A high-purity Ti sheet with dense preexisting twins(introduced by 10%cold rolling)was subjected to isochronal annealing at 500–800°C for 1 h and isothermal annealing at 600°C for 0.17–100 h,respectively.By...A high-purity Ti sheet with dense preexisting twins(introduced by 10%cold rolling)was subjected to isochronal annealing at 500–800°C for 1 h and isothermal annealing at 600°C for 0.17–100 h,respectively.By mainly utilizing electron backscatter diffraction(EBSD)and electron channel contrast(ECC)imaging techniques,the microstructure and texture evolution during the isochronal and isothermal annealing were investigated systematically.Results show that recrystallization nuclei appear in the specimen annealed at 600°C for 1 h.In contrast,recrystallization cannot be initiated for those annealed at lower temperatures or for a shorter time.With the increase in temperature or time,the fraction of the recrystallized structure increases with gradual grain coarsening.Nearly complete recrystallization is reached after 800°C-1 h or 600°C-100 h annealing.Due to the distribution heterogeneity of microstructure and stored energy induced by the dense preexisting twins,recrystallization nucleation preferentially occurs in some specific regions(twin-twin or twin-grain boundary junctions).Then,they selectively consume twin lamellar structures,leading to non-uniform grain growth.It is demonstrated that the recrystallization nucleation is dominated by the strain-induced boundary migration mechanism,allowing scattered texture components corresponding to the twin lamellar structures to be gradually encroached by those untwinned structures with the initial bimodal basal texture(BBT).Eventually,a strong BBT is always obtained after sufficient recrystallization.展开更多
The approximately equimolar ratio A1CrNiSiTi multi-principal element alloy （MPEA） coatings were fab- ricated by laser cladding on Ti-6Al-4V （Ti64） alloy. Scanning electron microscopy （SEM）, equipped with an ener...The approximately equimolar ratio A1CrNiSiTi multi-principal element alloy （MPEA） coatings were fab- ricated by laser cladding on Ti-6Al-4V （Ti64） alloy. Scanning electron microscopy （SEM）, equipped with an energy-dispersive spectroscopy （EDS）, and X-ray diffrac- tion （XRD） were used to characterize the microstructure and composition. Investigations show that the coatings consist of （Ti, Cr）5Si3 and NiA1 phases, formed by in situ reaction. The phase composition is initially explicated according to obtainable binary and ternary phase diagrams, and the formation Gibbs energy of TisSi3, VsSi3 and CrsSi3. Dry sliding reciprocating friction and wear tests of the A1CrNiSiTi coating and Ti64 alloy substrate without coating were evaluated. A surface mapping profiler was used to evaluate the wear volume. The worn surface was characterized by SEM-EDS. The hardness and wear resistance of the A1CrNiSiTi coating are well compared with that of the basal material （Ti64）. The main wear mechanism of the AICrNiSiTi coating is slightly adhesive transfer from GCrl5 counterpart, and a mixed layer com- posed of transferred materials and oxide is formed.展开更多
An annealed Inconel 718 alloy was surface-treated by pulsed laser at three different powers（100, 50 and 25 W）. Microstructural changes induced by the laser treatments were characterized by use of electron backscatte...An annealed Inconel 718 alloy was surface-treated by pulsed laser at three different powers（100, 50 and 25 W）. Microstructural changes induced by the laser treatments were characterized by use of electron backscatter diffraction and electron channeling contrast imaging techniques. Results show that both annealing twins and strengthening precipitates profusely existing in the as-received specimen are dissolved at elevated temperatures during the laser irradiation. Meanwhile, in the melting zone（MZ）, densities of low angle boundaries（LABs） are greatly increased with a large number of Laves phases preferentially distributed along such LABs. For different specimens, widths and depths of their MZs are found to be gradually reduced with decreasing the laser powers. Orientation analyses reveal that the columnar grains in the MZ of the 100 W specimen could inherit orientations existing in the matrix while lower laser powers promote the formation of more nuclei with scattered orientations to grow to be granular grains in the MZ. Hardness tests reveal that the MZs of all laser-treated specimens are softer than the matrix probably due to both precipitate dissolution and grain coarsening.展开更多
Multiple characterization and analysis techniques including electron backscatter diffraction（EBSD）, electron channeling contrast（ECC） imaging, transmission electron microscopy（TEM） and microhardness test were jo...Multiple characterization and analysis techniques including electron backscatter diffraction（EBSD）, electron channeling contrast（ECC） imaging, transmission electron microscopy（TEM） and microhardness test were jointly employed to investigate microstructural characteristics such as local composition, morphology, grain boundary characteristics and interphase orientation relationship of a forged Zr-2.5Nb alloy before and after β-air-cooling. Results show that the as-forged specimen is composed of equiaxed and lamellar α grains and continuous net-like β-Zr films. After the β-air-cooling, the microstructure of the specimen is featured by basket-weave Widmanst？tten structure, in which the inter-α-plate second phases are nanoscale β-Zr. Analyses for crystallographic orientations reveal that the Burgers relationship has been strictly followed during the β→α cooling. Compared to the as-forged specimen, the hardness of the β-air-cooled specimen is higher, which could be attributed to the decreased structural sizes of both α and β phases, and the increased fraction of high angle boundaries as well.展开更多
In this paper, electron backscatter diffraction and various other characterization and analysis techniques mclucilng X-raydiffraction, electron channeling contrast imaging and energy-dispersive spectrometry were joint...In this paper, electron backscatter diffraction and various other characterization and analysis techniques mclucilng X-raydiffraction, electron channeling contrast imaging and energy-dispersive spectrometry were jointly employed to investigatemicrostructural and textural changes of a hot-rolled Ti-6A1-4V （TC4） sheet after annealing at 800 ℃ for 5 h. In addition,the hardness variation induced by the annealing treatment is rationalized based on revealed microstructural and texturalcharacteristics. Results show that the TC4 sheet presents a typical dual-phase （α＋β） microstructure, with α-Ti as themajor phase and short-rod-shaped β-Ti （minority） uniformly distributed throughout the α matrix. Most of α grains cor-respond to the un-recrystallized structures with a typical rolling texture （c//TD and 〈11-20〉//ND） and dense low angleboundaries （LABs）. After the annealing, the stored energy in the as-received specimen is significantly reduced, along withgreatly decreased LABs density. Also, the annealing allows recrystallization and grain growth to occur, leading toweakening of the initial texture. Furthermore, the water quenching immediately after the annealing triggers martensitictransformation, which makes the high-temperature β phases be transformed into submicron α plates. The hardness of theannealed specimen is 320.5 HV, lower than that （367.0 HV） of the as-received specimen, which could be attributed toreduced LABs, grain growth and weakened texture. Nevertheless, the hardening effect from the fine martensitic platescould help to suppress a drastic hardness drop.展开更多
基金financially supported by the Cultivation Project of CQUT for Research and Innovation Group(No.2023TDZ006)the Graduate Student Innovation Program of CQUT(No.CYS23648)the Postdoctoral Science Foundation of China(No.2021M690174)。
文摘A high-purity Ti sheet with dense preexisting twins(introduced by 10%cold rolling)was subjected to isochronal annealing at 500–800°C for 1 h and isothermal annealing at 600°C for 0.17–100 h,respectively.By mainly utilizing electron backscatter diffraction(EBSD)and electron channel contrast(ECC)imaging techniques,the microstructure and texture evolution during the isochronal and isothermal annealing were investigated systematically.Results show that recrystallization nuclei appear in the specimen annealed at 600°C for 1 h.In contrast,recrystallization cannot be initiated for those annealed at lower temperatures or for a shorter time.With the increase in temperature or time,the fraction of the recrystallized structure increases with gradual grain coarsening.Nearly complete recrystallization is reached after 800°C-1 h or 600°C-100 h annealing.Due to the distribution heterogeneity of microstructure and stored energy induced by the dense preexisting twins,recrystallization nucleation preferentially occurs in some specific regions(twin-twin or twin-grain boundary junctions).Then,they selectively consume twin lamellar structures,leading to non-uniform grain growth.It is demonstrated that the recrystallization nucleation is dominated by the strain-induced boundary migration mechanism,allowing scattered texture components corresponding to the twin lamellar structures to be gradually encroached by those untwinned structures with the initial bimodal basal texture(BBT).Eventually,a strong BBT is always obtained after sufficient recrystallization.
基金the financial supports from the University Innovation Research Group of Chongqing,China(No.CXQT20023)the Graduate Student Innovation Program of Chongqing University of Technology,China(No.CLGYCX20203006)。
基金supported by the Chongqing Research Program of Basic Research and Frontier Technology(No.CSTC2013jcyjA50016)the National Natural Science Foundation of China(Nos.51401039,51571037 and 51204110)the Scientific and Technological Research Program of Chongqing Municipal Education Commission(No.KJ1709204).
文摘The approximately equimolar ratio A1CrNiSiTi multi-principal element alloy （MPEA） coatings were fab- ricated by laser cladding on Ti-6Al-4V （Ti64） alloy. Scanning electron microscopy （SEM）, equipped with an energy-dispersive spectroscopy （EDS）, and X-ray diffrac- tion （XRD） were used to characterize the microstructure and composition. Investigations show that the coatings consist of （Ti, Cr）5Si3 and NiA1 phases, formed by in situ reaction. The phase composition is initially explicated according to obtainable binary and ternary phase diagrams, and the formation Gibbs energy of TisSi3, VsSi3 and CrsSi3. Dry sliding reciprocating friction and wear tests of the A1CrNiSiTi coating and Ti64 alloy substrate without coating were evaluated. A surface mapping profiler was used to evaluate the wear volume. The worn surface was characterized by SEM-EDS. The hardness and wear resistance of the A1CrNiSiTi coating are well compared with that of the basal material （Ti64）. The main wear mechanism of the AICrNiSiTi coating is slightly adhesive transfer from GCrl5 counterpart, and a mixed layer com- posed of transferred materials and oxide is formed.
基金Project(CSTC2015ZDCY-ZTZX50002) supported by the Innovation Program of Common and Key Technologies in Major Industries of Chongqing,China
文摘An annealed Inconel 718 alloy was surface-treated by pulsed laser at three different powers（100, 50 and 25 W）. Microstructural changes induced by the laser treatments were characterized by use of electron backscatter diffraction and electron channeling contrast imaging techniques. Results show that both annealing twins and strengthening precipitates profusely existing in the as-received specimen are dissolved at elevated temperatures during the laser irradiation. Meanwhile, in the melting zone（MZ）, densities of low angle boundaries（LABs） are greatly increased with a large number of Laves phases preferentially distributed along such LABs. For different specimens, widths and depths of their MZs are found to be gradually reduced with decreasing the laser powers. Orientation analyses reveal that the columnar grains in the MZ of the 100 W specimen could inherit orientations existing in the matrix while lower laser powers promote the formation of more nuclei with scattered orientations to grow to be granular grains in the MZ. Hardness tests reveal that the MZs of all laser-treated specimens are softer than the matrix probably due to both precipitate dissolution and grain coarsening.
基金Project(51401040) supported by the National Natural Science Foundation of ChinaProject(CSTC2017JCYJAX0114) supported by the Fundamental and Cutting-edge Research Plan of Chongqing,China+1 种基金Project(E2015203250) supported by the Natural Science Foundation of Hebei Province,ChinaProject(14LGA005) supported by the Young Teachers Program of Yanshan University,China
文摘Multiple characterization and analysis techniques including electron backscatter diffraction（EBSD）, electron channeling contrast（ECC） imaging, transmission electron microscopy（TEM） and microhardness test were jointly employed to investigate microstructural characteristics such as local composition, morphology, grain boundary characteristics and interphase orientation relationship of a forged Zr-2.5Nb alloy before and after β-air-cooling. Results show that the as-forged specimen is composed of equiaxed and lamellar α grains and continuous net-like β-Zr films. After the β-air-cooling, the microstructure of the specimen is featured by basket-weave Widmanst？tten structure, in which the inter-α-plate second phases are nanoscale β-Zr. Analyses for crystallographic orientations reveal that the Burgers relationship has been strictly followed during the β→α cooling. Compared to the as-forged specimen, the hardness of the β-air-cooled specimen is higher, which could be attributed to the decreased structural sizes of both α and β phases, and the increased fraction of high angle boundaries as well.
基金supported by the Fundamental and Cutting-Edge Research Plan of Chongqing(cstc2017jcyjAX0114and cstc2015jcyjBX0048)the Scientific and Technological Research Program of Chongqing Municipal Education Commission(KJ1600924)the Education Reform Project for Professional Degree Graduate of Chongqing University of Technology(ZSSD103)
文摘In this paper, electron backscatter diffraction and various other characterization and analysis techniques mclucilng X-raydiffraction, electron channeling contrast imaging and energy-dispersive spectrometry were jointly employed to investigatemicrostructural and textural changes of a hot-rolled Ti-6A1-4V （TC4） sheet after annealing at 800 ℃ for 5 h. In addition,the hardness variation induced by the annealing treatment is rationalized based on revealed microstructural and texturalcharacteristics. Results show that the TC4 sheet presents a typical dual-phase （α＋β） microstructure, with α-Ti as themajor phase and short-rod-shaped β-Ti （minority） uniformly distributed throughout the α matrix. Most of α grains cor-respond to the un-recrystallized structures with a typical rolling texture （c//TD and 〈11-20〉//ND） and dense low angleboundaries （LABs）. After the annealing, the stored energy in the as-received specimen is significantly reduced, along withgreatly decreased LABs density. Also, the annealing allows recrystallization and grain growth to occur, leading toweakening of the initial texture. Furthermore, the water quenching immediately after the annealing triggers martensitictransformation, which makes the high-temperature β phases be transformed into submicron α plates. The hardness of theannealed specimen is 320.5 HV, lower than that （367.0 HV） of the as-received specimen, which could be attributed toreduced LABs, grain growth and weakened texture. Nevertheless, the hardening effect from the fine martensitic platescould help to suppress a drastic hardness drop.
