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  • Enhanced strength of the selective laser melted Al-Mg-Sc-Zr alloy by cold rolling
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-21
    Rulong Ma; Chaoqun Peng; Zhiyong Cai; Richu Wang; Zhaohui Zhou; Xiaogeng Li; Xuanyang Cao

    To further refine the coarse columnar grains (CGs) in selective laser melted (SLMed) alloy, an Al-4.0Mg-0.7Sc-0.4Zr-0.5Mn alloy was fabricated by selective laser melting (SLM) and then subjected to cold rolling and annealing at 300 °C for 1 h. Microstructural details and mechanical properties were examined by SEM, EBSD, TEM, and tensile tests. The results show that the microstructure of the SLMed alloy can be further refined by cold rolling. A yield strength of 573 MPa is obtained with an average grain size of 2.4 ± 1.3 μm in the CGs areas, a reduction of approximately 30% compared with the as-fabricated alloy. The enhanced strength of the rolled alloy is derived from the refined grains and high density of Al3(Sc, Zr) phase. Additionally, the Al3(Sc, Zr) particles can enhance the microstructure stability.

    更新日期:2020-01-21
  • Intragranular brittle precipitates improve strain hardening capability of Fe–30Mn–11Al-1.2C low-density steel
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-21
    P. Ren; X.P. Chen; L. Mei; Y.Y. Nie; W.Q. Cao; Q. Liu

    A strategy was developed to circumvent the trade-off between the yield strength and strain hardening capability in Fe–30Mn–11Al-1.2C low-density steel by coupling two-step aging and intermediate pre-strain processes. The improvement of strain hardening capability is attributed to the non-shearable intragranular DO3 particles.

    更新日期:2020-01-21
  • The effect of strain rate on mechanical properties and microstructure of a metastable FeMnCoCr high entropy alloy
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-21
    Z.F. He; N. Jia; H.W. Wang; Y. Liu; D.Y. Li; Y.F. Shen

    The relationship between mechanical properties and microstructures of a metastable dual-phase high entropy alloy Fe50Mn30Co10Cr10 under uniaxial tensile testing at different strain rates (10-3 s-1∼103 s-1) has been studied systematically. As the strain rate increases, yield strength, ultimate tensile strength and uniform elongation decrease first and then increase. Namely, when the strain rate is 10-3 s-1, yield strength and ultimate tensile strength are 280 MPa and 720 MPa, respectively, with the uniform elongation of 64.2%. When the strain rate is increased to 1 s-1, yield strength and ultimate tensile strength are 300 MPa and 672 MPa, respectively, and uniform elongation decreases to 49.2%. When the strain rate reaches 103 s-1, yield strength and ultimate tensile strength increase to 380 MPa and 810 MPa, respectively, while uniform elongation is elevated to 67%. As dynamic deformation is affected by the adiabatic heating, the stacking fault energy of the alloy is increased by ∼13 mJ m-2 at a strain rate of 103 s-1 compared with that in the quasi-static condition. Under quasi-static loading, martensitic transformation is the dominant deformation mechanism. Under dynamic loading, when the strain is low the deformation induced phase transformation dominates, whereas as the loading proceeds mechanical twinning becomes the dominant deformation mode. At the same time, the adiabatic temperature rise under dynamic tests also causes a reverse transformation from ε-martensite to austenite. Accordingly, the release of internal stress and the formation of soft and ductile austenite jointly contribute to the elevated uniform elongation of the material. Both mechanical twinning and martensitic reverse transformation promote the microstructure to be dynamically refined, so that the alloy shows the good plasticity while maintaining the high ultimate tensile strength at dynamic strain rates.

    更新日期:2020-01-21
  • Design of an in–situ multi–scale particles reinforced (Al2O3+ZrB2+AlN)/Al composite with high strength, elasticity modulus and thermal stability
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-21
    Yihan Bian; Tong Gao; Guiliang Liu; Xia Ma; Yingying Ren; Xiangfa Liu

    The thought of designing Al–based composites with attractive comprehensive properties, by using various particles as reinforcements simultaneously, has been put forward and verified in this paper. By in–situ synthesizing Al2O3 (<1 μm), ZrB2 (<300 nm) and AlN (<100 nm) particles, a novel (Al2O3+ZrB2+AlN)/Al composite has been prepared. It was found that the ultimate tensile strength of the composite is as high as 540 MPa at 25 °C and 200 MPa at 350 °C, while the elasticity modulus of the composite is 101 GPa. Besides, the composite also performs attractive thermal stability and the coefficient of thermal expansion is 15.8×10–6 K–1 at 500 °C. It is regarded that the synergistic effect of the multi–scale Al2O3, ZrB2 and AlN particles are responsible for the improved performance. This paper may be referred for designing multiphase reinforced composites to achieve various properties.

    更新日期:2020-01-21
  • Effect of temperature on deformation mechanisms of AZ31 Mg-alloy under tensile loading
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-21
    Thibaut Dessolier; Pierre Lhuissier; Francine Roussel-Dherbey; Frédéric Charlot; Charles Josserond; Jean-Jacques Blandin; Guilhem Martin

    Controlled in situ SEM tensile tests have been carried out between 200 and 300 °C at a constant strain rate of 5.10-5 s-1 to investigate the effect of temperature on deformation mechanisms operating in an Mg–3Al–1Zn (AZ31) Mg-alloy. Fiducial microgrids deposited using electron beam lithography are used to evidence grain boundary sliding as well as to determine the spatial strain heterogeneities as a function of temperature. Dislocation creep and grain boundary sliding coexist between 200 and 300 °C but their respective activity varies significantly as shown by the strain rate sensitivity value m which is about 0.2 at 200 °C but about 0.5 at both 250 and 300 °C. In addition, grain boundary sliding becomes predominant at 250 and 300 °C whereas its occurrence is relatively limited at 200 °C. Slip trace analysis shows that at 200 °C prism and pyramidal slip already exhibit a great activity. Spatial strain heterogeneities determined by digital image correlation (DIC) based on microgrid displacements develop during the early stage of plastic deformation and persist at larger strains. It is shown that the strain in the vicinity of grain boundaries intensifies when the temperature rises from 200 to 300 °C while the core of grains accommodates less deformation in agreement with the fact that grain boundary sliding is predominant at 250 and 300 °C.

    更新日期:2020-01-21
  • Influence of matrix property and interfacial reaction on the mechanical performance and fracture mechanism of TiC reinforced Al matrix lamellar composites
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-20
    Rui-Fen Guo; Ya Wang; Ping Shen; Alateng Shaga; Yun-Hai Ma; Qi-Chuan Jiang

    Freeze casting is a versatile approach for the design of lamellar metal−ceramic composites with unique combination of strength and toughness. However, previous studies mainly focused on ceramic factors such as content and lamellae structure, seldom concerning the effects of metal property and interfacial structures, which, in practice, are key factors in determining the mechanical performances of the composites. In this work, we prepared three kinds of Al/TiC lamellar-interpenetrated composites with different matrix compositions (pure Al, 6061Al (Al−0.4Cu−1.0Mg−0.6Si) and ZL107 (Al–7Si–5Cu)) via freeze casting and pressure infiltration, aiming at clarifying the roles of matrix property and interfacial reaction on the mechanical properties and fracture mechanisms of the composites. The flexural strengths of pure Al/TiC, 6061Al/TiC and ZL107/TiC composites reached 355 ± 10, 415 ± 15 and 459 ± 18 MPa, while the toughness values (characterized by crack-growth toughness) were 81.0 ± 2.0, 57.6 ± 1.2 and 43.4 ± 1.5 MPa m1/2, respectively. The exceptional damage tolerance of these lamellar composites was attributed to multiple toughening mechanisms such as crack deflection, uncracked-ligament bridging of ductile layers and plastic deformation of the metal matrix. However, the presence of Si in the 6061Al and ZL107 alloys weakened the stability of TiC and promoted interfacial reaction, leading to the formation of a certain number of (Al1-m, Sim)3Ti and Al4C3, which greatly weakened the toughness of the composites. Due to the combined effects of alloy plasticity, lamellar-interpenetrated structure and interfacial reaction, the fracture of the materials changed from a multiple cracking mode in the Al/TiC composite to a single crack propagating mode in the 6061Al/TiC and ZL107/TiC composites.

    更新日期:2020-01-21
  • Mechanical property evaluation of second phase particles in a Mg–8Al-0.5Zn alloy using micropillar compression
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-20
    R. Sarvesha; Ubaid-ur-Rehman Ghori; Yu Lung Chiu; Ian P. Jones; S.S. Singh; J. Jain

    This study investigates the mechanical properties of the second phase particles and Mg-matrix in a Mg–8Al-0.5Zn cast alloy by compression of machined micropillars. The stress-strain behavior showed that the Mg17Al12 particles exhibited a sudden and unusual failure after a significant strain burst. The Al8Mn5 particles were much more ductile, but also much stronger.

    更新日期:2020-01-21
  • The significant effect of trace yttrium level on the mechanical properties of cast Mg–6Al alloy through a refinement mechanism
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-20
    K. Korgiopoulos; M. Pekguleryuz

    It was observed that low level of yttrium (Y) has a modifying effect on the Mg17Al12 phase in the binary Mg-6wt%Al casting alloy. Scanning/transmission electron microscopy, mechanical testing and thermodynamic calculations were employed to understand the modification mechanism. It is found that Y at trace level refines the β-Mg17Al12 phase leading to increased tensile elongation and compressive strain to fracture. The refinement effect is lost with further increase in the Y level. Thermodynamic calculations (Scheil cooling) indicate that the formation temperature of the Al4MgY phase changes with the Y level. At trace levels, its nucleation temperature is the same as that of Mg17Al12, producing a co-precipitation/nucleation effect. As Y increases, Al4MgY forms at increasingly higher temperatures than β-Mg17Al12 with a loss of the refinement due to the disappearance of co-precipitation.

    更新日期:2020-01-21
  • Ex-situ EBSD analysis of hot deformation behavior and microstructural evolution of Mg–1Al–6Y alloy via uniaxial compression
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-20
    Mengna Zhang; Jinhui Wang; Yunpeng Zhu; Lei Zhang; Peipeng Jin

    The microstructure and texture evolution of as-extruded Mg-0.96 wt%Al-5.82 wt%Y (denoted as Mg–1Al–6Y) alloy with strain at a temperature of 350 °C and a strain rate of 0.1 s−1 were studied using ex-situ electron backscatter diffraction (EBSD). Moreover, the deformation mechanism was systematically analyzed. The results shown that weak <2-1-11> rare-earth texture and no twinning were observed in the as-extruded Mg–1Al–6Y alloy. The hot compression curve exhibited obvious work-hardening characteristics with a yield strength of 98 MPa. In the initial stage of deformation, {10–12} extension twinning was formed in some grains. As the strain increased, the number of {10–12} extension twinning and texture intensity gradually decreased, whereas the amount of low-angle grain boundaries increased. The Schmid factor (SF) of pyramidal slip remained at ∼0.4. In addition, the TEM characterization revealed that as the strain increased, dislocations multiplied, and the pyramidal dislocation was always observed. Therefore, the reduction of twinning and activation of pyramidal slip lead to the dominance of slip during the deformation. Hence, work hardening appeared in the compression curve of Mg–1Al–6Y alloy.

    更新日期:2020-01-21
  • The role of eutectic colonies in the tensile properties of a Sn–Zn eutectic solder alloy
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-20
    Lidiane Silva Ramos; Rodrigo Valenzuela Reyes; Leonardo Fernandes Gomes; Amauri Garcia; José Eduardo Spinelli; Bismarck Luiz Silva

    The growth of eutectic colonies in Sn–Cu, Sn–Zn and Sn–Ag–Cu eutectic alloys has already been reported in the literature. However, relationships between this kind of microstructure and mechanical properties remain undetermined for solders. The use of water-cooled copper (Cu) and AISI 1020 low-C steel molds and the eutectic Sn-9 wt.%Zn alloy make it possible to address this matter. The samples grown in the Cu mold demonstrated higher solidification rates than those developed in the low-C steel mold. Overall, the microstructure is constituted by Zn-lamellae embedded in a Sn-rich matrix. The Zn lamellae are not only uneven in thickness but also irregularly perforated. Due to Cu dissolution into the alloy, a small fraction of Cu5Zn8 intermetallic particles formed during solidification of the Sn-9 wt.%Zn alloy in the Cu mold. The contamination with Cu appears to be responsible for the improvement in the distribution of Zn-lamellae. The decrease in spacing between broken lamellae measured from SEM images, as well as a higher number of Zn particles per area, explain such occurrence. Ductility and tensile strength of different samples could allow the establishment of relationships among properties vs. eutectic colony spacing. For the Cu mold, the motion of Cu towards the alloy as well as higher solidification rates, allowed microstructures to be formed combining 60% of strain to fracture and 52 MPa of ultimate tensile strength. These achievements are mainly due to the finest spacings of both the eutectic colony (λχ = 36 μm) and the Zn lamellae (λL=0.9 μm), besides homogeneous distribution of Cu across the resulting microstructure.

    更新日期:2020-01-21
  • Evolution of tensile properties with transformation temperature in medium-carbon carbide-free bainitic steel
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-17
    Xiaoyan Long; Gengcen Zhao; Fucheng Zhang; Shan Xu; Zhinan Yang; Guojun Du; Ricardo Branco

    Different morphologies of carbide-free bainite were obtained through a series of isothermal heat treatments of a new medium-carbon bainitic steel, and the evolution of microstructures during tensile deformation was then observed. The results showed that the strength-ductility balance could reach its highest value near 350 °C. The retained austenite sustaining martensitic transformation, long bainite ferrite sheaf, and phase transformation dynamics were the main factors that caused high plasticity of the steel at 350 °C isothermal transformation. It is noteworthy that 350 °C is also a phase change sensitive point for most bainitic steels. Maintaining high work hardening rate at high strain is beneficial to increase elongation, which is attributed to the continuous martensitic transformation of the retained austenite with high volume fraction. The (200) austenite peak was separated using the Gaussian multi-peaks fitting method. It was found that the (200) austenite peak moves to the left with the increase of strain. The proportion of low angle peaks also increased with strain. This indicates that the transformation of the retained austenite always occurs in the low carbon region.

    更新日期:2020-01-21
  • Influence of annealing on the microstructure and mechanical properties of Ti/steel clad plates fabricated via cold spray additive manufacturing and hot-rolling
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-17
    Zhipo Zhao; Naeem ul Haq Tariq; Junrong Tang; Yupeng Ren; Hanhui Liu; Min Tong; Lisong Yin; Hao Du; Jiqiang Wang; Tianying Xiong

    A novel method was designed to fabricated Ti/steel clad plates via cold spray additive manufacturing (CSAM) and hot-rolling. In order to study the influence of annealing on the microstructure and mechanical properties of the Ti/steel clad plates, the as-rolled clad plates were subjected to different annealing temperatures in the order: 450, 550 and 650 °C. It was revealed that CSAM and hot-rolling promote metallurgical bonding between Ti/Ti as well as Ti/steel interfaces, thus resulting in Ti/steel clad plates with excellent mechanical properties. The annealing treatment promotes inter-diffusion of Ti and Fe across the Ti/steel interface and improves the microstructures of the as-rolled Ti/steel clad plates. The results show that when the annealing temperature is low (i.e. 450 °C), the elongation of the specimen increases while the ultimate tensile strength and shear strength both decrease through recovery and recrystallization mechanisms. However, when the annealing temperature is too high (i.e. 650 °C), the elongation and strength of the specimen decrease sharply due to the nucleation and growth of brittle TiC and FeTi compounds. The annealing, at 550 °C for 3 h, was pin-pointed as the optimum post-spray treatment to achieve superior ultimate tensile strength (564 Mpa), shear strength (280 Mpa) and elongation (18%) in the clad plate.

    更新日期:2020-01-21
  • Stress-induced hydrogen redistribution and corresponding fracture behavior of Q960E steel at different hydrogen content
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-17
    Bo Kan; Weijie Wu; Zixuan Yang; Jinxu Li

    The uptake and accumulation of hydrogen in materials during a service process is the primary prerequisite of hydrogen embrittlement. However, the actual hydrogen concentration that causes brittle fracture is unknown. In this study, slow strain rate tensile tests combined with finite element simulations (FESs) were used to study the influence of stress variation and initial hydrogen content C0 (0.91, 1.70, 2.90, and 3.41 ppm) on the hydrogen redistribution and fracture behavior of smooth tensile specimens of Q960E steel for the first time. Furthermore, the actual threshold hydrogen content for hydrogen-delayed cracking was also obtained. Results showed that the presence of hydrogen significantly increases the elongation loss but has a minimal effect on strength loss. The occurrence of brittle cracking depends on the duration and the quantity of accumulated hydrogen. Brittle fracture occurs only at low strain rates under low C0 of 0.91 and 1.70 ppm. However, a high strain rate can result in brittle fracture at high C0 of 2.90 and 3.41 ppm. FES and fracture behavior indicate that the critical hydrogen content that causes brittle fracture is 1.8 ppm. If the C0 is less than 1.8 ppm, brittle fracture is also observed at the center of the specimen by stress-induced hydrogen diffusion to achieve this critical value at low strain rate. A logarithmic relationship is observed between C0 and the brittle zone size with a constant strain rate.

    更新日期:2020-01-17
  • Control of texture and earing in aluminium alloy AA 8011A-H14 closure stock
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-17
    Olaf Engler; Johannes Aegerter; Dirk Calmer

    The development of crystallographic texture during the thermo-mechanical processing of aluminium sheet results in the formation of pronounced plastic anisotropy, including the well-known earing phenomenon. In the present study we track the evolution of texture, microstructure and the resulting earing profiles in Al alloy AA 8011A during down-stream processing to final-gauge sheet in temper H14. This processing, which includes two interannealings, followed by a mild final temper rolling pass, was designed for providing minimum earing for earing-critical packaging applications. Besides the experimental characterization of microstructure, texture and earing along the standard process chain, means to optimize the earing behaviour are addressed. This includes changes in the homogenization practice, possible omission of one of the two interannealings and variation of the interannealing gauge. The resulting earing properties are discussed in the light of the interplay of deformation and recrystallization with the resultant texture changes along the process chain.

    更新日期:2020-01-17
  • Fracture toughness of friction stir welded TA5 titanium alloy joint
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-17
    Fuyang Gao; Yufan Guo; Shengwen Qiu; Yan Yu; Wei Yu

    Fracture toughness of friction stir welded titanium alloy joints was investigated using Compact tension (CT) impact specimens. The fracture toughness slightly decreases to about 90% of the fracture toughness. The fracture surface was mainly ductile fracture mechanism with a large number of dimples. The crack propagation path was straight and mixed with intergranular and transgranular fracture. The stir zone of joint has a large number of fine ɑ grains with some dislocations. For texture, The stir zone has hard orientation {0002} <112(−)0>, the directions of cylinder and plate thickness are parallel. The reduction of fracture toughness in the stir zone is mainly related to microstructure and texture.

    更新日期:2020-01-17
  • Plasticity modeling for a metastable austenitic stainless steel with strain-induced martensitic transformation under cyclic loading conditions
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-17
    Cheng Luo; Wu Zeng; Jingyu Sun; Huang Yuan

    In the present paper, the strain-induced martensitic transformation and the cyclic plasticity model of a metastable austenitic steel AISI 348 under multi-axial cyclic loadings were studied. Cyclic loading tests under different stress triaxialities and strain amplitudes were carried out and used to verify the material model. Based on the Santacreu model, a kinetics model for evolution of martensitic transformation under multi-axial cyclic loading conditions was obtained by defining a threshold of equivalent plastic strain for phase transformation. The model can degenerate into a simplified form to describe strain-induced martensite evolution under monotonic loadings. The prediction of martensite content by the model matched well with experiments. By correlating the effect of martensitic transformation into isotropic hardening, a modified Ohno-Wang model was obtained and verified. The stress–strain response along the different loading paths and histories was well described by the introduced model.

    更新日期:2020-01-17
  • Micro-mechanical investigation of fatigue behavior of Al alloys containing defects
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-16
    Vidit Gaur; Fabien Briffod; Manabu Enoki

    A crystal plasticity finite element (CPFE) simulation framework has been proposed in this study for the prediction of combined detrimental effect of mean stress and defects on the fatigue behavior of aluminum alloy. Experimental data for mean-stress effect on fatigue life and crack growth behavior was obtained on metal inter gas (MIG) welded joints of Al-5083/Al-5.8%Mg alloy plates and has been detailed in authors’ previous work, referred later. The present study focuses on its prediction using computational framework only. A 2D representative model for material’s microstructure was used for the simulations, generated using an anisotropic tessellation algorithm using the EBSD measurements data. A total of 10 different microstructure models were generated for each loading condition using six-node plane strain type quadratic triangular (CPE6) elements of mesh size 6 μm. Two different types of cases were investigated: one without defect and other with a semi-circular surface defect. The simulated loadings at different stress ranges and stress ratios (R-ratio) were similar to the experimental conditions for the better comparison of the results. Significant heterogeneity in the distribution of R-ratios and the far-field applied R-ratio was observed. When defect was not considered, a clear deviation in the predicted fatigue lives from the experimental data was observed at different R-ratios: the predicted fatigue lives were higher than the experimentally observed fatigue lives. This was probably because of not considering the detrimental effect of defects on fatigue lives. But, when the defects were considered, the predicted results for different R-ratios was consistent with the experimental fatigue lives. The proposed CPFE simulation framework not only predicted well the effect of defects and mean stress on the fatigue lives, but also the scatter induced in them due to the defects.

    更新日期:2020-01-17
  • Microstructure and mechanical properties of bobbin tool friction stir welded ZK60 magnesium alloy
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-15
    Gaohui Li; Li Zhou; Sanfeng Luo; Fengbo Dong; Ning Guo

    Bobbin tool friction stir welding (BTFSW) technique was applied to a Mg–Zn–Zr alloy ZK60. The results indicated that the plates were joined successfully with no welding defect forming at the investigated processing parameters. BTFSW resulted in significant grain refinement and dissolution of the Mg4Zn7 precipitates in the stir zone (SZ). Extensive softening was observed in the SZ because the strengthening resulted from the grain refinement could not compensate the strength loss caused by the precipitates dissolution. The ultimate tensile strength of the joint reached 80.3–84.4% of that of the ZK60 parent metal. All the joints consistently fractured in the SZ adjacent to the thermo-mechanically affected zone (TMAZ) on the advancing side (AS). The extensive softening in the SZ makes it more susceptible to plastic deformation during transverse uniaxial tension, which is the precondition for the failing in the SZ-side. Within the SZ, the profuse activation of {10–12} extension twinning in the SZ-side on the AS (with <0001> crystal direction parallel to transverse direction) and basal slip in the adjacent region (with <0001> crystal direction at ∼45° to transverse direction) caused deformation incompatibility. Additionally, the abrupt change of microstructure from the TMAZ to the SZ aggravated the deformation incompatibility, leading the fracture to initiating in the SZ-side on the AS.

    更新日期:2020-01-15
  • Effect of caliber rolling reduction ratios on the microstructure and mechanical properties of 45 medium carbon steel
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-15
    B.X. Liu; K.Y. Fan; F.X. Yin; J.H. Feng; P.G. Ji

    Tempered medium carbon steel with poor low-temperature toughness always limits its practical applications, while temper forming process can realize the strengthening-toughening aim by changing the microstructure. In this work, a grade 45 medium carbon steel was deformed with different rolling reduction ratios of 28%, 52%, 78%, and 82% by caliber rolling at the temperature of 500oC, respectively. The texture intensity, high angle boundaries density, and elongated fibrous grains are gradually increased, as well as the tensile strength, fracture elongation, and low-temperature impact toughness are also improved with the increase of caliber rolling reduction ratio, and strengthening-toughening aim of 45-grade steel has been realized at high caliber rolling reduction ratio. Fibrous grains, <110>//RD texture, grain boundaries type, and carbides bimodal distribution resulted in the formation of crack bifurcation and delamination cracks during the tensile testing and impact testing, which can obviously decrease the ductile-brittle transition temperature and improve the low-temperature impact toughness. The caliber rolled 45 steel at the rolling reduction ratio of 82% obtains superior mechanical properties with the tensile strength of 964MPa, uniform elongation of 0.18, and low-temperature impact toughness of 176J at −40oC, which can effectively extend the practical low-temperature service range of 45-grade steel.

    更新日期:2020-01-15
  • Effect of carbon on microstructure and mechanical properties of HR3C type heat resistant steels
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-13
    J.M. Bai; Y. Yuan; P. Zhang; J.B. Yan

    The modified HR3C austenitic heat-resistant steels for applications of ultra-supercritical (USC) power plants were developed and investigated. As the C content breaks through the limitation of the HR3C composition range (>0.1 wt%), the evolution of carbides and mechanical properties after isothermal aging at 700 °C have not been understood. In this study, two modified HR3C with different C content were studied by tensile test and Charpy impact test at room temperature after long-term aging up to 10,000 h. The M23C6 carbide is rapidly precipitated at the interface (GBs, TBs or NbC/γ), and these carbides at grain boundaries (GBs) are gradually changed from a continuous distribution to a semi-continuous distribution, then finally agglomerate and coarsen near the GBs. Moreover, a new morphology type lamellar M23C6 carbide forms in the grain. The effect of lamellar carbides on mechanical properties at room temperature (RT) is not obvious because the strength of GB is rapidly weakened. Besides, the Larson-Miller parameter was obtained and the creep strength of the modified HR3C was extrapolated, by conducting creep rupture experiments on un-aged sample. The creep tests reveal that the rupture lives decrease with increasing C content. Lamellar carbides are precipitated and weaken the strength of grain during high temperature creep.

    更新日期:2020-01-14
  • Microstructure and mechanical properties of wire and arc additive manufactured AZ31 magnesium alloy using cold metal transfer process
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-13
    Xu Yang; Jianrui Liu; Zhennan Wang; Xin Lin; Fencheng Liu; Weidong Huang; Enquan Liang

    Wire and arc additive manufacturing (WAAM), using cold metal transfer (CMT) as heat source, exhibits a great potential for additive manufacturing of magnesium alloys due to low heat input. With the purpose of revealing the relationship between the microstructure and mechanical properties of WAAMed AZ31 material, the present study has been carried out. The manufactured AZ31 thin-walled deposit is mainly composed of columnar dendrite arrays, including dendritic α-Mg matrix, interdendritic eutectics (α-Mg and β-Mg17Al12) and some dispersive η-Al8Mn5 phases. The average primary dendrite arm spacing increases from 17 μm at the bottom to 39 μm at the top of the deposit, and the volume fraction of the interdendritic eutectic decreases from 52.1% to 39.3%. The microstructure of each layer except the top layer consists of vertical columnar dendrites and direction-changed columnar dendrites in sequence. The top layer appears equiaxed dendrites due to columnar to equiaxed transition (CET). The tensile properties present obvious anisotropic characteristics because of the epitaxial columnar dendritic growth along the building direction. The tensile properties also show obvious variation from the bottom to the top of the deposit because of the differing microstructures in different regions. The results are further analyzed in detail through the microstructure evolution resulted from the new manufacturing method.

    更新日期:2020-01-14
  • A mechanism-based quantitative multi-scale framework for investigating irradiation hardening of tungsten at low temperature
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-13
    Yuanyuan Wang; Xin Sun; Jijun Zhao

    We present the development and validation of a mechanism-based multi-scale modeling framework to quantitatively link the irradiation defect evolution kinetics at the microscopic scale to the macroscopic yield strength and flow stress evolution of tungsten irradiated at low temperature (0.08 < T/Tm < 0.18, where Tm is the melting point and is equal to 3673 K). The mechanism-based strength model, proposed as the superposition of thermal softening and modified dispersed barrier hardening, is developed to understand the underlying strengthening mechanisms. The thermal softening exponent as defined in the Johnson-Cook model is obtained by fitting unirradiated yield strength at different temperatures. A set of irradiation-induced defect kinetics equations with the thermodynamics parameters derived from the atomic calculations reported in the literature is used to determine the densities and sizes of defect clusters at the meso-scale, and the predicted irradiation damage characteristics are in reasonable quantitative agreement with experimental data from literature. The effects of irradiation condition (temperature and irradiation dose) and test temperature on yield strength are quantitatively predicted and compared with experimental measurements from the literature. The predicted irradiation hardening and strain hardening are compared with experimental data as model validation.

    更新日期:2020-01-13
  • A new strategy of tailoring strength and ductility of CoCrFeNi based high-entropy alloy
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-11
    Fukai Zheng; Guannan Zhang; Xiujuan Chen; Xiao Yang; Zengchao Yang; Yong Li; Jiangtao Li

    In this paper, a new strategy of high entropy alloy is presented, high strength and promising ductility are realized by precipitation strengthening mechanism. The structure of nano-L12 precipitates on the FCC high entropy alloy (HEA) matrix is formed, by adding Ni and Al with a fixed stoichiometric ratio (keeping Ni: Al = 3:1, Ni3Al) to CoCrFeNi matrix. The study found that the mechanical properties of the alloy can be effectively controlled by optimizing the addition of Ni3Al content. Through tension test and theoretical analysis, we found that, when the addition of Ni3Al reaches 0.75, the HEA exhibits the excellent comprehensive strength and ductility. With the tensile fracture strength, yield strength and elongation are 1200 MPa, 910 MPa, and 14%, respectively. Compared with the CoCrFeNi high entropy alloy without precipitates, the yield strength is increased by three times. TEM analysis and theoretical calculation show that the strengthening mechanism of the second phase is the main factor to improve the properties.

    更新日期:2020-01-13
  • An experimental study on strain-induced martensitic transformation behavior in SUS304 austenitic stainless steel during higher strain rate deformation by continuous evaluation of relative magnetic permeability
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-11
    Bo Cao; Takeshi Iwamoto; Pinaki Prasad Bhattacharjee

    In the past, it is experimentally revealed that the stacking fault energy (SFE) for the strain-induced martensitic transformation (SIMT) in metastable austenitic stainless steels is positively dependent on the strain rate, especially at impact strain rate; however, a conflicting view is recently reported that it is independent on the strain rate. To solve the conflict on the rate sensitivity of SFE, a non-destructive method to determine the martensitic volume fraction precisely under quasi-static tensile loading is effective and a method for measuring the relative magnetic permeability using AC voltage has been previously developed. However, this technique overestimates magnetic permeability during impact testing due to the eddy current generated at high frequencies, which can be avoided by applying DC voltage to the primary coil. In this work, quasi-static and impact tensile tests are performed on commercial SUS304 metastable austenitic stainless steel at various strain rates to determine its relative magnetic permeability during deformation. The obtained experimental data are utilized to investigate the SIMT behavior of SUS304 steel under quasi-static and impact tensions. As a result, it successfully captures the SIMT behavior in SUS304, especially during high strain rate deformation and the role of SFE on SIMT at higher strain rate is discussed.

    更新日期:2020-01-13
  • The grain size and orientation dependence of geometrically necessary dislocations in polycrystalline aluminum during monotonic deformation: Relationship to mechanical behavior
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-10
    Shiqi Zhang; Wei Liu; Jifang Wan; R.D.K. Misra; Qiang Wang; Chao Wang

    The evolution of geometrically necessary dislocations (GND) in aluminum was studied using high-resolution EBSD. Small grains had higher GND density than coarse grains and were most pronounced at a strain of ∼9.8%, due to GNDs were more homogeneously organized at strain >9.8%. Furthermore, <111> oriented grains with higher Taylor factor stored more GNDs than <100> grains.

    更新日期:2020-01-11
  • In situ compressive investigations on the effects of solid solution Gd on the texture and lattice strain evolution of Mg
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-10
    Yuling Xu; Yuanding Huang; Zhengye Zhong; Sihang You; Weimin Gan; Biquan Xiao; Emad Maawad; Norbert Schell; Felix Gensch; Fusheng Pan; Norbert Hort

    The present work studies the effects of solid solution Gd on the texture and lattice strain evolution of an extruded Mg15Gd alloy under uniaxial compression. In situ experiments were carried out using high energy X-ray diffraction on samples of the investigated materials with three different orientations. The original textures of the pure Mg and the Mg15Gd alloy exhibit basal planes that are preferentially parallel and perpendicular to the extrusion direction (ED), respectively. The c/a ratio of the Mg15Gd alloy decreases with increasing Gd content in the solid solution, leading to a different deformation behavior compared with pure Mg under the compressive load. The addition of Gd enhances the slip and twinning modes. However, prismatic slip is activated earlier in the Mg15Gd alloy due to the lower c/a ratio.

    更新日期:2020-01-11
  • Microstructure and tensile properties of Zr-containing ODS-FeCrAl alloy fabricated by laser additive manufacturing
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-09
    Yingnan Shi; Zheng Lu; Li Yu; Rui Xie; Yuhang Ren; Guang Yang

    Oxide dispersion strengthened (ODS) FeCrAl alloys have been considered as the promising candidate fuel cladding materials for the Gen-IV fission reactors due to excellent radiation tolerance, mechanical properties and corrosion resistance, but their manufacturing is complex process. Laser engineered net shaped (LENS) technology followed by post-build heat treatment was employed successfully to fabricate Zr-containing ODS-FeCrAl alloy. The microstructure of as-deposited and heat-treated alloys was characterized by optical microscope (OM), electron backscatter diffraction (EBSD), scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM). The tensile tests were carried out at room temperature. The results show that the coarse columnar grains with preferred orientation ([001] fibre texture) are obtained after LENS deposit and are remained after post-build heat treatment. The average width of columnar grains for both as-deposited and heat-treated samples is ∼180–190 μm. A slag-like layer which is made up of Y3Al5O12, ZrO2 and Al2O3 is observed at the surface of deposited sample. Some coarse appendage oxides which consist of Al2O3 and Y4Zr3O12 are distributed in the matrix of as-deposited sample. Post-build heat treatment produces high-density nanoscale Y4Zr3O12 oxides in the matrix. The formation mechanism of different type oxides is explained. Both as-deposited and heat-treated samples present anisotropic tensile properties. After post-build heat treatment, the tensile strength is improved significantly by the formation of high-density nanoscale Y4Zr3O12.

    更新日期:2020-01-09
  • Microstructural and mechanical properties evaluation of graphene reinforced stainless steel composite produced via selective laser melting
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-09
    Ajay Mandal; Jitendar Kumar Tiwari; N. Sathish; Avanish Kumar Srivastava

    Graphene (Gr)-reinforced 316L stainless steel (Gr/SS 316L) composite was fabricated through the selective laser melting (SLM) technique to avoid the agglomeration of graphene and develop a composite that has higher specific strength. Here, 316L stainless steel and graphene powder was first mixed using ball milling. The formed mixture was then used as raw powder for the SLM system. The fabricated composite underwent hardness and tensile tests. The obtained results reveal that the properties of the composite significantly improve with the addition of 0.2 wt% Gr. The hardness and yield strength of the composite increased by up to 25% (from 194 to 245 HV) and 70% (from 502 to 850 MPa), respectively. Experimental values were also compared with the theoretically calculated results, and the possible reasons behind the variation in both values were discussed. A micrograph and electron backscatter diffraction map of the composite was analysed under a field-emission scanning electron microscope to determine the microstructure and grain orientation. Raman mapping and X-ray diffraction were performed to analyse the distribution of Gr in the matrix and its effect on the formation of carbide, respectively. Finally, the SLM technique was found to be a practical method for synthesising Gr/SS 316L composites with superior mechanical properties.

    更新日期:2020-01-09
  • Effects of Mn addition on the microstructure and mechanical properties of Mg–Zn–Sn alloys
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-09
    Caihong Hou; Fugang Qi; Zhisong Ye; Nie Zhao; Dingfei Zhang; Xiaoping Ouyang

    The effects of Mn addition on the microstructure and mechanical properties of Mg–Zn–Sn alloys have been investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and uniaxial tensile tests. The results show that the addition of Mn can significantly improve the mechanical properties of the as-extruded and aged Mg–Zn–Sn alloys, which is mainly due to the grain refinement and precipitation strengthening. For the as-extruded alloys, the Mn element mainly exists in the form of α-Mn particle phase, which is dispersed in the matrix and play the role of fine grain strengthening and dispersion strengthening. For the single-aged and double-aged alloys, the dispersed α-Mn particle phases can also serve as the heterogeneous nucleation cores of rod-like β1' precipitates during the ageing treatment, which is beneficial to the nucleation rate of the precipitates. The crystallographic characteristics research shows that the directional relationship between α-Mg, β1' and α-Mn is [21¯1¯0]α∕∕[0001]β1’∕∕[012]Mn, i.e., the β1' phase can form a coherent interface on the α-Mn phase.

    更新日期:2020-01-09
  • Effect of austenitization of cold-rolled 10 wt% Mn steel on microstructure and discontinuous yielding
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-09
    Dong Hwi Kim; Jee-Hyun Kang; Joo Hyun Ryu; Sung-Joon Kim

    A cold-rolled 10 wt% Mn steel was austenitized before intercritical annealing. Austenite and ferrite fractions and austenite stability remained equivalent to those of the non-austenitized counterpart. However, martensite that was generated on quenching after austenitization did not recrystallize during intercritical annealing, and austenite formed along lath boundaries of martensite to yield a ferrite + austenite lamellar structure. The transition from interface strengthening to strain hardening in the lamellar structure was not as evident as in equiaxed structure, owing to the higher dislocation density and lower interface strengthening in the lamellar structure than in the equiaxed structure. Consequently, discontinuous yielding is effectively prohibited in the lamellar structure.

    更新日期:2020-01-09
  • Comparison of Al2O3/Er3Al5O12/ZrO2 ceramics with eutectic composition prepared using hot-pressing sintering and melt growing
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-08
    Shunheng Wang; Juncheng Liu

    Al2O3/Er3Al5O12(EAG)/ZrO2 ceramics with eutectic composition were prepared with hot-pressing sintering and melt growing. The samples were divided into four sets, non-directionally solidified eutectic ceramics (N-DSEC), directionally solidified eutectic ceramics (DSEC), rapidly quenched eutectic ceramics (RQEC) and hot-pressing sintered ceramics (HPSC), respectively. The relationship between their microstructures and mechanical properties was investigated. The results show that RQEC has the highest hardness of 17.3 GPa, HPSC has the highest fracture toughness of 6.8 MPa m1/2, while DSEC has the highest flexural strength of 721.8 MPa. The increase of density, the improvement of microstructural uniformity and the decrease of defects are beneficial to the mechanical properties of the samples. The refinement of microstructure can increase the hardness, but not significantly within a certain range of solidification rate. The fracture toughness increases with the interface amount at the low growth rate. However, but too fast solidification rate may produce excessive residual stress and amorphous structure in the samples, and decrease the fracture toughness. In addition, the reasonable weakening of interface bonding strength could improve the fracture toughness of Al2O3/EAG/ZrO2 ceramics with high density. However, the weakened interface at the sample surface is inclined to become the starting point of failure, which is harmful to the flexural strength.

    更新日期:2020-01-09
  • Characterization of TaC-based fibrous-monolithic ceramics made of fibers with different core/shell volume ratios and orientations
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-08
    Vahideh Shahedifar; Mahdi Ghassemi Kakroudi; Naser Pourmohammadi Vafa

    In this paper, TaC-based/graphite fibrous monolithic ceramics made of fibers with three core/shell volume ratios (75/25, 70/30, and 65/35) and two orientations of 0° and 0°/90° were prepared. Then, the effects of fiber core/shell volume ratio and fiber orientation on the microstructure and room temperature mechanical properties were investigated. Hot pressing at 1800 °C for 60 min under 40 MPa resulted in the maximum relative density for [0°] specimens with the minimum shell thickness. The work of fracture and fracture toughness of FM specimens with 0°/90° fibers orientations were calculated lower than samples with 0° fibers orientations at the same core/shell volume ratio. SEM observations of fracture surfaces and side surfaces of specimens approved these data. So that delamination and fiber pullout occurred in a minimized extent for the specimens with the bi-directional architecture of [0°/90°] compared to the unidirectional architecture of [0°]. The results disclosed that the fracture toughness of 6.6 ± 0.4 MPa m1/2 and work of fracture of 2145 ± 56 J/m2, as the highest values, were obtained for C70/S30-[0°] specimens.

    更新日期:2020-01-09
  • Influences of thermal exposure on the microstructural evolution and subsequent mechanical properties of a near-α high temperature titanium alloy
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-08
    Juan Li; Jianming Cai; Yaqun Xu; Wenlong Xiao; Xu Huang; Chaoli Ma

    The microstructural evolution with respect to the precipitation of silicides and ordered α2 phase in near-α TA29 Ti alloy during thermal exposure at 650 °C for different time has been investigated in this work, and the subsequent mechanical properties have been evaluated by tensile and fracture toughness tests. The results indicated that the (Ti, Zr)6Si3 silicides firstly precipitated in residual β films, and then began to precipitate within α plates. A large number of fine α2 precipitates showing sphercial shape concurrently formed in the α plates at a short time. The ordered α2 precipitates asymmetrically grew up along different crystallographic directions with increasing exposure time, leading to their spherical shape change to ellipsoidal shape and finally olive shape, in which the long axis was perpendicular to [0001]α as viewed along [2¯110]α direction. The number density of ordered α2 was obviously decreased after 1000 h due to Ostwald ripening. The precipitation of silicides and ordered α2 phase improved the tensile strength but deteriorated the ductility and fracture toughness, whereas the strength was decreased and the room temperature elongation was recovered slightly after long-term exposure because of α2 ripening.

    更新日期:2020-01-09
  • Densification, microstructure and mechanical properties of an Al-14.1Mg-0.47Si-0.31Sc-0.17Zr alloy printed by selective laser melting
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-08
    Jiang Bi; Zhenglong Lei; Yanbin Chen; Xi Chen; Ze Tian; Jingwei Liang; Xikun Qin; Xinrui Zhang

    In this paper, the corresponding densification, microstructure, precipitate phase and mechanical properties of Al-14.1Mg-0.47Si-0.31Sc-0.17Zr fabricated by selective laser melting were detailly investigated. The experimental result shows that the densification of SLM specimens increased first and then decreased with energy density. Even at the same energy density, the relative densities of the samples are also different, and the printed sample has a high densification under the condition of low laser power and scanning speed. Two typical microstructures (fine grain zone and coarse grain zone) were formed inside the printed samples due to the formation of Al3(Sc, Zr) particles (coherent with the Al matrix) during the solidification process of SLM. As fabricated at 200 W and 500 mm/s, the average grain size of the SLM sample is 2.07 (Y-Z plane) and 1.72 μm (X–Y plane), and the maximum values of nano-hardness and tensile strength were 2.19 GPa and 510 MPa, respectively. The mechanical properties increased due to the combined effect of fine grain strengthening and dispersed distribution of precipitates in Al matrix. With a low density (2.537 g/cm3) and high tensile strength, the components fabricated by this alloy have more extensive spreading values and prospects for applying due to the excellent mechanical performance.

    更新日期:2020-01-08
  • Study of newly developed Ti–Al–Co alloys foams for bioimplant application
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    Amit Abhash; Pradeep Singh; Venkat A N Ch; Sriram Sathaiah; Rajeev Kumar; Gaurav K. Gupta; D.P. Mondal

    Ti–Al–Co (6 wt% of Al and varying amount of Co content) alloys foams of different space holder contents (40 ± 2.5 to 70 ± 5% by volume with an increment of 10%) were fabricated using ammonium bicarbonate (NH4HCO3) as space holder. These foams were analysed in terms of cell morphology, microstructure, mechanical and corrosion properties. The cell sizes were almost invariant to the Co content and space holder content. The cell wall thickness increased with increase in relative density. It was found that with increase in Co contents in the Ti–Al–Co alloys, compressive strength, Young's modulus, energy absorption capacity and microhardness increases. Empirical relations were established to correlate these mechanical properties with Co wt%, strain rate (έ) and relative density. The experimentally obtained results were also verified with the existing analytical relation. It was observed that the openness of the foams increases with increase in space holder content. It was found that the Co concentration in the samples does not influence degree of openness but it influences the corrosion behaviour of the investigated foams. The corrosion rate (in mmpy) and electrochemical potential parameters were also obtained in simulated bio fluid, and compared with those of other Ti-alloys and found to be in close agreement with each other.To examine the suitability for bone implant application, the investigated Ti–Al–Co alloys foams were compared with human cortical as well as cancelleous bone in terms of macrostructural, microstructural, corrosion behaviour and mechanical properties. In every aspects these foams were found to be suited for bone implant application.

    更新日期:2020-01-07
  • Study on variations of microstructure and metallurgical properties in various heat-affected zones of SLM fabricated Nickel–Titanium alloy
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    Behzad Farhang; Bharath Bhushan Ravichander; Federico Venturi; Amirhesam Amerinatanzi; Narges Shayesteh Moghaddam

    Nickel–Titanium (NiTi) is a material of great interest in modern industry as its shape memory and superelastic behaviors provide unique and useful properties that can be incorporated into complex designs and applications. However, due to its poor machinability, it is difficult to realize its full potential with conventional manufacturing techniques. With the advent of additive manufacturing, the potential for the use of NiTi in modern designs has been reignited and the analysis and optimization of its mechanical properties are a pivotal point of current material science research. Furthermore, insight into the variations of these material properties and how they vary throughout an additively manufactured part is key to improving the quality and repeatability of these parts. In this research paper, samples are printed using a single set of process parameters. These samples are then cut and analyzed for grain structure, chemical composition, microstructure, and hardness. Finally, results are reported and variations in these material properties are summarized.

    更新日期:2020-01-07
  • A nanocrystalline AlCoCuNi medium-entropy alloy with high thermal stability via entropy and boundary engineering
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    H.W. Deng; Z.M. Xie; M.M. Wang; Y. Chen; R. Liu; J.F. Yang; T. Zhang; X.P. Wang; Q.F. Fang; C.S. Liu; Y. Xiong

    A promising strategy involving the synergetic effects of the high-entropy engineering and interface architectures has been proposed to realize the thermal stability of nanocrystalline alloys. A bulk dual-phase nanocrystalline (DPNC-) AlCoCuNi medium-entropy alloy was prepared by mechanical alloying (MA) and spark plasma sintering (SPS) process. These DPNC structures include Cu-rich and AlCoNi-rich nanocrystallines (NCs) with an average grain size of 46 nm. This DPNC-AlCoCuNi material could maintain the nanostructures as well as a high hardness of about 580 HV even after annealing at 900 °C for 50 h. The extremely high thermal stability has been attributed to the extensive thermal-stabled low-energy phase boundaries, low-angle grain boundaries, the high-entropy and sluggish diffusion effects.

    更新日期:2020-01-07
  • Structural and microstructural influence on deformation and fracture of dual-phase steels
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    Xinzhu Zheng; Hassan Ghassemi-Armaki; Ankit Srivastava

    The objective of this work is to demonstrate that the mechanical response of multiphase materials is fundamentally different in an imposed deformation field that is homogeneous, versus in an imposed deformation field that is heterogeneous, at a length-scale greater than the microstructural length-scale. To this end, we focus on two dual-phase steels with significantly different nominal chemical composition and microstructure. The mechanical response of the steels is characterized by in-situ SEM tensile tests of flat dog-bone and single-edge notch specimens. The experimental results show that the dog-bone specimens of the two steels exhibit very similar mechanical response but the mechanical response of their single-edge notch specimens differs significantly. This is in contrast to any classical analysis that will predict the same mechanical response in the presence of a notch for two materials that give the same mechanical response under uniaxial tension. The high resolution in-situ tests coupled with microstructure-based digital image correlation and finite element analysis are then used to elucidate how the interlacing of imposed heterogeneous deformation field and material microstructure affects the mechanical response of these steels. Our results clearly highlight that a mechanistic analysis of multiphase materials under imposed heterogeneous deformation field must involve explicit consideration of the length-scales associated with the material microstructure.

    更新日期:2020-01-07
  • Nitrogen-induced yield point phenomenon in an austenitic steel
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    J.-H. Shin; J.-S. Jeong; J. Lee; S.-D. Kim; J.H. Jang; Joonoh Moon; H.-Y. Ha; T.-H. Lee
    更新日期:2020-01-07
  • Consolidation of Ti6Al4V alloy and refractory nitride nanoparticles by spark plasma sintering method: Microstructure, mechanical, corrosion and oxidation characteristics
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    J.O. Abe; A.P.I. Popoola; O.M. Popoola

    Ti6Al4V alloy combines excellent mechanical and chemical characteristics attractive in some important applications in the automotive and aerospace industries but its insufficient hardness and high-temperature oxidation subdue its extensive use. This work was undertaken to modify the microstructure and improve the current limitation of Ti6Al4V alloy with the intention of not affecting its desirable properties. Therefore, the effects of different refractory nitrides: aluminium nitride (AlN), titanium nitride (TiN) and hexagonal boron nitride (h-BN) reinforcements on the microstructure, mechanical, chemical and oxidation properties of spark plasma sintered Ti6Al4V-based binary composites were investigated. Spark plasma sintering technique was effectively utilized to consolidate the Ti6Al4V powder and 3 wt% nanoparticles of AlN, TiN and h-BN respectively. The microstructure and phase composition of the sintered composites were examined by scanning electron microscopy, optical microscopy, and X-ray diffractometry; densification was evaluated according to Archimedes' principle and microhardness was measured by Vickers’ microhardness test. The corrosion and oxidation behaviour of the samples were studied by linear polarization experiment and thermal gravimetric analysis respectively. It was found that the binary composites produced attained almost full theoretical relative densification (98.23–99.54%) due to adequate diffusional mass transport in solidly bonded particles at the matrix-reinforcement interfaces. Ti6Al4V-3h-BN composite gave the optimal combination of relative densification (99.54%) and microhardness (7030 MPa) which exceeds 200% of the monolithic alloy and about 48% superior to both composites with AlN and TiN reinforcements. The yield and ultimate tensile strengths of the matrix were improved by approximately 47% via the AlN and TiN nanoparticle additions and significantly by 116% through the nano-h-BN addition. Ti6Al4V–3AlN demonstrated most superior electrochemical corrosion resistance with a current density of 3.66 μA/cm2 and a polarization resistance of 8760.2 Ω in the sulphuric acid medium while Ti6Al4V–3TiN with the least normalized weight gain of 0.85 mg/cm2 showed the greatest resistance against oxidation in the high-temperature oxidizing environment.

    更新日期:2020-01-07
  • A new method for preparing high entropy alloys: Electromagnetic pulse treatment and its effects on mechanical and corrosion properties
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    Y. Guo; L. Liu; W. Zhang; K.D. Yao; W. Chen; J. Ren; J.G. Qi; B. Wang; Z.F. Zhao; J. Shang; Y. Zhang; J. Xiang

    Electromagnetic pulse (EMP) treatment was firstly applied during the preparation process of CoCrFeNiCu high entropy alloy (HEA) and its mechanism was illustrated. The crystal structure, microstructure, mechanical properties, and corrosion properties of CoCrFeNiCu HEAs in current and magnetizing directions with different EMP frequencies were characterized. The results demonstrated that EMP can significantly influence the lattice parameter, microstructure, enhance mechanical and alter corrosion properties. When EMP applied, the dendrite arms were severely coarsened and the microstructure changed from typical dendrite to quasi-equiaxed morphology. The hardness and yield strength were increased by 18% and 23%, respectively. Meanwhile, corrosion current density decreased from 5.4 μA cm−2 to 1.4 μA cm−2. Anisotropy effect was revealed between the current and magnetizing directions in the same ingot, which is seldom reported before. The gap of interplanar distances, mechanical properties and corrosion properties between these two perpendicular directions became smaller and close to each other with increasing EMP frequency.

    更新日期:2020-01-07
  • Notch-tensile behavior of Al0.1CrFeCoNi high entropy alloy
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    Subhasis Sinha; Mageshwari Komarasamy; Tianhao Wang; Ravi Sankar Haridas; Priyanka Agrawal; Shivakant Shukla; Saket Thapliyal; Michael Frank; Rajiv S. Mishra

    Notch-tensile behavior of an Al0.1CrFeCoNi high entropy alloy (Al0.1-HEA) was studied using V-notch geometry and with local strain mapping using digital image correlation (DIC). A notch-strength ratio of 1.51 indicated notch strengthening. Further analysis of stress-strain response supplemented with microstructural analysis revealed that, while the presence of notch results in strengthening due to work hardening by twinning induced plasticity, the notch also contributes strongly to geometrical softening in the non-uniform ductility regime, and accounts for the onset of failure. The strain localization behavior of Al0.1-HEA due to the presence of V-notch was compared with three conventional alloys: Inconel 625 nickel-based superalloy, 304 stainless steel and Ti–6Al–4V titanium alloy. The study revealed that the nature of notch widening with increasing strain was dependent on material characteristics. The extent of notch widening impacted the local strain field and stress distribution, thereby influencing the propensity for crack initiation and growth. The experimental results were verified by finite element analysis.

    更新日期:2020-01-07
  • Tailoring the mechanical properties of Mg–Zn magnesium alloy by calcium addition and hot extrusion process
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    Z. Zareian; M. Emamy; M. Malekan; H. Mirzadeh; W.J. Kim; A. Bahmani

    Grain refinement and enhanced mechanical properties of Mg–2Zn-xCa alloys (with a wide range of calcium contents from 0 to 5 wt%) were studied in both as-cast and extruded conditions. It was revealed that Ca addition can effectively refine the grain size of the ingots based on the growth restriction factor (GRF) mechanism, where at high Ca additions, the dendritic microstructure was obtained. By increasing the amount of Ca, the binary Mg–Zn phase was replaced by the Ca2Mg6Zn3 phase and at high Ca contents, the Mg2Ca phase appeared in the microstructure. The tensile properties were enhanced at low Ca additions (up to 0.3 wt%) due to the grain refinement but they were deteriorated at higher Ca additions due to the formation of grain boundary second phases. Accordingly, the ultimate tensile strength (UTS) of 228 MPa and total elongation of 20% was obtained for the as-cast Mg–2Zn-0.3Ca (ZX20) alloy. During hot extrusion, significant grain refinement and the fracturing and dispersion of second phase particles were observed. The grain size refinement beyond ∼1 wt% Ca was negligible and extrusion defects were observed at higher Ca contents, and hence, the best combination of mechanical properties was obtained for the Mg–2Zn–1Ca (ZX21) alloy with UTS of 283 MPa and elongation to failure of 29%. This alloy showed a desirable work-hardening behavior and the best combination of tensile properties, where the product of tensile strength and total elongation reached as high as ∼8000 MPa%. Finally, the yield stress of the alloys was correlated to the average grain size via the classical Hall-Petch plot with a slope of 228.5 MPa μm−0.5.

    更新日期:2020-01-07
  • The enhanced superplasticity of a 2024 matrix nanocomposite reinforced by TiC particles
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    Huabing Yang; Kai Zhao; Jinfeng Nie; Xiangfa Liu
    更新日期:2020-01-07
  • A room temperature formable magnesium–silver–calcium sheet alloy with high ductility
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    Mingzhe Bian; Xinsheng Huang; Yasumasa Chino

    A newly developed magnesium sheet alloy, Mg–1.5Ag–0.1Ca in wt.%, shows a large index Erichsen value of 8.6 mm with a large average elongation to failure of 33% at room temperature (RT). The excellent RT formability and ductility are associated with a weak ring-like basal texture.

    更新日期:2020-01-07
  • Microstructure and microhardness of dissimilar weldment of Ni-based superalloys IN718-IN713LC
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    R.R. Ye; H.Y. Li; R.G. Ding; T.J.A. Doel; S. Bray; A. Walpole; P. Bowen

    Ni-based superalloys IN718 and IN713LC have been joined through linear friction welding (LFW) in this study. The variation of microstructure across the weld line developed during linear friction welding and after post weld heat-treatment (PWHT) has been investigated. Their effects on microhardness have also been studied. A clean weld region which is free of micro-porosity, micro-cracking and oxides, was achieved. Dynamic recrystallisation (full and partial) occurred on both sides of the weld, which produced much finer grains in the recrystallised zone. Dissolution of ‘parent’ γʹ/γʹʹ, towards the weld line was observed on each side of the weld. However, reprecipitation of γ′ was only found in the as-welded IN713LC. All these were found to have a huge impact on the hardness profile. A softer heat affected zone (HAZ) was found in the IN718 side with the lowest hardness value achieved at an axial position 0.6 mm from the weld line. The increased dissolution of γ'/γ'´ towards the weld line resulted in decreasing hardness towards the weld line. However, the formation of refined grains closer to the weld line increased the hardness towards the weld line from axial position 0.6 mm. In contrast, a harder HAZ was found in the IN713LC side, which resulted from the formation of finer reprecipitated γ′ and recrystallised grains. PWHT brought about reprecipitation and/or further reprecipitation of γʹ/γʹʹ in the IN718 and IN713LC HAZs, resulting in stronger HAZs.

    更新日期:2020-01-07
  • Fatigue behavior of AW7075 aluminum alloy in ultra-high cycle fatigue region
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    S. Fintová; I. Kuběna; L. Trško; V. Horník; L. Kunz

    Advanced electron microscopy methods were used with the aim to explain the differences in the response of strengthened AW 7075 – T6511 aluminum alloy to fatigue loading at 5 Hz and 20 kHz. The shift of the S–N curve to higher number of cycles to fracture for the specimens tested at high frequency was experimentally determined. This effect is not connected with a change of the fatigue crack initiation mechanism and site from the surface to material interior. The absence of slip markings and cracking of primary intermetallic particles on the surface of cycled specimens were characteristic features. A difference in the dislocation density and dislocation arrangement in the vicinity of the fatigue crack initiation sites was shown to be the only observable effect. However, consistent with the strengthened structure of the alloy, no specific dislocation structure due to the cyclic loading was observed, regardless of the loading frequency and stress amplitude.

    更新日期:2020-01-07
  • Specific forward/reverse latent heat and martensite fraction measurement during superelastic deformation of nanostructured NiTi wires
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-07
    Henrique Martinni Ramos de Oliveira; Hervé Louche; Estephanie Nobre Dantas Grassi; Denis Favier

    This study analyses the thermomechanical tensile behaviour of a cold drawn Ti-50.9at.%Ni wire submitted to heat treatment at 598 K for 30 min, which is below the recrystallization temperature (623 K). Such low temperature heat treatment induces a superelastic loop without a stress plateau. However, the absence or weakness of peaks on its differential scanning calorimetry prevents the determination of specific latent heat. This is a common effect of nanostructured materials such as superelastic wires. A method using strain and temperature field measurements was developed and used to determine thermal power and thermal energy during superelastic tensile tests through a heat balance. From these results and using a thermodynamic approach, forward and reverse specific latent heat and the martensite fraction are estimated as a function of strain and stress.

    更新日期:2020-01-07
  • Interface design of lead-free free-cutting titanium reinforced graphite brass composites and its effect on mechanical properties and cutting performance
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-03
    Xin Zhang; Chen Ma; Shufeng Li; Deng Pan; Feiyang Zheng

    Graphite (Gr) is used as a substitute element for lead to avoid environmental pollution and human hazards due to its solid lubrication and chip breaking similar to lead in brass. However, the mechanical properties of brass would be reduced due to non-wetting and weak interfacial bonding between Gr and brass matrix. Based on the preparation of graphite brass composites by powder metallurgy (P/M), the strength of the matrix is expected to be enhanced by solution and precipitation strengthening of titanium (Ti), and the interface bonding between Gr and brass matrix is improved by interfacial reaction of Ti with Cu and Gr to form intermetallic compounds. The results show that the addition of Gr can significantly improve the cutting performance of brass, but it is at the expense of mechanical properties. With the introduction of Ti, the formation of submicron Cu2Ti4O particles and nano Ti clusters effectively improves the mechanical properties of brass matrix. Meanwhile, TiC reaction layer formed on the interface significantly strengthens the interfacial bonding between graphite and the matrix, which is the basis of ensuring the good cutting performance of brass. The original graphite/brass non-reactive interface is transformed into graphite/reaction layer/brass and brass/precipitates/brass dual-interface structure. This study lays a research foundation for the development of lead-free free-cutting brass composites.

    更新日期:2020-01-04
  • Shear deformation behavior of Zircaloy-4 alloy plate
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-03
    Fusen Yuan; Geping Li; Fuzhou Han; Yingdong Zhang; Ali Muhammad; Wenbin Guo; Hengfei Gu

    Zircaloy-4 alloy is widely used in light water reactors. During cold rolling, this alloy is prone to cracking under shear stress. The microstructural characteristics after shear deformation have been investigated in this study in order to provide technical support for avoiding failure of this alloy. Shear tests for recrystallized Zircaloy-4 alloy plate were performed at room temperature using a designed shear testing device. Shear fracture surface and microstructure were carefully characterized by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) techniques, respectively. Results showed that grains in the initial plate are strongly oriented with their c-axis close to the transverse direction (TD). Shear fracture surface can be simply divided into two typical zones based on the morphology features: (I) smooth zone and (II) rough zone. The plate exhibited anisotropy of shear yield strength in the order given as: Normal direction (ND) slip and {101¯2}<1¯011> tensile twinning were the predominant deformation modes during the shear deformation. In addition, {101¯2}<1¯011> tensile twinning activity was high in grains oriented with their c-axis perpendicular to the shear stress direction (SSD). Furthermore, work hardening occurred due to slip and twinning in the shear deformation region (SDR), which substantially increased the microhardness of the SDR (198 HV) as compared to that of matrix (157 HV). Shear failure tended to occur on the RD-TD45° plane with external load.

    更新日期:2020-01-04
  • Effect of gradient microstructure pinned by δ phase on elevated temperature performances of GH4169
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-03
    Rong-shen Huang; Yong-an Sun; Lei-lei Xing; Guo-lin Song; Wei Liu; Qiu-lin Li

    A microstructure of gradient grains pinned by gradient δ phase was obtained within GH4169 by ultrasonic rolling followed by a post heat-treatment at either 900 °C or 954 °C for 5, 15 or 30 min, respectively. In order to evaluate the high temperature stability of such gradient microstructure, the variations of grain size and gradient microhardness of GH4169 were measured after being kept at 650 °C for 10–100 h. Hot tensile tests at 650 °C were conducted to reveal the effects of refined grains and δ phase on mechanical properties. The results showed that the amount of δ phase decreased with the depth increasing, while recrystallized grain size presented the opposite trend. And the cross-sectional microhardness within strengthened layer decreases as depth increases after post heat-treatment. The ultrasonic rolled sample treated at 900 °C for 15 min (900–15) brings a relatively finer δ phase which distributes both in grains and grain boundaries. Such microstructure results in a better pinning effect compared with the one treated at 954 °C for 15 min (954–15) with less δ phase only distributed in grain boundaries. The gradient refined grains and δ phase contributes to the improvement on tensile strength at 650 °C in Sample 900–15 with YS (Yield strength) = 903 MPa, UTS (Ultimate tensile strength) = 988 MPa (21% and 6% improvement compared with Sample 0-900-30, respectively). The gradient microstructure with refined grains pinned by δ phase showed good thermal stability and mechanical properties at 650 °C.

    更新日期:2020-01-04
  • Environmentally assisted cracking susceptibility of dark etched HAZ/ parent metal interface region of 18Ni 250 maraging steel weldment
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-03
    Renu N. Gupta; V.S. Raja

    Gas tungsten arc welding is widely employed to fabricate large sized motor casings made of 18Ni 250 maraging steel. However, small transverse cracks have been found to appear at the interface of the dark etched heat affected zone (HAZ) of such weldments after about a year of welding, prior to aging treatment. In order to understand the delayed cracking phenomena vis-à-vis the influence of multiple weld passes, thermal cycles were obtained at different locations of the heat affected zone. The results suggest the formation of two more HAZs designated as HAZ III and HAZ IV in addition to those two currently reported in the literature. The two regions namely, HAZ III and HAZ IV, respectively correspond to peak aging and under aging conditions of the alloy. In order to examine the effect of these thermal cycles on the environmentally assisted cracking of the weldment, thermal simulations corresponding to various HAZs were applied on to specimens with Gleeble. They were examined for their susceptibility to EAC in neutral and acidified 0.1 M NaCl solutions. The study reveals that it is only the HAZ IV, lying at the interface of the dark etched HAZ, corresponding to under aging condition, is responsible for the weld failure.

    更新日期:2020-01-04
  • Assessment in predictability of visco-plastic self-consistent model with a minimum parameter approach: Numerical investigation of plastic deformation behavior of AZ31 magnesium alloy for various loading conditions
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-03
    Qiang Chen; Li Hu; Laixin Shi; Tao Zhou; Mingbo Yang; Jian Tu

    By predicting the complex deformation mechanisms, visco-plastic self-consistent (VPSC) model has been found to be a useful tool for investigating plastic deformation behavior of magnesium alloy. The standard version of VPSC model involves a large number of adjustable parameters. Using independent arguments obtained from single tests, VPSC model with a minimum parameter approach immensely reduces the number of adjustable parameters, hence shows huge potential in simulating plastic deformation behavior of thin magnesium alloy sheet. The predictability of this new approach is thoroughly assessed in the present study. Although only the mechanical response of in-plane tension (IPT) in AZ31 magnesium alloy is applied to calibrated the corresponding material parameters, simulated results in terms of texture evolution using VPSC model with a minimum parameter approach show a relatively small difference by comparison with the predicted ones applying the standard version of VPSC model during IPT, in-plane compression (IPC), through-thickness compression (TTC), and plane strain compression (PSC), respectively. Furthermore, the corresponding activated deformation mechanisms during various deformation processes are further analyzed. With the exception of pyramidal slip, the predicted activities of remaining deformation mechanisms are generally consistent with each other. This phenomenon is identified to be the root of minor difference in texture evolution. Moreover, the predicted activities in pyramidal slip using VPSC model with a minimum parameter approach are relatively higher than the corresponding ones in the case with the standard version of VPSC model. However, these reported results are not beyond the maximum of published literature, and hence are acceptable when simulating various plastic deformation behavior of AZ31 magnesium alloy.

    更新日期:2020-01-04
  • Flash-butt welded Ti6242 joints preserved base-material strength and ductility
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-03
    Pingwei Xu; Lei Zhou; Moliu Han; Zhijian Wei; Yu Liang

    Microstructure and mechanical properties of flash-butt welded two-phase Ti–6Al–2Sn–4Zr–2Mo (Ti6242) alloy are investigated. High ductility that is at least comparable to that of the matrix and extra strain hardening are achieved in welded joints because of the formation of a particular semi-equiaxed structure in the double-affected zone (DAZ). Also, no strength loss is observed, and this is attributed to a uniform hardness distribution in a narrower welding zone. The soft DAZ, which is sandwiched between the welding seam and stress-affected zone, enables better deformation compatibility among these zones, and weakens their stress concentration. Furthermore, such semi-equiaxed structure effectively suppresses the formation of dense slip bands and crack nucleation and provides a strong barrier against its propagation. This work provides a new understanding of this particular microstructure, which is expected to have a higher combination of strength and ductility in Ti alloys.

    更新日期:2020-01-04
  • Effect of crystal orientation on the indentation behaviour of Ni-based single crystal superalloy
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-02
    Qi-Nan Han; Shao-Shi Rui; Wenhui Qiu; Yue Su; Xianfeng Ma; Zimu Su; Haitao Cui; Huiji Shi

    The indentation behaviours of Ni-based single crystal (NBSX) superalloy in different crystal orientations are studied by indentation tests and Electron Backscattered Diffraction (EBSD) analysis. The effects of crystal orientations on pile-up modes, dominant slip system distribution and geometrically necessary dislocation (GND) density distribution are revealed by experiments and crystal plasticity finite element (CPFE) simulation. The results and analysis of pyramid and cone indentations show that the pile-up modes produced by different azimuths are significantly different due to the off-plane displacement distribution. The differences of crystallographic slip behaviors under different crystal orientations induce different slip line and indentation symmetry patterns. EBSD observation and CPFE analysis indicate the dependence of GND density distribution on crystal orientations. The results of indentation tests, EBSD observation and CPFE simulation achieve good agreements.

    更新日期:2020-01-02
  • Enhanced precipitation strengthening of extruded Mg-8 wt.%Al-0.5 wt%Zn (AZ80) magnesium alloy by extension twinning
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-02
    Guoliang Shi; Jiawei Yuan; Ting Li; Kui Zhang; Xinggang Li; Yongjun Li; Minglong Ma

    Extension twinning is not only a key plastic deformation mode of Mg and its alloys at room temperature (RT), but also introduces high density of dislocations and changes crystal orientation (texture) which exert considerable influence on precipitation strengthening and mechanical properties. Using tensile test, quasi-in-situ hardness test, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the effects of extension twinning on age-hardening, precipitation behavior and mechanical properties of an extruded AZ80 bar were investigated. Extension twins were introduced into the bar by cold compressed (H1) along extrusion direction (ED), and two kinds of aging treatments, i.e. ‘on-line quenching + aging’ (T5) and ‘on-line quenching + H1 + aging’ (T10), were conducted at 150 °C. We clarified that extension twinning can significantly accelerate precipitation kinetics. For T5 aging, there is an incubation stage in the first 15 h, and then the hardness increases continually and slowly in the following 35 h. By contrast, for T10 aging, softening is caused in the first 2.5 h, and then the hardness increases linearly until 20 h and remains stable in the next 30 h. Discontinuous precipitation is predominant in T5 aging; however, discontinuous precipitation is mostly inhibited in T10 aging and at the same time nano-sized continuous precipitates with high number density are formed in both extension twins and matrixes. Extension twins contains higher dislocation density and thus denser continuous precipitates than matrixes. Both and dislocations can be seen in extension twins and matrixes. Mechanical properties have been largely improved by extension twins. Particularly, after T10 the ED tensile yield strength (Rp0.2) remarkably increases from 144 MPa (H1) to 206 MPa, indicating that dense nano-sized continuous precipitates can effectively hinder twin-boundary migration during the detwinning. Moreover, T10 can obviously diminish the machinal property anisotropy as compared with T5.

  • Developing a high-strength Al–11Si alloy with improved ductility by combining ECAP and cryorolling
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2020-01-01
    Dan Song; Guowei Wang; Zhikai Zhou; Edwin Eyram Klu; Bo Gao; Aibin Ma; Yuna Wu; Jiapeng Sun; Jinghua Jiang; Xiaolong Ma

    In this study, a high-strength Al–11Si alloy with an improved ductility was developed via a two-step processing route - equal-channel angular pressing (ECAP) and post-cryorolling. Specifically, the cast alloy was ECAP processed at 623 K for 16 passes, followed by multi-pass cryorolling with 50% thickness reduction. Herein, its mechanical properties was evaluated, and the underlying mechanisms for the improvement of both strength and ductility was investigated. Through systematic comparisons with other samples, including the cast, the cast-rolled, the ECAP-processed and the ECAP-annealed samples, we found the respective origin for the high strength and the improved ductility in the processed alloy. On the one hand, the high strength resulted from both grain boundary strengthening and dislocation strengthening caused by the thermo-mechanical processing. On the other hand, the improved ductility was primarily dictated by the uniform distribution of the very fine Si particles due to the attendant fragmentation of the Si phase during ECAP process. In addition, the results showed that the superior combination of strength and ductility could not be achieved by either processing step alone. This two-step processing route is also promising to benefit other Al–Si alloys for structural applications by optimizing their mechanical properties.

    更新日期:2020-01-01
  • Microstructural, physical and mechanical characterization of grinding sludge based aluminum metal matrix composite
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2019-12-31
    Kanhu Charan Nayak; Parag Rajendra Deshmukh; Ankit Kumar Pandey; Prem Kumar Vemula; Prashant P. Date

    In the present study, industrial waste has been used as reinforcement in pure aluminium to enhance the physical and mechanical properties. This can be effectively obtained by the creation of Aluminium Metal Matrix Composites (AMMC). The present research work is focused on the synthesis of grinding sludge (GS) based AMMC by powder metallurgy. The composites contain pure Al matrix reinforced with three different weight percentages of grinding sludge constituents (6, 16 and 29 wt%). After that, the microstructure, density, hardness and compressive strength at room temperature are investigated. The presence of AlFe and AlFe3 inter-metallic compounds has been examined using SEM (scanning electron microscope) area mapping and XRD (X-ray Diffraction). The density and hardness of composite materials were calculated for all samples. It is observed that the sample with 6 wt% GS sintered at a temperature of 700 °C shows 23% rise in compressive strength than that of the matrix when deformed to 48%. The strengthening mechanism of this sample indicates that the load-bearing, dislocation strengthening and phase transformation are the main contributors. The hardening behaviour based on the flow curves obtained from experiments has been studied using the Voce equation. Further, a modified Voce equation incorporating sintering temperature has been established for the Al/6 wt% GS composite material. This equation predicts the flow stress with good agreement to experimental flow stress concerning average absolute relative error (AARE) ranging from 0.37% to 4.44%.

    更新日期:2019-12-31
  • Compressive creep behavior of a γ-TiAl based Ti–45Al–8Nb–2Cr-0.2B alloy: The role of β(B2)-phase and concurrent phase transformations
    Mater. Sci. Eng. A (IF 4.081) Pub Date : 2019-12-31
    Vajinder Singh; Chandan Mondal; Rajdeep Sarkar; P.P. Bhattacharjee; P. Ghosal

    The primary and steady-state compressive creep deformation behavior of an as-cast high Nb containing γ-TiA1 alloy having remnant β(B2)-phase has been studied over the temperature range of 750–850 °C at constant initial applied stress levels between 75-200 MPa. The creep curves derived over the entire creep testing conditions show a prominent primary creep regime which is attributed to the presence of dislocation debris of the coarse γ-grains at the colony boundaries. The stress and temperature dependence of the steady-state creep rate follows the Norton-Bailey power law and the corresponding average value of the stress exponent and apparent activation energy are estimated to be 3.6 and 375 kJ/mol, respectively. The average value of the stress exponent in conjunction with the dislocation substructure of the crept samples suggests that the kinetics of creep deformation within the studied experimental conditions is controlled by the non-conservative motion (climb) of dislocations. Further misorientation analyses of the phase-resolved EBSD maps imply that for most of the conditions creep strain is carried by the γ-TiAl phase. Consequently, contrary to the commonly believed idea, the β(B2)-phase does not appear to deteriorate the creep resistance of the present alloy below suitable combinations of temperature and stress. Beyond these conditions, the concurrent deformation of γ-TiAl and β(B2)-phases is found to enhance the steady-state creep rate. In addition, characteristics of the dynamic transformation of β(B2) phase into γ and α2 phases during creep and its effect on the steady-state creep rate are further considered. Finally, the application potential of the present alloy is compared through a composite plot of Larson-Miller parameter with several other potential alloys reported in the literature.

    更新日期:2019-12-31
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