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  • Influence of Cu addition on corrosion behavior and tensile performance of Ni-30Co-16Cr-15Mo-6Fe alloy
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-17
    Biaobiao Yang; Yuhang Hou; Qian Lei; Yunping Li; Akihiko Chiba

    Corrosion behavior in 5.2 M aqueous hydrofluoric acid solution and tensile properties of Ni-30Co-16Cr-15Mo-6Fe-xCu (x = 0, 0.5, 2, and 6) (mass%) alloys are investigated. The corrosion resistance of alloy can be significantly improved by the slight additions of Cu (e.g. 0–2 mass%) without altering either the microstructure or the tensile properties of alloy. On the contrary, alloy with higher addition of Cu, characterized by Cu-rich phases both at grain boundaries and inside the matrix, demonstrates lower corrosion resistance and lower tensile strength. Interestingly, corrosion resistance in grain boundary of alloy gradually increases with Cu content increasing irrespective of the appearance of Cu-rich phases.

    更新日期:2020-01-17
  • Influence of inter/intra-granular κ-carbides on the deformation mechanism in lightweight Fe-20Mn-11.5Al-1.2C steel
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-17
    Chiwon Kim; Mathieu Terner; Hyun-Uk Hong; Chang-Hoon Lee; Seong-Jun Park; Joonoh Moon
    更新日期:2020-01-17
  • Effect of torsional rate on the gradient microstructure, texture evolutions and microhardness of pure copper
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-17
    Mingxue Zhang; Liping Deng; Bingshu Wang; Hongliang Xiang

    The effect of torsional rate on the microstructure and texture of pure Cu at an equivalent strain of 3.94 was investigated by electron backscatter diffraction technique. The microstructure, texture evolutions and microhardness at different regions along radial directions were quantitatively analyzed. The results demonstrated that the grain size and microhardness reduced gradually along the radial direction, showing characteristics of gradient distribution. However, the torsional rate didn't show significant effect on them. The texture results showed that typical torsion textures developed during deformation. A/-A texture and B/-B texture were the major components in the center and 1/4 layer, and showed similar changes at different regions. While at the edge, C texture prevailed, and its strength increased as the torsional rate rose. The torsional rate, however, didn't show significant effect on the texture development of A/-A and B/-B textures as well.

    更新日期:2020-01-17
  • Effect of martensite–austenite constituents on impact toughness of pre-tempered MnNiMo bainitic steel
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-16
    Changsheng Xie; Zhengdong Liu; Xikou He; Xitao Wang; Shibin Qiao

    The martensite-austenite constituents are known to deteriorate the impact toughness of alloyed steel. In order to reduce this adverse effect, the pre-tempering process at low temperatures was introduced before the tempering of intercritical heat treatment process of a MnNiMo bainitic steel. The effects of pre-tempering temperature on the decomposition of martensite-austenite constituents and impact toughness properties of the pre-tempered specimens were investigated. The results of instrumented Charpy V-notch impact testing show that the impact toughness of the materials can be significantly improved by the pre-tempering process, especially for the condition of pre-tempering at 400 °C. After pre-tempering at 400 °C, more martensite-austenite constituents are decomposed into ferrite and small carbides, resulting in the reduction of microcracks nucleation sites. The residual martensite-austenite constituents become mainly the island-like, which can effectively hinder the propagation of secondary cracks. In addition, the pre-tempering at 400 °C increases the fraction of high-angle grain boundaries and refines the size of blocks, which can effectively prevent or deflect the propagation of microcracks. All of those microstructure changes are beneficial to the crack propagation energy. The results suggest that the application of the pre-tempering process is a feasible method to enhance the impact toughness of the studied alloyed steel.

    更新日期:2020-01-17
  • Electron Backscatter Diffraction (EBSD) analysis of laser-cladded AISI 420 martensitic stainless steel
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-15
    Mohammad K. Alam; Mehdi Mehdi; Ruth Jill Urbanic; Afsaneh Edrisy

    Laser cladding is a novel method to coat part of a substrate or to produce a three-dimensional object in layers by layers following a computer-controlled instruction. In this study, laser-cladded AISI 420 martensitic stainless steel was characterized using the Electron Backscatter Diffraction (EBSD) technique to analyze the substructure of martensite in the selected zones such as the bead zone (BZ), the dilution zone (DZ), and the interface with the heat affected zone (HAZ) of the bead. The EBSD inverse pole figure (IPF) revealed planer and columnar grains at the interface and within the adjacent dilution zone, while equiaxed and a combination of both columnar and equiaxed grains were observed in the center of the bead and dilution zone. The Grain Orientation Spread (GOS) and grain average Image Quality (IQ) techniques were used to quantify the grain misorientation and residual strain/stress in those selected zones. The EBSD analysis with the GOS and IQ values confirmed deformation and strain in the crystal lattice structure of those respective zones. The GOS approach revealed that most of the grains at the BZ and HAZ were highly strained and 26–59% fraction of the grains was at a high angle of GOS (3°–5°) indicating the availability of highly deformed grains in both regions. The IQ value was compared and correlated with the experimental values of residual stresses (RS) measured by XRD methods to understand residual strain distribution in those zones. It was revealed that the IQ value is inversely proportional to the RS value found in an earlier study. This EBSD parameter is expected to be used as an alternative method of analyzing RS distribution in the laser-cladded coating.

    更新日期:2020-01-15
  • Effects of electroshock treatment on microstructure evolution and texture distribution of near-β titanium alloy manufactured by directed energy deposition
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-15
    Lechun Xie; Haojie Guo; Yanli Song; Chang Liu; Zhongqi Wang; Lin Hua; Liqiang Wang; Lai-Chang Zhang
    更新日期:2020-01-15
  • Does the stacking fault energy affect dislocation multiplication?
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-15
    Juan Li; Christoph Kirchlechner

    This paper investigates the interdependence of the stacking fault energy (SFE) and the stress required for dislocation multiplication. For this purpose copper-aluminum (Cu-Al) alloys with varying Al content are investigated by spherical nanoindentation. The load-displacement curve shows a characteristic pop-in, which is interpreted as elastic-plastic transition and correlated to the dislocation source nucleation and/or activation stress. The statistical analysis of the pop-in behaviour documents a strong dependence of the maximum shear stress beneath the indenter on the Al content, which cannot be explained by a variation in shear modulus. Instead, the pop-in stress clearly increases with increasing stacking fault energy.

    更新日期:2020-01-15
  • Microstructural characteristics and properties of spray formed Zn-rich Al-Zn-Mg-Cu alloy under various aging conditions
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-11
    Allah Ditta; Lijun Wei; Yanjin Xu; Sujun Wu

    In this study, the single- and dual-aging characteristics of a spray formed plus extruded Zn-rich Al-Zn-Mg-Cu alloy were investigated through hardness and electrical conductivity curves, tensile tests, and transmission electron microscopy. The results show that the single-aged alloy presents dual-peak hardness with aging time, while the hardness gradually drops with the progress of the dual-aging process. Accordingly, the peak-aged alloy which corresponds to the maximum hardness during single-aging, demonstrates excellent strength but relatively low conductivity, whereas the strength of the dual-aged alloy steadily decreases and conductivity increases with the extension of aging time. The microstructure of the peak-aged alloy exhibits the high volume fraction of fine and uniformly distributed intragranular precipitates consisting mainly of ή phase, and displays continuous grain boundary precipitates (GBPs) with no obvious precipitation free zone (PFZ). In the dual-aging process, the pre-aging treatment produces high density of very fine intragranular precipitates comprising of GP-I zones/partly transformed to ή, which gradually grow and finally convert to equilibrium η phase as the aging proceeds at second-step temperature, simultaneously, the GBPs show progressively more discontinuous distribution and widening PFZ. In addition, the corrosion susceptibility of the alloy is discussed with reference to the evolved microstructure and the conductivity values.

    更新日期:2020-01-13
  • Preparation of TA15 powder reinforced 45CrNiMoY alloy steel with high mechanical property by pre-laid laser cladding technology
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-11
    Mingwei Wei; Suiyuan Chen; Miao Sun; Jing Liang; Changsheng Liu; Mei Wang
    更新日期:2020-01-13
  • Significant improvement in mechanical properties of Mg-Zn-La alloy by minor Ca addition
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-11
    Xin Wang; Yuzhou Du; Dongjie Liu; Bailing Jiang
    更新日期:2020-01-13
  • High specific strength Mg-Li-Zn-Er alloy processed by multi deformation processes
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-11
    Qing Ji; Yang Wang; Ruizhi Wu; Zhen Wei; Xiaochun Ma; Jinghuai Zhang; Legan Hou; Milin Zhang

    Under the industrial demand of energy saving, weight loss has become one of the current concerns. By increasing the strength of Mg-Li alloy with high lithium content, the industrial demand can be met by higher specific strength. Mg-16Li-2.5Zn-2.5Er (LZ162-2.5Er) alloy is extruded at 100 °C and cold rolled subsequently. The microstructures and mechanical properties of as-cast, as-extruded and cold-rolled LZ162-2.5Er alloys were investigated. A highest specific strength of 178 kNm/kg was obtained. During extrusion, fine-grain strengthening is stimulated by dynamic recrystallization. The subsequent cold rolling increases the dislocation density and uniformizes the distribution of the second phases further, causing work hardening and dispersion strengthening. In this paper, a process of high specific strength Mg-Li alloys for lightweight industry is provided as a reference.

    更新日期:2020-01-13
  • A comparison of the dry sliding wear behavior of NiCoCr medium entropy alloy with 316 stainless steel
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-11
    Xiaobin Guo; Ian Baker; Francis E. Kennedy; Min Song

    The aim of this work was to determine the wear behavior of the f.c.c. medium entropy alloy NiCoCr, which has been shown by others to possess both a very good strength-ductility balance and an especially high fracture toughness. Pins of NiCoCr were tested in dry sliding wear against disks of yttria-stabilized zirconia at a sliding velocity of 0.1 m/s both in air and in argon. Identical wear tests on 316 stainless steel were performed for comparison. It was found that the wear rates of the NiCoCr pins were lower than those of the 316 stainless steel in air, but that the wear rates of the two materials were almost identical in dry argon. Scanning electron microscopy analysis of both the worn pins' surfaces and cross sections indicated that the worn surface of NiCoCr pins were flatter and showed less fracture due to the better toughness compared to the 316 stainless steel pins. Wear tests in air resulted in the formation of oxides. X-ray photoelectron spectroscopy of the NiCoCr pin showed that the oxides in the debris were Cr2O3 and Co2O3. The oxides play an important role in the development of a mechanically mixed layer, which formed on the NiCoCr pin's tip to protect the contacting material during wear tests in air.

    更新日期:2020-01-13
  • The interactions between dynamic precipitates and dynamic recrystallization in Mg-5Zn-1Mn alloys during hot compression
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-11
    Qin Wu; Hongge Yan; Jihua Chen; Weijun Xia; Min Song; Bin Su

    The interactions between dynamic precipitates and dynamic recrystallization (DRX) in hot compressed ZM51 alloys with strain rates from 1 s−1 to 20 s−1 were carefully investigated by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The DRX grain size and the precipitate volume fraction decrease, while the DRX volume fraction increases with increasing the strain rate (T = 300 °C, ε = 1.61). The proportion of β2′ phase is larger than that of β1′ phase, indicating that β2′ phase becomes the main precipitates at the later deformation stage. Grain boundary bowing is the main DRX mechanism at the strain rate of 1 s−1, while the twin-aided DRX mechanism dominates at the higher strain rates (έ ≥10 s−1). The DRX grain size, the volume fractions of the precipitates and DRX increase with increasing the strain (T = 300 °C, έ = 10 s−1). Increasing the strain didn't change the types of the precipitates, but led to the reduction of β1′ phase and the increase of β2′ phase. All the precipitates become spheroid. The higher DRX volume fraction with the lower precipitate volume fraction were detected at the higher strain rates (έ ≥10 s−1), while the situations at the lower strain rate (έ =1 s−1) were reverse. It is due to the fact that the precipitates can hinder the nucleation and growth of DRX because of their pinning effect on dislocations, twin boundaries, sub-grain boundaries and DRX grain boundaries. The precipitation sequence in the deformation process is more complex than that in the traditional aging process and the deformation accelerates the precipitation and phase transformation processes.

    更新日期:2020-01-13
  • Microstructure and mechanical properties of bimodal TiBi alloys fabricated by mechanical alloying and spark plasma sintering for biomedical applications
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-11
    Zhongjie Li; Anping Dong; Hui Xing; Hao Xu; Dafan Du; Ting Zhang; Huan She; Donghong Wang; Guoliang Zhu; Baode Sun

    In this study, the bimodal Ti-xBi (x = 0, 0.5, 1, 3, 5 at.%) alloys were fabricated using mechanical alloying (MA) and spark plasma sintering (SPS) from elemental powders. The microstructure evolution of mechanical alloyed (MAed) powder as well as the effect of Bi content on microstructure and mechanical properties of TiBi alloys are investigated. The microstructure of TiBi alloys consisted of bimodal structure with coarse grains (CG) region as “core” and ultrafine grains (UFG) region as “shell”. The TiBi matrix was α-Ti with hexagonal close-packed (HCP) structure while Bi-riched phase was identified as β-Ti with body-centered cubic (BCC) structure. The mechanical properties showed that the as-built bimodal alloys had high strength and large plastic deformation. The TiBi alloys showed ~22%–44% higher compressive yield strength compared with commercially pure Ti (CP-Ti) alloy for same the ball-milling time, and strengthening mechanisms are mainly ascribed to grain boundary strengthening and solid solution. When Bi content was 0.5%, the alloy exhibited excellent comprehensive mechanical properties with high compressive strength (yield strength of ~1080 MPa, ultimate compressive strength of ~2226 MPa) and excellent ductility (fracture strain of ~34.3%).

    更新日期:2020-01-13
  • Effect of post-processing annealing treatments on microstructure development and hydrogen embrittlement in API 5L X70 pipeline steel
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-11
    Enyinnaya Ohaeri; Joseph Omale; K.M. Mostafijur Rahman; Jerzy Szpunar

    The mechanical properties of steels are strongly influenced by microstructure and texture developed during thermomechanical processing. Here, different annealing treatments have been performed on pipeline steel at inter-critical temperatures. The aim of this study is to relate hydrogen embrittlement behavior to the microstructural characteristics obtained through one-step, and two-step annealing treatments. Similar grains orientation distributions were observed after the initial hot rolling and the two-step annealing procedures. However, in the later process a dual-phase (i.e. ferrite-martensite) structure was formed; unlike in the starting material where only segregated patches of martensite were observed inside a ferritic microstructure. The one-step treated steel was comprised of relatively large and primarily ferrite grains. As a result, the preliminary processing revealed the highest strength, with reduced ductility. The one-step treatment lowered strength, and ductility. Although the two-step treated steel showed the lowest strength, it was the most ductile with improved resistance to hydrogen embrittlement. The tempering operation introduced in the two-step process created minimal strain and tempered martensite within the steel. This reduced the tendency for hydrogen damage. A direct relationship was established between high tensile strength and increased embrittlement risks. Lowering the strength and hardness through double heat treatment cycles delayed the onset of cracking after pre-hydrogen charging.

    更新日期:2020-01-13
  • Effects of pre-strain on the surface residual stress and corrosion behavior of an Al-Zn-Mg-Cu alloy plate
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-11
    Lianghua Lin; Zhiyi Liu; Wenwei Zhuang; Haijian Peng

    The surface residual stress as well as corrosion behavior of an Al-Zn-Mg-Cu alloy plate is investigated under various pre-deformation conditions via X-ray diffraction, transmission electron microscopy, laser scanning microscope, open circuit potentials and electrochemical impedance spectroscopy measurements. Results reveal that the major extent of residual stresses from quenching can be relieved by 2% pre-strain, while the surface residual stress condition transforms from compression to tension if pre-strain exceeds 4%. During aging, the dislocations introduced by pre-strain promote the nucleation of large η phase and accelerate the coarsening of η′ precipitates. With increasing the pre-strain level, the number density of coarse η phase both at grain boundary and within matrix increases, resulting in a decrease in the corrosion resistance. In addition, the immersion test reveals an acceleration of corrosion when tensile residual stress exists in the surface of plate.

    更新日期:2020-01-13
  • Crystallographic texture development in extruded AA 2195 and AA 7075
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-10
    Judith M. Dickson; Thomas H. Sanders

    The addition of lithium to high strength aluminum alloys significantly improves specific strength as is the case with AA 2195. However, unlike non-lithium containing alloys, such as AA 7075, lithium containing alloys display anisotropic mechanical properties in low aspect ratio extruded sections. The goal of this study is to elucidate the origins of anisotropy in AA 2195 and to investigate processing methods to control mechanical properties. To this end, both AA 2195 and AA 7075 were systematically extruded over a range of aspect ratios from 2 to 15 while maintaining a constant extrusion ratio. Through crystallographic texture component analysis and the use of a newly proposed parameter termed the “Plate-Like Number”, this study indicates that the Copper texture is primarily responsible for previously observed anisotropic properties of AA 2195. A series of rolling studies analyzed using the Plate-Like Number suggest that a higher initial billet temperature will minimize the Copper texture component and thus reduce the anisotropy in extruded AA 2195.

    更新日期:2020-01-11
  • Microstructure and mechanical properties of Cu-graphene composites produced by two high pressure torsion procedures
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-10
    G. Korznikova; T. Czeppe; G. Khalikova; D. Gunderov; E. Korznikova; L. Litynska-Dobrzynska; M. Szlezynger

    True bulk nanostructured composites promising for a wide range of applications however being difficult to produce using established engineering techniques. Most of previous works aimed to design of Cu graphene composite used the approach of high temperature sintering inevitably associated with growth of Cu grains. Another advantageous approach of composites consolidation allowing to avoid heating of the sample is shear deformation under high pressure that has been earlier used for Al – graphene composite. Our work reports the first attempt of Al-graphene composite consolidation by means of is high pressure torsion (HPT). Two-step processing by constrained and non-constrained HPT was applied to produce bulk Cu-graphene composite with nanoscaled Cu grains laminated by graphene. After the constrained HPT high and low graphene content layers were interspersed in the microstructure. The second step of not-constrained HPT led to the refinement of graphene agglomerates to the range of 10 nm and Cu grains to the range of 100 nm with quite uniform distribution of graphene, preserving the equiaxial shape of the grains seldom in case of the composite structure. The process significantly increased microhardness of Cu-graphene composite from 1450 to 1900 MPa in the edge region after consolidation with even more pronounced increase from 1900 to 2950 after following constrained HPT. However, infusion of graphene resulted in a prominent decrease of both ductility from 15 to 4% and strength of the material. Brittle failure with low value of critical fracture stress should be related to the role of graphene as an obstacle for the dislocation movement. The dynamic recrystallization in the Cu-graphene composite during severe plastic deformation by not-constrained HPT suggests also that dispersed graphene may play role in the dislocation sinking at the micro-grains boundaries. The obtained results contribute to figuring out the major issues of Cu and graphene interaction under pressure and can be helpful in validation of prospective research plan in this field.

    更新日期:2020-01-11
  • Zoning additive manufacturing process histories using unsupervised machine learning
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-10
    Sean P. Donegan; Edwin J. Schwalbach; Michael A. Groeber

    Metal additive manufacturing (AM) is currently a highly active area of research within the materials processing and manufacturing community, owing to the promises of lower lead time, increased design flexibility, and location-specific process control. These benefits are balanced by a typically complex processing space, resulting in difficulties when attempting to generalize process-structure relationships across different component geometries. We develop a procedure for reducing the overall complexity of a representation of the AM processing space using techniques from time series analysis and dimensionality reduction. This procedure is highly generic and applicable to a variety of time sequenced signals. We then utilize this reduced feature space as input to a cluster analysis, producing zoned maps of process history. We apply the approach to several canonical geometries, describe its overall utility, and discuss the implications of the resulting zonings in terms of the underlying digital process.

    更新日期:2020-01-11
  • Examining the multi-scale complexity and the crystallographic hierarchy of isothermally treated bainitic and martensitic structures
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-10
    D. De-Castro; R. Rementeria; J. Vivas; T. Sourmail; J.D. Poplawsky; E. Urones-Garrote; J.A. Jimenez; C. Capdevila; F.G. Caballero
    更新日期:2020-01-11
  • Well-organized assembly of ZnO hollow cages and their derived Ag/ZnO composites with enhanced photocatalytic property
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-09
    HuaMin Cao; Zhao Liu; Tingzhi Liu; Shuwang Duo; Lin Huang; Siqin Yi; Linlin Cai
    更新日期:2020-01-09
  • 更新日期:2020-01-09
  • Precipitation reactions in a Cu-Ni-Al medium carbon alloyed dual hardening steel
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-09
    Matthias Hofinger; Christoph Turk; Miloslav Ognianov; Harald Leitner; Ronald Schnitzer

    Dual hardening steels achieve secondary hardening through the combined precipitation of intermetallic phases and carbides. The early stages of precipitation of a Cu-Ni-Al medium carbon alloyed dual hardening steel with a low alloying ratio of Cu/NiAl were investigated. Phase separation during continuous heating with 20 K min−1 was identified to occur in the temperature range from 360 °C to 620 °C by differential scanning calorimetry. The precipitates were characterized utilizing atom probe tomography. Different cluster search algorithms were used in order to determine the sequence of phase separation and thus identify the individual precipitation reactions. It was shown that phase separation starts with the formation of Cu (Ni, Al, Mn) clusters. At an ageing temperature of 580 °C, heterogeneous precipitation of VC-clusters at the interfaces between the Cu-precipitates and the iron matrix takes place. A phase separation of the Cu (Ni, Al, Mn) clusters into separate Cu and NiAl particles could not be observed up to an ageing temperature of 620 °C. The sequence of precipitation is thus determined to be Cu-VC-NiAl.

    更新日期:2020-01-09
  • High power diode laser nitriding of titanium in nitrogen gas filled simple acrylic box container: Microstructure, phase formation, hardness, dendrite and martensite solidification analyses
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-07
    J. Senthilselvan; K. Monisha; M. Gunaseelan; S. Yamini; S. Arun Kumar; K. Kanimozhi; J. Manonmani; S.M. Shariff; G. Padmanabham
    更新日期:2020-01-07
  • Microstructure, texture and mechanical anisotropy of Mg-Gd-Y-Zr sheets processed via different rolling routes and reductions
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-07
    Yi Yao; Chuming Liu; Yingchun Wan; Shilun Yu; Yonghao Gao; Shunong Jiang

    The dependence of microstructure, texture and mechanical anisotropy of Mg-Gd-Y-Zr alloy sheets on rolling routes (unidirectional rolling (UR) and cross rolling (CR)) and reductions (10% and 30% pass reduction) was investigated. Results show that the rolled sheets with pass reduction of 10% mainly consist of coarse deformed grains and {101¯2} ⟨101¯1⟩ tensile twins, and the UR sheet possesses twins with larger size and higher area fraction. With pass reduction increased to 30%, dynamic recrystallization (DRX) occurred in both UR and CR sheets, therein the CR sheet exhibited the lower DRX ratio due to the high degree of dynamic recovery induced by the CR route. Meanwhile, texture and deformation modes of the rolled sheets also exhibit rolling reduction dependence. For the case of 10% pass reduction, CR and UR sheets show the similar basal texture type and intensity, and thus prismatic ⟨a⟩ slip dominates plastic deformation during tensile tests. For the case of 30% pass reduction, CR sheet possesses a multiple-peak texture with more obvious peak inclination and spreading, while UR sheet shows a single-peak and weaker basal texture. The difference in texture results in the difference in deformation modes during tensile tests, i.e., prismatic ⟨a⟩ slip for UR sheet and basal ⟨a⟩ slip for CR sheet, respectively. Above differences further bring distinction to the mechanical anisotropy of the rolled sheets. For 10% pass reduction, CR and UR induce similar anisotropy. For 30% pass reduction, CR causes a more significant anisotropy than UR.

    更新日期:2020-01-07
  • Porous nanofibers comprised of hollow SnO2 nanoplate building blocks for high-performance lithium ion battery anode
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-07
    Jin-Sung Park; Yeon Jong Oh; Jong Hwa Kim; Yun Chan Kang

    Hollow nanoplates-aggregated SnO2 nanofibers were fabricated from electrospinning process and two-step heat treatment. Se particles were dissolved in electrospinning solution and played a critical role in the formation of small-sized SnSe nanoplates during the selenization heat treatment. During the oxidation heat treatment, due to the well-known Kirkendall diffusion process, the dense SnSe nanoplates were transformed into hollow SnO2 nanoplates. Three other SnO2 nanostructures including SnO2 hollow nanoplates, hollow nanofiber with hierarchical SnO2 nanocrystals, and SnO2 hollow nanofibers were prepared as comparison. The capacity of hollow nanoplate-aggregated SnO2 nanofibers after the 700th discharge process was 375 mA h g−1 when cycled at a high current density of 3 A g−1, whereas those of the comparison SnO2 nanostructured electrodes in the order listed were 78, 277, and 262 mA h g−1, respectively. The high structural stability of the synthesized hollow nanoplate-aggregated SnO2 nanofiber during repeated lithiation and delithiation processes resulted in lithium-ion battery anode with longer cycle life.

    更新日期:2020-01-07
  • Study of self-organized structure in carbon nanotube forest by fractal dimension and lacunarity analysis
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-07
    Adam Pander; Takatsugu Onishi; Akimitsu Hatta; Hiroshi Furuta
    更新日期:2020-01-07
  • Characterizations of weld defects, intermetallic compounds and mechanical properties of friction stir lap welded dissimilar alloys
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-03
    Raju Prasad Mahto; Ravi Kumar; Surjya Kanta Pal

    This experimental investigation describes the effect of tilt angle and rotational speed on the characteristics of welding defects, intermetallic compounds, weld strength and micro-hardness in friction stir welding of thin sheets of AA6061-T6 and AISI304. Qualitative and quantitative assessments of the welding defects have been made by using X-ray micro computed tomography and metallographic study. Three-dimensional tomography and special distribution of internal voids (pores) have been discussed by correlating it to different values of tool rotational speed and tilt angle. Internal defects were localized in the stir zone. Welding at a tilt angle of 1° reduced both surface and internal defects. Non-uniform thickness of intermetallic compound (FexAly) layer has been found in the weld zone whose thickness varied with the values of process parameters. Higher weld porosity, bigger steel hook defect and increased layer thickness of intermetallic compound caused a significant reduction in the joint strength and elongation.

    更新日期:2020-01-04
  • Ultra-layered sheet CuCo nanoparticles for optimized application in catalytic reduction of organic dye
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-03
    Serpil Kiliç Depren; Bilge Coşkuner Filiz; Büşra Nur Kulakli; Aysel Kantürk Figen
    更新日期:2020-01-04
  • The τ-plot, a multicomponent 1-D pole figure plot, to quantify the heterogeneity of plastic deformation
    Mater. Charact. (IF 3.22) Pub Date : 2020-01-03
    T.H. Simm; Y.B. Das; A.N. Forsey; S. Gungor; M.E. Fitzpatrick; D.G.L. Prakash; R.J. Moat; S. Birosca; J. Quinta da Fonseca; K.M. Perkins

    An approach is presented that allows multi-scale characterisations of heterogeneous deformation in crystalline materials by employing a range of characterisation techniques including: electron backscatter diffraction, digital image correlation and neutron diffraction powder measurements. The approach will be used to obtain critical information about the variations in parameters that characterise the deformed state in different crystallographic orientation texture components of a sample in a statistically significant way. These parameters include lattice strains, texture evolution, peak broadening, dislocation density, planar faults, phase changes and surface strain. This approach allows verification of models of plastic deformation to provide a more detailed view of plastic deformation heterogeneity at multiple length scales than obtained by other characterisation approaches. The approach demonstrated here is applied to two stainless steel alloys; an alloy that exhibits phase transformation during deformation and an alloy that remains the same phase all through deformation process.

    更新日期:2020-01-04
  • The effect of low Cu additions on precipitate crystal structures in overaged Al-Mg-Si(-Cu) alloys
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-30
    Jonas K. Sunde; Calin D. Marioara; Randi Holmestad
    更新日期:2019-12-30
  • Porous NiO–YSZ and Ni–YSZ composites fabricated using NiO–YSZ composite nanopowders and WO3 additive
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-28
    J. Kim; G.H. Kim; K. Park

    NiO–YSZ composite nanopowders were synthesized through a hydrothermal process without an additional mixing of NiO and YSZ nanopowders. Porous Ni–yttria stabilized zirconia (YSZ) composites, Ni–YSZ composites, with high porosity (25.0–32.8%) were fabricated by reducing NiO-YSZ composites in (94% Ar + 6% H2) gas. The electrical conductivity (14,221 Scm−1 at 30 °C) and bending strength (130 MPa) of Ni–YSZ composites were enhanced by the addition of WO3 (0.1 wt% WO3) to NiO–YSZ composite nanopowders. Furthermore, the Y2(WO4)3 with a negative coefficient of thermal expansion (CTE) reduced the CTE of Ni–YSZ composites. The CTE values of 0 and 0.6 wt% WO3–added Ni–YSZ composites were 13.8 × 10−6 and 12.4 × 10−6 °C−1, respectively. We demonstrate that the fabrication of NiO–YSZ composite nanopowders and the addition of WO3 to the NiO–YSZ composite nanopowders are highly effective methods for the fabrication of high-quality Ni–YSZ anode materials in solid oxide fuel cells.

    更新日期:2019-12-29
  • Effect of initial grain size on hot deformation behaviour of Cu-Cr-Zr-Ti alloy
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-28
    Aditya Sarkar; M.J.N.V. Prasad; S.V.S. Narayana Murty

    Hot uniaxial compression tests were carried out on Cu-0.8Cr-0.05Zr-0.05Ti (wt%) alloy specimens with three different grain sizes: 30 μm, 150 μm and 450 μm to study the effect of initial grain size on hot workability of the alloy. The deformation temperature and applied strain rate ranges were 600–900 °C and 0.001–1 s−1 respectively. At higher deformation temperatures, fine grained specimens exhibited early onset of dynamic recrystallization (DRX) as compared to coarse-grained specimens. Conversely, the work hardening plots of coarse-grained specimens exhibited plateaux at higher strain rates indicating occurrence of deformation twinning. Microstructure examination revealed a decrease in the extent of DRX and an increase in deformation twinning with increase in initial grain size. The failure in coarse-grained specimens was in the form of wedge cracking observed at triple junctions at lower deformation temperatures. The higher stress values exhibited by coarse-grained specimens as compared to fine grained specimens was found to be a result of absence of DRX and the strain being accommodated by deformation twinning rather than grain boundary sliding (GBS) due to limited grain boundary area. Processing maps using the dynamic material model (DMM) were plotted for all three initial grain sizes and were validated with optical microstructures. The ‘unstable/unsafe’ deformation domain was found to be wider with increase in initial grain size. The present study explicates that there is an increase in difficulty of hot working and reduced control of microstructure in the alloy with increase in initial grain size.

    更新日期:2019-12-29
  • Statistical analysis of dislocation substructure in commercially pure aluminum subjected to static and dynamic high pressure torsion
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-27
    Harishchandra Lanjewar; Soroosh Naghdy; Patricia Verleysen; Leo A.I. Kestens

    Severe plastic deformation, imposed under high hydrostatic pressure, introduces a considerable dislocation substructure in metals from the early stages of deformation, ultimately resulting in grain fragmentation. Characterization and quantification of the substructure require methods with a sufficiently high angular and spatial resolution to reveal the local heterogeneities in orientation differences and the length scales of the substructure. However, on the other hand, the statistical relevance of the observations should be assured which requires relatively large fields of view. In present work, the evolution of dislocation substructures during static and dynamic high pressure torsion processing of commercially pure aluminum is examined. Orientation data obtained by electron backscatter diffraction using two different mapping step sizes are utilized to assess the detection of the dislocation substructures and boundaries during the grain fragmentation stage. Accumulation of distortion in the crystal produces an increase in measurement noise at each pixel which is estimated using Kamaya's plots. The storage of dislocations and related angular misfits reduces the peak height of the probability density distribution of misorientation gradients, moves the peak to higher misorientation gradients and widens the distribution. Superposition of double Rayleigh distributions over the combined dislocation boundary data predicts a slightly higher median for the frequency of geometrically necessary boundaries and larger misorientation gradients across these boundaries in dynamically deformed material. In incidental dislocation boundaries, higher misorientation gradients are only observed at lower equivalent strains. Buildup of shear strain leads to the deterioration in the quality of the fitting to a double Rayleigh distribution and is linked to the complex evolution pattern of the dislocation boundaries. Finally, in statically deformed material, anisotropy in the substructure evolution is observed in the shear and radial planes.

    更新日期:2019-12-27
  • Microstructure evolution, texture and laser surface HEACs of Al-Mg-Si alloy for light automobile parts
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-27
    Jianing Li; Zhiyun Ye; Jin Fu; Wenjun Qi; Yan Tian; Liqiang Liu; Xiaolin Wang

    Effect of the rare earth (RE) elements and Cu on the microstructure performance and texture of the hot-rolled Al-Mg-Si alloys during the solution and artificial aging was investigated in this study. The results showed that Cube{100}〈001〉 and CubeND{001}〈310〉 textures were suppressed in a certain extent with the Ti/Zr addition, leading the Copper{112}〈111〉 and the {110}〈011〉 textures to be formed; the texture strength of Cube{100}<001> increased with Ce/Er-added, also the F{111}〈112〉 texture was varied, the strength of {110}//ND decreased. The orientation density of the hot-rolled T6 Al-Mg-Si-Cu alloys increased with the Ce/Er addition, the nucleation mechanism of the re-crystallization was the Cube texture, also the nucleation mechanism of the Cube texture and PSN were weaken. Then, the mixed powders of FeCoCrAlCu (high-entropy alloy powder)-MoSi2-Mn-Sb were deposited on the produced hot-rolled Ce/Er modified Al-Mg-Si-Cu alloy substrate by mean of a laser melting deposition (LMD) technique to form the high-entropy alloy composites (HEACs) to improve the surface performance of alloy substrate. Identification of the synthetic ultrafine nanocrystals (UNs) in LMD HEACs contributes theoretical/experimental basis to improve the quality of the laser 3D print materials. The research on the texture of the hot-rolled Al-Mg-Si-Cu alloy also the Co3Mo2Si UNs in laser-treated HEACs can provide the essential theoretical/experimental basis to improve the quality of the light alloys for the automobile parts.

    更新日期:2019-12-27
  • Microstructural characterization, mechanical properties and thermal expansion of antiperovskite manganese nitride Mn3.1Zn0.5Sn0.4N fabricated by combing vacuum sintering and spark-plasma sintering
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-27
    He Cao; Yishi Su; Duo Cui; Di Zhang; Qiubao Ouyang

    Due to the superior mechanical properties and negative thermal expansion, antiperovskite manganese nitrides have played an important role in many engineering applications, and one of which is that they can be used as ideal reinforced phases to fabricate composites with near-zero thermal expansion. In this study, one type of antiperovskite manganese nitride, Mn3.1Zn0.5Sn0.4N, was initially fabricated by vacuum sintering and subsequently densified by spark-plasma sintering (SPS). The bulk density, material phase and organization analysis are measured after it is densified at different SPS temperatures. Young's modulus, hardness and compressive strength are obtained by using nano-indentation and compression tests, respectively. It is seen that lattice constant, negative thermal expansion and magnetic transition temperature exhibit similar trends, which can be attributed to the lattice distortions caused by changing the SPS temperatures. From this analysis, a systematical study has been conducted to understand the relation between the microstructures, mechanical and thermal properties of antiperovskite manganese nitride.

    更新日期:2019-12-27
  • Orientations and interfaces between α′-Al13Cr4Si4 and the matrix in Al-Si-Cr-Mg alloy
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-27
    Shaohan Wang; Liang Dong; Xiaocang Han; Yun Fan; Bin Chen

    The orientation relationships and interfaces between α′-Al13Cr4Si4 and the matrix in Al-Si-Cr-Mg alloy are characterized by HAADF-STEM electron microscopy. Multiple orientation relationships are found between α′-Al13Cr4Si4 and Al matrix in Al-Si-Cr-Mg and four of them are rarely common. By unraveling the atomic structure of dispersoids, the crystal model of α′-Al13Cr4Si4 is approved by the atomic-resolution for the first time. The interface we investigated proves that orientation relationships always rely on specific planes of Al matrix.

    更新日期:2019-12-27
  • Effect of phase transformation on densification kinetics and properties of spark plasma sintered Al0.7CoCrFeNi high-entropy alloy
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-26
    Siyao Xie; Ruidi Li; Tiechui Yuan; Mei Zhang; Minbo Wang; Li Yin; Peng Cao
    更新日期:2019-12-27
  • Multimodal grain structure and tensile properties of cold-rolled titanium after short-duration annealing
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-26
    Tengfei Xu; Shiying Wang; Wenchang Wang; Penghua Liang; Xiaochen Li; Naotoshi Mitsuzaki; Zhidong Chen
    更新日期:2019-12-27
  • Effect of post-weld heat treatment on the microstructure and hardness of P92 steel in IN740H/P92 dissimilar weld joints
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-24
    Wi-Geol Seo; Jin-Yoo Suh; Jae-Hyeok Shim; Hansang Lee; Keunbong Yoo; Shi-Hoon Choi

    The microstructural factors that contribute to hardening mechanisms were investigated to explain the effect of post-weld heat treatment (PWHT) on the hardness of P92 steel in IN740H/P92 dissimilar weld joints. This study presents experimental analysis of the distribution of microstructural factors such as precipitate size, precipitate fraction, grain size and dislocation density in the heat-affected zone (HAZ) and base metal (BM) of the martensitic heat-resistant steel. Although precipitates mainly decorated the prior-austenite grain boundaries (PAGBs), packet boundaries (PBs), and block boundaries (BBs), their spatial distribution strongly depended on the distance from fusion line and the PWHT conditions. The grain size and the densities of geometrically necessary dislocations (GNDs) also exhibited a non-uniform distribution. The individual contributions of the microstructural factors to hardness were explained by introducing a simple hardening equation that considers the independent effect of different hardening mechanisms.

    更新日期:2019-12-25
  • Effects of deformation temperature on the evolution of second-phase and mechanical properties of large 2219 Al-Cu alloy rings
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-23
    Wanfu Guo; Youping Yi; Shiquan Huang; Xianchang Mao; Jie Fang; Hailin He; Bin Hu

    Transition rings of 2219 Al-Cu alloy for tanks with diameters exceeding 5 m require superior mechanical properties. However, the coarsening and agglomeration of Al2Cu second-phase particles deteriorate the mechanical properties of large 2219 Al-Cu alloy rings manufactured by the conventional hot rolling process. An improved process, including warm rolling and cold compression, was performed for improving the mechanical properties of such rings. The results showed that warm rolling can facilitate the dispersion and fragmentation of Al2Cu particles and that cold compression can lead to a significant accumulation of dislocations, as compared with hot rolling. Dispersed Al2Cu particles were beneficial for uniform distribution of Cu in the Al matrix after heat treatment; fragmented Al2Cu particles were dissolved more sufficiently during heat treatment, with the assistance of a larger number of dislocations per unit volume. More uniform and higher Cu content in the Al matrix of the sample undergoing the improved process leads to a more uniform distribution, greater area fraction, and larger size of θ′ phases, and improved yield strength. The elongations of the samples undergoing warm rolling increased significantly because of the positive change of fracture behavior owing to refinement of Al2Cu particles.

    更新日期:2019-12-23
  • Effect of Zn on precipitation evolution and mechanical properties of a high strength cast Al-Li-Cu alloy
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-21
    Jinshuo Zhang; Guohua Wu; Liang Zhang; Xiaolong Zhang; Chunchang Shi; Jiangwei Sun

    The influence of Zn addition on microstructure evolution and mechanical performance of a novel cast Al-Li-Cu-Mg alloy is studied in detail. The results reveal that Zn modifies the precipitation behaviors and improves the tensile strength effectively. As Zn content increases to 1 wt%, the precipitation of T1 (Al2CuLi) phase is greatly enhanced at the expense of S′ (Al2CuMg) phase. Zn atoms are observed to enrich in T1 phase by using high-angle annular dark field-scanning transmission electron microscope (HADDF-STEM), possibly attributed to some Cu atoms being substituted by Zn atoms. The precipitation of δ′ (Al3Li) is increased as Zn addition, suppressing the widening of δ′-precipitation-free zones. A more uniformly distribution of S'is also observed in the Zn-containing alloys. With the collaborative effect of both T1 and δ′ precipitates, the optimal ultimate tensile strength of 504 MPa is obtained in 1 wt% Zn-containing alloy aged at 175 °C for 64 h, which is the highest value in cast Al-Li alloy field at present.

    更新日期:2019-12-21
  • Microstructure stability and tensile properties of Cu-3Ag-1Zr alloy fabricated by rapid solidification and cold rolling
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-20
    Xiang Wu; Richu Wang; Chaoqun Peng; Guosheng Jiang

    A Cu-3Ag-1Zr alloy was fabricated by rapid solidification and cold rolling. The microstructure stability and tensile properties of this alloy after isochronal annealing at 350–900 °C were investigated. The results show that the microstructure of the Cu-3Ag-1Zr alloy after annealing at 350 °C for 1 h is dominated by the high-density dislocations, ultrafine grains, low angle grain boundaries (LABs) and second-phase particles (nano-sized Ag and micro-sized Cu4AgZr), which results in a high tensile strength of 637 MPa and moderate elongation of 12%. When annealed at 400 °C, the particle stimulated nucleation of recrystallization (PSN) occurs, and the fraction of LABs decreases to 38%, but over 90% of grains are smaller than 2 μm. The decreased tensile strength (465 MPa) and increased elongation (30%) are closely related to the fully recrystallized microstructure after annealing at 500 °C. The alloy exhibits excellent thermal stability when annealed between 500 and 800 °C, and no significant coarsening of grains and decrease in strength are observed due to the strong pinning effect of the stable Cu4AgZr particles at boundaries. The coarsening of the Cu4AgZr particles at 900 °C leads to the sharp increase in the grain size and drop of strength.

    更新日期:2019-12-20
  • Effect of porosities on brazed martensitic steel tensile properties: 2D and 3D pre-mortem vs post-mortem characterizations
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-20
    N. Vanderesse; D. Texier; P. Bocher

    A quantitative investigation of the porosity and its effects on mechanical properties was conducted on brazed materials presenting macroscopically brittle behavior with various defect levels. Three different techniques for evaluating the porosity and the fracture mechanisms were compared: (i) pre-mortem X-ray computed tomography (XCT), (ii) post-mortem laser scanning confocal microscopy (LSCM), and (iii) post-mortem scanning electron microscopy (SEM). The apparent surface area of the pores was evaluated by segmenting the height maps produced by LSCM and the electron backscattered images produced by SEM. The results show good agreement for different porosity levels. The LSCM height maps for opposite fracture faces were virtually stitched together in order to reconstruct three-dimensional (3D) images of the whole brazed joints. These proved to be similar to the XCT 3D segmented images, yet with some discrepancies due to local plastic deformation. Quantitative volume fraction and spatial distribution of pores were assessed as well as the identification of fracture mechanisms. Interestingly, it was noted that two specimens with different ultimate tensile strengths presented the same porosity amount, but different distributions. Two distinctive features were identified in the broken specimens: plastically teared pillars and walls that were separating the pores before fracture, and plateaus of approximately constant height with micro-sized dimples showing interfacial fracture. Although the specimens exhibited a macroscopic brittle behavior, these features are characteristic of ductile fracture. The most probable scenario for fracture was conjectured as follows: (i) Final fracture occurs in the near-surface region of the samples and conversely early damage develops in the volume, (ii) Interfacial fracture within plateaus is responsible of the rupture/strength of the brazed specimen but detrimental effect is induced by the tearing if highly voided regions are present in the joint.

    更新日期:2019-12-20
  • Comparison of Mercury Intrusion Porosimetry and multi-scale X-ray CT on characterizing the microstructure of heat-treated cement mortar
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-20
    Shanbin Xue; Peng Zhang; Jiuwen Bao; Linfeng He; Yu Hu; Shidi Yang

    In this contribution, the microstructure features of cement mortar exposed to various temperatures (105 °C, 200 °C, 400 °C, 600 °C, 800 °C) was investigated by combining Mercury Intrusion Porosimetry (MIP) and multi-scale X-ray computed tomography. The influence of exposure temperature and resolution of X-ray CT on the determination of microstructure parameters of heat-treated mortar was focused. Based on results of MIP test, it was found the porosity and pore size increased slightly when the exposure temperature varied from 105 °C to 200 °C and significant pore coarsening and micro-damage occurred once the temperature exceeded 400 °C. Bimodal pore size distribution (PSD) of the heat-treated mortar specimens was observed when the temperature reached 400 °C. To interpret the results of MIP test, the microstructure of heat-damaged mortar specimens was imaged using X-ray CT with a reconstructed voxel size of ~4.0 μm3 and then local volume inside the specimen was focused and scanned with a reconstructed voxel size of 1.5 μm3. A method was proposed to select proper threshold based on the MIP results for segmenting the void space from the X-ray CT images. The fracture aperture, 2D/3D fractal dimension, connectivity and tortuosity of the heat-damaged mortar specimens were further determined at different scale. By analyzing the fracture aperture determined from X-ray CT images, it was found the bimodal PSD revealed by MIP test can be associated with the creation of thermal micro-fractures. The fractal dimension increased remarkably when exposure temperature was raised from 400 °C to 600 °C while it varied slightly from 600 °C to 800 °C. Linear dependences between the fractal dimension and the volume fraction/tortuosity of micro-scale pores and fractures was found. The scale-dependent fractal properties of the heat-treated mortar were revealed with the capillary pressure data measured by MIP. The fractal dimension of micro-scale pores and fractures measured by MIP exhibited good consistency with that determined based on by X-ray CT images with a reconstructed voxel size of 1.5 μm3.

    更新日期:2019-12-20
  • Comprehensive study on the formation of grain boundary serrations in additively manufactured Haynes 230 alloy
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-20
    Maximilian Haack; Martin Kuczyk; André Seidel; Elena López; Frank Brueckner; Christoph Leyens

    Recently, grain boundary serrations have been introduced in conventionally processed Haynes 230 through a slow-cooling heat treatment. The aim of this work was to utilize these heat treatments to introduce serrations in additively manufactured (Laser Metal Deposition) Haynes 230. Contrary to expectations, serrations already formed during the fast-cooling of the Laser Metal Deposition process. Electron Backscatter Diffraction was used to elucidate the underlying phenomenon for the emergence of serrations during fast-cooling. As a result, a hypothesis regarding a new mechanism responsible for the formation of grain boundary serrations was formulated. Additionally, specific characteristics of the Laser Metal Deposition process have been identified. This includes a columnar-to-equiaxed transition (CET) for slower feed rates, leading to smaller grains despite lower cooling rates; the observation of an abrupt increase in grain growth for a raised solution annealing temperature; the fact that serrations hinder uncontrolled grain growth and finally that the LMD-process leads to a finer carbide morphology compared to conventional manufacturing methods, potentially leading to an increased precipitation strengthening effect.

    更新日期:2019-12-20
  • Quantifying elastic strain near coherent twin interface in magnesium with nanometric resolution
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-18
    J.S. Chen; Y. Liu; R.J. McCabe; J. Wang; C.N. Tomé
    更新日期:2019-12-19
  • Shear instability and considerably localized melting in quasi-static compression
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-17
    Yun-Shuai Su; Shu-Xin Li; Guan-Nan Yang; Feng Yu; Si-Yuan Lu; Yong-Gang Wang

    It is a big challenge to identify whether or not a high temperature rise at high strain rate is a prerequisite for shear instability in crystalline materials. In contrast to the prevailing report of shear instability at high strain rate loading, the shear band (SB) was generated at quasi-static loading in a martensite steel. This gives strong evidence that the high temperature rise is not essential as the quasi-static loading is not able to generate enough heat to initiate the shear instability. Different from the conventional narrow SB at high strain rate loading, a large patch of SB was firstly observed. Considerably localized melting occurred due to the abrupt fracture of SB. SB displays different TEM microstructures at melting and no-melting places. This indicates the significance of distinguishing the microstructure formed during shear instability from the one affected by the fracture of SB. The result suggests that the strain localization mechanism in this material is attributed to the microstructural change instead of the thermal softening. The findings provide a new insight into understanding the formation mechanism of SB from the perspective of microstructural evolution in crystalline materials.

    更新日期:2019-12-18
  • Characterization of nano-sized particles in 14%Cr oxide dispersion strengthened (ODS) steel using classical and frontier microscopy methods
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-17
    Yael Templeman; Sergey Rogozhkin; Artem Khomich; Aleksander Nikitin; Malki Pinkas; Louisa Meshi
    更新日期:2019-12-18
  • Ultrafine eutectic coatings from Fe-Nb-B powder using laser cladding
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-17
    Chaiane M. Caneda; João B. Fogagnolo; Claudio S. Kiminami; Conrado R.M. Afonso

    In this paper, a laser cladding process was proposed to obtain ultrafine eutectic Fe-Nb-B alloy coatings on AISI 1020 steel substrate in which the power and scanning speed were defined. The laser cladding process can be used as a rapid solidification processing route to produce single laser tracks and coatings (overlapped tracks) with pre-placed powders deposited onto a mild steel substrate in order to obtain a minimal dilution between the coating/substrate. This research aims to produce a coating of Fe74.25Nb8.25B17.5 (at.%) alloy over the AISI 1020 steel substrate by laser cladding using a pre-placed powder method to investigate the parameters on coating production, dilution, microstructure, and properties. The final goal is to find an appropriate processing parameter range to obtain coatings with high hardness and possibly good wear resistance. The microstructure and behavior of powder, cladding layers and coatings were examined by X-ray Diffractometry, Differential Scanning Calorimetry, Scanning Electron Microscopy and Transmission Electron Microscopy of selected samples prepared with a Dual Beam microscope using a Focused Ion Beam. For the processing conditions used, the coatings showed larger exothermic crystallization peaks. The results of microhardness from coatings showed values of hardness over 700 HV.

    更新日期:2019-12-18
  • Thermal stability of plasma-sprayed NiAl/CrB2 composite coatings investigated through in-situ TEM heating experiment
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-13
    Jerzy Morgiel; Olena Poliarus; Małgorzata Pomorska; Łukasz Maj; Maciej Szlezynger

    Nickel aluminide coatings - produced using atmospheric plasma spraying method - attracted considerable attention due to their high melting temperature and oxidation resistance. What is more, an addition of CrB2 allows to significantly increase their wear resistance. Such coatings are typically used up to 500 °C, what requires thermal stability of their microstructure. Therefore, in this paper, the in-situ TEM heating of APS-deposited NiAl coating with addition of 15 wt% of CrB2 up to 800 °C was performed in order to follow the microstructure changes and eventual phase transformations. The TEM observations backed with phase analysis showed that the amorphous veins present in the NiAl matrix of as-deposited coating transform into Ni6AlB3 phase at approaching 500 °C. On the other hand, the CrB2/NiAl interface preserved its shape and remains free from any precipitates even up to 800 °C. The ex-situ TEM microstructure observations of NiAl + CrB2 coating, carried out after high-temperature wear test (500 °C, ~15 min), showed that after it amorphous channels indeed turns crystalline. In addition, the NiAl matrix presents significantly higher dislocation density, being a result of repeated loading received during the wear test.

    更新日期:2019-12-13
  • Interface failure behavior of yttria stabilized zirconia (YSZ), La2Zr2O7, Gd2Zr2O7, YSZ/La2Zr2O7 and YSZ/Gd2Zr2O7 thermal barrier coatings (TBCs) in thermal cyclic exposure
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-12
    Abdullah Cahit Karaoglanli; Kadir Mert Doleker; Yasin Ozgurluk

    Gas turbine engines are exposed to severe oxidation and thermal shock under service conditions. Thermal barrier coatings (TBCs) are used to protect metallic components of gas turbines against such failures. Yttria stabilized zirconia (YSZ) has been the most common top coating material for TBC systems. However, rare earth zirconates such as La2Zr2O7 and Gd2Zr2O7 stand out as alternatives to YSZ top coating for TBCs. In this study, Inconel 718 substrates were coated with CoNiCrAlY using cold gas dynamic spray (CGDS) technique, which is a promising technology for bond coat spraying. All the ceramic top coats were produced by electron beam physical vapor deposition (EB-PVD) method that provides high strain tolerance under thermal loadings. To predict the lifetime of TBCs, the samples were subjected to furnace cycling tests at 1150 °C. After the tests, the microstructure of thermally grown oxide (TGO) layers, crack formations and chemical compatibility between the coating layers were investigated in detail. Results show that TBCs with double layered rare earth zirconate exhibit longer lifetime as compared to single layered TBCs.

    更新日期:2019-12-13
  • Quantitative multiscale correlative microstructure analysis of additive manufacturing of stainless steel 316L processed by selective laser melting
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-12
    Matjaž Godec; Stefan Zaefferer; Bojan Podgornik; Mario Šinko; Elena Tchernychova
    更新日期:2019-12-13
  • Gas injection approach for synthesis of hydroxyapatite nanorods via hydrothermal method
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-12
    Hassan Nosrati; Rasoul Sarraf Mamoory; Dang Quang Svend Le; Cody Eric Bünger; Reza Zolfaghari Emameh; Fatemeh Dabir
    更新日期:2019-12-13
  • Significant influence of rolling modes on martensitic transformation, microstructural evolution and texture development in a 304 stainless steel
    Mater. Charact. (IF 3.22) Pub Date : 2019-12-12
    Guosheng Sun; Linxiu Du; Jun Hu; Bin Zhang

    A 304 stainless steel was deformed by two different rolling modes (unidirectional cold rolling and cross rolling) at room temperature. The effects of rolling modes on martensitic transformation, microstructural evolution, and texture development were investigated. The results showed that martensitic transformation was enhanced significantly by cross rolling. The underlying reason was the increase in the amounts of nucleation sites for α′-martensite, i.e., intersections of shear bands. The transformation of austenite to martensite was found to be followed the sequence of γ → ε → α′ regardless of rolling modes. Rolling modes had great influences on deformation textures in both the remaining austenite and α′-martensite. For unidirectional cold-rolled samples, the main texture components of deformed austenite were Brass ({110}〈112〉) and S ({123}〈634〉) texture, while the α′-martensite phase exhibited {112}〈110〉, {223}〈121〉, and {554}〈225〉 orientations. However, ζ-fiber (〈110〉//ND) component, which was characterized by oscillation between Brass and G/B ({110}〈111〉) texture, was formed in remaining austenite during cross rolling, accompanied by a weakening of S component. Meanwhile, the α′-martensite phase in cross-rolled samples exhibited η-fiber (〈001〉//ND), and the dominant texture components were Rotated Cube ({001}〈110〉) and {001}〈160〉. The stability of the orientations during cross rolling can be responsible for texture development in both austenite and α′-martensite.

    更新日期:2019-12-13
  • Improvement in compressive creep resistance of Al-0.2Zr alloy with L12 structured Sc-enriched precipitates
    Mater. Charact. (IF 3.22) Pub Date : 2019-11-28
    Jiayi Zhang, Bin Wang, Hao Wang, Chaomin Zhang

    The influence of Sc microalloying on compressive creep behaviors of Al-0.2Zr and Al-0.2Zr-0.1Sc alloy have been studied. The steady state creep rate of Al-0.2Zr-0.1Sc alloy ranged from 1.124 × 10−9 s−1 to 1.926 × 10−8 s−1 at 90–150 °C /70 MPa. By contrast, the steady state creep rate of Al-0.2Zr alloy ranged from 6.862 × 10−8 s−1 to 8.560 × 10−7 s−1, indicating that Sc addition significantly improve the compressive creep resistance of Al-0.2Zr alloy. According to the TEM micrographs, except for Al3(Zr,Sc) precipitates precipitated during aging, a large number of fine dispersed Al3Sc precipitates precipitated after creep for 70 h, which significantly hinder movements of dislocations and grain boundaries. As a result, the steady-state creep rate of Al-0.2Zr-0.1Sc alloy slightly decreases after 70 h at 150 °C /70 MPa. The critical creep stress value of Al-0.2Zr alloy is 47.2 MPa, and that of Al-0.2Zr-0.1Sc alloy is 68.4 MPa. The higher critical creep stress value indicates the more excellent compressive creep resistance.

    更新日期:2019-12-11
  • Interfacial reaction between solid Ni and liquid Al in tens of seconds: Dissolution kinetics of solid Ni and formation of intermetallic compounds
    Mater. Charact. (IF 3.22) Pub Date : 2019-11-28
    Gaoyang Yu, Huimin Wang, Shuhai Chen, Lu Wei, Jihua Huang, Jian Yang, Zhiyi Zhao

    The interfacial reaction between solid Ni and liquid Al, such as dissolution behaviors of solid Ni and formation mechanisms of intermetallic compounds, are not thoroughly clarified yet, especially under the conditions of short holding time and high reaction temperature. In this study, a hot-dip method was designed to investigate the isothermal interfacial reaction mechanism of solid Ni and liquid Al at temperature of 700 °C, 800 °C and 900 °C for 0–40 s. The dissolution behavior of solid Ni in liquid Al was analyzed. The dissolution rate constant, KNi, and dissolution activation energy, Ea, were calculated. The microstructure analysis with scanning electron microscope (SEM) and transmission electron microscopy (TEM) revealed that the dissolved thickness of solid Ni in pure liquid Al has linear relationship with the reaction time. The microstructure of the reaction interface consisted of Ni, Ni based solid solution, Al3Ni2 layer, adhered Al3Ni layer, free Al3Ni, Al3Ni + Al eutectic structure and Al. Ni based solid solution structure firstly formed at the holding stage. Nano-scale Al3Ni2 and irregular adhered Al3Ni appeared at the interface during fast cooling stage.

    更新日期:2019-12-11
  • In-situ investigation of the evolution of microstructure and texture during load reversal of commercially pure titanium using synchrotron X-ray diffraction
    Mater. Charact. (IF 3.22) Pub Date : 2019-11-28
    M.V. Krishna, Vivek Kumar Sahu, Atasi Ghosh, Heinz-Guenter Brokmeier, Nilesh Prakash Gurao

    Understanding of the deformation micro-mechanism as a function of grain orientation during cyclic loading is of significant importance to have failure safe design of structural components made of commercially pure titanium (CP-Ti). The evolution of deformation microstructure and texture of commercially pure titanium samples with prismatic-pyramidal (orientation A) and near basal (orientation B) as initial texture along the loading direction has been investigated during load reversal at ±8% and ± 12% strain using in-situ synchrotron X-ray diffraction. The synchrotron X-ray diffraction results have been further complemented with Elastic-Plastic Self-Consistent (EPSC) simulation of the texture data and ex-situ Electron backscatter diffraction (EBSD) scan taken at the same region. Orientation A showed partially reversible texture whereas orientation B showed non-reversible texture with mechanical reversibility. The partial textural reversibility has been attributed to the prism to basal slip transition which toggles the c-axis between the normal and transverse direction during the tension-compression cycle. With an increase in strain from 8 to 12%, microstrain and dislocation density in the basal plane of orientation A decreases sharply. On the other hand, for the same level of strain in orientation B, microstrain increases but the dislocation density of basal plane shows insignificant change. The crystal orientation map obtained from ex-situ EBSD of deformed microstructure complements to the fact indicating, with increase in strain, deformation of basal oriented grains show non-Schmid behaviour of contraction twin propagation due to local strain incompatibility in orientation A. On the other hand, the prism oriented grains of orientation B have mostly deformed by extension twinning, which reorients them towards basal orientation. The deformation proceeds by lateral thickening of twins due to the lower elastic stiffness of the twinned region compared to the grain matrix. The extension twin boundaries get converted to contraction twin boundaries at higher strain during load reversal.

    更新日期:2019-12-11
  • Ferroelectric domain structures in strained BiFeO3 ceramics synthesized by spark plasma sintering
    Mater. Charact. (IF 3.22) Pub Date : 2019-11-28
    Liwei Zhang, Hua Ke, Hongjun Zhang, Huijiadai Luo, Fangzhe Li, Lu Cao, Wen Wang, Dechang Jia, Yu Zhou

    The ferroelectric domain structures were analyzed in strained multiferroic BiFeO3 ceramics via X-ray diffraction (XRD), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). XRD refinements indicate that the SPS method introduced the large strain into the ceramic samples even though ~50% strain reduction could be conducted through annealing process. The large strain increased the contents of unusual 71° ± 1° grain boundaries and deformed 71° domain walls (~89° twin boundaries) both in the as-sintered sample and the annealed sample, which could accommodate the grain boundary energy and the large thermal strain. The large strain was more conducive to form typical curved and bridge-like 180° domain morphologies. And the domain topographies heavily relied on the grain orientations.

    更新日期:2019-12-11
  • Effect of Si content on microstructure and compressive properties of open-cell Mg composite foams reinforced by in-situ Mg2Si compounds
    Mater. Charact. (IF 3.22) Pub Date : 2019-11-28
    Jiaan Liu, Lianren Zhang, Shengjun Liu, Zhiwu Han, Zhiqiang Dong

    The open-cell Mg-xSi (x = 1, 5, 9 wt%) foams reinforced by in-situ Mg2Si compounds were prepared by pressure infiltration process. The optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were used to investigate the microstructure, chemical components and phase compositions of the foams, respectively. Compressive strength and energy absorbing characteristics of the foams containing varied Si additions were assessed via compressive test. The experimental results exhibit that the microstructure of the foams is depending on Si content. Mg1Si foams are mainly composed of eutectic Mg2Si and α-Mg, while Mg5Si and Mg9Si foams mainly consist of the primary Mg2Si, eutectic Mg2Si and α-Mg. The compressive strength of the foams is elevated initially and then decreased when the Si content is increased from 1 to 9 wt%, but the energy absorption capacity is reduced with the increase of Si content. The related mechanism was discussed and a schematic diagram was drawn to reflect the role of coarse primary Mg2Si in fracture behavior of the foams.

    更新日期:2019-12-11
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