The nucleation,variant selection,and orientation dependence of the strain-induced martensitic transformation(SIMT)process in biomedical Co-Cr-W-Ni alloys were investigated.The experimental results show that theε-hexa...The nucleation,variant selection,and orientation dependence of the strain-induced martensitic transformation(SIMT)process in biomedical Co-Cr-W-Ni alloys were investigated.The experimental results show that theε-hexagonal-close-packed phase was preferentially formed at theΣ3 twin boundaries and high-angle grain boundaries during the tensile process.The theoretical analysis shows that the variant selection of SIMT is governed by Schmid’s law.However,the SIMTedε-phase did not form equally on the two sides of the annealing twins,even though they had the same Schmid factor.This phenomenon is related to the mechanical work developed by the formation of theε-phase.Only the side which has both high Schmid factor and high mechanical work can initiate the SIMT process.A strong<111>fiber texture was formed,and theε-variants tended to appear in grains with orientations close to the<111>and<100>directions during the tensile process.These results can provide theoretical guidance for controlling the SIMT process of Co-Cr-W-Ni alloys to fabricate more reliable stents.展开更多
Single-pass compression tests of an aluminaforming austenite(AFA) alloy(Fe–20Cr–30Ni–0.6Nb–2Al–Mo) were performed using a Gleeble-3500 thermal–mechanical simulator. By combining techniques of electron back-scatt...Single-pass compression tests of an aluminaforming austenite(AFA) alloy(Fe–20Cr–30Ni–0.6Nb–2Al–Mo) were performed using a Gleeble-3500 thermal–mechanical simulator. By combining techniques of electron back-scattered diffraction(EBSD) and transmission electron microscopy(TEM), the dynamic recrystallization(DRX) behavior of the alloy at temperatures of 950–1100 ℃ and strain rates of 0.01–1.00 s^(-1) was investigated. The regression method was adopted to determine the thermal deformation activation energy and apparent stress index and to construct a thermal deformation constitutive model. Results reveal that the flow stress is strongly dependent on temperature and strain rate and it increases with temperature decreasing and strain rate increasing. The DRX phenomenon occurs more easily at comparably higher deformation temperatures and lower strain rates. Based on the method for solving the inflection point via cubic polynomial fitting of strain hardening rate(h) versus strain(e) curves, the ratio of critical strain(ec) to peak strain(ep) during DRX was precisely predicted. The nucleation mechanisms of DRX during thermal deformation mainly include the strain-induced grain boundary(GB)migration, grain fragmentation, and subgrain coalescence.展开更多
基金financially supported by the National Key R&D Program of China(No.2017 YFA 0403804).
文摘The nucleation,variant selection,and orientation dependence of the strain-induced martensitic transformation(SIMT)process in biomedical Co-Cr-W-Ni alloys were investigated.The experimental results show that theε-hexagonal-close-packed phase was preferentially formed at theΣ3 twin boundaries and high-angle grain boundaries during the tensile process.The theoretical analysis shows that the variant selection of SIMT is governed by Schmid’s law.However,the SIMTedε-phase did not form equally on the two sides of the annealing twins,even though they had the same Schmid factor.This phenomenon is related to the mechanical work developed by the formation of theε-phase.Only the side which has both high Schmid factor and high mechanical work can initiate the SIMT process.A strong<111>fiber texture was formed,and theε-variants tended to appear in grains with orientations close to the<111>and<100>directions during the tensile process.These results can provide theoretical guidance for controlling the SIMT process of Co-Cr-W-Ni alloys to fabricate more reliable stents.
基金financially supported by the National Natural Science Foundation of China (No. 2012AA03A501)the Ordinary University Graduate Student Scientific Research Innovation Projects by Jiangsu Province (No. KYLX-1027)
文摘Single-pass compression tests of an aluminaforming austenite(AFA) alloy(Fe–20Cr–30Ni–0.6Nb–2Al–Mo) were performed using a Gleeble-3500 thermal–mechanical simulator. By combining techniques of electron back-scattered diffraction(EBSD) and transmission electron microscopy(TEM), the dynamic recrystallization(DRX) behavior of the alloy at temperatures of 950–1100 ℃ and strain rates of 0.01–1.00 s^(-1) was investigated. The regression method was adopted to determine the thermal deformation activation energy and apparent stress index and to construct a thermal deformation constitutive model. Results reveal that the flow stress is strongly dependent on temperature and strain rate and it increases with temperature decreasing and strain rate increasing. The DRX phenomenon occurs more easily at comparably higher deformation temperatures and lower strain rates. Based on the method for solving the inflection point via cubic polynomial fitting of strain hardening rate(h) versus strain(e) curves, the ratio of critical strain(ec) to peak strain(ep) during DRX was precisely predicted. The nucleation mechanisms of DRX during thermal deformation mainly include the strain-induced grain boundary(GB)migration, grain fragmentation, and subgrain coalescence.
