To improve the yield strength of metastableβ-Ti alloys with transformation-induced plasticity(TRIP)and twinning-induced plasticity effects,a novel strategy combining heterostructure strengthening with the TRIP effect...To improve the yield strength of metastableβ-Ti alloys with transformation-induced plasticity(TRIP)and twinning-induced plasticity effects,a novel strategy combining heterostructure strengthening with the TRIP effect was developed.A metastableβ-Ti alloy with a nominal composition of Ti-4Mo-3Cr-1Fe-1Al was used as the base alloy.By adjusting the annealing temperature after cold rolling,heterostructured samples comprising soft recrystallizedβ-grains and hard un-recrystallizedβ-grains andα-phase were prepared.Compared with the homogeneous coarse-grained sample,the yield strength of the heterostructured sample significantly increased from 610 to905 MPa,while maintaining excellent plasticity(32.7%),overcoming the traditional trade-off between strength and ductility.The observed high yield strength is attributed to significant back-stress strengthening caused by the accumulation of a large number of geometrically necessary dislocations at the interfaces between the soft and hard regions.Meanwhile,the exceptional plasticity is attributed to the activation of stress-induced martensite(SIM)within the metastableβmatrix.The sequential activation of dislocation slips and SIM is achieved through the construction of a heterostructured structure.This work provides a new strategy for designing metastableβ-Ti alloys with high strength and plasticity by coupling heterostructure strengthening and transformation-induced plasticity.展开更多
This work gives a comparison on the microstructural characteristics,textural discrepancies,and twinning behaviors of lamellar and equiaxed nearβ-Ti alloys during multi-pass cross rolling with a rolling reduction of 2...This work gives a comparison on the microstructural characteristics,textural discrepancies,and twinning behaviors of lamellar and equiaxed nearβ-Ti alloys during multi-pass cross rolling with a rolling reduction of 20%,50%and 80%.The results showed that the restoration mechanism of the alloy inβphase is strongly dependent on theαmorphologies,and in comparison,strain path has weaker influences on the grain refinement of theβmatrix.Therefore,the texture intensities of bothαandβphases were weakened owing to the dynamic recrystallization(DRX)of the two phases in the equiaxed microstructure.While,with regard to the lamellar microstructure,dynamic recovery(DRV)of theβphase predominated,forming elongatedβsubgrains.Besides,theαandβmatrix in lamellar microstructures obeyed the Burgers orientation relationship,which was gradually broken down until the final reduction.Lastly,the{1101}twinning exhibits a strong size effect.With the continuous DRX ofαphases,theα-twinning is suppressed owing to progressive grain refinement.The activation ofβ-twinning,namely{332}?113?and{112}?111?,in nearβ-Ti alloys is heavily dependent on the deficientβ-stabilizing elements and the local stress concentration.These findings provide an effective way to obtain ultra-fine grain microstructures of this alloy.展开更多
Deformation kinking as an uncommon plastic deformation mechanism has been reported in several materials while the relevant microstructure evolution and grain refinement behavior at a large strain remain unclear so far...Deformation kinking as an uncommon plastic deformation mechanism has been reported in several materials while the relevant microstructure evolution and grain refinement behavior at a large strain remain unclear so far.In this study,the issue was systematically investigated by utilizing cold forging to impose severe plastic deformation(SPD)on Ti-11 V metastableβ-Ti alloys.It is found that the formation of kink bands experiences dislocation gliding,pre-kinking and the ripening of pre-kinks in sequences.The kink bands are subsequently thickened through the coalescence of multiple kink bands in a manner of high accommodation.Ordinary dislocation slip is developed as a dominant deformation mechanism when deformation kinking is exhausted.The resulting grain refinement involves transverse breakdown and longitudinal splitting of dislocation walls and cells,which fragment kink bands into smallβ-blocks.Further refinement of theβ-blocks is still governed by dislocation activities,and finally nanograins with a diameter of~15 nm are produced at a large strain of 1.2.Alternatively,it is revealed that nanocrystallization is highly localized inside kink bands while the outer microstructure maintains original coarse structures.Such localized refinement characterization is ascribed to the intrinsic soft nature of kink bands,shown as low hardness in nanoindentation testing.The intrinsic softening of kink bands is uncovered to originate from the inner degraded dislocation density evidenced by both experimental measurement and theoretical calculation.These findings enrich fundamental understanding of deformation kinking,and shed some light on exploring the deformation accommodation mechanisms for metal materials at large strains.展开更多
Traditional theoretical and empirical calculation methods can guide the design of β-and metastable β-alloys for bio-titanium. However, it is still difficult to obtain novel near-β-Ti alloys with low modulus. This s...Traditional theoretical and empirical calculation methods can guide the design of β-and metastable β-alloys for bio-titanium. However, it is still difficult to obtain novel near-β-Ti alloys with low modulus. This study developed a method that combines machine learning with calculation of phase diagrams(CALPHAD) to facilitate the design of near-β-Ti alloys. An elastic modulus database of Ti–Nb–Zr–Mo–Ta–Sn system was constructed first, and then three features(the electron to atom ratio, mean absolute deviation of atom mass, and mean electronegativity) were selected as the key factors of modulus by performing a three-step feature selection. With these features, a highly accurate model was built for predicting the modulus of near-β-Ti alloys. To further ensure the accuracy of modulus prediction, machine learning with the elastic constants calculated was leveraged by CALPHAD database. The root mean square error of the well-trained model can be as low as 6.75 GPa. Guided by the prediction of machine learning and CALPHAD, three novel near-β-Ti alloys with elastic modulus below 50 GPa were successfully designed in this study. The best candidate alloy(Ti–26Nb–4Zr–4Sn–1Mo–Ta) exhibits an ultra-low modulus(36.6 GPa) after cold rolling with a thickness reduction of 20%. Our method can greatly save time and resources in the development of novel Ti alloys, and experimental verifications have demonstrated the reliability of this method.展开更多
In this study, microstructural adjustments and mechanical properties of a cold-rolled near β-type alloy Ti-25Nb-3Zr-3Mo-2Sn （wt%） sheet were investigated. Microstructures and phase transformation products strongly ...In this study, microstructural adjustments and mechanical properties of a cold-rolled near β-type alloy Ti-25Nb-3Zr-3Mo-2Sn （wt%） sheet were investigated. Microstructures and phase transformation products strongly depended on aging temperatures. Solution treatments within single β-phase field removed the stress-induced at martensites and produced a few new lath-shaped ones, but metastable β phase still dominated. This is exactly the reason why current alloy exhibits the lowest modulus （54 GPa） and best elongation to fracture （39 %）, but the worst yield strength of only 340 MPa, at solutiontreated state. A fairly large number of ellipsoidal ω phase nanoparticles precipitated throughout parent β phase during aging at 380℃. These ω nanoparticles possess remarkable strengthening effect, but deteriorate ductility seriously. A novel post-aging process was proposed to remove brittle ω phase. By contrast, aging at 450 ℃ resulted in sufficient precipitation of fine needle-like α phase. This brought about the best combination of high yield strength （770 MPa） and moderate elastic modulus （75 GPa） and good elongation （15 %） for biomedical implants.展开更多
The effect ofωiso andαprecipitation on microstructure,microhardness,tensile properties and impact toughness of Ti-25Nb-10Ta-1Zr-0.2Fe(TNTZF)alloy was investigated.The results showed that the solution treated TNTZF a...The effect ofωiso andαprecipitation on microstructure,microhardness,tensile properties and impact toughness of Ti-25Nb-10Ta-1Zr-0.2Fe(TNTZF)alloy was investigated.The results showed that the solution treated TNTZF alloy with a small amount of nano-sizedωath particles inβmatrix possesses tensile strength of 697 MPa,elongation of~34%,Young’s modulus(YM)of 75 GPa,and impact toughness of 58.7 J/cm^(2).After aging at relatively lower temperatures of 400℃,the hardness and modulus of the alloy increased significantly,while the plasticity and toughness dropped sharply due to the precipitation ofωiso phase.ωiso phase displayed an ellipsoidal morphology with high volume fraction and a size of about 50 nm after aging at 400℃,leading to the highest hardness of 364 HV and YM of 108 GPa,along with completely embrittlement since elongation and toughness were almost zero.A brittle impact fracture morphology was observed in the alloy,which is dominated by intergranular fracture,with a mixed fracture characteristics of cleavage surfaces,terraces and tiny dimples.When aged at 550℃,plate-likeαdistributed inβmatrix uniformly and inβgrain boundaries in parallel,resulting in the high strength of 804 MPa,as well as lowest YM of 72 GPa,elongation of 9%and toughness of 35.8 J/cm^(2).The fracture morphology of the alloy aged at 550℃showed a ductile fracture mechanism with a large number of dimples.展开更多
基金financially supported by the National Natural Science Foundation of China(No.52071339)
文摘To improve the yield strength of metastableβ-Ti alloys with transformation-induced plasticity(TRIP)and twinning-induced plasticity effects,a novel strategy combining heterostructure strengthening with the TRIP effect was developed.A metastableβ-Ti alloy with a nominal composition of Ti-4Mo-3Cr-1Fe-1Al was used as the base alloy.By adjusting the annealing temperature after cold rolling,heterostructured samples comprising soft recrystallizedβ-grains and hard un-recrystallizedβ-grains andα-phase were prepared.Compared with the homogeneous coarse-grained sample,the yield strength of the heterostructured sample significantly increased from 610 to905 MPa,while maintaining excellent plasticity(32.7%),overcoming the traditional trade-off between strength and ductility.The observed high yield strength is attributed to significant back-stress strengthening caused by the accumulation of a large number of geometrically necessary dislocations at the interfaces between the soft and hard regions.Meanwhile,the exceptional plasticity is attributed to the activation of stress-induced martensite(SIM)within the metastableβmatrix.The sequential activation of dislocation slips and SIM is achieved through the construction of a heterostructured structure.This work provides a new strategy for designing metastableβ-Ti alloys with high strength and plasticity by coupling heterostructure strengthening and transformation-induced plasticity.
基金financial supports from the National Natural Science Foundation of China(No.51871242)Scientific and technological innovation projects of Hunan Province,China(No.2017GK2292)the National Key R&D Program of China(2018YFB0704100)。
文摘This work gives a comparison on the microstructural characteristics,textural discrepancies,and twinning behaviors of lamellar and equiaxed nearβ-Ti alloys during multi-pass cross rolling with a rolling reduction of 20%,50%and 80%.The results showed that the restoration mechanism of the alloy inβphase is strongly dependent on theαmorphologies,and in comparison,strain path has weaker influences on the grain refinement of theβmatrix.Therefore,the texture intensities of bothαandβphases were weakened owing to the dynamic recrystallization(DRX)of the two phases in the equiaxed microstructure.While,with regard to the lamellar microstructure,dynamic recovery(DRV)of theβphase predominated,forming elongatedβsubgrains.Besides,theαandβmatrix in lamellar microstructures obeyed the Burgers orientation relationship,which was gradually broken down until the final reduction.Lastly,the{1101}twinning exhibits a strong size effect.With the continuous DRX ofαphases,theα-twinning is suppressed owing to progressive grain refinement.The activation ofβ-twinning,namely{332}?113?and{112}?111?,in nearβ-Ti alloys is heavily dependent on the deficientβ-stabilizing elements and the local stress concentration.These findings provide an effective way to obtain ultra-fine grain microstructures of this alloy.
基金supported by the National Natural Science Foundation of China(Nos.51871176,51722104,51922017,51972009)the National Key Research and Development Program of China(Nos.2017YFA0700701,2017YFB0702301)+2 种基金the 111 Project 2.0 of China(No.PB2018008)Natural Science Basic Research Plan in Shaanxi Province of China(No.2018JM5098)the Fundamental Research Funds for the Central Universities(No.xtr022019004)。
文摘Deformation kinking as an uncommon plastic deformation mechanism has been reported in several materials while the relevant microstructure evolution and grain refinement behavior at a large strain remain unclear so far.In this study,the issue was systematically investigated by utilizing cold forging to impose severe plastic deformation(SPD)on Ti-11 V metastableβ-Ti alloys.It is found that the formation of kink bands experiences dislocation gliding,pre-kinking and the ripening of pre-kinks in sequences.The kink bands are subsequently thickened through the coalescence of multiple kink bands in a manner of high accommodation.Ordinary dislocation slip is developed as a dominant deformation mechanism when deformation kinking is exhausted.The resulting grain refinement involves transverse breakdown and longitudinal splitting of dislocation walls and cells,which fragment kink bands into smallβ-blocks.Further refinement of theβ-blocks is still governed by dislocation activities,and finally nanograins with a diameter of~15 nm are produced at a large strain of 1.2.Alternatively,it is revealed that nanocrystallization is highly localized inside kink bands while the outer microstructure maintains original coarse structures.Such localized refinement characterization is ascribed to the intrinsic soft nature of kink bands,shown as low hardness in nanoindentation testing.The intrinsic softening of kink bands is uncovered to originate from the inner degraded dislocation density evidenced by both experimental measurement and theoretical calculation.These findings enrich fundamental understanding of deformation kinking,and shed some light on exploring the deformation accommodation mechanisms for metal materials at large strains.
基金financially supported by the National Natural Science Foundation of China (No.52071339)the Natural Science Foundation of Hunan Province,China (No.2020JJ4739)Guangxi Key Laboratory of Information Materials(Guilin University of Electronic Technology),China (No.201009-K)。
文摘Traditional theoretical and empirical calculation methods can guide the design of β-and metastable β-alloys for bio-titanium. However, it is still difficult to obtain novel near-β-Ti alloys with low modulus. This study developed a method that combines machine learning with calculation of phase diagrams(CALPHAD) to facilitate the design of near-β-Ti alloys. An elastic modulus database of Ti–Nb–Zr–Mo–Ta–Sn system was constructed first, and then three features(the electron to atom ratio, mean absolute deviation of atom mass, and mean electronegativity) were selected as the key factors of modulus by performing a three-step feature selection. With these features, a highly accurate model was built for predicting the modulus of near-β-Ti alloys. To further ensure the accuracy of modulus prediction, machine learning with the elastic constants calculated was leveraged by CALPHAD database. The root mean square error of the well-trained model can be as low as 6.75 GPa. Guided by the prediction of machine learning and CALPHAD, three novel near-β-Ti alloys with elastic modulus below 50 GPa were successfully designed in this study. The best candidate alloy(Ti–26Nb–4Zr–4Sn–1Mo–Ta) exhibits an ultra-low modulus(36.6 GPa) after cold rolling with a thickness reduction of 20%. Our method can greatly save time and resources in the development of novel Ti alloys, and experimental verifications have demonstrated the reliability of this method.
基金financially supported by Industrial Science Technology Project of Shaanxi Province (No. 2015GY160)Western Metal Materials Innovation Fund (No. XBCL03-18)International Cooperation and Exchanges of State Commission of Science Technology of China (No. 2014DFA30880)
文摘In this study, microstructural adjustments and mechanical properties of a cold-rolled near β-type alloy Ti-25Nb-3Zr-3Mo-2Sn （wt%） sheet were investigated. Microstructures and phase transformation products strongly depended on aging temperatures. Solution treatments within single β-phase field removed the stress-induced at martensites and produced a few new lath-shaped ones, but metastable β phase still dominated. This is exactly the reason why current alloy exhibits the lowest modulus （54 GPa） and best elongation to fracture （39 %）, but the worst yield strength of only 340 MPa, at solutiontreated state. A fairly large number of ellipsoidal ω phase nanoparticles precipitated throughout parent β phase during aging at 380℃. These ω nanoparticles possess remarkable strengthening effect, but deteriorate ductility seriously. A novel post-aging process was proposed to remove brittle ω phase. By contrast, aging at 450 ℃ resulted in sufficient precipitation of fine needle-like α phase. This brought about the best combination of high yield strength （770 MPa） and moderate elastic modulus （75 GPa） and good elongation （15 %） for biomedical implants.
基金supported by the Natural Science Foundation of Hunan Province(2023JJ50055,2023JJ30081)the Science Research Foundation of Hunan Provincial Education Department(21A0546)+1 种基金the Youth Project of the National Natural Science Foundation of China(62003056)the Open Fund of Hunan Engineering Research Center of Research and Development of Degradable Materials and Molding Technology(2023KFKT05).
文摘The effect ofωiso andαprecipitation on microstructure,microhardness,tensile properties and impact toughness of Ti-25Nb-10Ta-1Zr-0.2Fe(TNTZF)alloy was investigated.The results showed that the solution treated TNTZF alloy with a small amount of nano-sizedωath particles inβmatrix possesses tensile strength of 697 MPa,elongation of~34%,Young’s modulus(YM)of 75 GPa,and impact toughness of 58.7 J/cm^(2).After aging at relatively lower temperatures of 400℃,the hardness and modulus of the alloy increased significantly,while the plasticity and toughness dropped sharply due to the precipitation ofωiso phase.ωiso phase displayed an ellipsoidal morphology with high volume fraction and a size of about 50 nm after aging at 400℃,leading to the highest hardness of 364 HV and YM of 108 GPa,along with completely embrittlement since elongation and toughness were almost zero.A brittle impact fracture morphology was observed in the alloy,which is dominated by intergranular fracture,with a mixed fracture characteristics of cleavage surfaces,terraces and tiny dimples.When aged at 550℃,plate-likeαdistributed inβmatrix uniformly and inβgrain boundaries in parallel,resulting in the high strength of 804 MPa,as well as lowest YM of 72 GPa,elongation of 9%and toughness of 35.8 J/cm^(2).The fracture morphology of the alloy aged at 550℃showed a ductile fracture mechanism with a large number of dimples.
