An extra-low interstitial near alpha alloy Ti-3Al-2Zr-2Mo(wt%) was fabricated by hydrogenation and thermomechanical consolidation(TMC) of the coarse and spherical pre-alloyed powder with particle sizes of 60 to 270 μ...An extra-low interstitial near alpha alloy Ti-3Al-2Zr-2Mo(wt%) was fabricated by hydrogenation and thermomechanical consolidation(TMC) of the coarse and spherical pre-alloyed powder with particle sizes of 60 to 270 μm. The coarse powder is a byproduct of pre-alloyed powder produced for selective laser and electron beam additive manufacturing. The TMC process involves powder compaction, fast sintering,in-situ dehydrogenation and an immediate hot extrusion to form a fully dense and fine-grained martensitic microstructure. Further dehydrogenation in vaccum at 700 °C converted the martensitic microstructure into an interwoven α/β microstructure which exhibited an improved yield strength, apparent necking and premature cracking at grain boundary α(α_(GB)) ribbons. A further annealing of 880 ℃/1 h/AC led to the formation of a fine-grained α/β_(t)composite structure, which achieved an enhance ultimate tensile strength of 835 MPa and excellent tensile ductility of 16.0%. Analysis of the deformation behavior of the alloy in different states revealed that the α/β_(t)composite structures brought about an enhanced strain hardening capability by heterogeneous deformation effect of hard β_(t)and soft α-laths, which inhibited the formation of microcracks and consequently improved the coordinated deformation.展开更多
The strain rate()dependence of ultra-low temperature strength and ductility was investigated systematically on a cryogenic near alpha titanium alloy Ti-3Al-3Mo-3Zr-0.2Y additively manufactured by electron beam selecti...The strain rate()dependence of ultra-low temperature strength and ductility was investigated systematically on a cryogenic near alpha titanium alloy Ti-3Al-3Mo-3Zr-0.2Y additively manufactured by electron beam selective melting(EBSM).As increases under quasi-static tension at 77 and 20 K,ductility monotonically decreases when yield strength(YS)keeps ascending.As increases from 5.6×10^(-4) s^(-1) once by one order of magnitude,elongation-to-fracture declines from 20.0%to 16.5%and 15.7%at 20 K.However,unlike the regular monotone increase at 298 and 77 K,ultimate tensile strength(UTS)at 20 K rises to 1460 MPa first then drops to 1320 MPa.This study further examined how strain rate affects slipping,twinning and strain hardening behavior.The monotone increase in YS is primarily attributed to the increased CRSS for slips and the enhanced tendency of pyramidal〈a〉and〈c+a〉slipping and<100>34°twinning at 20 K.On the other hand,the monotone decrease of ductility is essentially ascribed to the intensified deformation localization characterized by micro shear bands,multiple necking and single necking.More importantly,the mechanisms of abnormal UTS variation and disappearance of serration flow at 20 K are discussed in terms of strain hardening levels,degree of shear deformation localization and the interaction of slips and twins.This study provides deep insights into strain rate effect on cryogenic mechanical behavior of EBSM-built titanium alloy.展开更多
基金financially supported by the“Xing Liao Talent Plan”of Liaoning Province,China(No.XLYC1802080)the Fundamental Research Fund for the Central Universities(No.02080022117003)。
文摘An extra-low interstitial near alpha alloy Ti-3Al-2Zr-2Mo(wt%) was fabricated by hydrogenation and thermomechanical consolidation(TMC) of the coarse and spherical pre-alloyed powder with particle sizes of 60 to 270 μm. The coarse powder is a byproduct of pre-alloyed powder produced for selective laser and electron beam additive manufacturing. The TMC process involves powder compaction, fast sintering,in-situ dehydrogenation and an immediate hot extrusion to form a fully dense and fine-grained martensitic microstructure. Further dehydrogenation in vaccum at 700 °C converted the martensitic microstructure into an interwoven α/β microstructure which exhibited an improved yield strength, apparent necking and premature cracking at grain boundary α(α_(GB)) ribbons. A further annealing of 880 ℃/1 h/AC led to the formation of a fine-grained α/β_(t)composite structure, which achieved an enhance ultimate tensile strength of 835 MPa and excellent tensile ductility of 16.0%. Analysis of the deformation behavior of the alloy in different states revealed that the α/β_(t)composite structures brought about an enhanced strain hardening capability by heterogeneous deformation effect of hard β_(t)and soft α-laths, which inhibited the formation of microcracks and consequently improved the coordinated deformation.
基金supported by the National Natural Science Foundation of China(No.52271026)the Applied Basic Re-search Program of Liaoning province(No.2023JH2/101300158)the Fundamental Research Fund for the Central Universities(No.N2202010).
文摘The strain rate()dependence of ultra-low temperature strength and ductility was investigated systematically on a cryogenic near alpha titanium alloy Ti-3Al-3Mo-3Zr-0.2Y additively manufactured by electron beam selective melting(EBSM).As increases under quasi-static tension at 77 and 20 K,ductility monotonically decreases when yield strength(YS)keeps ascending.As increases from 5.6×10^(-4) s^(-1) once by one order of magnitude,elongation-to-fracture declines from 20.0%to 16.5%and 15.7%at 20 K.However,unlike the regular monotone increase at 298 and 77 K,ultimate tensile strength(UTS)at 20 K rises to 1460 MPa first then drops to 1320 MPa.This study further examined how strain rate affects slipping,twinning and strain hardening behavior.The monotone increase in YS is primarily attributed to the increased CRSS for slips and the enhanced tendency of pyramidal〈a〉and〈c+a〉slipping and<100>34°twinning at 20 K.On the other hand,the monotone decrease of ductility is essentially ascribed to the intensified deformation localization characterized by micro shear bands,multiple necking and single necking.More importantly,the mechanisms of abnormal UTS variation and disappearance of serration flow at 20 K are discussed in terms of strain hardening levels,degree of shear deformation localization and the interaction of slips and twins.This study provides deep insights into strain rate effect on cryogenic mechanical behavior of EBSM-built titanium alloy.
