查看更多>>摘要：? 2022 Elsevier Inc.Herein, W–xTa alloys (x = 0, 10, 20, 30, 40, and 50 wt%) were fabricated using the arc-melting method to improve the strain capacity of tungsten. The effects of Ta on the microstructure and mechanical properties of the fabricated alloys were investigated. The W[sbnd]Ta alloys with different Ta contents formed a single-phase W[sbnd]Ta solid solution after arc melting, and their average grain size changed from 1056 to 243 μm with increasing Ta content, indicating a grain refinement effect. The hardness, compressive strength, and compressive strain of W improved after the addition of Ta, with the compressive strength and compressive strain of W[sbnd]40Ta reaching 1.63 GPa and 9.54%, respectively, thus achieving the best comprehensive mechanical properties. The fracture surface diagram suggested that a mixed fracture mode of intergranular fracture and transgranular dissociation fracture gradually formed with the increasing of Ta content. Transmission electron microscopic analysis showed that the dislocation density of the compressed W[sbnd]40Ta alloy increased considerably compared with that of pure W, edge dislocation slip was also found to be an important slip mechanism in addition to screw dislocation slip. This study provides insights into the performance optimization, reinforcement design, and strengthening mechanisms of W–xTa alloys.
查看更多>>摘要：? 2021The object of this study is to investigate the influence of extrusion temperature on the microstructure, mechanical properties and in vitro corrosion behavior of Mg–2Zn–1Gd–0.4Mn–0.1Sr (ZGMS) alloy. The results show that as–extruded ZMGS alloy mainly contains α–Mg and Mg3Zn3Gd2 (W) phases, and the W phase is uniformly distributed in the Mg matrix. With decreasing extrusion temperature, the grain size is refined, and numerous nano–sized W particles dynamically precipitate during extrusion process. The mechanical properties of as–extruded experimental alloy is significantly improved with decreased extrusion temperature.This is owing to the effects of grain boundary strengthening, precipitation strengthening and dislocation strengthening. The experimental alloy exhibits the lowest corrosion rate and relatively uniform corrosion after extrusion at 360 °C. The corrosion products layer are mainly composed of Ca10(PO4)6(OH)2, Ca3(PO4)2 Mg(OH)2 and MgHPO4. The as–extruded alloy owns excellent mechanical properties (yield strength of 206.3 MPa ultimate tensile strength of 261.1 MPa and elongation of 27.3%) and corrosion rate (0.17 mg/cm2/day) after extruded at 360 °C. The alloy presents tremendous potential in degradable implant applications. Additionally, the relationship between microstructure and corrosion behavior was systematically discussed.
查看更多>>摘要：? 2022 Elsevier Inc.We evaluated the texture distribution in the thickness direction of the spun workpieces and clarified the mechanism of the change in the crystal orientation of the texture during metal spinning. Blank aluminum disks with a thickness of 1.44 mm were deformed into circular truncated cone cups by under-, true shear, and over-spinning and into cylindrical cups by 13 passes of conventional spinning. Crystal orientation analysis using electron backscatter diffraction revealed that the calculations of the orientation densities for small Miller indices could lead to a systematic evaluation of high intensity texture. The orientation density of Cu {121}<11ˉ1> decreased or that of B {110}<11ˉ2> increased on the roller side of the shear-spun part, of the workpieces formed by shear spinning, and on the roller side of the wall part and on the mandrel side of the open-edge part, of the workpieces formed by conventional spinning. The cosine similarity and Euclidean distance showed that the texture distributions obtained by shear spinning and that of the wall part obtained by conventional spinning were similar. Based on the stress state and preferred crystal orientation in deep drawing, the mechanism of the change in crystal orientation during spinning were described. The density of the texture with {110} (corresponding to B in this study) parallel to a disk plane increased when tensile stress was applied in the circumferential direction, contrarily, when compressive stress was applied in a similar fashion the density of the texture with {112} (corresponding to Cu) parallel to the disk plane increased.
查看更多>>摘要：? 2022The heterogeneous interface constituted by Cu and Al were diffusion-bonded with CuZn alloy fibre interlayer under different bonding parameters, which was compared with directly bonded Cu/Al interface to analyze the effects of the different intermetallic compounds (IMCs) occurred at the joining interface on the interface mechanical properties. The interface microstructure was analyzed by scanning electron microscope (SEM), the compositions profiles across the joining interface were measured by energy dispersive spectroscopy (EDS), the phase and grain in the bonding interface of a Cu/Al bond were carefully investigated via electron backscatter diffraction technique (EBSD), the results show that the interface phase of Cu/Al composites grows irregularly, which leads to the low uniformity of interface properties. By adding CuZn alloy fibre, the interface of Cu/Al shows cellular skeleton and promotes the uniform diffusion of interface. When the bonding time was 570 °C for 60 min, the average shear strength of Cu/CuZn/Al interface reached 60.7 MPa. Compared with Cu/Al interface, the standard deviation of shear strength decreased from 18.7 to 1.6, and the variance decreased from 3.7 to 1.1.
查看更多>>摘要：? 2022Mo element significantly affects the microtexture evolution of α in α + β titanium alloys. In this study, the evolution of microtexture during thermomechanical processing in Ti-6Al-2Sn-4Zr-2Mo (Ti6242) and Ti-6Al-2Sn-4Zr-6Mo (Ti6246) alloy was investigated. The β annealing treatments and α + β solution-treatments were conducted to display the microstructure characteristics before thermal deformation. Then, the thermal compression in the (α + β) phase region was applied to trace the evolution of lamellae orientation in conjunction with the electron backscatter diffraction. The results show a strong prior colony microtexture before thermal deformation. {10?12} and {10?11} twins are activated in Ti6246 during thermal compression, which strongly weakens the microtexture of the prior α colony. Besides, the lower volume fraction of the primary α phase, the smaller α colony, the thinner lamellae and the lower aspect ratio of α grains contribute to weak prior colony microtexture in Ti6246 alloy. This study shows the effect of Mo content on the microtexture evolution during thermomechanical processing.
查看更多>>摘要：? 2022Copper-rich precipitation can effectively strengthen stainless steel; however, the underlying mechanism is still unclear due to an insufficient understanding of the transformation of Cu-rich precipitates. Herein, using a high-resolution transmission electron microscope, we characterized the evolution of nanoscale Cu-rich precipitates during the aging of precipitation-hardening stainless steel and determined their effects on mechanical properties. Results indicate that the structure of the Cu-rich nanoprecipitates consecutively evolved from B2 (ordered Fe-Cu) to BCC (body-centered cubic) to 9R (the stacking structure of Cu-atom layers is ABC/BCA/CAB/A) and eventually to FCC (face-centered cubic) with aging. Consequently, the dislocation-precipitation interaction changes from a cutting to a looping mechanism. The BCC-structured Cu-rich nanoprecipitates formed at 480 °C after 1 h of aging exhibit excellent strength and ductility combination properties of 412 MPa and 18%, respectively.
查看更多>>摘要：? 2021In this study, composites reinforced by amorphous Al2O3 (am-Al2O3) and Al11La3 particles, formed through Al-La2O3 in-situ reaction, were fabricated by high energy ball milling (HEBM) and hot-pressing. The difference in high-temperature strength of composites hot-pressed at different temperatures could be as high as 44%, and the reason was disclosed by careful microstructure characterization. It was found that the in-situ reaction could be divided into three processes, accompanied by the crystallization of am-Al2O3 and coarsening of Al11La3. Am-Al2O3 could not only directly strengthen the composites, but also inhibit the coarsening of Al11La3 by forming a film on its surface. Therefore, when the hot-pressing temperature reached the crystallization temperature of am-Al2O3 (590 °C), am-Al2O3 film transformed into discontinuous γ-Al2O3 particles, resulting in rapid coarsening of Al11La3 as well as the degeneration of strengthening efficiency. By maintaining Al2O3 in an amorphous state and Al11La3 in fine size, the highest tensile strength of the composites could reach 190 MPa at 350 °C.
查看更多>>摘要：? 2022 Elsevier Inc.It is still a challenge to develop Mg[sbnd]Li alloy with a good balance of strength, plasticity and electromagnetic shielding effectiveness. Herein, a reasonable combination strategy for it was put forward through the processing steps: 1) dissolve the excess phase in the matrix by solid solution treatment, 2) promote the dynamic precipitation of the second phase and the formation of fine recrystallization by rolling, and 3) obtain the subgrain and more hard MgLi2Al and soft AlLi particles by subsequent aging treatment. Finally, the comprehensive improvement in strength, plasticity and electromagnetic shielding effectiveness of Mg-9Li-3Al-1Zn alloy was achieved. The ultimate tensile strength was increased by 34% compared to the as-cast alloy. The plasticity of the as-aged alloy was improved from 9.2% to 24.6% through the combination of the soft AlLi phase and subgrains, meanwhile, the electromagnetic shielding effectiveness at 1500 MHz was increased from 87 dB to 91 dB.
查看更多>>摘要：? 2022Brazing C/C composites and Ti6Al4V (TC4) can expand their practical applications, but the too much brittle TiC at C/C side is harmful to joint strength. The key to high-quality brazing joints is to control the excessive diffusion of Ti element from TC4 and TiC reaction layer at C/C. Herein, a new type of CuZr brazing alloy was designed, since Cu element can react with Ti, and Ti element are infinitely miscible in Zr. The interfacial microstructures showed that CuZr alloy reacted with Ti to form Ti2Cu + (Zr, Ti)2Cu, preventing diffusing Ti and optimizing reaction layer thickness. The effects of brazing temperature and holding time on microstructure changes were analyzed. When the temperature and holding time was insufficient, TiC+ZrC reaction layer was formed not well and inhomogeneous Ti(s, s) and Ti2Cu were dispersed in (Zr, Ti)2Cu, leading to a relatively low shear strength. Microstructures of continuous TiC+ZrC reaction layer and homogeneous (Zr, Ti)2Cu + Ti2Cu were optimized as temperature and holding time increased. Optimal microstructure of the joints was brazed at 970 °C for 10 min, which was C/C-TiC+ZrC/Ti2Cu + (Zr, Ti)2Cu/Ti(s, s)-TC4, and the joint reached the maximum shear strength about 54.2 MPa.
查看更多>>摘要：? 2022In order to better understand the mechanisms of environmentally-assisted cracking (EAC) of 7xxx aluminium aerospace alloys, large scale serial sectioning using the newly developed femtosecond laser plasma focused ion-beam (laser PFIB) has been performed on both AA7050 and AA7085 alloys containing environmentally-assisted cracks introduced during accelerated laboratory testing. The samples were firstly scanned using X-ray computed tomography in order to reveal the long-range crack morphology and allow for targeted lift out of the crack tip regions for serial sectioning. This paper describes the optimisation of the methodology for both the liftout procedure and subsequent serial sectioning using laser-PFIB. Electron backscatter diffraction (EBSD) mapping at each slice allowed for 3D reconstruction of statistically valid volumes of material, up to 0.5 mm3 with a fine voxel size (1 μm). High resolution secondary electron imaging at each slice allowed for 3D reconstruction of the crack volume, and the datasets were combined in order to investigate the interaction of the crack with the microstructure. Optimisation of both the liftout geometry and the slicing procedure resulted in significant reduction in laser-induced curtaining artefacts and higher quality data acquisition. For these alloys, laser slicing alone was sufficient to provide a deformation free surface allowing for EBSD indexing rates up to ~95% acquired at high speeds of ~2000 Hz leading to reasonable acquisition times of ~4–5 days for each dataset. The datasets have shown that the grains in these alloys are much larger and more complex than previously realised, and the interaction of these cracks with the microstructure have shown that complex-shaped recrystallised grains can lead to significant crack deflection in these alloys and so may help to explain the observed differences in EAC behaviour.
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