The critical driving force for martensitic transformation fcc ( gamma ) yields hcp ( epsilon ) in ternary Fe-Mn-Si alloys increases with the content of Mn and decreases with that of Si. Thermodynamical prediction of ...The critical driving force for martensitic transformation fcc ( gamma ) yields hcp ( epsilon ) in ternary Fe-Mn-Si alloys increases with the content of Mn and decreases with that of Si. Thermodynamical prediction of M//s in ternary Fe-Mn-Si alloys was established. The fcc ( gamma ) yields hcp ( epsilon ) martensitic transformation in Fe-Mn-Si is a semi-thermoelastic and the nucleation process does not strongly depend on soft mode. Nucleation occurs directly through an overlapping of stacking fault rather than pole mechanism, and it is suggested that stacking fault energy (SFE) is the main factor controlling nucleation. Based on the phenomenological theory of martensite crystallography, a shuffle on (0001)//h//c//p plane is required when d//1//1//1 does not equal d//0//0//0//2. The derived principal strain in Bain distortion is smaller, i, e., more reasonable than the values given by Christian. Alloying elements strengthening the austenite, lowering SFE of gamma phase and reducing T//N** gamma temperature may be beneficial to shape memory effect of Fe-Mn-Si based alloys. Accordingly, Fe-Mn-Si-RE and Fe-Mn-Si-Cr-N (or Fe-Mn-Si-Ni-Cr-N) are worthy to be recommended as shape memory materials with improved shape memory effect. (Edited author abstract) 48 Refs.展开更多
Plastic deformation of three CuZnAl shape memory alloys in martensitic state was investi- gated by means of optical and electron metallography,dilatometry and electric resistiviy de- termination.Two of the alloys are ...Plastic deformation of three CuZnAl shape memory alloys in martensitic state was investi- gated by means of optical and electron metallography,dilatometry and electric resistiviy de- termination.Two of the alloys are in martensitic state at ambient temperature,and the A_f temperature of the third one is far below the ambient temperature.The effect of deformation of alloys in martensitic state on the course and temperature of transformation as well as the hysteresis of transformation cycles has been analyzed and the “effect of the first cycle” has also been discussed.展开更多
Existing experimental results have shown that four types of physical mechanisms, namely, martensite transformation, martensite reorientation, magnetic domain wall motion and magnetization vector rotation, can be activ...Existing experimental results have shown that four types of physical mechanisms, namely, martensite transformation, martensite reorientation, magnetic domain wall motion and magnetization vector rotation, can be activated during the magneto-mechanical deformation of NiMnGa ferromagnetic shape memory alloy (FSMA) single crystals. In this work, based on irreversible thermodynamics, a three-dimensional (3D) single crystal constitutive model is constructed by considering the aforementioned four mechanisms simultaneously. Three types of internal variables, i.e., the volume fraction of each martensite variant, the volume fraction of magnetic domain in each variant and the deviation angle between the magnetization vector, and easy axis are introduced to characterize the magneto-mechanical state of the single crystals. The thermodynamic driving force of each mechanism and the thermodynamic constraints on the constitutive model are obtained from Clausius's dissipative inequality and constructed Gibbs free energy. Then, thermodynamically consistent kinetic equations for the four mechanisms are proposed, respectively. Finally, the ability of the proposed model to describe the magneto-mechanical deformation of NiMnGa FSMA single crystals is verified by comparing the predictions with corresponding experimental results. It is shown that the proposed model can quantitatively capture the main experimental phenomena. Further, the proposed model is used to predict the deformations of the single crystals under the non-proportional mechanical loading conditions.展开更多
The influence of quenching temperature on the shape memory effect(SME)of the Fe-Mn-Si polycrystalline alloys and their martensitic transformation temperature have been studied.The SME of the hot-rolled specimen may be...The influence of quenching temperature on the shape memory effect(SME)of the Fe-Mn-Si polycrystalline alloys and their martensitic transformation temperature have been studied.The SME of the hot-rolled specimen may be remarkably enhanced by selecting quenching temperature of 600—800℃.It has been shown that SME is influenced not only by the distribution of ε-phase morphology but also by its pre-existence.展开更多
By designing the shape of the original surface curve(sine-wave and square-wave),macroscopic domains with different dislocation density were introduced into the TiNi alloys and materials were endued with the characteri...By designing the shape of the original surface curve(sine-wave and square-wave),macroscopic domains with different dislocation density were introduced into the TiNi alloys and materials were endued with the characteristics of composites. Dilatometer(DL) and the differential scanning calorimeter(DSC) were used to study the properties of in-situ composites of TiNi alloys. The results show that the reverse transformation temperature range of in-situ TiNi composites with sine-wave surface is significantly enlarged. However,two endothermic peaks appear on DSC curves in the first heating process for these samples with square-wave surface. It is presumed that the interactions between the dislocation texture and martensite variants introduced when the TiNi martensite is cold rolled at room temperature might be responsible to the phenomena,which are compared with cold-rolled sheets with flat surface. All the phenomena above show it is feasible to control the thermal properties of a material by a proper design of the dislocation texture.展开更多
Ni_(47)Ti_(44)Nb_(9)shape memory alloy(SMA)is a promising material in the aerospace field due to its wide transformation hysteresis.The application of shape memory effect depends on multistep thermomechan-ical loading...Ni_(47)Ti_(44)Nb_(9)shape memory alloy(SMA)is a promising material in the aerospace field due to its wide transformation hysteresis.The application of shape memory effect depends on multistep thermomechan-ical loading,viz.,low-temperature deformation and subsequent heating to recovery.Low-temperature deformation prestrain plays a pivotal role in shape memory properties tailoring of SMA components.However,microstructure evolution and deformation mechanisms of Ni_(47)Ti_(44)Nb_(9)SMA subjected to vari-ous prestrain levels are still unclear.To this end,microstructure evolution and shape memory behaviors of Ni_(47)Ti_(44)Nb_(9)alloy subjected to multistep thermomechanical loading with prestrain levels of 8%-16%at-28℃(M_(s)+30℃)were investigated.The results demonstrate that the stress-strain curve of the specimen exhibits four distinct stages at a maximal prestrain of 16%.Whereas stageⅡand stageⅢend at prestrains of∼8%and∼12%,respectively.In stageⅡ,the stress-induced martensitic transformation is accompanied by the dislocation slip of the NiTi matrix andβ-Nb inclusions.In stageⅢ,in addition to the higher density of dislocations and further growth of stress-induced martensite variants(SIMVs),(001)compound twins are introduced as a result of the(001)deformation twinning in stress-induced martensite.More{20-1}martensite twins are gradually introduced in stageⅣ.Correspondingly,after subsequent unloading and heating,a higher density of{114}austenite twins form in the specimen with a larger prestrain of 16%.With increasing prestrain from 8%to 16%,the recoverable strainε_(re)^(T)upon heating increases first and then decreases.Theε_(re)^(T)obtains a maximum of 7.03%at 10%prestrain and de-creases to 6.17%at 16%prestrain.The increase ofε_(re)^(T)can be attributed to the formation of new SIMVs,the further growth of existing SIMVs,and the recoverable(001)compound twins.While the decrease ofε_(re)^(T)is mainly associated with the irrecoverable strain by{20−1}martensite twins.The effect ofβ-Nb inclusions on the evolution of SIMVs is also found herein that deformedβ-Nb inclusions can significantly hinder the growth and recoverability of adjacent stress-induced martensite.展开更多
A macroscopic phenomenological constitutive model considering the martensite transformation and its reverse is constructed in this work to describe the thermo-magneto- mechanically coupled deformation of polycrystalli...A macroscopic phenomenological constitutive model considering the martensite transformation and its reverse is constructed in this work to describe the thermo-magneto- mechanically coupled deformation of polycrystalline magnetic shape memory alloys （MSMAs） by referring to the existing experimental results. The proposed model is established in the frame- work of thermodynamics by introducing internal state variables. The driving force of martensite transformation, the internal heat production and the thermodynamic constraints on constitutive equations are obtained by Clausius dissipative inequality and constructed Gibbs free energy. The spatiotemporal evolution equation of temperature is deduced from the first law of thermodynam- ics. The demagnetization effect occurring in the process of magnetization is also addressed. The proposed model is verified by comparing the predictions with the corresponding experiments. It is concluded that the thermo-magneto-mechanically coupled deformation of MSMAs including the magnetostrietive and magnetocaloric effects at various temperatures can be reasonably described by the proposed model, and the magnetocaloric effect can be significantly improved over a wide range of temperature by introducing an additional applied stress.展开更多
Near-equiatomic NiTi shape memory alloys are known to exhibit Lüders-type deformation associated with a stress-induced transformation.Many studies have been conducted in the past mainly focusing on the macroscopi...Near-equiatomic NiTi shape memory alloys are known to exhibit Lüders-type deformation associated with a stress-induced transformation.Many studies have been conducted in the past mainly focusing on the macroscopic characteristics of the phenomenon and some theories have been proposed in the literature to explain its mechanisms,but some aspects of this phenomenon are still unclear,particularly at the microscopic scale.This study investigated the local strain evolution during the initiation and propagation of Lüders band in a pseudoelastic NiTi alloy during tensile deformation by means of digital image correlation(DIC)analysis.Based on the evidence collected,distinct stages of Lüders band formation and propagation are defined and the corresponding local strain rates are obtained.These local strain rates are much higher than the global strain rate of the testing,giving insight to the mechanism of this phenomenon.展开更多
文摘The critical driving force for martensitic transformation fcc ( gamma ) yields hcp ( epsilon ) in ternary Fe-Mn-Si alloys increases with the content of Mn and decreases with that of Si. Thermodynamical prediction of M//s in ternary Fe-Mn-Si alloys was established. The fcc ( gamma ) yields hcp ( epsilon ) martensitic transformation in Fe-Mn-Si is a semi-thermoelastic and the nucleation process does not strongly depend on soft mode. Nucleation occurs directly through an overlapping of stacking fault rather than pole mechanism, and it is suggested that stacking fault energy (SFE) is the main factor controlling nucleation. Based on the phenomenological theory of martensite crystallography, a shuffle on (0001)//h//c//p plane is required when d//1//1//1 does not equal d//0//0//0//2. The derived principal strain in Bain distortion is smaller, i, e., more reasonable than the values given by Christian. Alloying elements strengthening the austenite, lowering SFE of gamma phase and reducing T//N** gamma temperature may be beneficial to shape memory effect of Fe-Mn-Si based alloys. Accordingly, Fe-Mn-Si-RE and Fe-Mn-Si-Cr-N (or Fe-Mn-Si-Ni-Cr-N) are worthy to be recommended as shape memory materials with improved shape memory effect. (Edited author abstract) 48 Refs.
文摘Plastic deformation of three CuZnAl shape memory alloys in martensitic state was investi- gated by means of optical and electron metallography,dilatometry and electric resistiviy de- termination.Two of the alloys are in martensitic state at ambient temperature,and the A_f temperature of the third one is far below the ambient temperature.The effect of deformation of alloys in martensitic state on the course and temperature of transformation as well as the hysteresis of transformation cycles has been analyzed and the “effect of the first cycle” has also been discussed.
基金the National Natural Science Foundation of China (Grant 11602203)Young Elite Scientist Sponsorship Program by the China Association for Science and Technology (Grant 2016QNRC001)Fundamental Research Funds for the Central Universities (Grant 2682018CX43).
文摘Existing experimental results have shown that four types of physical mechanisms, namely, martensite transformation, martensite reorientation, magnetic domain wall motion and magnetization vector rotation, can be activated during the magneto-mechanical deformation of NiMnGa ferromagnetic shape memory alloy (FSMA) single crystals. In this work, based on irreversible thermodynamics, a three-dimensional (3D) single crystal constitutive model is constructed by considering the aforementioned four mechanisms simultaneously. Three types of internal variables, i.e., the volume fraction of each martensite variant, the volume fraction of magnetic domain in each variant and the deviation angle between the magnetization vector, and easy axis are introduced to characterize the magneto-mechanical state of the single crystals. The thermodynamic driving force of each mechanism and the thermodynamic constraints on the constitutive model are obtained from Clausius's dissipative inequality and constructed Gibbs free energy. Then, thermodynamically consistent kinetic equations for the four mechanisms are proposed, respectively. Finally, the ability of the proposed model to describe the magneto-mechanical deformation of NiMnGa FSMA single crystals is verified by comparing the predictions with corresponding experimental results. It is shown that the proposed model can quantitatively capture the main experimental phenomena. Further, the proposed model is used to predict the deformations of the single crystals under the non-proportional mechanical loading conditions.
文摘The influence of quenching temperature on the shape memory effect(SME)of the Fe-Mn-Si polycrystalline alloys and their martensitic transformation temperature have been studied.The SME of the hot-rolled specimen may be remarkably enhanced by selecting quenching temperature of 600—800℃.It has been shown that SME is influenced not only by the distribution of ε-phase morphology but also by its pre-existence.
基金Project (50471021) supported by the National Natural Science Foundation of ChinaProject (20050425002) supported by Research Fund for Doctoral Program of Higher Education
文摘By designing the shape of the original surface curve(sine-wave and square-wave),macroscopic domains with different dislocation density were introduced into the TiNi alloys and materials were endued with the characteristics of composites. Dilatometer(DL) and the differential scanning calorimeter(DSC) were used to study the properties of in-situ composites of TiNi alloys. The results show that the reverse transformation temperature range of in-situ TiNi composites with sine-wave surface is significantly enlarged. However,two endothermic peaks appear on DSC curves in the first heating process for these samples with square-wave surface. It is presumed that the interactions between the dislocation texture and martensite variants introduced when the TiNi martensite is cold rolled at room temperature might be responsible to the phenomena,which are compared with cold-rolled sheets with flat surface. All the phenomena above show it is feasible to control the thermal properties of a material by a proper design of the dislocation texture.
基金support from the National Natural Science Foundation of China(No.51775441)the National Science Fund for Excellent Young Scholars(No.51522509).
文摘Ni_(47)Ti_(44)Nb_(9)shape memory alloy(SMA)is a promising material in the aerospace field due to its wide transformation hysteresis.The application of shape memory effect depends on multistep thermomechan-ical loading,viz.,low-temperature deformation and subsequent heating to recovery.Low-temperature deformation prestrain plays a pivotal role in shape memory properties tailoring of SMA components.However,microstructure evolution and deformation mechanisms of Ni_(47)Ti_(44)Nb_(9)SMA subjected to vari-ous prestrain levels are still unclear.To this end,microstructure evolution and shape memory behaviors of Ni_(47)Ti_(44)Nb_(9)alloy subjected to multistep thermomechanical loading with prestrain levels of 8%-16%at-28℃(M_(s)+30℃)were investigated.The results demonstrate that the stress-strain curve of the specimen exhibits four distinct stages at a maximal prestrain of 16%.Whereas stageⅡand stageⅢend at prestrains of∼8%and∼12%,respectively.In stageⅡ,the stress-induced martensitic transformation is accompanied by the dislocation slip of the NiTi matrix andβ-Nb inclusions.In stageⅢ,in addition to the higher density of dislocations and further growth of stress-induced martensite variants(SIMVs),(001)compound twins are introduced as a result of the(001)deformation twinning in stress-induced martensite.More{20-1}martensite twins are gradually introduced in stageⅣ.Correspondingly,after subsequent unloading and heating,a higher density of{114}austenite twins form in the specimen with a larger prestrain of 16%.With increasing prestrain from 8%to 16%,the recoverable strainε_(re)^(T)upon heating increases first and then decreases.Theε_(re)^(T)obtains a maximum of 7.03%at 10%prestrain and de-creases to 6.17%at 16%prestrain.The increase ofε_(re)^(T)can be attributed to the formation of new SIMVs,the further growth of existing SIMVs,and the recoverable(001)compound twins.While the decrease ofε_(re)^(T)is mainly associated with the irrecoverable strain by{20−1}martensite twins.The effect ofβ-Nb inclusions on the evolution of SIMVs is also found herein that deformedβ-Nb inclusions can significantly hinder the growth and recoverability of adjacent stress-induced martensite.
基金Financial supports by the National Natural Science Foundation of China （11602203）, Young Elite Scientist Sponsorship Program by CAST （No. 2016QNRC001） and Fundamental Research Funds for the Central Universities （2682018CX43） are appreciated.
文摘A macroscopic phenomenological constitutive model considering the martensite transformation and its reverse is constructed in this work to describe the thermo-magneto- mechanically coupled deformation of polycrystalline magnetic shape memory alloys （MSMAs） by referring to the existing experimental results. The proposed model is established in the frame- work of thermodynamics by introducing internal state variables. The driving force of martensite transformation, the internal heat production and the thermodynamic constraints on constitutive equations are obtained by Clausius dissipative inequality and constructed Gibbs free energy. The spatiotemporal evolution equation of temperature is deduced from the first law of thermodynam- ics. The demagnetization effect occurring in the process of magnetization is also addressed. The proposed model is verified by comparing the predictions with the corresponding experiments. It is concluded that the thermo-magneto-mechanically coupled deformation of MSMAs including the magnetostrietive and magnetocaloric effects at various temperatures can be reasonably described by the proposed model, and the magnetocaloric effect can be significantly improved over a wide range of temperature by introducing an additional applied stress.
基金financial support from the Australian Research Council in grants DP180101744 and DP180101955support from the US National Science Foundation under Grant DMR-1923929。
文摘Near-equiatomic NiTi shape memory alloys are known to exhibit Lüders-type deformation associated with a stress-induced transformation.Many studies have been conducted in the past mainly focusing on the macroscopic characteristics of the phenomenon and some theories have been proposed in the literature to explain its mechanisms,but some aspects of this phenomenon are still unclear,particularly at the microscopic scale.This study investigated the local strain evolution during the initiation and propagation of Lüders band in a pseudoelastic NiTi alloy during tensile deformation by means of digital image correlation(DIC)analysis.Based on the evidence collected,distinct stages of Lüders band formation and propagation are defined and the corresponding local strain rates are obtained.These local strain rates are much higher than the global strain rate of the testing,giving insight to the mechanism of this phenomenon.
