The inconsistencies regarding the fundamental correlation between Gd content and slip(twinning)activities of Mg alloys appeal further investigations.However,the traditional slip dislocations analysis by TEM is time-co...The inconsistencies regarding the fundamental correlation between Gd content and slip(twinning)activities of Mg alloys appeal further investigations.However,the traditional slip dislocations analysis by TEM is time-consuming,and that by SEM/EBSD cannot recognize the partial slip modes.These urge a more efficient and comprehensive approach to easily distinguish all potential slip modes occurred concurrently in alloy matrix.Here we report a modified lattice rotation analysis that can distinguish all slip systems and provide statistical results for slip activities in Mg alloy matrix.Using this method,the high ductility of Mg-Gd alloy ascribed to the enhanced non-basal slips,cross-slip,and postponed twinning activities by Gd addition is quantitatively clarified.展开更多
Zr was added to Ti−Nb−Fe alloys to develop low elastic modulus and high strengthβ-Ti alloys for biomedical applications.Ingots of Ti−12Nb−2Fe−(2,4,6,8,10)Zr(at.%)were prepared by arc melting and then subjected to hom...Zr was added to Ti−Nb−Fe alloys to develop low elastic modulus and high strengthβ-Ti alloys for biomedical applications.Ingots of Ti−12Nb−2Fe−(2,4,6,8,10)Zr(at.%)were prepared by arc melting and then subjected to homogenization,cold rolling,and solution treatments.The phases and microstructures of the alloys were analyzed by optical microscopy,X-ray diffraction,and transmission electron microscopy.The mechanical properties were measured by tensile tests.The results indicate that Zr and Fe cause a remarkable solid-solution strengthening effect on the alloys;thus,all the alloys show yield and ultimate tensile strengths higher than 510 MPa and 730 MPa,respectively.Zr plays a weak role in the deformation mechanism.Further,twinning occurs in all the deformed alloys and is beneficial to both strength and plasticity.Ti−12Nb−2Fe−(8,10)Zr alloys with metastableβphases show low elastic modulus,high tensile strength,and good plasticity and are suitable candidate materials for biomedical implants.展开更多
We utilized electron backscatter diffraction to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy(Mg–9.80 Gd–3.78 Y–1.12 Sm–0.48 Zr)during instantaneous hot indirect extrusi...We utilized electron backscatter diffraction to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy(Mg–9.80 Gd–3.78 Y–1.12 Sm–0.48 Zr)during instantaneous hot indirect extrusion.An equiaxed fine-grained(average grain size of 3.4±0.2μm)microstructure with a weak texture was obtained.The grain refinement was mainly attributed to the discontinuous dynamic recrystallization(DDRX)and continuous DRX(CDRX)processes during the hot indirect extrusion process.The twin boundaries formed during the initial deformation stage effectively increased the number of high angle grain boundaries(HAGBs),which provided sites for new grain nuclei,and hence,resulted in an improved DDRX process.Along with DDRX,CDRX processes characterized by low angle grain boundary(LAGB)networks were also observed in the grain interior due to effective dynamic recovery(DRV)at a relatively high temperature of 773 K and high strain rates.Thereafter,LAGB networks were transformed into HAGB networks by the progressive rotation of subgrains during the CDRX process.展开更多
Twinning-detwinning(TDT)behavior in a strongly basal-textured Mg-Li alloy during two-step compression(RD)-compression(ND)process was investigated using quasi-in-situ EBSD.TDT behavior and TDT variants selection were s...Twinning-detwinning(TDT)behavior in a strongly basal-textured Mg-Li alloy during two-step compression(RD)-compression(ND)process was investigated using quasi-in-situ EBSD.TDT behavior and TDT variants selection were statistically discussed with the loading path for the first time.Non-Schmid twinning behavior was observed in the first step compression,owing to the local stress fluctuations by neighboring twins;in contrast,Schmid’s law well predicted the detwinning variants selection.This asymmetrical TDT behavior was first investigated to date related with the strong basal texture and loading path.Besides,with the progress of compression,Schmid factors for twinning demonstrated a decreasing tendency;however,those for detwinning during the second step displayed an abnormally increasing trend,fundamentally stemming from prior twinning behavior.展开更多
The impact produced when cavitation bubbles collapse can be utilized to modify surfaces in the same way as shot peening and it is called cavitation peening (CP). CP is one of a number of surface modification technique...The impact produced when cavitation bubbles collapse can be utilized to modify surfaces in the same way as shot peening and it is called cavitation peening (CP). CP is one of a number of surface modification techniques used to improve the fatigue strength of metallic materials by introducing compressive residual stress. Although it has been shown by an X-ray diffraction method that CP decreases the micro-strain related to dislocations in the sub-surface of a polycrystalline material, the mechanism for this decrease is unclear. In this paper, the movement of dislocations by CP was observed using transmission electron microscopy (TEM).展开更多
Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam(PBF-EB)tech-nology.In this st...Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam(PBF-EB)tech-nology.In this study,mechanical stimulation was suggested to suppress smoke of gas-atomized(GA)Ti-48Al-2Cr-2Nb powder using Al_(2)O_(3) and WC ball milling.The deformation mechanism of the GA powder depending on the ball milling media was discussed based on the developed particle morphology distribu-tion map and contact mechanics simulation.It was revealed that the rapid decrement of flowability and packing density after WC ball milling owing to the formation of angular fragments by the brittle fracture.The variation of surface and electrical properties by mechanical stimulation was investigated via XPS,TEM,and Impedance analysis.The electrical resistivity of the ball-milled powders gradually decreased with increasing milling duration,despite the increased oxide film thickness,and the capacitive response disappeared in Al-60 and WC-30 via metal-insulator transition.This could be due to the accumulation of strain and defects on the oxide film via mechanical stimulation.The smoke mechanism of ball-milled powders was discussed based on the percolation theory.In the smoke experiment,smoke was more suppressed for WC-10 and WC-20 than that for Al-40 and Al-50,respectively,despite the longer charge dissipation time.This could be due to the high probability of contact with conductive particles.For the Al-60 and WC-30 powders,smoke was further restricted by the formation of a percolation cluster with metal-like electrical conductivity.We believe that this study will contribute to a better understanding of the smoke mechanism and process optimization of the PBF-EB.展开更多
The deformation mechanism of slips and twins has a considerable influence on the plasticity of magnesium alloys. However, the roles of slips and twins in the room-temperature deformation of Mg-rare earth(Mg-RE) alloys...The deformation mechanism of slips and twins has a considerable influence on the plasticity of magnesium alloys. However, the roles of slips and twins in the room-temperature deformation of Mg-rare earth(Mg-RE) alloys with high contents of rare earth elements is rarely investigated. Here, the microstructural evolution and deformation mechanism of an aged Mg-5 Y-2 Nd-3 Sm-0.5 Zr alloy during uniaxial compression at room temperature were systematically investigated using in-situ electron-backscattered diffraction and transmission electron microscopy. The results indicated that in the early stage of deformation, the Mg-RE alloy was mainly controlled by the slip of dislocations in the basal plane and the coordinated c-axis strain of the {10-12} twin. With an increase in the strain, the grain orientation became more suitable for the initiation of pyramidal Ⅱ dislocations in the later stage of deformation;these dominated the deformation mechanism. In the twin evolution of the Mg-RE alloy, there were three types of twin-twin interaction behaviors:(i) single twin variant 'parallel' structure,(ii) single twin variant 'cross' structure, and(iii) multi twin variant 'cross' structure. In addition, three types of twin-grain boundary interaction behaviors were summarized:(i) twin 'refracting through' grain boundary,(ii) twin'parallel through' grain boundary, and(iii) twin 'fusing through' grain boundary, which are expected to act as new means and solutions for the twin strengthening of magnesium alloys.展开更多
The dual-phase Re_(0.5)MoNbW(TaC)_(0.5) composite,consisting of refractory body-centered cubic(BCC)highentropy alloy and carbide with many fine eutectic structures,was successfully synthesized by arc melting.The phase...The dual-phase Re_(0.5)MoNbW(TaC)_(0.5) composite,consisting of refractory body-centered cubic(BCC)highentropy alloy and carbide with many fine eutectic structures,was successfully synthesized by arc melting.The phase stability,high-temperature mechanical properties and strengthening mechanism of the ascast composite were studied.The microstructure of the composite remained stable after annealing at 1300℃for 168 h.It exhibited remarkably high-temperature strength,yield strength~901 MPa,and true ultimate compressive strength~1186 MPa at 1200℃.The BCC phase and carbide exhibited a semi-coherent interface with good bonding after severe deformation at 1200℃.The dipolar dislocation walls in BCC phase,restricted dynamic interaction between defects in carbide,and the pinning effect of semi-coherent interface offered effective strengthening effects.展开更多
The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for th...The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for the onset of dynamic recrystallization （DRX） were determined based on the conventional strain hardening rate curves （dσ/dε versus σ）.The progress of DRX was analyzed by constructing a model of volume fraction of DRX based on flow curves.The strain rate sensitivity （SRS） and activation volume V were calculated.The results show that the DRX almost can happen under all deformation conditions even at high Z deformations where dynamic recovery （DRV） is the main softening mechanism.The DRX fraction curves can well predict the DRX behavior.The strain has significant effects on SRS at the strain rates of 0.01s-1 and 10s-1 which are mainly due to off-equilibrium saturation of dislocation storage and annihilation while the effects of the temperature on the SRS are based on the uniformity of microstructure distribution.The formation of ＂forest＂ of dislocation is contributed to the low activation volume V＊（about 168b3） which is independent of Z values at the initial deformation.The cross-slip due to dislocation piled up beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions at high strain （ε=0.6） while the fine DRX grains coarsed is the main reason for the high activation volume at low Z under the same strain conditions.展开更多
Powder bed fusion with electron beam(PBF-EB),allows Co-Cr-Mo(CCM) implants with patientcustomization to be fabricated with high quality and complex geometry.However,the variability in the properties of PBF-EB-built CC...Powder bed fusion with electron beam(PBF-EB),allows Co-Cr-Mo(CCM) implants with patientcustomization to be fabricated with high quality and complex geometry.However,the variability in the properties of PBF-EB-built CCM alloy,mainly due to the lack of understanding of the mechanisms that govern microstructural heterogeneity,brings limitations in extensive application.In this study,the microstructural heterogeneity regarding the γ-fcc→ε-hcp phase transformation was characterized.The phase transformation during PBF-EB was analyzed depending on the thermal history that was elucidated by the numerical simulation.It revealed that isothermal γ→ε transformation occurred during the fabrication.Importantly,the difference in γ/ε phase distribution was a result of the thermal history determining which method phase transformation was taking place,which can be influenced by the PBF-EB process parameters.In the sample with a low energy input(Earea=2.6 J/mm2),the martensitic transformation was dominant.As the building height increased from the bottom,the e phase fraction decreased.On the other hand,in the sample with a higher energy input(Earea=4.4 J/mm2),the ε phase fo rmed via diffusional-massive transformation and only appea red in a short range of the lower part away from the bottom.展开更多
We investigated the effects of Al concentration on the reciprocated motion of twin boundaries in pre-strained Mg-Al-Zn alloys through a combination of applied compression and tension,in-situ electron-backscattering di...We investigated the effects of Al concentration on the reciprocated motion of twin boundaries in pre-strained Mg-Al-Zn alloys through a combination of applied compression and tension,in-situ electron-backscattering diffraction observations,and high-angle annular dark-field scanning transmission electron microscopy observations.The twin growth was restricted by increased Al concentration,which resulted in the occurrence of smaller-sized twins.The reverse motion of twin boundaries was also restricted,resulting in the formation of higher fractions of secondary twins and 2–5°boundaries during reverse tension.The secondary twins and 2–5°boundaries mainly contributed to the increased ultimate tensile strength of the pre-strained Mg alloys.This effect is more significant in Mg alloys with larger pre-compression.Moreover,the increased amount of the Al solute atoms,rather than the precipitates,mainly contributed to the increased strengthening effect on the twin boundary motion.Our research contributes to development of high-strength Mg alloys by stabilizing twin boundaries.展开更多
基金supported by the grant from the Natural Science Foundation of China(51871244)the Hunan Provincial Innovation Foundation for Postgraduate(CX20200172)the Fundamental Research Funds for the Central Universities of Central South University(1053320190103)
文摘The inconsistencies regarding the fundamental correlation between Gd content and slip(twinning)activities of Mg alloys appeal further investigations.However,the traditional slip dislocations analysis by TEM is time-consuming,and that by SEM/EBSD cannot recognize the partial slip modes.These urge a more efficient and comprehensive approach to easily distinguish all potential slip modes occurred concurrently in alloy matrix.Here we report a modified lattice rotation analysis that can distinguish all slip systems and provide statistical results for slip activities in Mg alloy matrix.Using this method,the high ductility of Mg-Gd alloy ascribed to the enhanced non-basal slips,cross-slip,and postponed twinning activities by Gd addition is quantitatively clarified.
基金the Natural Science Foundation of Shanghai,China(No.15ZR1428400)Shanghai Engineering Research Center of High-Performance Medical Device Materials,China(No.20DZ2255500)the Project of Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development,Tohoku University,sponsored by Ministry,Education,Culture,Sports,Science and Technology,Japan,and the Grant-in Aid for Scientific Research(C)(No.20K05139)from JSPS(Japan Society for the Promotion of Science),Tokyo,Japan.
文摘Zr was added to Ti−Nb−Fe alloys to develop low elastic modulus and high strengthβ-Ti alloys for biomedical applications.Ingots of Ti−12Nb−2Fe−(2,4,6,8,10)Zr(at.%)were prepared by arc melting and then subjected to homogenization,cold rolling,and solution treatments.The phases and microstructures of the alloys were analyzed by optical microscopy,X-ray diffraction,and transmission electron microscopy.The mechanical properties were measured by tensile tests.The results indicate that Zr and Fe cause a remarkable solid-solution strengthening effect on the alloys;thus,all the alloys show yield and ultimate tensile strengths higher than 510 MPa and 730 MPa,respectively.Zr plays a weak role in the deformation mechanism.Further,twinning occurs in all the deformed alloys and is beneficial to both strength and plasticity.Ti−12Nb−2Fe−(8,10)Zr alloys with metastableβphases show low elastic modulus,high tensile strength,and good plasticity and are suitable candidate materials for biomedical implants.
基金financial support from the National Natural Science Foundation of China(Grant no.51571084)financial support from the Grant-in-Aid for Early-Career Scientists(Grant no.18K14024)financial support from the China Scholarship Council(Grant No.201908410208)
文摘We utilized electron backscatter diffraction to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy(Mg–9.80 Gd–3.78 Y–1.12 Sm–0.48 Zr)during instantaneous hot indirect extrusion.An equiaxed fine-grained(average grain size of 3.4±0.2μm)microstructure with a weak texture was obtained.The grain refinement was mainly attributed to the discontinuous dynamic recrystallization(DDRX)and continuous DRX(CDRX)processes during the hot indirect extrusion process.The twin boundaries formed during the initial deformation stage effectively increased the number of high angle grain boundaries(HAGBs),which provided sites for new grain nuclei,and hence,resulted in an improved DDRX process.Along with DDRX,CDRX processes characterized by low angle grain boundary(LAGB)networks were also observed in the grain interior due to effective dynamic recovery(DRV)at a relatively high temperature of 773 K and high strain rates.Thereafter,LAGB networks were transformed into HAGB networks by the progressive rotation of subgrains during the CDRX process.
基金supported by the grant from the Natural Science Foundation of China(51871244)the Hunan Provincial Innovation Foundation for Postgraduate(CX20200172)the Fundamental Research Funds for the Central Universities of Central South University(1053320190103)。
文摘Twinning-detwinning(TDT)behavior in a strongly basal-textured Mg-Li alloy during two-step compression(RD)-compression(ND)process was investigated using quasi-in-situ EBSD.TDT behavior and TDT variants selection were statistically discussed with the loading path for the first time.Non-Schmid twinning behavior was observed in the first step compression,owing to the local stress fluctuations by neighboring twins;in contrast,Schmid’s law well predicted the detwinning variants selection.This asymmetrical TDT behavior was first investigated to date related with the strong basal texture and loading path.Besides,with the progress of compression,Schmid factors for twinning demonstrated a decreasing tendency;however,those for detwinning during the second step displayed an abnormally increasing trend,fundamentally stemming from prior twinning behavior.
文摘The impact produced when cavitation bubbles collapse can be utilized to modify surfaces in the same way as shot peening and it is called cavitation peening (CP). CP is one of a number of surface modification techniques used to improve the fatigue strength of metallic materials by introducing compressive residual stress. Although it has been shown by an X-ray diffraction method that CP decreases the micro-strain related to dislocations in the sub-surface of a polycrystalline material, the mechanism for this decrease is unclear. In this paper, the movement of dislocations by CP was observed using transmission electron microscopy (TEM).
基金This work was partially supported by JSPS KAKENHI(grant numbers 18H03834 and 21k14432)This research was also supported by“Materials Integration for Revolutionary Design System of Structure Materials”of the Cross-Ministerial Strategic Innovation Promotion Program(SIP)of Japan Science and Technology(JST).This work was also based on the results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization(NEDO)(JPNP14014).This work was partly supported by the Technology Research Association for Future Additive Manufacturing(TRAFAM).This work is also based on the results obtained from a project(JPNP19007)commissioned by the New Energy and Industrial Technology Development Organization(NEDO).
文摘Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam(PBF-EB)tech-nology.In this study,mechanical stimulation was suggested to suppress smoke of gas-atomized(GA)Ti-48Al-2Cr-2Nb powder using Al_(2)O_(3) and WC ball milling.The deformation mechanism of the GA powder depending on the ball milling media was discussed based on the developed particle morphology distribu-tion map and contact mechanics simulation.It was revealed that the rapid decrement of flowability and packing density after WC ball milling owing to the formation of angular fragments by the brittle fracture.The variation of surface and electrical properties by mechanical stimulation was investigated via XPS,TEM,and Impedance analysis.The electrical resistivity of the ball-milled powders gradually decreased with increasing milling duration,despite the increased oxide film thickness,and the capacitive response disappeared in Al-60 and WC-30 via metal-insulator transition.This could be due to the accumulation of strain and defects on the oxide film via mechanical stimulation.The smoke mechanism of ball-milled powders was discussed based on the percolation theory.In the smoke experiment,smoke was more suppressed for WC-10 and WC-20 than that for Al-40 and Al-50,respectively,despite the longer charge dissipation time.This could be due to the high probability of contact with conductive particles.For the Al-60 and WC-30 powders,smoke was further restricted by the formation of a percolation cluster with metal-like electrical conductivity.We believe that this study will contribute to a better understanding of the smoke mechanism and process optimization of the PBF-EB.
基金the financial support from the National Natural Science Foundation of China(No.51571084)the financial support from the Grant-in-Aid for Early-Career Scientists(No.18K14024)financial support from the China Scholarship Council(No.201908410208)。
文摘The deformation mechanism of slips and twins has a considerable influence on the plasticity of magnesium alloys. However, the roles of slips and twins in the room-temperature deformation of Mg-rare earth(Mg-RE) alloys with high contents of rare earth elements is rarely investigated. Here, the microstructural evolution and deformation mechanism of an aged Mg-5 Y-2 Nd-3 Sm-0.5 Zr alloy during uniaxial compression at room temperature were systematically investigated using in-situ electron-backscattered diffraction and transmission electron microscopy. The results indicated that in the early stage of deformation, the Mg-RE alloy was mainly controlled by the slip of dislocations in the basal plane and the coordinated c-axis strain of the {10-12} twin. With an increase in the strain, the grain orientation became more suitable for the initiation of pyramidal Ⅱ dislocations in the later stage of deformation;these dominated the deformation mechanism. In the twin evolution of the Mg-RE alloy, there were three types of twin-twin interaction behaviors:(i) single twin variant 'parallel' structure,(ii) single twin variant 'cross' structure, and(iii) multi twin variant 'cross' structure. In addition, three types of twin-grain boundary interaction behaviors were summarized:(i) twin 'refracting through' grain boundary,(ii) twin'parallel through' grain boundary, and(iii) twin 'fusing through' grain boundary, which are expected to act as new means and solutions for the twin strengthening of magnesium alloys.
基金supported by the State Key Program of National Natural Science Foundation of China[Grant No.51932006]National Natural Science Foundation of China[Grant No.51521001]+3 种基金the“111”Project[Grant No.B13035]the Joint Fund[Grant No.6141A02022255]the major program of specialized technological innovation of Hubei Province,China[Grant No.2019AFA176]support from China Scholarship Council(No.201906950060)。
文摘The dual-phase Re_(0.5)MoNbW(TaC)_(0.5) composite,consisting of refractory body-centered cubic(BCC)highentropy alloy and carbide with many fine eutectic structures,was successfully synthesized by arc melting.The phase stability,high-temperature mechanical properties and strengthening mechanism of the ascast composite were studied.The microstructure of the composite remained stable after annealing at 1300℃for 168 h.It exhibited remarkably high-temperature strength,yield strength~901 MPa,and true ultimate compressive strength~1186 MPa at 1200℃.The BCC phase and carbide exhibited a semi-coherent interface with good bonding after severe deformation at 1200℃.The dipolar dislocation walls in BCC phase,restricted dynamic interaction between defects in carbide,and the pinning effect of semi-coherent interface offered effective strengthening effects.
基金supported by the Chongqing Natural Science Foundation(No.CSTC2009BA4065)
文摘The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for the onset of dynamic recrystallization （DRX） were determined based on the conventional strain hardening rate curves （dσ/dε versus σ）.The progress of DRX was analyzed by constructing a model of volume fraction of DRX based on flow curves.The strain rate sensitivity （SRS） and activation volume V were calculated.The results show that the DRX almost can happen under all deformation conditions even at high Z deformations where dynamic recovery （DRV） is the main softening mechanism.The DRX fraction curves can well predict the DRX behavior.The strain has significant effects on SRS at the strain rates of 0.01s-1 and 10s-1 which are mainly due to off-equilibrium saturation of dislocation storage and annihilation while the effects of the temperature on the SRS are based on the uniformity of microstructure distribution.The formation of ＂forest＂ of dislocation is contributed to the low activation volume V＊（about 168b3） which is independent of Z values at the initial deformation.The cross-slip due to dislocation piled up beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions at high strain （ε=0.6） while the fine DRX grains coarsed is the main reason for the high activation volume at low Z under the same strain conditions.
基金supported by Grants-in-Aid for Scientific Research (KAKENHI) (Nos. 26289252, 15K14154, 17H01329 and 18H03834) from the Japan Society for the Promotion of Science (JSPS)partly supported by the Japan Ministry of Economy, Trade and Industry (METI)+2 种基金the New Energy and Industrial Technology Development Organization (NEDO)the Technology Research Association for Future Additive Manufacturing (TRAFAM)the “Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development” project。
文摘Powder bed fusion with electron beam(PBF-EB),allows Co-Cr-Mo(CCM) implants with patientcustomization to be fabricated with high quality and complex geometry.However,the variability in the properties of PBF-EB-built CCM alloy,mainly due to the lack of understanding of the mechanisms that govern microstructural heterogeneity,brings limitations in extensive application.In this study,the microstructural heterogeneity regarding the γ-fcc→ε-hcp phase transformation was characterized.The phase transformation during PBF-EB was analyzed depending on the thermal history that was elucidated by the numerical simulation.It revealed that isothermal γ→ε transformation occurred during the fabrication.Importantly,the difference in γ/ε phase distribution was a result of the thermal history determining which method phase transformation was taking place,which can be influenced by the PBF-EB process parameters.In the sample with a low energy input(Earea=2.6 J/mm2),the martensitic transformation was dominant.As the building height increased from the bottom,the e phase fraction decreased.On the other hand,in the sample with a higher energy input(Earea=4.4 J/mm2),the ε phase fo rmed via diffusional-massive transformation and only appea red in a short range of the lower part away from the bottom.
基金funded by Japan Society for the Promotion of Science(grant no.18K14024)。
文摘We investigated the effects of Al concentration on the reciprocated motion of twin boundaries in pre-strained Mg-Al-Zn alloys through a combination of applied compression and tension,in-situ electron-backscattering diffraction observations,and high-angle annular dark-field scanning transmission electron microscopy observations.The twin growth was restricted by increased Al concentration,which resulted in the occurrence of smaller-sized twins.The reverse motion of twin boundaries was also restricted,resulting in the formation of higher fractions of secondary twins and 2–5°boundaries during reverse tension.The secondary twins and 2–5°boundaries mainly contributed to the increased ultimate tensile strength of the pre-strained Mg alloys.This effect is more significant in Mg alloys with larger pre-compression.Moreover,the increased amount of the Al solute atoms,rather than the precipitates,mainly contributed to the increased strengthening effect on the twin boundary motion.Our research contributes to development of high-strength Mg alloys by stabilizing twin boundaries.
