The effect of age hardening on the microstructure,martensitic transformation behavior,and shape memory properties of the(Ni_(50)Ti_(30)Hf_(20))_(95)V_(5)alloy was investigated by scanning electron microscopy,transmiss...The effect of age hardening on the microstructure,martensitic transformation behavior,and shape memory properties of the(Ni_(50)Ti_(30)Hf_(20))_(95)V_(5)alloy was investigated by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,differential scanning calorimetry,microhardness,and bending tests.The results demonstrate a significant influence of V addition on the microstructure of the alloy.V addition leads to the formation of a(Ni,V)_(2)(Ti,Hf)-type Laves phase,which coexists with B19'martensite at room temperature.Aging at 550℃results in precipitation hardening due to the formation of nano-scale orthorhombic H-phase,with the peak hardness observed after 3 h of aging.The alloy at peak hardness state exhibits higher transformation strain and lower unrecovered strain compared to the solution-treated sample.The aged sample achieves a maximum transformation strain of 1.56%under 500 MPa.展开更多
The evolution of Ti3Ni4 precipitates in Ti49.2Ni50.8 alloy during equal channel angular pressing(ECAP) and intermediate annealing was investigated by transmission electron microscopy. The solution-treated Ti49.2Ni50.8...The evolution of Ti3Ni4 precipitates in Ti49.2Ni50.8 alloy during equal channel angular pressing(ECAP) and intermediate annealing was investigated by transmission electron microscopy. The solution-treated Ti49.2Ni50.8 alloy was aged at 450 ℃ for 10 to 60 min to obtain Ti3Ni4 precipitates ranging from 37 to 75 nm. After ECAP at 450 ℃ for one pass, Ti3Ni4 precipitates introduced by aging for 10 and 30 min totally dissolve into the matrix;however, those produced by aging for 60 min become smaller. The critical size of Ti3Ni4 precipitates to totally dissolve into matrix is determined to be in the range of 37-68 nm. The dislocation density of ECAP-processed samples depends on the initial size of Ti3Ni4 precipitates after aging. With increasing the duration of initial aging from 10 to 60 min, the dislocation density firstly increases and then decreases.展开更多
Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys.This paper discusses the precipitation,coarsening and age hardening of H...Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys.This paper discusses the precipitation,coarsening and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy during isothermal aging at temperatures between 450℃and 650℃for time to 75 h.The H-phase mean size and volume fraction were determined using transmission electron microscopy.Precipitation kinetics was analyzed using the Johnson-Mehl-Avrami-Kolmogorov equation and an Arrhenius type law.From these analyses,a Time-Temperature-Transformation diagram was constructed.The evolution of H-phase size suggests classical matrix diffusion limited Lifshitz-Slyozov-Wagner coarsening for all considered temperatures.The coarsening rate constants of H-phase precipitation have been determined using a modified coarsening rate equation for nondilute solutions.Critical size of H-phase precipitates for breaking down the precipitate/matrix interface coherency was estimated through a combination of age hardening and precipitate size evolution data.Moreover,time-temperature-hardness diagram was constructed from the precipitation and coarsening kinetics and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy.展开更多
It is important to understand the correlation between grain morphology and intervariant boundaries of theαphase after heat treatment belowβtransus of the electron beam melted(EBMed)Ti-6 Al-4 V alloy.Scanning electro...It is important to understand the correlation between grain morphology and intervariant boundaries of theαphase after heat treatment belowβtransus of the electron beam melted(EBMed)Ti-6 Al-4 V alloy.Scanning electron microscopy(SEM)and electron backscatter diffraction(EBSD)analysis have shown about 99%αphase and 1%βphase in the heat-treated samples when the temperature rises to 950℃.Four distinct types ofαgrain morphology have been found:allotromorphousα,relatively coarseαplate,large precipitationαand granularα.A single peak of the intervariant boundary with the misorientation of 60°/[1120]associated with Burgers orientation relationship(OR)was found in the allotromorphousαcolony.Multiple intervariant boundaries mixed with a fraction of general high-angle grain boundary(GHABs,not Burgers OR)were present in the relatively coarseαplate colony.Almost only low-angle grain boundaries(LABs)with the misorientation of<5°were found in the large precipitationαgrains.βphase tends to distribute around the boundaries of relatively coarseαplates.It suggests that different formation mechanisms are involved in the distinct types ofαgrain morphology.展开更多
Duplex stainless steel UNS S31803 samples were cross-rolled with a true strain of ε = 2 followed by annealing at 1323 K for 2 min and 240 min, respectively. The distributions of intervariant boundary planes in the pr...Duplex stainless steel UNS S31803 samples were cross-rolled with a true strain of ε = 2 followed by annealing at 1323 K for 2 min and 240 min, respectively. The distributions of intervariant boundary planes in the precipitated austenite（A） from ferrite（F） and phase boundary planes conforming to Kurdjumov-Sache（K-S） orientation relationship（OR） were characterized by electron backscatter diffraction（EBSD） and the five-para me ter analysis（FPA） method, respectively. The intervariant boundary planes with misorientation angle of 60° around 〈111 〉 and 〈011 〉 occur frequently and tend to terminate on the {111} plane. At the grain size level of 4 μm, the phase boundary appears to be connected with the K-S OR terminating on{110}F ｜｜ {111}A at the early stage of annealing. When the grain size reaches approximately 20 μm, phase boundary was modified into {541}F｜｜{533}A due to twinning in austenite during annealing.展开更多
Implant-related infection is one of the most catastrophic complications after surgery,since it may trigger osteomyelitis and necessitate reoperation,increasing the pain suffered by and the burden placed on the patient...Implant-related infection is one of the most catastrophic complications after surgery,since it may trigger osteomyelitis and necessitate reoperation,increasing the pain suffered by and the burden placed on the patient.Producing a new alloy with an antibacterial effect for use as a biomedical material is an urgent requirement.In this article,Ti-6 Al-4 V-5 Cu was synthesized under two different heat treatment schemes(solution temperatures of 850℃and 950℃).Through comprehensive observation of the microstructure,phase,copper ion release,biocompatibility,corrosion resistance and antibacterial effect in vitro and in vivo,it was determined that cell viability and corrosion resistance of Ti-6 Al-4 V-5 Cu was better than Ti-6 Al-4 V.More importantly,the obtained alloy,especially samples treated at 850℃,showed prominent antibacterial ability.Meanwhile,we also found that the main antibacterial mechanism of the alloy was contact sterilization via the extensive precipitation of Ti_(2)Cu instead of Cu ion release,and the content,surface area of Ti_(2)Cu could affect the antibacterial effect.These findings provide a very promising scheme by which to balance the biocompatibility and antibacterial effect of Ti-based,Cu-bearing alloys,which could improve their performance in orthopedic and dental applications.展开更多
High-pressure torsion(HPT)processing under a pressure of 6.0 GPa was applied to Ti29.7Ni50.3Hf20(at.%)alloy.Two types of structure were observed after HPT with 3 revolutions:first one is the mixture of amorphous phase...High-pressure torsion(HPT)processing under a pressure of 6.0 GPa was applied to Ti29.7Ni50.3Hf20(at.%)alloy.Two types of structure were observed after HPT with 3 revolutions:first one is the mixture of amorphous phase and retained nanocrystalline;second is the alternating bands of amorphous phase and high defect density crystalline.As a result,post deformation annealing(PDA)at 500-700℃leads to the non-uniform distribution of martensite and parent phase grains.The grains of martensite are twice larger compared to that of parent phase.The nanocrystalline and ultrafine grains form after annealing at 500-600℃and 700℃,respectively.The twinning mechanism does not change with the reduction of martensitic grains up to^35 nm.The relationship between strength and grain size in Ti29.7Ni50.3Hf20 alloy obeys the classical Hall-Petch relationship with a coefficient of 10.80±0.39 GPa nm^1/2.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52201207,52271169)。
文摘The effect of age hardening on the microstructure,martensitic transformation behavior,and shape memory properties of the(Ni_(50)Ti_(30)Hf_(20))_(95)V_(5)alloy was investigated by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,differential scanning calorimetry,microhardness,and bending tests.The results demonstrate a significant influence of V addition on the microstructure of the alloy.V addition leads to the formation of a(Ni,V)_(2)(Ti,Hf)-type Laves phase,which coexists with B19'martensite at room temperature.Aging at 550℃results in precipitation hardening due to the formation of nano-scale orthorhombic H-phase,with the peak hardness observed after 3 h of aging.The alloy at peak hardness state exhibits higher transformation strain and lower unrecovered strain compared to the solution-treated sample.The aged sample achieves a maximum transformation strain of 1.56%under 500 MPa.
基金financial supports from the National Natural Science Foundation of China (51671064)the National Key R&D Program of China (2017YFE0123500)。
文摘The evolution of Ti3Ni4 precipitates in Ti49.2Ni50.8 alloy during equal channel angular pressing(ECAP) and intermediate annealing was investigated by transmission electron microscopy. The solution-treated Ti49.2Ni50.8 alloy was aged at 450 ℃ for 10 to 60 min to obtain Ti3Ni4 precipitates ranging from 37 to 75 nm. After ECAP at 450 ℃ for one pass, Ti3Ni4 precipitates introduced by aging for 10 and 30 min totally dissolve into the matrix;however, those produced by aging for 60 min become smaller. The critical size of Ti3Ni4 precipitates to totally dissolve into matrix is determined to be in the range of 37-68 nm. The dislocation density of ECAP-processed samples depends on the initial size of Ti3Ni4 precipitates after aging. With increasing the duration of initial aging from 10 to 60 min, the dislocation density firstly increases and then decreases.
基金supported by the National Natural Sci-ence Foundation of China(Nos.52050410340 and 51971072)the Fundamental Research Funds for the Central University(No.3072021CFJ1002).
文摘Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys.This paper discusses the precipitation,coarsening and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy during isothermal aging at temperatures between 450℃and 650℃for time to 75 h.The H-phase mean size and volume fraction were determined using transmission electron microscopy.Precipitation kinetics was analyzed using the Johnson-Mehl-Avrami-Kolmogorov equation and an Arrhenius type law.From these analyses,a Time-Temperature-Transformation diagram was constructed.The evolution of H-phase size suggests classical matrix diffusion limited Lifshitz-Slyozov-Wagner coarsening for all considered temperatures.The coarsening rate constants of H-phase precipitation have been determined using a modified coarsening rate equation for nondilute solutions.Critical size of H-phase precipitates for breaking down the precipitate/matrix interface coherency was estimated through a combination of age hardening and precipitate size evolution data.Moreover,time-temperature-hardness diagram was constructed from the precipitation and coarsening kinetics and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy.
基金financially supported by the Key R&D Plan of the Ministry of Science and Technology(No.2018YFB1105900)the Shandong Province Key R&D Project(No.2018GGX103017)the Zibo City and SDUT Integration Project(No.2018ZBXC154)。
文摘It is important to understand the correlation between grain morphology and intervariant boundaries of theαphase after heat treatment belowβtransus of the electron beam melted(EBMed)Ti-6 Al-4 V alloy.Scanning electron microscopy(SEM)and electron backscatter diffraction(EBSD)analysis have shown about 99%αphase and 1%βphase in the heat-treated samples when the temperature rises to 950℃.Four distinct types ofαgrain morphology have been found:allotromorphousα,relatively coarseαplate,large precipitationαand granularα.A single peak of the intervariant boundary with the misorientation of 60°/[1120]associated with Burgers orientation relationship(OR)was found in the allotromorphousαcolony.Multiple intervariant boundaries mixed with a fraction of general high-angle grain boundary(GHABs,not Burgers OR)were present in the relatively coarseαplate colony.Almost only low-angle grain boundaries(LABs)with the misorientation of<5°were found in the large precipitationαgrains.βphase tends to distribute around the boundaries of relatively coarseαplates.It suggests that different formation mechanisms are involved in the distinct types ofαgrain morphology.
基金financially by the National Natural Science Foundation of China (Nos. 51471100 and 51171095)
文摘Duplex stainless steel UNS S31803 samples were cross-rolled with a true strain of ε = 2 followed by annealing at 1323 K for 2 min and 240 min, respectively. The distributions of intervariant boundary planes in the precipitated austenite（A） from ferrite（F） and phase boundary planes conforming to Kurdjumov-Sache（K-S） orientation relationship（OR） were characterized by electron backscatter diffraction（EBSD） and the five-para me ter analysis（FPA） method, respectively. The intervariant boundary planes with misorientation angle of 60° around 〈111 〉 and 〈011 〉 occur frequently and tend to terminate on the {111} plane. At the grain size level of 4 μm, the phase boundary appears to be connected with the K-S OR terminating on{110}F ｜｜ {111}A at the early stage of annealing. When the grain size reaches approximately 20 μm, phase boundary was modified into {541}F｜｜{533}A due to twinning in austenite during annealing.
基金financially supported by the Harbin Medical University Graduate Research Innovation Fund[201801140]。
文摘Implant-related infection is one of the most catastrophic complications after surgery,since it may trigger osteomyelitis and necessitate reoperation,increasing the pain suffered by and the burden placed on the patient.Producing a new alloy with an antibacterial effect for use as a biomedical material is an urgent requirement.In this article,Ti-6 Al-4 V-5 Cu was synthesized under two different heat treatment schemes(solution temperatures of 850℃and 950℃).Through comprehensive observation of the microstructure,phase,copper ion release,biocompatibility,corrosion resistance and antibacterial effect in vitro and in vivo,it was determined that cell viability and corrosion resistance of Ti-6 Al-4 V-5 Cu was better than Ti-6 Al-4 V.More importantly,the obtained alloy,especially samples treated at 850℃,showed prominent antibacterial ability.Meanwhile,we also found that the main antibacterial mechanism of the alloy was contact sterilization via the extensive precipitation of Ti_(2)Cu instead of Cu ion release,and the content,surface area of Ti_(2)Cu could affect the antibacterial effect.These findings provide a very promising scheme by which to balance the biocompatibility and antibacterial effect of Ti-based,Cu-bearing alloys,which could improve their performance in orthopedic and dental applications.
基金supported by National Key R&D Program of China[grant number 2017YFE0123500]National Natural Science Foundation of China[grant number 51971072,51671064]+2 种基金the Fundamental Research Funds for the Central University[grant number HEUCFG201836]the support from the RFBR-CNPq-DST research project№19-58-80018the support in part from the Russian Foundation for Basic Research(project No.20-03-00614)。
文摘High-pressure torsion(HPT)processing under a pressure of 6.0 GPa was applied to Ti29.7Ni50.3Hf20(at.%)alloy.Two types of structure were observed after HPT with 3 revolutions:first one is the mixture of amorphous phase and retained nanocrystalline;second is the alternating bands of amorphous phase and high defect density crystalline.As a result,post deformation annealing(PDA)at 500-700℃leads to the non-uniform distribution of martensite and parent phase grains.The grains of martensite are twice larger compared to that of parent phase.The nanocrystalline and ultrafine grains form after annealing at 500-600℃and 700℃,respectively.The twinning mechanism does not change with the reduction of martensitic grains up to^35 nm.The relationship between strength and grain size in Ti29.7Ni50.3Hf20 alloy obeys the classical Hall-Petch relationship with a coefficient of 10.80±0.39 GPa nm^1/2.
