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
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
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 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.
