Thermal cycle training of CuZnAl shape memory alloys with different transformation temperatures was carried out.The influence of different pre-strains,heat treatments and media on the shape memory effect(SME)of CuZnAl...Thermal cycle training of CuZnAl shape memory alloys with different transformation temperatures was carried out.The influence of different pre-strains,heat treatments and media on the shape memory effect(SME)of CuZnAl alloys with different transformation temperatures was studied by means of scanning electron microscopy(SEM)and X-ray diffractometry(XRD).Experimental results show that despite respective variation in heat treatment,medium and cycling number,the recovery rate always decreases as pre-strain increases.The decline is obvious when pre-strain is less than 2.6% but not so sharp when pre-strain exceeds 2.6%.Larger pre-strain results in more than one slip system and causes intercutting of the martensite strips among martensitic variants,then leads to the decline of SME.The SME of alloys with transformation temperatures below 347 K is larger than that of alloys beyond 361 K by 20%?40%.The recovery rate of two-step aged alloy is higher than that of step-quenched alloy by 20%?25%.During thermal cycling,the recovery rate in oil is better than that in water.展开更多
The thermal-mechanical (T-M) cycles at constant strain of a polycrystalline CuZnAl alloy have been studied in the. present work. In-situ optical microscopic observations have been made to reveal the features of the ph...The thermal-mechanical (T-M) cycles at constant strain of a polycrystalline CuZnAl alloy have been studied in the. present work. In-situ optical microscopic observations have been made to reveal the features of the phase transitions during T-M cycling. The variation of stress-temperature (S-T) curves and electrical resistance-temperature (R-T) curves accompanying with T-M cycling have been measured by tensile test and electrical resistance measurements. It has been found that the polycrystalline CuZnAl alloy shows apparent morphology changes and properties variations in the first cycle during T-M cycling which is called the first cycle effect in the present work. The stable transformation procedure in the T-M cycle is: martensiteparent phase +residual acicular martensite. This residual martensite possesses the character of stress-induced martensite.展开更多
The variations of the shape memory effects in the Cu-13Zn-15Al(mole fraction,%) alloy upon successive heating (the rate of heating is 5 ℃/min) have been st udied by means of ρ—T curve,shape memory effect measuremen...The variations of the shape memory effects in the Cu-13Zn-15Al(mole fraction,%) alloy upon successive heating (the rate of heating is 5 ℃/min) have been st udied by means of ρ—T curve,shape memory effect measurement,optical met allographical observation and X-ray diffraction. The first abnormal reverse sha pe memory effect occurs when the tested alloy is heated to the temperature below 320 ℃;when it is heated to the temperature between 320 ℃ and 450 ℃,the forward shape memory effect occurs;in the two stages,the shape of the sample r emains the same as that in the furnace when it is taken out from the furnace and air-cooled;when the tested alloy is heated to the temperature above 450 ℃,the shape of the sample remains unchanged during heating,but the second reverse shape memory effect occurs after it is air-quenched.展开更多
The effects of composite rare earths La+Ce on properties of CuZnAl shape memory alloys were studied bymetallograph examination, tensile and bending tests, electric resistivity measurements, EDS and SEM. The test resul...The effects of composite rare earths La+Ce on properties of CuZnAl shape memory alloys were studied bymetallograph examination, tensile and bending tests, electric resistivity measurements, EDS and SEM. The test resultsshow that the grain size of CuZnAl shape memory alloys could be diminished effectively and the mechanical propertiesimproved obviously by the addition of composite rare earths La+Ce (La: Ce=1: 1). Meanwhile, the excellent shapememory properties remained unchanged. The results of microanalyses indicate that the composite rare earths were segregated at grain boundaries and impeded the grain growth, leading to the improvement of the mechanical properties ofCuZnAl alloys. If the amount of composite rare earths La+Ce was greater than 0. 10%, the shape memorial propertiesbecame poor.展开更多
DSC was used to study the effects of predeformation on the reverse martensitic transformation of near-equiatomic TiNi alloy. Both the start temperature As and the finish temperature Af of the reverse transformation in...DSC was used to study the effects of predeformation on the reverse martensitic transformation of near-equiatomic TiNi alloy. Both the start temperature As and the finish temperature Af of the reverse transformation increased with increasing degree of predeformation, but the algebraic difference between As and Af decreased with increasing predeformation until it reached a minimum value, then remained unchanged with further deformation. Transformation heat also increased with increasing predeformation until it reached a maximum value, then decreased with further predeformation. All the phenomena above were considered to be closely related with the release of elastic strain energy during predeformation.展开更多
Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each tem...Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each temperature.The isothermal aging kinetics fits in Avrami equation and the time exponent n decreases with the increase in aging temperature.The apparent activation energy for the isothermal aging process was measured to be 109.0kJ/mol,which is about equal to that of a relaxation internal friction peak at about 200℃ (f≈1 Hz) in the alloy.展开更多
The effect of Ta addition on the martensitic transformation characteristics and the X-ray visibility on NiTi shape memory alloy have been studied in (Ni51Ti49)1-xTax system. It was found that the transformation temper...The effect of Ta addition on the martensitic transformation characteristics and the X-ray visibility on NiTi shape memory alloy have been studied in (Ni51Ti49)1-xTax system. It was found that the transformation temperatures of the Ni51Ti49 binary alloy increased drastically by an addition of 0~4 at. pet Ta, but only slightly when the concentration exceeded 4 at. pct; the addition of Ta greatly decreases the sensitivity of the martensitic transformations to the variation in the Ni-Ti ratio. The addition of Ta to the NiTi binary alloy can improve its X-ray visibility.展开更多
Improvement of shape, memory effect (SME) in Fe-Mn-Si based alloys has been investigated, compared with that by conventional 'training' treatment. It is found that SME in Fe-Mn-Si alloy can be greatly improved...Improvement of shape, memory effect (SME) in Fe-Mn-Si based alloys has been investigated, compared with that by conventional 'training' treatment. It is found that SME in Fe-Mn-Si alloy can be greatly improved by ausforming and 3.8%recovery strain and 2.2% complete recovery strain can be reached by ausforming at 973 K when dynamic recrystallization has just occurred. The mechanism for the improvement of SME is proposed.展开更多
Ti–51at%Ni shape memory alloys(SMAs) were successfully produced via a powder metallurgy and microwave sintering technique.The influence of sintering parameters on porosity reduction,microstructure,phase transformatio...Ti–51at%Ni shape memory alloys(SMAs) were successfully produced via a powder metallurgy and microwave sintering technique.The influence of sintering parameters on porosity reduction,microstructure,phase transformation temperatures,and mechanical properties were investigated by optical microscopy,field-emission scanning electron microscopy(FE-SEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests,and microhardness tests.Varying the microwave temperature and holding time was found to strongly affect the density of porosity,presence of precipitates,transformation temperatures,and mechanical properties.The lowest density and smallest pore size were observed in the Ti–51at%Ni samples sintered at 900°C for 5 min or at 900°C for 30 min.The predominant martensite phases of β2 and β19′ were observed in the microstructure of Ti–51at%Ni,and their existence varied in accordance with the sintering temperature and the holding time.In the DSC thermograms,multi-transformation peaks were observed during heating,whereas a single peak was observed during cooling;these peaks correspond to the presence of the β2,R,and β19′ phases.The maximum strength and strain among the Ti–51at%Ni SMAs were 1376 MPa and 29%,respectively,for the sample sintered at 900°C for 30 min because of this sample's minimal porosity.展开更多
The effect of thermal cycling and aging in martensitic state in Ti-Pd-Ni alloys were investigated by DSC and TEM observations. It is shown that the thermal cycling causes the decreases in M, and Af temperatures in Ti5...The effect of thermal cycling and aging in martensitic state in Ti-Pd-Ni alloys were investigated by DSC and TEM observations. It is shown that the thermal cycling causes the decreases in M, and Af temperatures in Ti50Pd50-xNix (x=10, 20, 30) alloys, but no obvious thermal cycling effect was observed in Ti50Pd50Pd40Ni10 alloys and the aging effect shows a curious feature, i.e., the Af temperature does not saturate even after relatively long time aging, which is considered to be due to the occurrence of recovery recrystallization during aging.展开更多
A NiTi shape memory alloy (SMA) modified by Ta ion implantation was subjected to oxidation treatment in air at 723 and 873 K. Atomic force microscopy (AFM), Auger electron spectroscopy (AES), and grazing inciden...A NiTi shape memory alloy (SMA) modified by Ta ion implantation was subjected to oxidation treatment in air at 723 and 873 K. Atomic force microscopy (AFM), Auger electron spectroscopy (AES), and grazing incidence X-ray diffraction (GIXRD) measurements were conducted to investigate the surface characteristics, including surface topography, elemental depth profiles, and surface phase structures. The surface roughness of the Ta-implanted NiTi increases after oxidation, and the higher the oxidation temperature is, the larger the value is. The surface of the Ta-implanted NiTi oxidized at 723 K is a nanolayer mainly composed of TiO2/Ta2O5 and TiO with depressed Ni content. The Ta-implanted NiTi oxidized at 873 K is mainly covered by rutile TiO2 in several micrometers of thickness. Potentiodynamic polarization tests indicated that the corrosion resistance of the Ta-implanted NiTi was improved after thermal oxidation at 723 K, but a negative impact was found for the Ta-implanted NiTi oxidized at 873 K.展开更多
The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy(SMA) was studied by means of scanning electron microscopy(SEM),transmission electron micr...The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy(SMA) was studied by means of scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffractometer,and differential scanning calorimeter(DSC).Experimental results show that bainite,γ2,and α phase precipitates occur with the aging effect in the alloy.After aging at 300°C,the bainitic precipitates appear at the early stages of aging,while the precipitates of γ2 phase are observed for a longer aging time.When the aging temperature increases,the bainite gradually evolves into γ2 phase and equilibrium α phase(bcc) precipitates from the remaining parent phase.Thus,the bainite,γ2,and α phases appear,while the martensite phase disappears progressively in the alloy.The bainitic precipitates decrease the reverse transformation temperature while the γ2 phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase.On the other hand,these precipitations cause an increasing in hardness of the alloy.展开更多
The recovery strain, stress and transformation temperature of different pre-strained specimens of Ti44Ni47Nb9 were investigated by tensile test and electrical resistance measurement. The results indicated that pre-str...The recovery strain, stress and transformation temperature of different pre-strained specimens of Ti44Ni47Nb9 were investigated by tensile test and electrical resistance measurement. The results indicated that pre-strain increases the reverse martensitic transformation temperature (A ' (s)) and hysteresis (A(s) - M-s). The recovery strain and stress are higher if the specimens are pre-strained between M-s and A(s) temperature than outside this temperature range. There exists an optimal pre-strain value, about 10%, at which the specimen exhibits maximum recovery strain and stress.展开更多
The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36l\li49Hf15 high temperature shape memory alloy (SMA) has been investigated by bending tests. The res...The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36l\li49Hf15 high temperature shape memory alloy (SMA) has been investigated by bending tests. The results indicated that the training procedure is beneficial to get the better TWSME. The two-way shape memory strain increases with increasing the training strain. And it decreases with increasing the training temperature. The TWSME obtained in the present alloy shows poorer stability compared with that obtained in the TiNi alloys.展开更多
An investigation of the influence of deformation on shape recovery has been put forward in Cu-Zn-Al shape memory alloys.Starting at a model of the re-orientation of martensitic va- riants,the principle and essentialit...An investigation of the influence of deformation on shape recovery has been put forward in Cu-Zn-Al shape memory alloys.Starting at a model of the re-orientation of martensitic va- riants,the principle and essentiality of the influence of the amount of pre-deformation ε on shape recovery rate η is elucidated.展开更多
The microstructure,phase transformation,compression property and strain recovery characteristics of equiatomic Ru-Nb high temperature shape memory alloy were investigated by means of optical microscope,X-ray diffracti...The microstructure,phase transformation,compression property and strain recovery characteristics of equiatomic Ru-Nb high temperature shape memory alloy were investigated by means of optical microscope,X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests and transmission electron microscopy(TEM).When cooling the alloy specimen from high temperature to room temperature,β(parent phase)→β’(interphase)→β″(martensite) two step phase transformation occurs.The microstructure at room temperature shows regularly arranged band morphology with the monoclinic crystal structure.The twinning relationship between the martensite bands was determined to be(101) Type I.Reorientation and of the martensite bands inside the variant and dislocation were found during compression at room temperature.The maximum complete recovery strain is about 1.5%.展开更多
The bainite structure in a Cu-Zn-A1 alloy related to the reverse shape memory effect has been observed by means of TEM.The reverse memory effect may be improved by up to one order of magnitude under applied constraint...The bainite structure in a Cu-Zn-A1 alloy related to the reverse shape memory effect has been observed by means of TEM.The reverse memory effect may be improved by up to one order of magnitude under applied constraint stress.The widespread propagation of bainite was confirmed to be the diffusion controlled shear process by the parabolic configuration of side interface of bainite plate and the twisting of intersected bainite plates.展开更多
A new finite strain elatoplastic J2-flow model with coupling effects of both isotropic and anisotropic hardening is proposed with the co-rotational logarithmic rate.In terms of certain single-variable shape functions ...A new finite strain elatoplastic J2-flow model with coupling effects of both isotropic and anisotropic hardening is proposed with the co-rotational logarithmic rate.In terms of certain single-variable shape functions representing uniaxial loading and unloading curves,explicit multi-axial expressions for the three hardening quantities incorporated in the new model proposed are derived in unified forms for the purpose of automatically and accurately simulating complex pseudoelastic-to-plastic transition effects of shape memory alloys(SMAs)under multiple loading-unloading cycles.Numerical examples show that with only a single parameter of direct physical meaning for each cycle,accurate and explicit simulations may be achieved for extensive data from multiple cycle tests.展开更多
基金Project(BE2004027) supported by the Science and Technology Foundation of Jiangsu Province,China
文摘Thermal cycle training of CuZnAl shape memory alloys with different transformation temperatures was carried out.The influence of different pre-strains,heat treatments and media on the shape memory effect(SME)of CuZnAl alloys with different transformation temperatures was studied by means of scanning electron microscopy(SEM)and X-ray diffractometry(XRD).Experimental results show that despite respective variation in heat treatment,medium and cycling number,the recovery rate always decreases as pre-strain increases.The decline is obvious when pre-strain is less than 2.6% but not so sharp when pre-strain exceeds 2.6%.Larger pre-strain results in more than one slip system and causes intercutting of the martensite strips among martensitic variants,then leads to the decline of SME.The SME of alloys with transformation temperatures below 347 K is larger than that of alloys beyond 361 K by 20%?40%.The recovery rate of two-step aged alloy is higher than that of step-quenched alloy by 20%?25%.During thermal cycling,the recovery rate in oil is better than that in water.
文摘The thermal-mechanical (T-M) cycles at constant strain of a polycrystalline CuZnAl alloy have been studied in the. present work. In-situ optical microscopic observations have been made to reveal the features of the phase transitions during T-M cycling. The variation of stress-temperature (S-T) curves and electrical resistance-temperature (R-T) curves accompanying with T-M cycling have been measured by tensile test and electrical resistance measurements. It has been found that the polycrystalline CuZnAl alloy shows apparent morphology changes and properties variations in the first cycle during T-M cycling which is called the first cycle effect in the present work. The stable transformation procedure in the T-M cycle is: martensiteparent phase +residual acicular martensite. This residual martensite possesses the character of stress-induced martensite.
文摘The variations of the shape memory effects in the Cu-13Zn-15Al(mole fraction,%) alloy upon successive heating (the rate of heating is 5 ℃/min) have been st udied by means of ρ—T curve,shape memory effect measurement,optical met allographical observation and X-ray diffraction. The first abnormal reverse sha pe memory effect occurs when the tested alloy is heated to the temperature below 320 ℃;when it is heated to the temperature between 320 ℃ and 450 ℃,the forward shape memory effect occurs;in the two stages,the shape of the sample r emains the same as that in the furnace when it is taken out from the furnace and air-cooled;when the tested alloy is heated to the temperature above 450 ℃,the shape of the sample remains unchanged during heating,but the second reverse shape memory effect occurs after it is air-quenched.
文摘The effects of composite rare earths La+Ce on properties of CuZnAl shape memory alloys were studied bymetallograph examination, tensile and bending tests, electric resistivity measurements, EDS and SEM. The test resultsshow that the grain size of CuZnAl shape memory alloys could be diminished effectively and the mechanical propertiesimproved obviously by the addition of composite rare earths La+Ce (La: Ce=1: 1). Meanwhile, the excellent shapememory properties remained unchanged. The results of microanalyses indicate that the composite rare earths were segregated at grain boundaries and impeded the grain growth, leading to the improvement of the mechanical properties ofCuZnAl alloys. If the amount of composite rare earths La+Ce was greater than 0. 10%, the shape memorial propertiesbecame poor.
基金the National Natural Science Foundation of China under grant No. 59601004,59731030.
文摘DSC was used to study the effects of predeformation on the reverse martensitic transformation of near-equiatomic TiNi alloy. Both the start temperature As and the finish temperature Af of the reverse transformation increased with increasing degree of predeformation, but the algebraic difference between As and Af decreased with increasing predeformation until it reached a minimum value, then remained unchanged with further deformation. Transformation heat also increased with increasing predeformation until it reached a maximum value, then decreased with further predeformation. All the phenomena above were considered to be closely related with the release of elastic strain energy during predeformation.
文摘Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each temperature.The isothermal aging kinetics fits in Avrami equation and the time exponent n decreases with the increase in aging temperature.The apparent activation energy for the isothermal aging process was measured to be 109.0kJ/mol,which is about equal to that of a relaxation internal friction peak at about 200℃ (f≈1 Hz) in the alloy.
基金Shanxi Province Natural Science FOundation State Key Laboratory of Solidilication Processing.
文摘The effect of Ta addition on the martensitic transformation characteristics and the X-ray visibility on NiTi shape memory alloy have been studied in (Ni51Ti49)1-xTax system. It was found that the transformation temperatures of the Ni51Ti49 binary alloy increased drastically by an addition of 0~4 at. pet Ta, but only slightly when the concentration exceeded 4 at. pct; the addition of Ta greatly decreases the sensitivity of the martensitic transformations to the variation in the Ni-Ti ratio. The addition of Ta to the NiTi binary alloy can improve its X-ray visibility.
文摘Improvement of shape, memory effect (SME) in Fe-Mn-Si based alloys has been investigated, compared with that by conventional 'training' treatment. It is found that SME in Fe-Mn-Si alloy can be greatly improved by ausforming and 3.8%recovery strain and 2.2% complete recovery strain can be reached by ausforming at 973 K when dynamic recrystallization has just occurred. The mechanism for the improvement of SME is proposed.
基金financial support under the University Research Grant No.Q.J130000.3024.00M57
文摘Ti–51at%Ni shape memory alloys(SMAs) were successfully produced via a powder metallurgy and microwave sintering technique.The influence of sintering parameters on porosity reduction,microstructure,phase transformation temperatures,and mechanical properties were investigated by optical microscopy,field-emission scanning electron microscopy(FE-SEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests,and microhardness tests.Varying the microwave temperature and holding time was found to strongly affect the density of porosity,presence of precipitates,transformation temperatures,and mechanical properties.The lowest density and smallest pore size were observed in the Ti–51at%Ni samples sintered at 900°C for 5 min or at 900°C for 30 min.The predominant martensite phases of β2 and β19′ were observed in the microstructure of Ti–51at%Ni,and their existence varied in accordance with the sintering temperature and the holding time.In the DSC thermograms,multi-transformation peaks were observed during heating,whereas a single peak was observed during cooling;these peaks correspond to the presence of the β2,R,and β19′ phases.The maximum strength and strain among the Ti–51at%Ni SMAs were 1376 MPa and 29%,respectively,for the sample sintered at 900°C for 30 min because of this sample's minimal porosity.
基金This work was supported by a Grant-in-Aid fOrEncouragement of Young Scientists (W.C.) (l998-1999) from the Ministry of Educat
文摘The effect of thermal cycling and aging in martensitic state in Ti-Pd-Ni alloys were investigated by DSC and TEM observations. It is shown that the thermal cycling causes the decreases in M, and Af temperatures in Ti50Pd50-xNix (x=10, 20, 30) alloys, but no obvious thermal cycling effect was observed in Ti50Pd50Pd40Ni10 alloys and the aging effect shows a curious feature, i.e., the Af temperature does not saturate even after relatively long time aging, which is considered to be due to the occurrence of recovery recrystallization during aging.
基金supported by the National Natural Science Foundation of China (No.50971007)the Program for New Century Excellent Talents in Universities from the Ministry of Education of China (No.NCET-09-0024)
文摘A NiTi shape memory alloy (SMA) modified by Ta ion implantation was subjected to oxidation treatment in air at 723 and 873 K. Atomic force microscopy (AFM), Auger electron spectroscopy (AES), and grazing incidence X-ray diffraction (GIXRD) measurements were conducted to investigate the surface characteristics, including surface topography, elemental depth profiles, and surface phase structures. The surface roughness of the Ta-implanted NiTi increases after oxidation, and the higher the oxidation temperature is, the larger the value is. The surface of the Ta-implanted NiTi oxidized at 723 K is a nanolayer mainly composed of TiO2/Ta2O5 and TiO with depressed Ni content. The Ta-implanted NiTi oxidized at 873 K is mainly covered by rutile TiO2 in several micrometers of thickness. Potentiodynamic polarization tests indicated that the corrosion resistance of the Ta-implanted NiTi was improved after thermal oxidation at 723 K, but a negative impact was found for the Ta-implanted NiTi oxidized at 873 K.
文摘The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy(SMA) was studied by means of scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffractometer,and differential scanning calorimeter(DSC).Experimental results show that bainite,γ2,and α phase precipitates occur with the aging effect in the alloy.After aging at 300°C,the bainitic precipitates appear at the early stages of aging,while the precipitates of γ2 phase are observed for a longer aging time.When the aging temperature increases,the bainite gradually evolves into γ2 phase and equilibrium α phase(bcc) precipitates from the remaining parent phase.Thus,the bainite,γ2,and α phases appear,while the martensite phase disappears progressively in the alloy.The bainitic precipitates decrease the reverse transformation temperature while the γ2 phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase.On the other hand,these precipitations cause an increasing in hardness of the alloy.
文摘The recovery strain, stress and transformation temperature of different pre-strained specimens of Ti44Ni47Nb9 were investigated by tensile test and electrical resistance measurement. The results indicated that pre-strain increases the reverse martensitic transformation temperature (A ' (s)) and hysteresis (A(s) - M-s). The recovery strain and stress are higher if the specimens are pre-strained between M-s and A(s) temperature than outside this temperature range. There exists an optimal pre-strain value, about 10%, at which the specimen exhibits maximum recovery strain and stress.
文摘The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36l\li49Hf15 high temperature shape memory alloy (SMA) has been investigated by bending tests. The results indicated that the training procedure is beneficial to get the better TWSME. The two-way shape memory strain increases with increasing the training strain. And it decreases with increasing the training temperature. The TWSME obtained in the present alloy shows poorer stability compared with that obtained in the TiNi alloys.
文摘An investigation of the influence of deformation on shape recovery has been put forward in Cu-Zn-Al shape memory alloys.Starting at a model of the re-orientation of martensitic va- riants,the principle and essentiality of the influence of the amount of pre-deformation ε on shape recovery rate η is elucidated.
基金The project is financially supported by the National Natural Science Foundation of China ( No 50531020)
文摘The microstructure,phase transformation,compression property and strain recovery characteristics of equiatomic Ru-Nb high temperature shape memory alloy were investigated by means of optical microscope,X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests and transmission electron microscopy(TEM).When cooling the alloy specimen from high temperature to room temperature,β(parent phase)→β’(interphase)→β″(martensite) two step phase transformation occurs.The microstructure at room temperature shows regularly arranged band morphology with the monoclinic crystal structure.The twinning relationship between the martensite bands was determined to be(101) Type I.Reorientation and of the martensite bands inside the variant and dislocation were found during compression at room temperature.The maximum complete recovery strain is about 1.5%.
文摘The bainite structure in a Cu-Zn-A1 alloy related to the reverse shape memory effect has been observed by means of TEM.The reverse memory effect may be improved by up to one order of magnitude under applied constraint stress.The widespread propagation of bainite was confirmed to be the diffusion controlled shear process by the parabolic configuration of side interface of bainite plate and the twisting of intersected bainite plates.
基金Project supported by the National Natural Science Foundation of China(No.11372172)and the Start-up Fund from Jinan University in Guangzhou of China。
文摘A new finite strain elatoplastic J2-flow model with coupling effects of both isotropic and anisotropic hardening is proposed with the co-rotational logarithmic rate.In terms of certain single-variable shape functions representing uniaxial loading and unloading curves,explicit multi-axial expressions for the three hardening quantities incorporated in the new model proposed are derived in unified forms for the purpose of automatically and accurately simulating complex pseudoelastic-to-plastic transition effects of shape memory alloys(SMAs)under multiple loading-unloading cycles.Numerical examples show that with only a single parameter of direct physical meaning for each cycle,accurate and explicit simulations may be achieved for extensive data from multiple cycle tests.