The microstructure evolution and phase composition of an α+β titanium alloy, Ti-3Al-5Mo-4.5V(wt.%),have been investigated. Electron probe micro analysis(EPMA) quantitative results manifest that the stability of β p...The microstructure evolution and phase composition of an α+β titanium alloy, Ti-3Al-5Mo-4.5V(wt.%),have been investigated. Electron probe micro analysis(EPMA) quantitative results manifest that the stability of β phase decreases with increasing quenching temperature, which is influenced by the significant variation of β-stabilizing elements concentration. Detailed microstructure analysis shows that the β→ωphase transformation does occur when quenching at 750℃ and 800 ℃. The ω-reflections change from incommensurate ω-spots(750 ℃) to ideal ω-spots(800 ℃) as the β stability of the alloy decreases. Further the decrease of β phase stability encourages the formation of athermal α " martensite, which has the following orientation relationships: [111]β//[110]α",[100]p//[100]α " and [-110]p//[00-1]α" with respect to the β matrix.展开更多
Atomized, pre-alloyed Ti-24Nb-4Zr-7.9Sn （wt%） powder was used to fabricate solid, prototype components by electron beam melting （EBM）. Vickers microindentation hardness values were observed to average 2 GPa for th...Atomized, pre-alloyed Ti-24Nb-4Zr-7.9Sn （wt%） powder was used to fabricate solid, prototype components by electron beam melting （EBM）. Vickers microindentation hardness values were observed to average 2 GPa for the precursor powder and 2.5 GPa for the solid, EBM-fabricated products. The powder and solid product microstructures were examined by optical and electron microscopy. X-ray diffraction analyses showed that they had bcc β-phase microstructure. However, it was found by transmission electron microscopy that the EBM-fabricated product had plate morphology with space -100-200 nm. Although the corresponding selected area diffraction patterns can be indexed by β-phase plus α＂-martensite with orthorhombic crystal structure, the dark-field analyses failed to observe the α＂-martensite. Such phenomenon was also found in deformed gum metals and explained by stress-induced diffusion scattering due to phonon softening.展开更多
Evolution of deformation mechanisms and mechanical properties of Ti-3Al-5Mo-4.5V alloy with different β phase stability have been systematically investigated. β phase stability alteration is achieved through quenchi...Evolution of deformation mechanisms and mechanical properties of Ti-3Al-5Mo-4.5V alloy with different β phase stability have been systematically investigated. β phase stability alteration is achieved through quenching temperature variation from dual α+β field(700℃) to single β field(880℃). Tensile tests at ambient temperature show that apparent yield strength of the alloy experiences an abrupt decrease followed by a significant increase from 700℃ to 880℃. Work hardening behavior is characterized by transition from the initial two-regime feature to the three-stage outlook. Concurrently, the maximum working hardening rate drops from 14000 MPa to 3000 MPa, which is concurrent with the shrinking volume fraction of primary a phase. Detailed discussion about the relationship between deformation mechanisms and β phase stability has been outlined.展开更多
A heterogeneous microstructure in terms of local orientation distribution is often found in near-α titanium alloys. The presence of large regions with similar crystallographic orientation, called ‘macrozones',co...A heterogeneous microstructure in terms of local orientation distribution is often found in near-α titanium alloys. The presence of large regions with similar crystallographic orientation, called ‘macrozones',could drastically decrease the fatigue performance of titanium alloys. The present work reports on the crystallographic orientation of a near-α titanium alloy, Ti60, billet after annealing in an α+β phase field.The texture was found to be weak, and no obvious macrozone was found in our measured zone where the variant selection is suppressed. Meanwhile, in-depth electron backscattered diffraction(EBSD) analysis was applied to evaluate the final microstructure, and the mechanisms by which they formed were analyzed.展开更多
The deformation behavior of as-built and hot isostatically pressed(HIP)Ti-6Al-4V alloys fabricated using electron beam rapid manufacturing(EBRM)were investigated in this work.The deformation characteristics were chara...The deformation behavior of as-built and hot isostatically pressed(HIP)Ti-6Al-4V alloys fabricated using electron beam rapid manufacturing(EBRM)were investigated in this work.The deformation characteristics were characterized using a laser scanning confocal microscope and electron back-scattered diffraction(EBSD).In the as-built sample,prismatic slip was the main mode of deformation,as well as a small amount of basal slip and cross-slip.Some planar slip lines with large length scales were observed across severalαlamellae.After hot isostatical pressing,prismatic and basal slip were the main mode of deformation,accompanied by abundant cross-slip and multiple slip,and most of the slip lines were blocked within an a lamellae.These differences in deformation behavior were associated with the coarsening of a laths and the more retained p phase after HIP compared to the as-built alloy.More cross-slip and multiple slip can lead to superior elongation-to-failure and a greater strain hardening effect in the HIP alloy compared to the as-built sample.展开更多
The characteristic of the surface morphology of primary α phase was studied in a deformed near-α tita- nium alloy. Dendritic α phase emerged on the surfaces of primary α phase when the alloy was air-cooled in α ...The characteristic of the surface morphology of primary α phase was studied in a deformed near-α tita- nium alloy. Dendritic α phase emerged on the surfaces of primary α phase when the alloy was air-cooled in α ＋β phase field after deformation. The dendritic α grain has the same orientation with its original primary α grain. The formation of the dendritic α phase could be explained by interface instability in epi- taxial growth process of the primary α phase. The dislocations induced by deformation could facilitate the formation of dendritic α phase leading to the dendritic α phase and more obvious with the increase of strain. The growth of dendritic α phase was finally limited by the nucleation of second α phase with cooling.展开更多
Temperature-independent elastic modulus is termed as Elinvar effect,which is available by tuning the continuous spin transition of ferromagnetic alloys via composition optimization and the first-order martensitic tran...Temperature-independent elastic modulus is termed as Elinvar effect,which is available by tuning the continuous spin transition of ferromagnetic alloys via composition optimization and the first-order martensitic transformation of shape memory alloys via plastic deformation.However,these reversible mechanisms are restricted generally in a narrow temperature range of less than 300 K.Here reports,by tuning a spinodal decomposition in a Ti-Nb-based titanium alloy via aging treatment,both the Elinvar effect in a wide temperature range of about 500 K and a high strength-to-modulus ratio of about 1.5%can be obtained by a continuous and reversible crystal ordering mechanism.The results demonstrate that the alloy aged at 723 K for 4 h has a nanoscale plate-like modulatedβ+α"two-phase microstructure and its elastic modulus keeps almost constant from 100 to 600 K.Synchrotron and in-situ X-ray diffraction measurements reveal that the crystal ordering parameter of theα"phase increases linearly with temper-ature from 0.88 at 133 K to 0.97 at 523 K but its volume fraction keeps a constant of about 33.8%.This suggests that the continuous ordering of theα"phase toward the high modulusαphase induces a posi-tive modulus-temperature relation to balance the negative relation of the elastically stableβphase.The aged alloy exhibits a high yield strength of 1200 MPa,good ductility of 16%and a high elastic admissible strain of 1.5%.Our results provide a novel strategy to extend the Elinvar temperature range and enhance the strength by tuning the crystal ordering of decomposition alloys.展开更多
Molecular dynamics simulation of uniaxial tension along [001] has been performed to study the influence of various surface defects on the initiation of plastic deformation and fracture of γ-TiAl single crystals.The r...Molecular dynamics simulation of uniaxial tension along [001] has been performed to study the influence of various surface defects on the initiation of plastic deformation and fracture of γ-TiAl single crystals.The results indicate that brittle fracture occurs in perfect bulk; surfaces and edges will be detrimental to the strength of materials and provide dislocation nucleation site. The defects on surfaces and edges cause further weakening with various effects depending on defect type, size, position and orientation,while the edge dimples are the most influential. For γ-TiAl rods with surface dimples, dislocations nucleate from an edge of the rod when dimples are small, dimple dislocation nucleation occurs only when the dimples are larger than a strain rate dependent critical size. The dislocations nucleated upon [001]tension are super dislocations with Burger vectors 〈011] or 1/2 〈 112] containing four 1/6 〈 112 〉 partials. The effects of surface scratches are orientation and shape sensitive. Scratches parallel to the loading direction have little influence, while sharp ones perpendicular to the loading direction may cause crack and thus should be avoided. This simulation also shows that, any type of surface defect would lower strength,and cause crack in some cases. But some may facilitate dislocation nucleation and improve ductility of TiAl if well controlled.展开更多
Transcatheter aortic heart valves(TAHVs) have been widely used for aortic valve replacements, with less trauma and lower clinical risk compared with traditional surgical heart valve replacements. In the present study,...Transcatheter aortic heart valves(TAHVs) have been widely used for aortic valve replacements, with less trauma and lower clinical risk compared with traditional surgical heart valve replacements. In the present study, composites of poly(ethylene glycol) diacrylate(PEGDA) hydrogels and anisotropic highshrinkage polyethylene terephthalate/polyamide6(PET-PA6) fabric(PEGDA/PET-PA6) were fabricated as artificial heart valve leaflets. Dynamic mechanical analyses(DMA) indicated that PEGDA/PET-PA6 composites possessed anisotropic mechanical properties(i.e., storage moduli ~23.30 ± 1.36 MPa parallel to the aligned fabric fibers and ~9.68 ± 0.90 MPa perpendicular to the aligned fibers at 1 Hz) that were comparable to aortic valve leaflets. The PEGDA/PET-PA6 composites with smooth surfaces were highly hydrophilic(contact angle ~41.6°± 3.8°) and had low-fouling properties without platelet adhesion,suggesting a low risk of thrombogenicity when they interacted with blood. Furthermore, transcatheter aortic heart valves were fabricated using nitinol self-expanding frames and PEGDA/PET-PA6 composites as artificial leaflets, which presented excellent hemodynamic performance with a large orifice area(1.75cm2) and low regurgitation(3.41%), thus meeting the requirements of ISO 5840-3 standard. Therefore,PEGDA/PET-PA6 composites had suitable mechanical properties, good biocompatibility, and low-fouling properties, indicating that they might be used for TAHVs in the future.展开更多
The effect of base material（BM） on microstructure and crystallographic orientation evolution of a Ti–6Al–4V electron-beam welded joint was investigated. Meanwhile, the crystallographic orientation of prior b grain...The effect of base material（BM） on microstructure and crystallographic orientation evolution of a Ti–6Al–4V electron-beam welded joint was investigated. Meanwhile, the crystallographic orientation of prior b grains was studied by advanced electron backscattered diffraction data processing. The inhomogeneity of microstructure within welded joint was formed due to the different microstructures of BM. By comparing microstructure details of the welded joint, including microstructure morphology and crystallographic orientation with those of the base material, it can be found that both the microstructure morphology and crystallographic orientation of the EBW joint would be controlled by BM.展开更多
As to multifunctional titanium alloys with high strength and low elastic modulus, thermal training is crucial to tune their thermal expansion from positive to negative, resulting in a novel linear expansion which is s...As to multifunctional titanium alloys with high strength and low elastic modulus, thermal training is crucial to tune their thermal expansion from positive to negative, resulting in a novel linear expansion which is stable in a wide temperature range. Aided by the high-order Hooke's law of elastic solids,a reversible atomic rearrangement mechanism was proposed to explain the novel findings which are unexpected from typical shape memory alloys. To confirm this continuous mechanism, a Ti-Nb based alloy, which possesses a nanoscale spongy microstructure consisting of the interpenetrated Nb-rich and Nb-lean domains produced by spinodal decomposition, was used to trace the crystal structure change by in-situ high energy synchrotron X-ray diffraction analyses. By increasing exposure time, the overlapped diffraction peaks can be separated accurately. The calculated results demonstrate that, in the nanoscale Nb-lean domains, the crystal structure parameters vary linearly with changing temperature along the atomic pathway of the bcc-hcp transition. This linear relationship in a wide temperature range is unusual for first-order martensitic shape memory alloys but is common for Invar alloys with high-order spin transitions. Furthermore, the alloy exhibits smooth DSC curves free of transformation-induced heat peaks observed in shape memory alloys, which is consistent with the proposed mechanism that the reversible transition is of high-order.展开更多
As one of the fundamental outcomes of dislocation self-interaction,dislocation dipoles have an important influence on the plastic deformation of materials,especially on fatigue and creep.In this work,superdislocation ...As one of the fundamental outcomes of dislocation self-interaction,dislocation dipoles have an important influence on the plastic deformation of materials,especially on fatigue and creep.In this work,superdislocation dipoles inγ-TiAl andα_(2)-Ti_(3)Al were systematically investigated by atomistic simulations,with a variety of dipole heights,orientations and annealing tempe ratures.The results indicate that non-screw super-dipoles transform into locally stable dipolar or reconstructed cores at low temperature,while into isolated or interconnected point defect clusters and stacking fault tetrahedra at high temperature via short-range diffu sion.Non-screw super-dipoles inγ-TiAl andα_(2)-Ti_(3)Al exhibit similar features as fcc and hcp metals,respectively.Generally,over long-term annealing where diffusion is significant,60°superdipoles inγ-TiAl are stable,whereas the stability of super-dipoles inα2-Ti3 Al increases with dipole height and orientation angle.The influence on mechanical properties can be well evaluated by integrating these results into mesoscale or constitutive models.展开更多
The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At ...The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At high strain rates,amorphization occurred near the edge of the contact region where severe shear strain induced a large number of stacking faults(SFs)and dislocations.In contrast,the central part of the contact region underwent less deformation with significantly fewer dislocations.Moreover,instead of amorphization by consuming SFs and dislocations,there was a gradual increase in the density of dislocations and SFs during the process of amorphization.These local amorphous regions eventually grew into shear bands.展开更多
Twin structures have been intensively studied for improving the strength and plasticity of metallic materials[1-8].To achieve a high strength of alloys without loss of ductility,researchers have controlled the microst...Twin structures have been intensively studied for improving the strength and plasticity of metallic materials[1-8].To achieve a high strength of alloys without loss of ductility,researchers have controlled the microstructures containing a high density of twin boundaries(TBs),which can hinder and generate dislocations[9-13].展开更多
The effect of pre-strain on phase transformation of TiNi shape memory alloy film was studied by differential scanning calorimeter measurement (DSC). Compared with un-defarmed TiNi film, the reverse transformation of p...The effect of pre-strain on phase transformation of TiNi shape memory alloy film was studied by differential scanning calorimeter measurement (DSC). Compared with un-defarmed TiNi film, the reverse transformation of pre-strained specimens was elevated to a higher temperature on the first heating, but martensite and reverse transformation on subsequent thermal cycles occurred at a lower temperature. The evolution of transformation behavior in pre-strained TiNi film was related to the change of elastic strain energy, irreversible energy and internal stress field.展开更多
Digital elevation model(DEM)matching techniques have been extended to DEM deformation detection by substituting a robust estimator for the least squares estimator,in which terrain changes are treated as gross errors.H...Digital elevation model(DEM)matching techniques have been extended to DEM deformation detection by substituting a robust estimator for the least squares estimator,in which terrain changes are treated as gross errors.However,all existing methods only emphasise their deformation detecting ability,and neglect another important aspect:only when the gross error can be detected and located,can this system be useful.This paper employs the gross error judgement matrix as a tool to make an in-depth analysis of this problem.The theoretical analyses and experimental results show that observations in the DEM matching algorithm in real applications have the ability to detect and locate gross errors.Therefore,treating the terrain changes as gross errors is theoretically feasible,allowing real DEM deformations to be detected by employing a surface matching technique.展开更多
基金supported from the National Natural Science Foundation of China(No.51401221,51622401 and 51628402)support from the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB06050100)
文摘The microstructure evolution and phase composition of an α+β titanium alloy, Ti-3Al-5Mo-4.5V(wt.%),have been investigated. Electron probe micro analysis(EPMA) quantitative results manifest that the stability of β phase decreases with increasing quenching temperature, which is influenced by the significant variation of β-stabilizing elements concentration. Detailed microstructure analysis shows that the β→ωphase transformation does occur when quenching at 750℃ and 800 ℃. The ω-reflections change from incommensurate ω-spots(750 ℃) to ideal ω-spots(800 ℃) as the β stability of the alloy decreases. Further the decrease of β phase stability encourages the formation of athermal α " martensite, which has the following orientation relationships: [111]β//[110]α",[100]p//[100]α " and [-110]p//[00-1]α" with respect to the β matrix.
基金supportcd in part by Murchison Endowed Chairs at UTEPan MOST Grant 2012CB933901 at IMR
文摘Atomized, pre-alloyed Ti-24Nb-4Zr-7.9Sn （wt%） powder was used to fabricate solid, prototype components by electron beam melting （EBM）. Vickers microindentation hardness values were observed to average 2 GPa for the precursor powder and 2.5 GPa for the solid, EBM-fabricated products. The powder and solid product microstructures were examined by optical and electron microscopy. X-ray diffraction analyses showed that they had bcc β-phase microstructure. However, it was found by transmission electron microscopy that the EBM-fabricated product had plate morphology with space -100-200 nm. Although the corresponding selected area diffraction patterns can be indexed by β-phase plus α＂-martensite with orthorhombic crystal structure, the dark-field analyses failed to observe the α＂-martensite. Such phenomenon was also found in deformed gum metals and explained by stress-induced diffusion scattering due to phonon softening.
基金supported by the National Natural Science Foundation of China(No.51401221,51622401 and 51628402)the support from the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB06050100)
文摘Evolution of deformation mechanisms and mechanical properties of Ti-3Al-5Mo-4.5V alloy with different β phase stability have been systematically investigated. β phase stability alteration is achieved through quenching temperature variation from dual α+β field(700℃) to single β field(880℃). Tensile tests at ambient temperature show that apparent yield strength of the alloy experiences an abrupt decrease followed by a significant increase from 700℃ to 880℃. Work hardening behavior is characterized by transition from the initial two-regime feature to the three-stage outlook. Concurrently, the maximum working hardening rate drops from 14000 MPa to 3000 MPa, which is concurrent with the shrinking volume fraction of primary a phase. Detailed discussion about the relationship between deformation mechanisms and β phase stability has been outlined.
文摘A heterogeneous microstructure in terms of local orientation distribution is often found in near-α titanium alloys. The presence of large regions with similar crystallographic orientation, called ‘macrozones',could drastically decrease the fatigue performance of titanium alloys. The present work reports on the crystallographic orientation of a near-α titanium alloy, Ti60, billet after annealing in an α+β phase field.The texture was found to be weak, and no obvious macrozone was found in our measured zone where the variant selection is suppressed. Meanwhile, in-depth electron backscattered diffraction(EBSD) analysis was applied to evaluate the final microstructure, and the mechanisms by which they formed were analyzed.
基金financially supported by the National Key Research and Development Program of China (No.2017YFB1103100)the Avic Science Foundation of China (No.20175492002)the National Natural Science Foundation of China (No.51801213)
文摘The deformation behavior of as-built and hot isostatically pressed(HIP)Ti-6Al-4V alloys fabricated using electron beam rapid manufacturing(EBRM)were investigated in this work.The deformation characteristics were characterized using a laser scanning confocal microscope and electron back-scattered diffraction(EBSD).In the as-built sample,prismatic slip was the main mode of deformation,as well as a small amount of basal slip and cross-slip.Some planar slip lines with large length scales were observed across severalαlamellae.After hot isostatical pressing,prismatic and basal slip were the main mode of deformation,accompanied by abundant cross-slip and multiple slip,and most of the slip lines were blocked within an a lamellae.These differences in deformation behavior were associated with the coarsening of a laths and the more retained p phase after HIP compared to the as-built alloy.More cross-slip and multiple slip can lead to superior elongation-to-failure and a greater strain hardening effect in the HIP alloy compared to the as-built sample.
文摘The characteristic of the surface morphology of primary α phase was studied in a deformed near-α tita- nium alloy. Dendritic α phase emerged on the surfaces of primary α phase when the alloy was air-cooled in α ＋β phase field after deformation. The dendritic α grain has the same orientation with its original primary α grain. The formation of the dendritic α phase could be explained by interface instability in epi- taxial growth process of the primary α phase. The dislocations induced by deformation could facilitate the formation of dendritic α phase leading to the dendritic α phase and more obvious with the increase of strain. The growth of dendritic α phase was finally limited by the nucleation of second α phase with cooling.
基金supported by the National Natural Science Foundation of China (Nos.51771209 and 51901042)the Foun-dation 91960202 and CAS (No.QYZDJ-SSW-JSC031).
文摘Temperature-independent elastic modulus is termed as Elinvar effect,which is available by tuning the continuous spin transition of ferromagnetic alloys via composition optimization and the first-order martensitic transformation of shape memory alloys via plastic deformation.However,these reversible mechanisms are restricted generally in a narrow temperature range of less than 300 K.Here reports,by tuning a spinodal decomposition in a Ti-Nb-based titanium alloy via aging treatment,both the Elinvar effect in a wide temperature range of about 500 K and a high strength-to-modulus ratio of about 1.5%can be obtained by a continuous and reversible crystal ordering mechanism.The results demonstrate that the alloy aged at 723 K for 4 h has a nanoscale plate-like modulatedβ+α"two-phase microstructure and its elastic modulus keeps almost constant from 100 to 600 K.Synchrotron and in-situ X-ray diffraction measurements reveal that the crystal ordering parameter of theα"phase increases linearly with temper-ature from 0.88 at 133 K to 0.97 at 523 K but its volume fraction keeps a constant of about 33.8%.This suggests that the continuous ordering of theα"phase toward the high modulusαphase induces a posi-tive modulus-temperature relation to balance the negative relation of the elastically stableβphase.The aged alloy exhibits a high yield strength of 1200 MPa,good ductility of 16%and a high elastic admissible strain of 1.5%.Our results provide a novel strategy to extend the Elinvar temperature range and enhance the strength by tuning the crystal ordering of decomposition alloys.
基金supported by the National Basic Research Program of China (No.2011CB606404)the National Natural Science Foundation of China (No.51171195)the GM Research Project
文摘Molecular dynamics simulation of uniaxial tension along [001] has been performed to study the influence of various surface defects on the initiation of plastic deformation and fracture of γ-TiAl single crystals.The results indicate that brittle fracture occurs in perfect bulk; surfaces and edges will be detrimental to the strength of materials and provide dislocation nucleation site. The defects on surfaces and edges cause further weakening with various effects depending on defect type, size, position and orientation,while the edge dimples are the most influential. For γ-TiAl rods with surface dimples, dislocations nucleate from an edge of the rod when dimples are small, dimple dislocation nucleation occurs only when the dimples are larger than a strain rate dependent critical size. The dislocations nucleated upon [001]tension are super dislocations with Burger vectors 〈011] or 1/2 〈 112] containing four 1/6 〈 112 〉 partials. The effects of surface scratches are orientation and shape sensitive. Scratches parallel to the loading direction have little influence, while sharp ones perpendicular to the loading direction may cause crack and thus should be avoided. This simulation also shows that, any type of surface defect would lower strength,and cause crack in some cases. But some may facilitate dislocation nucleation and improve ductility of TiAl if well controlled.
基金supportedby the National Natural Science Foundation of China(Nos.31670981 and 31300788)the Hundred-Talent Program from Chinese Academy of Sciences
文摘Transcatheter aortic heart valves(TAHVs) have been widely used for aortic valve replacements, with less trauma and lower clinical risk compared with traditional surgical heart valve replacements. In the present study, composites of poly(ethylene glycol) diacrylate(PEGDA) hydrogels and anisotropic highshrinkage polyethylene terephthalate/polyamide6(PET-PA6) fabric(PEGDA/PET-PA6) were fabricated as artificial heart valve leaflets. Dynamic mechanical analyses(DMA) indicated that PEGDA/PET-PA6 composites possessed anisotropic mechanical properties(i.e., storage moduli ~23.30 ± 1.36 MPa parallel to the aligned fabric fibers and ~9.68 ± 0.90 MPa perpendicular to the aligned fibers at 1 Hz) that were comparable to aortic valve leaflets. The PEGDA/PET-PA6 composites with smooth surfaces were highly hydrophilic(contact angle ~41.6°± 3.8°) and had low-fouling properties without platelet adhesion,suggesting a low risk of thrombogenicity when they interacted with blood. Furthermore, transcatheter aortic heart valves were fabricated using nitinol self-expanding frames and PEGDA/PET-PA6 composites as artificial leaflets, which presented excellent hemodynamic performance with a large orifice area(1.75cm2) and low regurgitation(3.41%), thus meeting the requirements of ISO 5840-3 standard. Therefore,PEGDA/PET-PA6 composites had suitable mechanical properties, good biocompatibility, and low-fouling properties, indicating that they might be used for TAHVs in the future.
文摘The effect of base material（BM） on microstructure and crystallographic orientation evolution of a Ti–6Al–4V electron-beam welded joint was investigated. Meanwhile, the crystallographic orientation of prior b grains was studied by advanced electron backscattered diffraction data processing. The inhomogeneity of microstructure within welded joint was formed due to the different microstructures of BM. By comparing microstructure details of the welded joint, including microstructure morphology and crystallographic orientation with those of the base material, it can be found that both the microstructure morphology and crystallographic orientation of the EBW joint would be controlled by BM.
基金supported in part by NSF of China(51771209,51631007,51571190)MOST of China(2016YFC1102600,2017YFC1104901)CAS(QYZDJ-SSW-JSC031)。
文摘As to multifunctional titanium alloys with high strength and low elastic modulus, thermal training is crucial to tune their thermal expansion from positive to negative, resulting in a novel linear expansion which is stable in a wide temperature range. Aided by the high-order Hooke's law of elastic solids,a reversible atomic rearrangement mechanism was proposed to explain the novel findings which are unexpected from typical shape memory alloys. To confirm this continuous mechanism, a Ti-Nb based alloy, which possesses a nanoscale spongy microstructure consisting of the interpenetrated Nb-rich and Nb-lean domains produced by spinodal decomposition, was used to trace the crystal structure change by in-situ high energy synchrotron X-ray diffraction analyses. By increasing exposure time, the overlapped diffraction peaks can be separated accurately. The calculated results demonstrate that, in the nanoscale Nb-lean domains, the crystal structure parameters vary linearly with changing temperature along the atomic pathway of the bcc-hcp transition. This linear relationship in a wide temperature range is unusual for first-order martensitic shape memory alloys but is common for Invar alloys with high-order spin transitions. Furthermore, the alloy exhibits smooth DSC curves free of transformation-induced heat peaks observed in shape memory alloys, which is consistent with the proposed mechanism that the reversible transition is of high-order.
基金the National Key Research and Development Program of China(No.2016YFB0701304 and 2017YFB0306201)the Natural Science Foundation of China(Nos.51671195 and 91960202)+4 种基金the Frontier and Key Projects of the Chinese Academy of Sciences(Nos.QYZDJ-SSW-JSC031-01 and XXH13506-304)the Natural Science Foundation of Liaoning(No.20180510032)the Aeronautical Science Foundation of China(No.20160292002)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDC01000000)The Project is sponsored by the“Liaoning BaiQianWan”Talents Program。
文摘As one of the fundamental outcomes of dislocation self-interaction,dislocation dipoles have an important influence on the plastic deformation of materials,especially on fatigue and creep.In this work,superdislocation dipoles inγ-TiAl andα_(2)-Ti_(3)Al were systematically investigated by atomistic simulations,with a variety of dipole heights,orientations and annealing tempe ratures.The results indicate that non-screw super-dipoles transform into locally stable dipolar or reconstructed cores at low temperature,while into isolated or interconnected point defect clusters and stacking fault tetrahedra at high temperature via short-range diffu sion.Non-screw super-dipoles inγ-TiAl andα_(2)-Ti_(3)Al exhibit similar features as fcc and hcp metals,respectively.Generally,over long-term annealing where diffusion is significant,60°superdipoles inγ-TiAl are stable,whereas the stability of super-dipoles inα2-Ti3 Al increases with dipole height and orientation angle.The influence on mechanical properties can be well evaluated by integrating these results into mesoscale or constitutive models.
基金the National Natural Science Foundation of China(U2241245,91960202 and 52271012)the National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact(6142902220301)+2 种基金the Aeronautical Science Foundation of China(2022Z053092001)the Shanghai Engineering Research Center of High-Performance Medical Device Materials(20DZ2255500)the Opening Project of National Key Laboratory of Shock Wave and Detonation Physics(2022JCJQLB05702).
文摘The mechanical response of a single crystal titanium sample against(0001)α surface impact was investigated using molecular dynamics simulation.Remarkably,non-uniform plastic deformation was observed in the sample.At high strain rates,amorphization occurred near the edge of the contact region where severe shear strain induced a large number of stacking faults(SFs)and dislocations.In contrast,the central part of the contact region underwent less deformation with significantly fewer dislocations.Moreover,instead of amorphization by consuming SFs and dislocations,there was a gradual increase in the density of dislocations and SFs during the process of amorphization.These local amorphous regions eventually grew into shear bands.
基金support by the National Key Research Program of China(No.2021YFB3702604)and the National Science and Technology Ma-jor Project(No.J2019-VI-0005-0119).Hao Wang acknowledges the financial support of the National Natural Science Foundation of China(Nos.U2241245 and 91960202)+2 种基金the Aeronautical Sci-ence Foundation of China(No.2022Z053092001)the Opening Project of National Key Laboratory of Shock Wave and Detonation Physics(No.2022JCJQLB05702)the Shanghai Engineering Re-search Center of High-Performance Medical Device Materials(No.20DZ2255500).
文摘Twin structures have been intensively studied for improving the strength and plasticity of metallic materials[1-8].To achieve a high strength of alloys without loss of ductility,researchers have controlled the microstructures containing a high density of twin boundaries(TBs),which can hinder and generate dislocations[9-13].
文摘The effect of pre-strain on phase transformation of TiNi shape memory alloy film was studied by differential scanning calorimeter measurement (DSC). Compared with un-defarmed TiNi film, the reverse transformation of pre-strained specimens was elevated to a higher temperature on the first heating, but martensite and reverse transformation on subsequent thermal cycles occurred at a lower temperature. The evolution of transformation behavior in pre-strained TiNi film was related to the change of elastic strain energy, irreversible energy and internal stress field.
基金This research is supported by the National High Technology Plan(863)of the People’s Republic of China,Project No.2009AA12Z207.
文摘Digital elevation model(DEM)matching techniques have been extended to DEM deformation detection by substituting a robust estimator for the least squares estimator,in which terrain changes are treated as gross errors.However,all existing methods only emphasise their deformation detecting ability,and neglect another important aspect:only when the gross error can be detected and located,can this system be useful.This paper employs the gross error judgement matrix as a tool to make an in-depth analysis of this problem.The theoretical analyses and experimental results show that observations in the DEM matching algorithm in real applications have the ability to detect and locate gross errors.Therefore,treating the terrain changes as gross errors is theoretically feasible,allowing real DEM deformations to be detected by employing a surface matching technique.
