength, good ductility, and high electrical conductivity.

    更新日期:2017-11-20
  • Effect of Sn element on the formation of LPSO phase and mechanical properties of Mg-6Y-2Zn alloy
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-16
    Junjie Gao, Yu’an Chen, Yi Wang

    The long period stacking ordered (LPSO) phase is a key strengthening precipitate phase in the Mg-Y-Zn based alloys. Fully controlled by the chemical ordering and stacking faults, the LPSO phase could be strongly modified by alloying elements. This work explored the effect of trace Sn addition on the Mg-6Y-2Zn alloy, with an emphasis on the LPSO phase and corresponding changes of mechanical properties in the as-cast, as-annealed and as-extruded states. Results show that the 18R LPSO phase forms as needles and distributes at grain boundaries. Meanwhile, its length and density are stimulated dramatically by the Sn addition in the as-cast state. After annealing, the content of the 18R increases accompanied by the change of morphology shapes from needle to block. Additionally, fine 14H LPSO lamellas are precipitated both in grains and between 18R phases. In contrast to the as-annealed Sn-free alloy, the area fraction of 18R phase in the Sn-containing Mg alloy increases from 35% to 58%, the 14H is also promoted to a certain extent. Tensile tests conducted on as-extruded state revealed remarkable mechanical properties improvement in the Sn-containing alloy over its ternary equivalents. The relevant mechanisms are also investigated in detail.

    更新日期:2017-11-20
  • Friction-stir welding of a ductile high entropy alloy: microstructural evolution and weld strength
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-16
    Z.G. Zhu, Y.F. Sun, F.L. Ng, M.H. Goh, P.K. Liaw, H. Fujii, Q.B. Nguyen, Y. Xu, C.H. Shek, S.M.L. Nai, J. Wei

    High entropy alloys (HEAs) are a novel subset of metallic systems with complex compositions usually yielding simple phase formation. To verify their potential engineering applications, a novel Co16Fe28Ni28Cr28 HEA with a low content of expensive Co was developed and its welding characteristics through friction-stir welding (FSW) were investigated. The HEA shows a stable face-centered-cubic (FCC) structure with an excellent ductility of about 70%. The microstructural evolution during FSW was dominated by discontinuous recrystallization through grain bulging and the B/ View the MathML source B ¯ {112}<110> shear texture formed in the stir zone (SZ). A white band (WB) containing W-rich and Cr-rich phases was detected in the SZ. The WB exhibited refined grains compared with the normal SZ, which may be associated with the particle-stimulated nucleation (PSN). The present understanding of the microstructural evolution during FSW of HEAs may help tailor the weld properties to pave the way for their engineering applications.

    更新日期:2017-11-20
  • Manufacturing of Cu-based Metallic Glasses Matrix Composites by Spark Plasma Sintering
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-15
    S. Cardinal, J.M. Pelletier, G.Q. Xie, F. Mercier

    A preliminary study has shown that bulk metallic glasses of the CuZrAl type of large dimension may be manufactured from amorphous powders densified by a process of sintering such as spark plasma sintering (SPS). However, to remedy the lack of plasticity of these materials, the addition of ductile crystalline particles was carried out in the present study. The zirconium was chosen because its properties are close to those of the amorphous matrix. The same sintering parameters as those optimized for the metallic glass are also applicable for the production of the composite for the different zirconium volume fractions retained, respectively 5, 10, 20, 30, 40 and 50%. The materials obtained are dense. X-ray diffraction clearly indicates that only the amorphous matrix CuZrAl and the crystalline zirconium are present. Young's modulus as well as the elastic limit decrease only very slightly with the addition of crystalline particles. Decrease in hardness is more pronounced. On the other hand, the plastic deformation increases with the addition of zirconium, reaching about 4.9% for the alloy containing 50% zirconium. The analysis of the fracture surfaces clearly shows the role of the ductile crystalline particles, namely the deceleration of the shear bands. The influence of volume fraction and size of the crystalline particles and of matrix toughness is discussed from a mechanical point of view. Therefore, SPS is a solution to solve both the problem of size and low ductility of amorphous metal, since it is possible to control microstructure and so to control mechanical properties.

    更新日期:2017-11-17
  • Effects of high silicon contents on graphite morphology and room temperature mechanical properties of as-cast ferritic ductile cast irons. Part I – Microstructure
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-15
    Rodolfo González-Martínez, Urko de la Torre, Jacques Lacaze, Jon Sertucha

    Studying a series of near eutectic spheroidal graphite cast irons with various amounts of silicon up to 9.12 wt.% confirmed that: 1. silicon stabilizes ferrite to such an extent that ferrite is the Fe-rich phase appearing during solidification at the highest silicon contents; 2. silicon triggers graphite degeneracy such as chunky graphite. As well-known, cerium and magnesium do also increase the risk of chunky graphite formation while antimony counteracts cerium. Based on the metallographic observations of the present work, an index is proposed to evaluate the risk of chunky graphite appearance from the silicon, magnesium, cerium and antimony contents. Above a critical value of this index, the risk for chunky graphite formation increases steadily. Using data from previous studies, it is further demonstrated that the critical value decreases with increase in casting modulus as expected. The evolution of mechanical properties of the prepared cast irons will be presented in a second part of this study.

    更新日期:2017-11-17
  • Effects of initial microstructures on hot tensile deformation behaviors and fracture characteristics of Ti-6Al-4V alloy
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-14
    Y.C. Lin, Xing-You Jiang, Ci-jun Shuai, Chun-Yang Zhao, Dao-Guang He, Ming-Song Chen, Chao Chen

    The effects of heat treatment processing on the microstructures of Ti-6Al-4V alloy are systematically studied. Static globularization behavior of lamellar α phase is found when the alloy is cooled in air or furnace from 950–960 °C (below the β-transus temperature, about 975 °C). Three kinds of microstructures (basket-weave, globular-lamellar, and equiaxed microstructures) are obtained by different heat treatments. The uniaxial tensile tests of the studied alloy with different initial microstructures are conducted at the elevated temperature and different strain rates. It is found that the initial microstructures have obvious effects on the tensile properties and fracture mechanisms. The alloy with basket-weave microstructures exhibits the most obvious work hardening behavior and the highest strength. The alloy with globular-lamellar microstructures has the better ductility than that with basket-weave microstructures. Furthermore, the alloy with equiaxed microstructures has the best ductility, because the equiaxed α phases can delay the formation and coalescence of microvoids. Meanwhile, α phases are elongated, bent and spherized, which contributes to the flow softening during tensile deformation. Especially, the alloy with initial equiaxed microstructures finally transforms to bimodal microstructures after tensile fracture. Additionally, the alloys with three different initial microstructures all show a primary ductile fracture.

    更新日期:2017-11-15
  • Improved microstructural homogeneity and mechanical property of medium manganese steel with Mn segregation banding by alternating lath matrix
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-14
    Juhua Liang, Zhengzhi Zhao, Di Tang, Nan Ye, Shufeng Yang, Weining Liu

    The influence of Mn segregation banding on the microstructure homogeneity and mechanical property of medium manganese system steels with both equiaxed and lath-like microstructures has been investigated by adding the pre-quenching treatment before the intercritical austenitization and subsequent quenching & partitioning process (IQP). Both the crack observation and KAM characterization in these two types of microstructure intuitively indicate different micro-cracking resistance and in-grain strain accommodation of intercritical ferrite during the deformation. The excessive inhomogeneous microstructure and blocky retained austenite with low stability accelerate the failure of the material with Mn segregation banding. The fine lath-like ferrites with great contact ratio to the surrounding martensites improve the microstructural homogeneity under pre-quenching process. The alternative arrangement of lath-like soft ferrite and hard martensite results in optimal mechanical properties of material with Mn segregation banding.

    更新日期:2017-11-15
  • Microstructure and flow stress evolution during hot deformation of 304L austenitic stainless steel in variable thermomechanical conditions
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-14
    K. Huang, R.E. Logé

    Most of industrial hot deformation processes are performed in variable conditions where the strain rate and/or deformation temperature are not constant. In this work, hot compression tests in both constant and varying strain rate conditions were performed on 304 L austenitic stainless steel using a Gleeble 3800 machine. The variations in microstructure and flow stress during and after the transient deformation stage are carefully analysed. It is clearly shown that, following the abrupt increase of strain rate, both the flow stress and substructural changes are subjected to a transient period over strains of ~0.2, before reaching states similar to those developed through constant strain rate conditions at the new strain rate. When the strain rate was rapidly decreased, the flow stress transient stage extended over a lower strain interval than the substructure transient period. It is shown that local misorientation distributions are good indicators of the deformation microstructure of low SFE materials as they capture small variations in deformation structures which cannot be analysed from stress-strain curves alone.

    更新日期:2017-11-15
  • Effect of minor additions on the microstructures and stress rupture properties of a directionally solidified Ni-based superalloy
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-14
    H.W. Zhang, X.Z. Qin, X.W. Li, L.Z. Zhou

    The effects of C, Zr and Y/Ce on the microstructures and stress rupture properties of a directionally solidified Ni-based superalloys were investigated. The morphology of MC carbides does not change in as-cast alloys, as the C content is increased or the Zr is added. However, the Y/Ce additions promote the transformation of MC carbide morphology from blocky to script-like type. Compared with that in as-cast alloys, there is no obvious change in the morphologies of MC carbide or chemical compositions after heat treatment. The increasing of C content and the addition of Zr or Y/Ce significantly decreases and increases the amount of the γ/γ′ eutectic, respectively. After a solid solution treatment and subsequently a two-stage aging treatment, the γ′ phase is characteristic with two kinds of shapes and sizes, and the volume fraction of cuboidal γ′ phase is much larger than that of spherical γ′ phases. More MC carbide and residual eutectic result from the decreasing of cuboidal γ′ phase volume fraction. The decrease in volume fraction of cuboidal γ′ phase is principally responsible for the reduction of the stress rupture property. In addition, script-like carbide and residual eutectic remaining after heat treatment play the secondary role in the degradation of the stress rupture properties. The less regularly arranged cuboidal γ′ phase can damage the stress rupture life to some extent. The spherical γ′ phase re-dissolves into γ′ matrix widening the spacing between large cuboidal γ′ phase, and the addition of Zr inhibits grain boundary sliding and cracking; these two facts are beneficial to the rupture elongation.

    更新日期:2017-11-15
  • Crystallographic texture and lattice strain evolution during tensile load of swaged brass
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-14
    Nowfal Al-Hamdany, Heinz-Günter Brokmeier, Weimin. Gan

    Evolutions of texture and lattice strain of swaged brass samples were investigated by neutron diffraction at STRESS-SPEC under tensile deformation using a unique tension/compression rig. The two phased sample BS1 (61% α-brass and 39% β-brass) became 100% α-brass after 400 °C annealing (sample BS2). The starting texture of the as-received material BS1 was the typical <111>, <200> double fiber. This texture develops firstly by in-situ tension to a moderate strengthening. After annealing (BS2) the <111> fiber survives with surprisingly high strength and develops by in-situ tension a very strong <111> fiber of 39 mrd. Line broadening and lattice strain behaviour shows the development of the elastic strain and plastic strain.

    更新日期:2017-11-15
  • Improving hydrogen embrittlement resistance of Hadfield steel by thermo-mechanical flash-treatment
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-13
    Mahmoud Khedr, Wei Li, Xu Zhu, Pengwei Zhou, Shan Gao, Xuejun Jin

    Nano-twins microstructures were introduced in a high carbon manganese steel by a novel flash thermo-mechanical treatment in order to achieve high resistance to hydrogen embrittlement. Nano-twinned grains decreased hydrogen diffusivity through the bulk material, although it absorbed more hydrogen than the twins-free specimens. Moreover, it was shown that after electrochemical hydrogen charging, the nano-twins microstructures can reduce dislocations glide during plastic deformation, resulting in forming of fine twin plates.

    更新日期:2017-11-14
  • Ultra-high strengthening efficiency of graphene nanoplatelets reinforced magnesium matrix composites
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-13
    Xian Du, Wenbo Du, Zhaohui Wang, Ke Liu, Shubo Li

    Homogeneous magnesium alloy (ZK60) reinforced by low content of graphene nanoplatelets (GNPs) was fabricated by facile melt stirring and hot extrusion processes with cost effectiveness. GNPs were pre-dispersed with Mg powder and extruded into rods used as precursor for melting, which effectively guaranteed the integrity and dispersion of GNPs. In composites, GNPs closely combined with the magnesium matrix in nanoscale. Compared with ZK60 alloy, the composite with only 0.05 wt.% GNPs can perform 62% enhancement in yield strength up to 256 MPa, exhibiting an ultra-high strengthening efficiency of 1550. Based on theoretical analysis, load transfer of GNPs contributed most (~72%) to the strength improvement of GNP/ZK60 composite, due to the 2D interfacial contacting and continuous combination of GNPs with matrix. This study explored the strengthening potential and mechanism of GNPs in metal matrix composites with insight of scale-up fabrication.

    更新日期:2017-11-14
  • Spark plasma sintering of a commercial TiAl 48-2-2 powder: densification and creep analysis
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-13
    David Martins, Fanny Grumbach, Audrey Simoulin, Pierre Sallot, Katia Mocellin, Michel Bellet, Claude Estournès

    Commercial 48-2-2 TiAl powder was densified by spark plasma sintering. Fully dense materials with duplex and lamellar microstructures were obtained. An original protocol was developed to avoid carbide formation due to reactions between TiAl and graphite molds. TiAl materials with lamellar microstructures and high creep behavior were produced.

    更新日期:2017-11-14
  • Tailoring microstructure, tensile properties and fracture process via transient directional solidification of Zn-Sn alloys
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-13
    Washington L.R. Santos, Clarissa B. Cruz, José E. Spinelli, Noé Cheung, Amauri Garcia

    The aim of the present study is to determine interrelations of microstructure length-scale, tensile properties and fracture mechanisms of hypoeutectic Zn-Sn alloys. Three compositions were subjected to transient directional solidification: Zn-10, 20 and 40 wt.%Sn. Grainy-faceted cleavage has been observed as the predominant mode of fracture, which propagated across the Zn-rich plate cells. A clear influence of the formed microstructure and proportion of eutectic may be noted in the fracture features, with alveolar structures also appearing in fracture surfaces. Growth laws relating the eutectic spacing with the growth rate are proposed, which are able to encompass both steady-state and transient solidification conditions. Hall-Petch type equations are developed relating the yield and ultimate tensile strengths, σy and σu, respectively, to the cellular spacing, λ, in which smaller λ values resulted in higher σy and σu..

    更新日期:2017-11-14
  • Multiple strengthening sources and adiabatic shear banding during high strain-rate deformation of AISI 321 austenitic stainless steel: effects of grain size and strain rate
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-13
    A.A. Tiamiyu, A.G. Odeshi, J.A. Szpunar

    The dynamic impact response of AISI 321 steel at strain rate of 4000, 5500, 6500 and 7500 s−1 was investigated using the split Hopkinson pressure bar system. The alloy samples processed to have grain size of 0.24, 3, 13 and 34 µm were studied. While the yield strength and hardness increases with decrease in grain size, strain hardening rate is comparable for all grain sizes. Microstructural evaluation of the impacted specimens using high-resolution electron backscattered diffraction (HR-EBSD) technique showed grain boundary strengthening, deformation twinning, deformation-induced martensitic transformation, dislocation multiplication during slip and precipitation of carbides that act as barriers to dislocation motion as additional source of strengthening. Slip and twinning were the dominant deformation mechanisms observed in the steel. Twinning, dislocation multiplication during slip and carbide precipitation contributed more strongly to strain-hardening in coarse-grained (CG) specimen while stain-induced martensite and grain boundary strengthening are the most beneficial to strengthening in the ultra-fine-grained (UFG) specimens. The temperature rise in the specimens during impact increases with strain rate. This slowed the kinetics of twinning, phase transformation and dislocation interaction especially in CG structure. Both XRD and HR-EBSD texture results confirmed the development of {110}||CD (CD: compression direction) texture in the austenite phase at the expense of {100}||CD and {111}||CD fibres. Thermomechanical instability leading to the formation of adiabatic shear band (ASB) occurred in the test specimens as they deformed at high strain rates. While the amount of deformation twinning and αʹ-martensite decreases towards the ASB, only the carbides and small fraction of αʹ-martensite are observed inside the ASB. Grain refinement via rotational dynamic recrystallization occurred within the ASB. The extent of grain refinement increased with increase in initial grain size of the test specimen.

    更新日期:2017-11-14
  • Effects of solutioning and ageing treatments on properties of Inconel-713C nickel-based superalloy under creep loading
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-13
    Mahboobeh Azadi, Armin Marbout, Sama Safarloo, Mohammad Azadi, Mehdi Shariat, Mohammad Hassan Rizi

    As nickel-based superalloys have been widely used in turbine blades of turbo-chargers in automobile industries, this article has presented the creep behavior of the Inconel-713C nickel-based superalloy. For this objective, forced-controlled creep testing has been performed at the temperature of 850 °C and under the stress of 585.5 MPa. Then, the effect of the solutioning process on creep (time-dependent) properties of the superalloy was investigated. Optical and scanning electron microscopies were utilized to study the material microstructure, before and after creep testing. The X-ray diffraction (XRD) spectrometry was also used to detect different phases in the superalloy. Results showed that solutioning at 1200 °C for 1 h had a lowering effect on the creep rupture time of the Inconel-713C superalloy, as the mean size of the γ’ particles crystallite was about 6.8 nm. When the superalloy was aged for 16 h at 930 °C, an insignificant effect with respect to the as-cast sample could be observed, due to the precipitation of NbC carbides (at grain boundaries) and the coarsening behavior of γ’ particles. Consequently, different microstructures led to different creep fracture mechanisms for this alloy. The decomposition of MC carbides to M23C6 was also observed for all samples after creep testing.

    更新日期:2017-11-14
  • Effect of tempering on microstructure and mechanical properties of 3Mn-Si-Ni martensitic steel
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-12
    Yan-jun Zhao, Xue-ping Ren, Zhi-liu Hu, Zhi-ping Xiong, Jian-min Zeng, Bao-yu Hou

    The dependence of microstructures and mechanical properties on tempering temperature (from 180 to 650 °C) in a designed 3Mn-Si-Ni martensitic steel was systematically analyzed. Microstructure was characterized using scanning and transmission electron microscopy; mechanical properties were measured using uniaxial tensile test and Charpy V-notch impact test. After tempering at different temperatures, recovery, partial recrystallization, carbides precipitation and decomposition of residual austenite were observed. After tempering at 230°C, an excellent combination of strength (1550 MPa) and toughness (91.5 J) was achieved, due to high dislocation density and ε-carbides precipitation. However, with an increase in tempering temperature from 320 to 550°C, tempered martensite embrittlement was observed, where impact energy was ~ 10 J. It was ascribed to cementite formation instead of transition carbides and decomposition of residual austenite. With an increase in tempering temperature up to 650°C, high fracture impact toughness of 75 J was obtained with deteriorated tensile strength of 850 MPa due to strong recovery and partial recrystallization.

    更新日期:2017-11-13
  • Microstructural Evolution of Adiabatic Shear Bands in Pure Copper during Impact at High Strain Rates
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-11
    Solomon Boakye-Yiadom, Nabil Bassim

    A systematic study was conducted on copper of commercial purity (99.9% purity) to elucidate the sequence of events that leads to the evolution of adiabatic shear bands and the structure of the evolved shear bands after strain localization during deformation at high strain rates and large strains. A direct impact Hopkinson Pressure Bar was used to deform different specimens at increasing impact momentum and strain rate followed by microstructural characterization using metallographic techniques and transmission electron microscopy. It was observed that sequential occurrence of emergence of dislocations from grain and twin boundaries, formation of dislocation cell structures and substructures with varying cell sizes and cell walls, dislocation-nucleation controlled softening and extensive micro twinning characterized the structure of the evolved adiabatic shear bands as a function of impact momentum and strain rate. The dislocation cell structures and substructures were typically made up of high-density dislocation walls surrounding low-density dislocation cell interiors. The microhardness distribution within the evolved shear bands increased up to a peak value at a critical impact momentum and strain rate (≥ 45 kg m/s and ≥6827 s-1). Above this threshold, microhardness of the regions within the evolved shear bands decreased because of the occurrence of softening. However, the first specimen that exhibited softening had high-density dislocation cell walls surrounding dislocation-free cell interiors with no observed recrystallized grains. Despite the onset of softening both within and outside the shear bands, the regions within the shear bands were always harder than the regions outside the shear bands. The shear bands that exhibited significant softening were clad with vast distribution of microtwins in addition to evolved refined grains and sub-grains. It is discussed that thermally activated dislocation processes as a result of the rise in temperature during impact, dynamic recovery and dynamic recrystallization do not necessarily result in strain localization in the impacted copper specimens because their effects are observed in the structure of the evolved shear bands at a latter stage when strain localization had already occurred.

    更新日期:2017-11-13
  • Spall damage of a Ta particle-reinforced metallic glass matrix composite under high strain rate loading
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-11
    X.C. Tang, W.R. Jian, J.Y. Huang, F. Zhao, C. Li, X.H. Xiao, X.H. Yao, S.N. Luo

    We investigate deformation and damage of a Zr-based bulk metallic glass (BMG) and its Ta particle-reinforced composite (MGMC) under impact loading, as well as quasi-static tension for comparison. Yield strength, spall strength, and damage accumulation rate are obtained from free-surface velocity histories, and MGMC appears to be more damage-resistant. Scanning electron microscopy, electron back scattering diffraction and x-ray computed tomography, are utilized for characterizing microstructures, which show features consistent with macroscopic measurements. Different damage and fracture modes are observed for BMG and MGMC. Multiple well-defined spall planes are observed in BMG, while isolated and scattered cracking around reinforced particles dominates fracture of MGMC. Particle–matrix interface serves as the source and barrier to crack nucleation and propagation under both quasi-static and impact loading. Deformation twinning and grain refinement play a key role in plastic deformation during shock loading but not in quasi-static loading. In addition, 3D cup-cone structures are resolved in BMG, but not in MGMC due to its heterogeneous stress field.

    更新日期:2017-11-13
  • Correlation of precipitate evolution with Vickers hardness in Haynes® 282® superalloy: In-situ high-energy SAXS/WAXS investigation
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-11
    Sylvio Haas, Joel Andersson, Martin Fisk, Jun-Sang Park, Ulrich Lienert

    The aim of this work is to characterize the precipitation kinetics in Haynes® 282® superalloys using in-situ high-energy Small Angle X-ray Scattering (SAXS) together with Wide Angle X-ray Scattering (WAXS). The phases identified by WAXS include γ γ (matrix), γ γ ’ (hardening precipitates), MC (metallic carbides), and M23C6 /M6C (secondary metallic carbides). The γ’ γ ’ -precipitates are spheroids with a diameter of several nanometres, depending on the temperature and ageing time. From the SAXS data, quantitative parameters such as volume fraction, number density and inter-particle distance were determined and correlated with ex-situ Vickers microhardness measurements. The strengthening components associated with precipitates and solid solutions are differentiated using the measured Vickers microhardness and SAXS model parameters. A square root dependence between strengthening attributable to the precipitates and the product of volume fraction and mean precipitate radius is found. The solid solution strengthening component correlates with the total volume fraction of precipitates.

    更新日期:2017-11-11
  • Dissimilar friction stir lap welding of magnesium to aluminum using plasma electrolytic oxidation interlayer
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-11
    Y. Gao, Y. Morisada, H. Fujii, J. Liao

    Joining the die-cast non-combustible magnesium alloy AMX602 to the die-cast aluminum alloy ADC12 via friction stir lap welding (FSLW) was investigated. The aluminum alloy on the top can more easily form a sound dissimilar joint than that on the bottom. Strong dissimilar joints were achieved after the magnesium alloy was subjected to a plasma electrolytic oxidation treatment. After the welding process, the plasma electrolytic oxidation interlayer was stirred and flowed into the aluminum alloy side. The growth of the intermetallic compound was restrained by the plasma electrolytic oxidation interlayer by reducing the reaction time of the magnesium alloy and aluminum alloy.

    更新日期:2017-11-11
  • Modeling of Dynamic Recrystallization of Magnesium Alloy using Cellular Automata Considering Initial Topology of Grains
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-11
    Lixiao Wang, Gang Fang, Lingyun Qian

    A two-dimensional cellular automaton (CA) model was established on MATLAB platform for quantitative and topographic simulation of the microstructure evolution of magnesium alloy ZM21 during hot deformation. A probabilistic approach was employed to improve the grain topology accuracy of discrete simulation method. Not only the average grain size but also more details including the grain size distribution of the measured microstructure were reflected in the initial conditions of CA simulation. Quantitative relationship between the parameters defined in the CA model and actual deformation condition was built to increase the applicability of the established model. The dynamic recrystallization (DRX) of magnesium alloy ZM21 was predicted using the CA model. Simulation results, including grain topology, average grain size, grain size distribution and DRX fraction were obtained and compared with experimental results. The good agreement between simulated and experimental results indicated that the established CA model is reliable to predict the microstructure evolution during the hot deformation of magnesium alloy. The influences of initial grain size and its distribution on the microstructure evolution were investigated. It indicated that fine and homogeneous microstructure at initial stage is favorable for the DRX process in hot deformation of magnesium alloy.

    更新日期:2017-11-11
  • Creep rupture behavior of Hastelloy C276-BNi2 brazed joint
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-11
    Yun Luo, Wenchun Jiang, Yucai Zhang, Muming Hao, Shan-Tung Tu

    This paper studied the creep rupture behavior of Hastelloy C276-BNi2 brazed joint by experimental. Based on a series of creep rupture tests at 600 °C under 110~250 MPa, a relation between the stress and rupture time was achieved to evaluate the creep life of brazed joint. The results show that all the brazed joints were fractured in brazed seam immediately after the second creep stage. The creep model, fracture behavior and failure mechanism are dependent on the level of applied stress. The creep behavior of the brazed joint should be depicted by two-regime Norton (2RN) creep model rather than single Norton model. The creep damage tolerance factor was used to identify the cause of creep damage. From low to high stress level, the failure mode is changed from intergranular brittle to transgranular ductile fracture due to the increases of damage tolerance factor with applied stress increases.

    更新日期:2017-11-11
  • Effects of caliber rolling on microstructure and mechanical properties in twinning-induced plasticity (TWIP) steel
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-10
    Joong-Ki Hwang

    The effect of caliber rolling on microstructure and mechanical properties of Fe-Mn-Al-C twinning-induced plasticity (TWIP) steel has been investigated to find alternative methods of wire drawing process using the numerical simulation, electron backscatter diffraction (EBSD) techniques, transmission electron microscopy (TEM), and hardness test. Behavior of twinning, texture, and effective strain was different with areas of rolled wire due to the difference in stress state and strain. The center area had maximum twin density, low angle boundary (LAB), effective strain, and hardness; whereas the surface area had minimum values. In comparison with wire drawing process, caliber rolling process imposed higher stain with slightly uniform distribution on wire, indicating that caliber rolling can manufacture high strength wires more effectively. For instance, after the area reduction of 22%, the tensile strength and hardness inhomogeneity factor of specimen processed by caliber rolling had 47% higher and 15% lower than those of wire drawing process, respectively. In other words, caliber rolling process was suitable to make high strength materials deformed and hardened by twinning mechanism such as TWIP steels due to the characteristics of imposing severe strain with multi-direction, multi-pass with different shape at each pass, and alternating the loading direction between passes. Therefore, caliber rolling process can be a strong candidate in replacement of wire drawing process, especially TWIP steels.

    更新日期:2017-11-11
  • Microstructural Evolution and Mechanical Behavior of W-Si-C Multi-phase Composite Prepared by Arc-melting
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-10
    Kejia Kang, Lianmeng Zhang, Guoqiang Luo, Jian Zhang, Rong Tu, Chuandong Wu, Qiang Shen

    In this work, to improve the strain capacity of tungsten, β-SiC was added to form W-Si-C multi-phase composites composed of W, W2C, and W5Si3 using the arc-melting method. The relationship between microstructure and mechanical behavior was investigated, and a microstructural evolution mechanism was proposed. The grain size of the W was refined significantly from 1071.8 to 5.4 μm as the SiC content increased. The micro-hardness (3.67 to 12.79 GPa) and ultimate compressive strength (UCS) (0.90 to 2.29 GPa) of the W-Si-C multi-phase composite obviously increased as the β-SiC content increased to 4 wt% due to the grain refinement and segregation of the W2C and W5Si3 at the grain boundaries. The highest strain of UCS (21.9%) was obtained at 1 wt% SiC, which is three times of that of pure W (7.4%) and is a result of the refined W grain size and the potentiation of W5Si3.

    更新日期:2017-11-10
  • Ni-Cr-Ta-Al-C complex phase alloy – design, microstructure and properties
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-10
    Piotr Bala, Jerzy Morgiel, Grzegorz Cios, Krzysztof Wieczerzak, Tomasz Tokarski

    In this paper, the concept, microstructure and properties of the Ni-Cr-Ta-Al-C complex phase alloy are presented. The alloy was designed to work at elevated temperatures, in a chemically aggressive environment and under harsh wear conditions. The alloy was examined in an as-cast state and after heat treatment using a number of complementary techniques such as: scanning electron microscopy, 3D reconstruction by means of focused ion beam-scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nanoindentation, dilatometry, hardness measurements and in-situ tensile tests at elevated temperatures. The microstructure of the alloy is comprised of a dendritic chromium-rich nickel-based matrix, which is strengthened by spheroidal precipitations of the γ’ Ni3(AlTa) phase as well as Chinese script-like TaC and Cr7C3 carbides. Analysing hardness and microstructural changes of the alloy after solution treatment and after aging in different conditions allows to optimise the alloy's heat treatment procedure. It was found that the alloy achieved the highest hardness values after aging at 800 °C, which is related with the evolution of the γ’ phase. Additionally, it was discovered that primary carbides are stable up to at least 1150 °C, which is promising from the viewpoint of working at elevated temperatures and under harsh wear conditions. The herein reported results show that the combination of eutectic carbides and ordered γ’ phase for strengthening and, possibly, improving wear resistance of the alloy is effective up to at least 850 °C.

    更新日期:2017-11-10
  • Texture analysis and development of ultrafine grained structure during thermo-mechanical treatment in a gamma-TiAl intermetallic
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-10
    Niloofar Navaei Lavasani, Hamid Reza Jafarian, Hossein Arabi, N. Park

    Gamma titanium aluminide intermetallic alloys are lightweight heat-resistant materials and their thermo-mechanical properties are affected by hot working. The aim of this study was initially to evaluate the texture developed in a cast Ti-48Al-2Cr alloy during thermo-mechanical treatment at 1000 ℃℃ at different strain rates of 0.001, 0.01 and 0.1 s−1. In addition, development of ultrafine grained microstructure was assessed for different strain rates. The results of pole figures suggested that the amount of the strain rate is one of the most crucial parameter affecting the type of texture developed. So that, when the rate of strain increased from 0.001 to 0.1 s−1 the texture changed from Copper to Brass. The results also showed that by increasing the strain rate yield strength, hardness increased substantially. Microstructural study showed that by increasing strain rates, the mean size of the grains reduced even down to nano-range (i.e. <100 nm). A high-volume fraction of dynamic recrystallization occurred when strain rate was more than 0.01 s−1. Abnormal grain growth is also observed when the samples are hot strained by low strain rates.

    更新日期:2017-11-10
  • Hot Corrosion and Low Cycle Fatigue of a Cr2AlC-Coated Superalloy
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-10
    J.L. Smialek, J.A. Nesbitt, T.P. Gabb, A. Garg, R.A. Miller

    Low temperature Type II hot corrosion is a serious problem for low cycle fatigue (LCF) failure of advanced turbine disk alloys operating at increased temperatures. Accordingly, the present effort studied 15-20 μm corrosion resistant Cr2AlC sputter coatings on Low Solvus High Refractory (LSHR) disk alloy LCF test specimens. These were cycled to failure at 840/-430 MPa and 0.33 Hz, after 500 h oxidation and 50 h of Mg-Na2SO4 hot salt corrosion, all at 760°C. The coating successfully prevented hot corrosion pitting that was responsible for a 90% decrease in uncoated LCF specimens. However, fractography identified unintentional 15-30 μm deep defects produced by grit blast surface preparation of coated samples. These acted as failure origins and introduced anomalous life reduction for some coated test specimens. Furthermore, the presence and growth of an undesirable Cr7C3 second phase diminished protectiveness by promoting internal oxidation and embrittlement of the coating.

    更新日期:2017-11-10
  • Effect of stress ratio on high cycle fatigue properties in Mg-6Zn-1Mn alloy
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-10
    Daliang Yu, Dingfei Zhang, Qingwei Dai, Wei Lan, Jian Peng, Junyao Xu, Fugang Qi, Fusheng Pan

    This work investigated the effect of loading mode on high cycle fatigue properties in Mg-6Zn-1Mn (ZM61) alloys. Extruded, T5 treated and double-aged ZM61 alloys were used in this study. High cycle fatigue tests were carried by a servo-hydraulic fatigue testing system under zero-tension load (R= 0) and fully reversed tension-compression load (R= −1), respectively. The results showed that all the three alloys exhibited more outstanding high cycle fatigue strength under zero-tension load than under tension-compression load. By observing microstructures of post-fatigued specimens, a large number of low angle grain boundaries appeared in zero-tension load specimens, but <img height="15" border="0" style="vertical-align:bottom" width="34" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0921509317314077-si0001.gif">{101̅2} twins were found in tension-compression load specimens. The variations of fatigue properties in zero-tension load and tension-compression load were related to deformation mechanisms under different load conditions. The fatigue deformation mechanism in Mg-6Zn-1Mn alloy under zero-tension load was mainly dislocation slip, while under tension-compression load, the activation of <img height="17" border="0" style="vertical-align:bottom" width="36" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0921509317314077-si0002.gif">{101̅2} twinning in compression half cycles resulted in the deteriorative fatigue strength.

    更新日期:2017-11-10
  • Microstructural tailoring and mechanical properties of a multi-alloyed near β titanium alloy Ti-5321 with various heat treatment
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-10
    Lei Ren, Wenlong Xiao, Hui Chang, Yongqing Zhao, Chaoli Ma, Lian Zhou

    A new near β-Ti alloy Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe (Ti-5321) with a unique combination of high strength and good fracture toughness was designed. The microstructure was tailored by changing the solution and ageing conditions, and the influences of microstructural evolution on tensile properties and fracture toughness of the alloy were investigated. The results showed that the volume fraction and size of primary α phase were decreased with increasing the solution temperature, while the morphology of secondary α precipitates was related to ageing temperature. The ultimate tensile strength (UTS), total elongation (EL) and fracture toughness can be achieved in a range of 1147–1439 MPa, 3–26% and 57–76 MPa·m1/2, respectively, depending on the heat treatment parameters. An excellent balance of high strength and good ductility was realized after the solution treatment at 830 °C and ageing at 620 °C for 480 min, in which the UTS, EL and fracture toughness were 1238 MPa, 20% and 73 MPa·m1/2, respectively. Morphological features of the fractography were discussed against the different microstructural morphologies, and this provided further information on the fracture behavior of the alloy.

    更新日期:2017-11-10
  • Ultrarapid formation of multi-phase reinforced joints of hypereutectic Al-Si alloys via an ultrasound-induced liquid phase method using Sn-51In interlayer
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-09
    Lin Zhu, Qian Wang, Lei Shi, Xin Zhang, Tianhao Yang, Jiuchun Yan, Xiaoyu Zhou, Shengyong Chen

    Ultrarapid formation of hypereutectic Al-Si alloys /Sn-51In/ hypereutectic Al-Si alloys joints was achieved within 0.2 s via an ultrasound-induced liquid phase method at 180 °C in air. Ultrasonic vibration accelerated the element inter-diffusion between aluminium and indium to induce liquid phase. The joints consisted of Si particles, an Al-In solid solution and intermetallic compounds. The migration behaviour of Si particles, which were regarded as tracers, under the influence of ultrasonic vibration was used to investigate the joint formation. As the ultrasonic vibration time increased, the shear strength of the joints increased. The existence of Sn in the interlayer considerably affected the joint shear strength by forming intermetallic compounds.

    更新日期:2017-11-10
  • Investigating of the tensile mechanical properties of structural steels at high strain rates
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-09
    A.R. Khalifeh, A.Dehghan Banaraki, H. Danesh Manesh, M.Dehghan Banaraki

    St37 and St52 structural steel plates were tested in uniaxial tension at room temperature over various strain rates ranging from 0.001/s to 0.1/s. The yield stress, flow stress and fracture behavior of steels were analyzed. It was found that the strain rate has a strong effect on the tensile mechanical properties of St37 steel, while St52 has a less sensitive strain rate and that the yield strength of both steels exhibits a higher strain sensitivity rate than the other mechanical properties. An increase in the loading rate from 0.001/s to 0.1/s led to a %30 increase in the lower yield strength of St37 steel and an increase of %6 for St52. The equations were derived to express the yield stress behavior with the strain rate. The ductile dimple fracture was observed in static and dynamic conditions; however, increasing the strain rate resulted in a pronounced cleavage-type fracture in both steels. The St37 fracture strain decreased considerably by increasing the strain rate.

    更新日期:2017-11-10
  • Mechanical properties of porous silicon and oxidized porous silicon by nanoindentation techniques
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-08
    Souheyla Fakiri, Alex Montagne, Khadidja Rahmoun, Alain Iost, Katir Ziouche

    A study of mechanical properties of mesoporous silicon (PS) is presented in this article. PS was prepared by electrochemical etching of a heavily doped P++ silicon wafer in a hydrofluoric acid electrolyte. The mechanical properties of PS and oxidized PS obtained by thermal treatment, were characterized by the nanoindentation technique associated to the continuous stiffness measurement option. The morphology of PS and oxidized PS were both characterized by scanning electron microscope. It is shown that the Young's modulus and hardness are related to the PS preparing conditions and decrease with increasing porosity. In particular, oxidation improves the mechanical properties of the mesoporous silicon. Surprisingly, modulus and hardness decrease with penetration depth, whereas a compaction could be expected resulting in a rising modulus and hardness. These results are mainly attributed to micro cracks formation, highlighted by focused ion beam cross section.

    更新日期:2017-11-10
  • Effects of heat treatment on the microstructure and microplastic deformation behavior of SiC particles reinforced AZ61 magnesium metal matrix composite
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-08
    Song-Jeng Huang, Addisu Negash Ali

    In this paper, solution and ageing heat treatment processes were used to improve microplastic deformation behaviors of as-cast SiCp/AZ61 magnesium metal matrix composites (Mg MMCs) fabricated by stir casting method. Higher percentages of SiC particle reinforcements showed higher microhardness values. Ageing heat treatment process was seen significant on the 12 h aged 2 wt% SiCp/AZ61 Mg MMC which induced lower microhardness value. At the 12 h ageing of 2 wt% SiCp/AZ61 Mg MMC the formations of particle free regions and discontinuous secondary phases were observed. For a higher ageing time, the secondary phases distribution became continuous and laminar structure. The addition of 5 wt% SiC particles resulted in the formation of Mg2Si phase throughout the whole heat treatment processes. The addition of SiC particles reinforcements increased the phase heterogeneity during ageing heat treatment processes. XRD patterns revealed the presence of nanocrystalline MgSiO3 phase on the 12 h aged 2 wt% SiCp/AZ61 Mg MMC. Using reference intensity ration (RIR) method a 51.6% of MgSiO3 phase was determined which can cause the formation of microplastic deformation behavior. And also, the maximum average crystallite size, compressive microstrain and microcrack-free phase boundaries were observed on the 12 h aged 2 wt% SiCp/AZ61 Mg MMC.

    更新日期:2017-11-10
  • Effects of Strain Rate on Mechanical Properties and Deformation Behavior of an Austenitic Fe-25Mn-3Al-3Si TWIP-TRIP Steel
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-08
    J.T. Benzing, W.A. Poling, D.T. Pierce, J. Bentley, K.O. Findley, D. Raabe, J.E. Wittig

    The effects of quasi-static and low-dynamic strain rate (<img height="11" border="0" style="vertical-align:bottom" width="6" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0921509317314661-si0001.gif">ε̇ = 10-4 /s to <img height="11" border="0" style="vertical-align:bottom" width="6" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0921509317314661-si0002.gif">ε̇ = 102 /s) on tensile properties and deformation mechanisms were studied in a Fe-25Mn-3Al-3Si (wt%) twinning and transformation-induced plasticity [TWIP-TRIP] steel. The fully austenitic microstructure deforms primarily by dislocation glide but due to the room temperature stacking fault energy [SFE] of 21±3 mJ/m2 for this alloy, secondary deformation mechanisms such as mechanical twinning (TWIP) and epsilon martensite formation (TRIP) also play an important role in the deformation behavior. The mechanical twins and epsilon-martensite platelets act as planar obstacles to subsequent dislocation motion on non-coplanar glide planes and reduce the dislocation mean free path. A high-speed thermal camera was used to measure the increase in specimen temperature as a function of strain, which enabled the use of a thermodynamic model to predict the increase in SFE. The influence of strain rate and strain on microstructural parameters such as the thickness and spacing of mechanical twins and epsilon-martensite laths was quantified using dark field transmission electron microscopy, electron channeling contrast imaging, and electron backscattered diffraction. The effect of sheet thickness on mechanical properties was also investigated. Increasing the tensile specimen thickness increased the product of ultimate tensile strength and total elongation, but had no significant effect on uniform elongation or yield strength. The yield strength exhibited a significant increase with increasing strain rate, indicating that dislocation glide becomes more difficult with increasing strain rate due to thermally-activated short-range barriers. A modest increase in ultimate tensile strength and minimal decrease in uniform elongation were noted at higher strain rates, suggesting adiabatic heating, slight changes in strain-hardening rate and observed strain localizations as root causes, rather than a significant change in the underlying TWIP-TRIP mechanisms at low values of strain.

    更新日期:2017-11-10
  • Cyclic Deformation and Microcrack Initiation During Stress Controlled High Cycle Fatigue of a Titanium Alloy
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-08
    Changsheng Tan, Qiaoyan Sun, Lin Xiao, Yongqing Zhao, Jun Sun

    Cyclic plastic deformation, slip characteristics and crack nucleation in Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-0.1Si (TC21) with different morphologies of equiaxed and lamellar α phase were systematically analyzed during high-cycle fatigue. The heterogeneous plastic deformation could take place within different α morphologies during high-cycle fatigue even though the cyclic stress amplitude is much less than yield strength. Slip is the dominant deformation mode in the equiaxed primary α, while the slip and <img height="17" border="0" style="vertical-align:bottom" width="32" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0921509317314685-si0001.gif">(101¯1) deformation twin are prevalent in the primary α lath. Interactions between slip, twin and interface result in ledges at the primary α lath interface. The relationship between cyclic slip irreversibility, accumulated irreversible strain, and fatigue life is established. A critical parameter, accumulated irreversible strain per area in the crack initiation region (region I), was calculated to be (8.1±2)×10−4·μm−2 for initiating fatigue crack. Fatigue cracks will nucleate when the accumulated irreversible strain exceeds the critical value. The primary α lath is the dominant site for crack initiation. The cracks initiate and propagate in interface and slip band, and easily connect each other in the primary α lath. In comparison, most cracks lie within an individual or occupy several equiaxed α phases and often cease in front of the phase boundary, which delays the connection of microcracks. It indicates that the primary α lath is more detrimental than the equiaxed primary α phase during high cycle fatigue.

    更新日期:2017-11-10
  • Impact of the heating rate on the annealing behavior and resulting mechanical properties of UFG HSLA steel
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-08
    J. Niehuesbernd, E. Bruder, C. Müller

    The formability of materials with ultrafine grained (UFG) microstructures produced by severe plastic deformation processes is often limited due to low strain hardening capabilities and strain localizations. Most commonly, heat treatments are used to regain the formability. However, conventional furnace heat treatments can lead to grain growth and significant losses in strength. One approach to address this issue is to increase the heating and cooling rates of the heat treatments. The present work focuses on the heating rate dependencies of the microstructure evolution and resulting mechanical properties of a UFG high strength low alloy (HSLA) steel. Electron backscatter diffraction (EBSD) measurements are used to characterize the microstructure and texture. Bending tests and uniaxial tensile tests are conducted to provide insight into the mechanical properties that are related to the obtained microstructures, with an emphasis on the tendency for strain localizations. The investigations reveal a distinct effect of the heating rate on the annealing behavior, i.e., continuous vs. discontinuous growth. Thus, resulting microstructures and mechanical properties are not only a function of time and temperature but also depend on the heating rate. In this context, the application of laser annealing is shown to be a suitable approach to impede strain localizations in the form of shear bands without sacrificing much of the strength of the UFG material obtained by severe plastic deformation.

    更新日期:2017-11-10
  • Interrelationships between Yield Strength, Low-Temperature Impact Toughness, and Microstructure in Low-Carbon, Copper-Precipitation-Strengthened, High-Strength Low-Alloy Plate Steels
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-08
    S.W. Thompson

    Interrelationships between room-temperature yield strength and low-temperature impact toughness are examined for low-carbon, copper-precipitation-strengthened, high-strength low-alloy (HSLA) plate steels. Three steels, designated as HSLA-80, HSLA-80/100, and HSLA-100, are compared based on plots of yield strength versus 50% shear fracture-appearance transition temperature, followed by comparison of yield strength versus energy absorbed during Charpy V-notch testing at −84°C. Analysis of both approaches produced similar outcomes, indicating that either is acceptable for predicting the influence of microstructure on the combination of strength and toughness. Data from over 15 studies including over 160 data points are amassed into a single master plot. Strengthening for the highest-strength steels is associated with a strength-toughness vector with slope equal to −0.67 J/MPa. A grain-refinement vector is associated with a slope of approximately +0.18 J/MPa. Since austenite grain size variation was virtually nonexistent in this study, variation of effective grain size was related to the differences in crystal size and/or packet size for low-carbon martensite (finest), low-carbon bainite, and polygonal ferrite (coarsest). A detrimental effect of untempered, brittle, medium-carbon martensite islands was hypothesized. Tempering of this microconstituent during aging heat treatment reduces, but does not eliminate, the negative effect of these islands. Base microstructures of low-carbon martensite show a superior combination of strength and impact toughness, followed by low-carbon martensite with islands of stable austenite, low-carbon bainite, and polygonal ferrite. A vector approach to strength-toughness in HSLA-100 steels is used to clarify property differences from previous studies. Future developments for this class of steels should address grain refinement and changes in processing or alloying that avoid islands of medium-carbon martensite.

    更新日期:2017-11-10
  • Acoustic energy enabled dynamic recovery in aluminium and its effects on stress evolution and post-deformation microstructure
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-08
    Anagh Deshpande, Keng Hsu

    It is now well established that simultaneous application of acoustic energy during deformation results in lowering of stresses required for plastic deformation. This phenomenon of acoustic softening has been used in several manufacturing processes, but there is no consensus on the exact physics governing the phenomenon. To further the understanding of the process physics, in this manuscript, after-deformation microstructure of aluminium samples deformed with simultaneous application of kilohertz range acoustic energy was studied using Electron-Backscatter Diffraction analysis. The microstructure shows evidence of acoustic energy enabled dynamic recovery. It is found that the subgrain sizes increase with an increase in acoustic energy density applied during deformation. A modified Kocks-Mecking (KM) model for crystal plasticity has been used to account for the observed acoustic energy enabled dynamic recovery. Using the modified KM model, predicted stress versus strain curves were plotted and compared with experimental results. Good agreements were found between predictions and experimental results. The manuscript identifies an analogy between microstructure evolution in hot deformation and that in acoustic energy assisted deformation.

    更新日期:2017-11-10
  • High-pressure sintering of bulk MoSi2: microstructural, physical properties and mechanical behavior
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-08
    Hao Liang, Fang Peng, Haihua Chen, Lijie Tan, Qiang Zhang, Cong Fan, Shixue Guan, Xiaolin Ni, Akun Liang, Xiaozhi Yan, Qiwei Hu

    In this study, using MoSi2 powder as starting material, the bulk MoSi2 samples were sintered at 1000°C–1600°C under 5.5 GPa in a DS6 × 14MN cubic press. Furthermore, their sintering behavior and mechanical properties were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and indentation tests. XRD results elucidate that MoSi2 can still maintain its body-centered-tetragonal structure after the high pressure and high temperature (HPHT) sintering. SEM images imply the combination between grain growths and re-crystallization. Strong covalent bonding between the grains is crucial for improving the mechanical properties of samples. But re-crystallization results in a large number of pores between grains in the sintered body, so that the density and hardness was reduced. Indentation tests indicate that sintered MoSi2 have hardness values of 13.6–15.0 GPa, which increase with increasing temperature and is harder than polycrystalline and single crystal MoSi2. The results demonstrate that the sintered MoSi2 at 5.5 GPa/1300°C possesses outstanding mechanical properties, including a high relative density (6.23g/cm36.23g/cm3), Vickers hardness (15.0 GPa) and fracture toughness (10.7 MPa·m1/2) at applied load of 29.4 N. In addition, the oxidation resistance of the prepared samples is measured using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. The results show that the oxidation resistance has been significantly improved from this work compared with polycrystalline MoSi2.

    更新日期:2017-11-10
  • Partially-recrystallized, Nb-alloyed TWIP steels with a superior strength-ductility balance
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-07
    Hojun Gwon, Jin-Kyung Kim, Bian Jian, Hardy Mohrbacher, Taejin Song, Sung-Kyu Kim, Bruno C. De Cooman

    We investigated the effect of Nb micro-alloying in the range of 0.01 to 0.l wt.-% on the microstructures and mechanical properties of Fe17Mn0.6C1.5Al (wt. -%) TWIP steel. EBSD analysis shows that the Nb addition retards recrystallization in both the hot-rolled and cold-rolled and annealed TWIP steels. The Nb addition in the cold-rolled and annealed TWIP steel leads to an increase in yield strength. This phenomenon is due to a combined effect of precipitation hardening and a low degree of recrystallization. Recovery annealing of the cold-rolled TWIP steels at 650 °C results in a good combination of yield strength and ductility. The steels containing 0.01 wt.-% and 0.025 wt.-% of Nb show a superior combination of UTS×TE exceeding 40,000 MPa∙% and yield strength higher than 800 MPa. The design of TWIP steels utilizing both precipitation hardening and partial recrystallization opens a way to develop steels with a superior combination of yield strength and ductility.

    更新日期:2017-11-10
  • Deformation Mode and Strain Path Dependence of Martensite Phase Transformation in a Medium Manganese TRIP Steel
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-06
    Wei Wu, Yu-Wei Wang, Panagiotis Makrygiannis, Feng Zhu, Grant A. Thomas, Louis G. Hector, Xiaohua Hu, Xin Sun, Yang Ren

    The martensite phase transformation dependence upon deformation modes and strain paths in a medium manganese (10 wt.%) TRIP steel stamped into a T-shape panel was quantified through combination of a 3D digital image correlation and synchrotron X-ray diffraction. The T-shape emulates a portion of a common anti-intrusion component. The stamping speed was kept intentionally slow (1 mm/s) so as to avoid excessive heat generation. The steel, which belongs to the third generation advanced high strength steel (3GAHSS) family, was chosen for two reasons: (1) it is two-phase, i.e. austenite and ferrite, with martensite resulting from deformation-induced phase transformation; (2) the 66 vol.% initial retained austenite volume fraction (RAVF) enabled a thorough examination of the martensite phase transformation at large deformation levels without exhaustion. Strain fields were coupled with measured RAVF values of small specimens extracted from specific locations on a formed T-shape panel. This enabled an exploration of the effects of linear, bilinear and non-linear strain paths as well as deformation modes such as tension, plane strain, biaxial tension and equibiaxial tension. Results suggest a significant martensite phase transformation dependence on deformation mode and strain path in the absence of fracture and when martensite phase transformation is unaffected by heat generated during forming. In general, the uniaxial and biaxial tension deformation modes facilitate the martensite phase transformation, while the smallest amount of martensite phase transformation occurs under plane strain. Some discussion as to further application of the experimental methods detailed in this study to other 3GAHSS and the effects of fracture on martensite phase transformation is provided.

    更新日期:2017-11-10
  • Correlation of defect density with texture evolution during cold rolling of a Twinning-Induced Plasticity (TWIP) steel
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-05
    Kunjan Kumar Anand, Bhupeshwar Mahato, Christian Haase, Ashok Kumar, Sandip Ghosh Chowdhury

    TWIP steels have been cynosure owing to their great potential to be used in the automotive industry. In the present work, an austenitic Fe-22.5Mn-1.5Al-0.35 C steel has been investigated for its cold deformation behavior. X-ray line profile analysis has been used to investigate the evolution of dislocation density, crystallite size, microstrain, twin and stacking fault probability during cold rolling. The steel has been cold rolled up to 80% thickness reduction and a high dislocation density of the order of 1015m−2 is estimated after high degrees of plastic deformation. The microstrain and crystallite size show tendencies to saturate towards higher degrees of deformation. Texture analysis reveals transformation of an initially formed Copper-type texture into a Brass-type texture after medium degrees of rolling reduction. The correlation between microstructural defects and texture evolution has been discussed.

    更新日期:2017-11-10
  • Microstructure evolution within adiabatic shear band in peak aged ZK60 magnesium alloy
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-04
    Lihong Jiang, Yang Yang, Zhen Wang, Haibo Hu

    Microstructure evolution in adiabatic shear band (ASB) in the peak aged ZK60 magnesium alloy cylindrical tube specimen after explosive radial compression was systematically investigated. High strain rate compression tests were performed by means of the radial collapse of thick-walled cylinder technique to achieve nominal strain rates of about 104s−1. The TEM results indicate that the elongated grains and deformed twins are the major characteristics in the boundary of the shear band. The central region in ASB was found to consists of ultrafine and equiaxed grains with a typical size of 100 nm. And it was found that precipitates within ASB were significantly reduced, namely the precipitates instantaneous dissolution during adiabatic shearing. It is proposed that fine equiaxed grains within ASB are the result of rotational dynamic recrystallization during localization. The free energy difference between the precipitates and matrix provided a thermodynamic condition for the dissolution of precipitates. Diffusion rate increased due to high strain rate, high shear stress (large strain) and adiabatic temperature rise, which caused instantaneous dissolution of precipitates.

    更新日期:2017-11-10
  • Microstructure evolution in Alloy 617 B after a long-term creep and thermal aging at 700 °C
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-04
    Magdalena Speicher, Florian Kauffmann, Jae-Hyeok Shim, Mahesh Chandran

    Changes in the microstructure of heat-resistant materials may influence their long-term behaviour. For this reason, materials chosen for high temperature-based applications, e.g. advanced ultra-supercritical (A-USC) steam power plants, must exhibit long-term microstructure stability. Therefore, changes in the microstructure of frequently used materials must be determined and correlated with their creep behaviour to assure a reliable operation of components. In this work, a long-term study investigated the microstructure of a creep rupture specimen made of a nickel-based alloy 617 B. The creep tests were carried out at 700 °C for up to 45,148 h. By using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) the virgin, thermal-loaded and creep states were characterized. The precipitate location, number and size have been determined. The experiment results were compared, discussed and correlated to the creep and failure behaviour. Furthermore, the long-term precipitation kinetics of Alloy 617 B was simulated, which considered its thermal history, using the MatCalc software. The simulated precipitates fraction and size were compared with the experimental data obtained in this study. The comparison between the experimental and simulation results demonstrated comparable gamma prime (γ') phases. The simulation results of the carbides identified at the grain boundaries were satisfactory. However, the size of the intragranular fine carbides M23C6 was not reproduced correctly.

  • Microstructural and Mechanical Properties of a Beta-type Titanium Alloy Joint Fabricated by Friction Stir Welding
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-03
    Huihong Liu, Hidetoshi Fujii

    Friction stir welding (FSW) was performed on β-type Ti-15V-3Cr-3Al-3Sn alloy (Ti-15-3, mass%) plates to fabricate a sound weld joint. The microstructural and mechanical properties of the weld joint were systematically investigated in order to understand the response of the β-type titanium alloys to the FSW. The results show that a defect-free Ti-15-3 alloy weld joint can be successfully fabricated by the FSW. In the thermo-mechanically affected zone (TMAZ), the microstructural evolution is predominantly driven by discontinuous dynamic recrystallization because of the low stacking fault energy of the alloy that results in a low dislocation mobility; while in the stir zone (SZ) it is mainly promoted by continuous dynamic recrystallization due to the high temperature and high strain achieved in the SZ which improve the dislocation mobility. The material flow field within the SZ shows an incline of ~10° towards the advancing side (AS) around the welding direction (WD). The base material and the weld-associated zones (TMAZ and SZ) show comparable mechanical properties, which is due to the competitive effects of the dislocation density, grain diameter and grain orientation. This homogeneous mechanical property distribution makes the Ti-15-3 alloy joint preferred for industrial applications.

    更新日期:2017-11-10
  • As-cast Magnesium AM60-Based Hybrid Nanocomposite Containing Alumina Fibres and Nanoparticles: Microstructure and Tensile Behavior
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-01
    Junxiang Zhou, Luyang Ren, Xinyu Geng, Li Fang, Henry Hu

    Magnesium AM60 based metal matrix hybrid nanocomposite (MHNC) reinforced with alumina (Al2O3) fibre and nano-sized Al2O3 particles was successfully fabricated by a perform-squeeze casting technique under an applied pressure of 90 MPa. Tensile properties of the unreinforced AM60 alloy, Al2O3 fibre/AM60 composite, hybrid composite containing both Al2O3 fibres, and micron and/or nano-sized Al2O3 particles were evaluated. The addition of fibres and/or micron-sized particles significantly improves the ultimate tensile and yield strengths of the matrix alloy from 171 and 81 MPa to 192 and 142 MPa, respectively, while a substantial reduction (73%) in ductility from 6.0% to only 1.6% is observed. The replacement of the micron particles with the nano-sized Al2O3 particles into the hybrid composite restores the ductility from 1.6% to 3.5%. Microstructure analyses via optical (OM) and scanning electron (SEM) microscopes suggest that the homogeneous distribution, clean interfacial structure and grain refinement result in the high strengths of the magnesium hybrid nano composite (MHNC). The observation by transmission electron microscopy (TEM) indicates that the presence of a relatively low dislocation density in the matrix grains of the MHNC benefits the ductility restoration. The SEM fractography shows that the fracture mode of the composites is the evolution of localized damages, such as particles and fibres damage and cracking, matrix fracture, and interface debonding, which are consistent with the tensile results.

    更新日期:2017-11-10
  • Damage analysis of hot-rolled AZ31 Mg alloy sheet during uniaxial tensile testing under different loading directions
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-11-01
    Weiying Huang, Qinghuan Huo, Zhengwu Fang, Zhenyu Xiao, Yong Yin, Zhen Tan, Xuyue Yang

    Uniaxial tensile loading was applied to study the mechanical anisotropy of the hot-rolled AZ31 Mg alloy sheet at room temperature. Tensile direction was varied in the transverse plane and in the angles of 0°, 10°, 20° and 45° from the rolling direction. The tensile tests showed an unexpected result that the 10° sample had the best combination of strength and ductility. To clearly explain the anisotropic behaviors, the damage evolution assisted by crystal plasticity finite element model was successfully employed. The simulated results showed that the prismatic and pyramidal slips induced heavy damage in the 0° sample. Also, the pyramidal slip caused the premature failure in the 20° sample. The high-density basal dislocations led to high ductility and low strength in the 45° sample. A new perspective was thus obtained in which the 10° sample sustained slight damage and had the best combination of strength and ductility.

    更新日期:2017-11-01
  • Stability of retained austenite in martensitic high carbon steels. Part I: Thermal stability
    Mater. Sci. Eng. A (IF 3.094) Pub Date : 2017-10-31
    Wen Cui, David San-Martín, Pedro E.J. Rivera-Díaz-del-Castillo

    Thermal stability of retained austenite in 1C-1.5Cr steels with two Si and Mn contents is studied. Time-resolved high resolution synchrotron X-ray radiation and dilatometry are employed. The threshold transformation temperatures, decomposition kinetics, associated transformation strain, as well as the influence of Si and Mn were investigated. The coefficients of linear thermal expansion for both the bulk materials and individual phases are also obtained. The results indicate that an increase in the Mn and Si contents show little influence on the onset of retained austenite decomposition, but result in more thermally stable austenite. The decomposition is accompanied by a simultaneous increase in ferrite content which causes an expansive strain in the order of 10−410−4, and subsequent cementite development from <img height="12" border="0" style="vertical-align:bottom" width="69" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0921509317314302-si0097.gif">300−350°C which causes a contraction that helps to neutralise the expansive strain. During decomposition, a continuous increase in the carbon content of austenite, and a reduction in that of the tempered-martensite/ferrite phase was observed. This process continued at elevated temperatures until full decomposition was reached, which could take less than an hour at a heating rate of <img height="12" border="0" style="vertical-align:bottom" width="41" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0921509317314302-si0098.gif">0.05°C/s. Additionally, the observation of austenite peak splitting on samples with high Mn and Si contents suggests the existence of austenite of different stabilities in such matrix.

    更新日期:2017-11-01
  • Some contents have been Reproduced with permission of the American Chemical Society.
    Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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