In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature sintering.The average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 nm.After low tempe...In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature sintering.The average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 nm.After low temperature sintering of these composite nanopowders,the formed W-Y2 O3 alloys possess a smaller grain size of 510 nm while maintaining a comparatively higher density of 97.8%.Besides a few submicron Y2 O3 particles(about 100-300 nm)with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries,lots of nano Y2 WO6 particles(<20 nm)exist in W matrix.Moreover,many Y6 WO12(<10 nm)particles exist within submicron Y2 O3 particles.The formation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases,resulting in the purification of W matrix and the strengthening of phase boundaries.The combined action of the above factors makes the hardness of the sintered W-Y2 O3 alloys in our work as high as 656.6±39.0 HV0.2.Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2 O3 alloys.展开更多
Large-area bulk ultrafine grained （UFG） pure Cu was successfully prepared by multiple-pass overlapping friction stir processing （FSP） under additional rapid cooling. Overlapping FSP did not exert a significant eff...Large-area bulk ultrafine grained （UFG） pure Cu was successfully prepared by multiple-pass overlapping friction stir processing （FSP） under additional rapid cooling. Overlapping FSP did not exert a significant effect on the microstructure and mechanical properties of the FSP UFG Cu. Similar average grain size was achieved in the transitional zone （TZ） of the multiple-pass FSP sample compared to that in the nugget zone of the single-pass FSP sample, and the TZ exhibited a strong {111}（112） type A fiber shear texture, Very weak softening occurred in the TZ of the multiple-pass FSP UFG Cu, resulting in a relatively uniform hardness distribution throughout the whole processed zone. A high yield strength of - 310 MPa and a uniform elongation of - 13% were achieved in the bulk FSP UFG Cu. This study provides an effective strategy to prepare large-area bulk IUFG materials.展开更多
Tensile properties, microstructural evolution and fracture toughness of Al 2014 alloy subjected to cryorolling followed by warm rolling (CR + WR) have been investigated in the present study. The solution-treated (ST) ...Tensile properties, microstructural evolution and fracture toughness of Al 2014 alloy subjected to cryorolling followed by warm rolling (CR + WR) have been investigated in the present study. The solution-treated (ST) Al 2014 alloy is cryorolled followed by warm rolling process at different temperatures (110, 170 and 210 ℃). The mechanical properties and microstructural features of deformed and undeformed Al 2014 alloys were characterised by optical microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The CR + WR samples at 170 ℃ showed an improved hardness (179 HV), tensile (UTS 499 MPa, YS 457 MPa) and fracture toughness (KQ = 37.49 MPa y/m, Kee = 37.39 MPa √m and J integral = 33.25 kJ/mm^2) with respect to ST alloy as measured from the tensile and fracture toughness test. The improved mechanical properties of CR + WR alloy are attributed to grain boundary strengthening, combined recovery and recrystallisation, precipitation hardening and dynamic ageing effect during the deformation. The precipitation of metastable spherical phase Al2Cu was responsible for the improved tensile and fracture properties of finegrained Al 2014 alloy observed in the present work.展开更多
The objectives of this study were to produce ultrafine-grained(UFG) AA2024 aluminum alloy by cryorolling followed by aging and to evaluate its corrosion behavior. Solutionized samples were cryorolled to ~85% reduction...The objectives of this study were to produce ultrafine-grained(UFG) AA2024 aluminum alloy by cryorolling followed by aging and to evaluate its corrosion behavior. Solutionized samples were cryorolled to ~85% reduction in thickness. Subsequent aging resulted in a UFG structure with finer precipitates of Al_2CuMg in the cryorolled alloy. The(1) solutionized and(2) solutionized and cryorolled samples were uniformly aged at 160°C/24 h and were designated as CGPA and CRPA, respectively; these samples were subsequently subjected to corrosion studies. Potentiodynamic polarization studies in 3.5 wt% NaCl solution indicated an increase in corrosion potential and a decrease in corrosion current density for CRPA compared to CGPA. In the case of CRPA, electrochemical impedance spectroscopic studies indicated the presence of two complex passive oxide layers with a higher charge transfer resistance and lower mass loss during intergranular corrosion tests. The improved corrosion resistance of CRPA was mainly attributed to its UFG structure, uniform distribution of fine precipitates, and absence of coarse grain-boundary precipitation and associated precipitate-free zones as compared with the CGPA alloy.展开更多
The texture and mechanical properties of cross-rolled zircaloy-2 at 77 and 300 K were investigated.Crossrolling at 77 K was performed to impart different thickness reductions of 25% and 50%,while at 300 K with 25%,50%...The texture and mechanical properties of cross-rolled zircaloy-2 at 77 and 300 K were investigated.Crossrolling at 77 K was performed to impart different thickness reductions of 25% and 50%,while at 300 K with 25%,50%,75% and 85% reductions to the sample.EBSD analysis of deformed sample showed that near-basal orientation is not deformed completely after 50% rolling reduction.The activation of prismatic silp,{1122} contraction twin and {1012} extension twin were evident from the deformed microstructure at 77 K.The propensity for activation of basal slip〈a〉 at77 K was also observed.The deformation of the sample at 300 K occurs by prismatic,basal 〈a〉 and pyramidal 〈c＋a〉slips,which were predicted by pole figures.After annealing,the tensile strengths（735 and 710 MPa） are almost the same for 50% cryo-cross-rolled and room-temperature cross-rolled zircaloy-2 with almost 2.7% difference in their ductility.KAM analysis of the deformed samples was made to estimate the stored strain energy and dislocation density.Annealing of deformed sample at 673 K for 30 min results in recrystallization,which leads to the formation of ultrafine grains.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51822404 and 51574178)the Science and Technology Program of Tianjin(No.18YFZCGX00070)+1 种基金the Natural Science Foundation of Tianjin(No.18JCYBJC17900)the Seed Foundation of Tianjin University(Nos.2018XRX-0005 and 2019XYF-0066)。
文摘In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature sintering.The average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 nm.After low temperature sintering of these composite nanopowders,the formed W-Y2 O3 alloys possess a smaller grain size of 510 nm while maintaining a comparatively higher density of 97.8%.Besides a few submicron Y2 O3 particles(about 100-300 nm)with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries,lots of nano Y2 WO6 particles(<20 nm)exist in W matrix.Moreover,many Y6 WO12(<10 nm)particles exist within submicron Y2 O3 particles.The formation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases,resulting in the purification of W matrix and the strengthening of phase boundaries.The combined action of the above factors makes the hardness of the sintered W-Y2 O3 alloys in our work as high as 656.6±39.0 HV0.2.Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2 O3 alloys.
文摘Large-area bulk ultrafine grained （UFG） pure Cu was successfully prepared by multiple-pass overlapping friction stir processing （FSP） under additional rapid cooling. Overlapping FSP did not exert a significant effect on the microstructure and mechanical properties of the FSP UFG Cu. Similar average grain size was achieved in the transitional zone （TZ） of the multiple-pass FSP sample compared to that in the nugget zone of the single-pass FSP sample, and the TZ exhibited a strong {111}（112） type A fiber shear texture, Very weak softening occurred in the TZ of the multiple-pass FSP UFG Cu, resulting in a relatively uniform hardness distribution throughout the whole processed zone. A high yield strength of - 310 MPa and a uniform elongation of - 13% were achieved in the bulk FSP UFG Cu. This study provides an effective strategy to prepare large-area bulk IUFG materials.
文摘Tensile properties, microstructural evolution and fracture toughness of Al 2014 alloy subjected to cryorolling followed by warm rolling (CR + WR) have been investigated in the present study. The solution-treated (ST) Al 2014 alloy is cryorolled followed by warm rolling process at different temperatures (110, 170 and 210 ℃). The mechanical properties and microstructural features of deformed and undeformed Al 2014 alloys were characterised by optical microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The CR + WR samples at 170 ℃ showed an improved hardness (179 HV), tensile (UTS 499 MPa, YS 457 MPa) and fracture toughness (KQ = 37.49 MPa y/m, Kee = 37.39 MPa √m and J integral = 33.25 kJ/mm^2) with respect to ST alloy as measured from the tensile and fracture toughness test. The improved mechanical properties of CR + WR alloy are attributed to grain boundary strengthening, combined recovery and recrystallisation, precipitation hardening and dynamic ageing effect during the deformation. The precipitation of metastable spherical phase Al2Cu was responsible for the improved tensile and fracture properties of finegrained Al 2014 alloy observed in the present work.
文摘The objectives of this study were to produce ultrafine-grained(UFG) AA2024 aluminum alloy by cryorolling followed by aging and to evaluate its corrosion behavior. Solutionized samples were cryorolled to ~85% reduction in thickness. Subsequent aging resulted in a UFG structure with finer precipitates of Al_2CuMg in the cryorolled alloy. The(1) solutionized and(2) solutionized and cryorolled samples were uniformly aged at 160°C/24 h and were designated as CGPA and CRPA, respectively; these samples were subsequently subjected to corrosion studies. Potentiodynamic polarization studies in 3.5 wt% NaCl solution indicated an increase in corrosion potential and a decrease in corrosion current density for CRPA compared to CGPA. In the case of CRPA, electrochemical impedance spectroscopic studies indicated the presence of two complex passive oxide layers with a higher charge transfer resistance and lower mass loss during intergranular corrosion tests. The improved corrosion resistance of CRPA was mainly attributed to its UFG structure, uniform distribution of fine precipitates, and absence of coarse grain-boundary precipitation and associated precipitate-free zones as compared with the CGPA alloy.
基金BRNS,Bombay for their financial grant to this work (No.BRN-577-MMD)
文摘The texture and mechanical properties of cross-rolled zircaloy-2 at 77 and 300 K were investigated.Crossrolling at 77 K was performed to impart different thickness reductions of 25% and 50%,while at 300 K with 25%,50%,75% and 85% reductions to the sample.EBSD analysis of deformed sample showed that near-basal orientation is not deformed completely after 50% rolling reduction.The activation of prismatic silp,{1122} contraction twin and {1012} extension twin were evident from the deformed microstructure at 77 K.The propensity for activation of basal slip〈a〉 at77 K was also observed.The deformation of the sample at 300 K occurs by prismatic,basal 〈a〉 and pyramidal 〈c＋a〉slips,which were predicted by pole figures.After annealing,the tensile strengths（735 and 710 MPa） are almost the same for 50% cryo-cross-rolled and room-temperature cross-rolled zircaloy-2 with almost 2.7% difference in their ductility.KAM analysis of the deformed samples was made to estimate the stored strain energy and dislocation density.Annealing of deformed sample at 673 K for 30 min results in recrystallization,which leads to the formation of ultrafine grains.
