The thermal-elastic martensitic transformation from high-temperature Ni_(2)In-type hexagonal structure to low-temperature TiNiSi-type orthorhombic structure has been widely studied in MnMX(M=Ni or Co,and X=Ge or Si)al...The thermal-elastic martensitic transformation from high-temperature Ni_(2)In-type hexagonal structure to low-temperature TiNiSi-type orthorhombic structure has been widely studied in MnMX(M=Ni or Co,and X=Ge or Si)alloys.However,the answer to how the orthorhombic martensite nucleates and grows within the hexagonal parent is still unclear.In this work,the hexagonal-orthorhombic martensitic transformation in a Co and Ge co-substituted MnNiSi is investigated.One can find some orthorhombic laths embedded in the hexagonal parent at a temperature above the martensitic transformation start temperature(M_(s)).With the the sample cooing to M_(s),the laths turn broader,indicating that the martensitic transformation starts from these pre-existing orthorhombic laths.Microstructure observation suggests that these pre-existing orthorhombic laths do not originate from the hexagonal-orthorhombic martensitic transformation because of the difference between atomic occupations of doping elements in the hexagonal parent and those in the preexisting orthorhombic laths.The phenomenological crystallographic theory and experimental investigations prove that the pre-existing orthorhombic lath and generated orthorhombic martensite have the same crystallography relationship to the hexagonal parent.Therefore,the orthorhombic martensite can take these pre-existing laths as embryos and grow up.This work implies that the martensitic transformation in MnNiSi_(1-x)(CoNiGe)_(x) alloy is initiated by orthorhombic embryos.展开更多
Controlling the content of athermal martensite and retained austenite is important to improving the mechanical properties of high-strength steels,but a mechanism for the accurate description of martensitic transformat...Controlling the content of athermal martensite and retained austenite is important to improving the mechanical properties of high-strength steels,but a mechanism for the accurate description of martensitic transformation during the cooling process must be addressed.At present,frequently used semi-empirical kinetics models suffer from huge errors at the beginning of transformation,and most of them fail to exhibit the sigmoidal shape characteristic of transformation curves.To describe the martensitic transformation process accurately,based on the Magee model,we introduced the changes in the nucleation activation energy of martensite with temperature,which led to the varying nucleation rates of this model during martensitic transformation.According to the calculation results,the relative error of the modified model for the martensitic transformation kinetics curves of Fe-C-X(X = Ni,Cr,Mn,Si) alloys reached 9.5% compared with those measured via the thermal expansion method.The relative error was approximately reduced by two-thirds compared with that of the Magee model.The incorporation of nucleation activation energy into the kinetics model contributes to the improvement of its precision.展开更多
Transformation induced plasticity (TRIP) and twinning induced plasticity (TWlP) effects had been widely studied in single austenite steel. But in duplex γ & α(δ) phase, such as welding materials of stainles...Transformation induced plasticity (TRIP) and twinning induced plasticity (TWlP) effects had been widely studied in single austenite steel. But in duplex γ & α(δ) phase, such as welding materials of stainless steel, they had been less studied. Tensile shear loading experiment of resistance spot welding specimens prepared with 2 mm 301L sheets, was carried out at 15℃ and -50℃. Optical microscopy and scanning electron microscopy (SEM) as well as X-ray diffraction (XRD) were used to investigate the microstructure of weld nugget, and specimens fracture surface. The results showed that the initial weld nugget was composed of 8.4% α(δ) ferrite and 91.6% austenite. Tensile shear load bearing capacity of spot welding specimen at -50℃ was 24.8 kN, 17.7% higher than that at 15℃. About 78.5 vol. pct. martensite transformation was induced by plastic deformation at -50℃, while about 67.9 vol. pct transformation induced at 15℃. The plasticity of spot welding joint decreased with the decline of experimental temperature.展开更多
A method of fuzzy identification based on T-S fuzzy model was proposed for predicting temperature Ms from chemical composition, austenitizing temperature and time for low alloy steel. The degree of membership of each ...A method of fuzzy identification based on T-S fuzzy model was proposed for predicting temperature Ms from chemical composition, austenitizing temperature and time for low alloy steel. The degree of membership of each sample was calculated with fuzzy clustering algorithm. Kalman filtering was used to identify the consequent parameters. Compared with the results obtained by empirical models based on the same data, the results by the fuzzy method showed good precision. The accuracy of the fuzzy model is almost 6 times higher than that of the best empirical model. The influence of alloying elements, austenitizing temperature and time on Ms was analyzed quantitatively by using the fuzzy model. It is shown that there exists a nonlinear relationship between the contents of alloying elements in steels and their Ms, and the effects of austenitizing temperature and time on Ms temperature cannot be neglected.展开更多
The effect of annealing temperature on the martensitic transformation of a Ti49.2Ni50.8 alloy processed by equal channel angular pressing (ECAP) was investigated by X-ray diffraction (XRD), transmission electron m...The effect of annealing temperature on the martensitic transformation of a Ti49.2Ni50.8 alloy processed by equal channel angular pressing (ECAP) was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The as-ECAP processed and subsequently annealed Ti49.2Ni50.8 alloys consist of B2 parent phase, Ti4Ni2O phase and B19′ martensite at room temperature. Upon cooling, all samples show B2→R→B19′ two-stage transformation. Upon heating, when the annealing temperature is less than 400℃, the samples show B19′→R→B2 two-stage transformation; when the annealing temperature is higher than 500 ℃, the samples show B19′→B2 single-stage transformation. The B2-R transformation is characterized by wide interval due to the dislocations introduced during ECAP.展开更多
In this paper a first-principles study of the electronic structure and stability of B2 Ti1-xNiHfx (x = 0.2, 0.4, 0.6) and B19′ Ti1-xNiHfx(x = 0, 0.5) alloys is presented. The calculations are performed by the pla...In this paper a first-principles study of the electronic structure and stability of B2 Ti1-xNiHfx (x = 0.2, 0.4, 0.6) and B19′ Ti1-xNiHfx(x = 0, 0.5) alloys is presented. The calculations are performed by the plane-wave pseudopotential method in the framework of the density functional theory with the generalized gradient approximation. This paper calculates the lattice parameters, density of states, charge density, and heats of formation. The results show that the electronic structure and stability of B2 Ti1-xNiHfx change gradually with Hf content. However, Hf content has little effect on the electronic structure and stability of B19′ Ti1-xNiHfx. The mechanism of the effect of Hf content on martensitic transformation temperature of TiNiHf alloys is studied from the electronic structure.展开更多
Internal friction (IF) spectra during reverse martensitic transformation from 35 to 135°C at different temperature rates of 0.5,0.75,and 1°C/min for Ti50Ni27Cu23 shape memory alloy (SMA) samples were mea...Internal friction (IF) spectra during reverse martensitic transformation from 35 to 135°C at different temperature rates of 0.5,0.75,and 1°C/min for Ti50Ni27Cu23 shape memory alloy (SMA) samples were measured with a dynamic mechanical analyzer,respectively.The IF spectra were characterized by IF peak increasing progressively and peak shifting toward high temperature with an increase in temperature rate.An iterative approach was used to calculate the precise intrinsic and approximate transitory IF contributions to the normal IF spectrum.The quantitatively analyzed results indicate that the transitory IF of this alloy is nonlinearly dependent on the temperature rate and obeys a power law with a power coefficient of 0.55.The predicted and experimental IF spectra at different temperature rates of 0.75 and 1°C/min agree well with each other,respectively.展开更多
In order to study the relation between martensitic transformation temperature range AT (where AT is the difference between martensitic transformation start and finish temperature) and lattice distortion ratio (c/a...In order to study the relation between martensitic transformation temperature range AT (where AT is the difference between martensitic transformation start and finish temperature) and lattice distortion ratio (c/a) of martensitic transforma~ tion, a series of Ni46Mnz8_xGa22Co4Cux (x = 2-5) Heusler alloys is prepared by arc melting method. The vibration sample magnetometer (VSM) experiment results show that AT increases when x 〉 4 and decreases when x 〈 4 with x increasing, and the minimal AT (about 1 K) is found at x = 4. Ambient X-ray diffraction (XRD) results show that AT is proportional to c/a for non-modulated Ni46Mn28_xGa22Co4Cux (x = 2-5) martensites. The relation between AT and c/a is in agreement with the analysis result obtained from crystal lattice mismatch model. About 1000-ppm strain is found for the sample at x = 4 when heating temperature increases from 323 K to 324 K. These properties, which allow a modulation of AT and temperature-induced strain during martensitic transformation, suggest Ni46Mn24Ga22Co4Cu4 can be a promising actuator and sensor.展开更多
The effect of Fe on the martensitic transformation of TaRu high-temperature shape memory alloys has been investigated using first-principles calculations.The site preference of Fe in TaRu alloys has been clarified for...The effect of Fe on the martensitic transformation of TaRu high-temperature shape memory alloys has been investigated using first-principles calculations.The site preference of Fe in TaRu alloys has been clarified for the first time,and the results show that Fe is predicted to occupy Ru sites.The addition of Fe increases the stability of the Ta 50 Ru 50 x Fe x β phase,leading to a significant decrease in the β to β ' martensitic transformation temperature.In addition,the mechanism of the Fe alloying effect is explained on the basis of the electronic structure.展开更多
This paper investigates the effects of substitution of Si for Ga on the martensitic transformation behaviours in Ni-Fe-Ga alloys by using optical metallographic microscope and differential scanning calorimetry (DSC)...This paper investigates the effects of substitution of Si for Ga on the martensitic transformation behaviours in Ni-Fe-Ga alloys by using optical metallographic microscope and differential scanning calorimetry (DSC) methods. The structure type of Ni55.5Fe18Ga26.5-xSix alloys is determined by x-ray diffraction (XRD), and the XRD patterns show the microstructure of Ni-Fe-Ga-Si alloys transformed from body-centred tetragonal martensite (with Si content x = 0) to body-centred cubic austenite (with x = 2) at room temperature. The martensitic transformation temperatures of the Ni55.sFelsGa26.5-xSi~ alloys decrease almost linearly with increasing Si content in the Si content range of x _~ 3. Thermal treatment also plays an important role on martensitic transformation temperatures in the Ni-Fe-Ga^Si alloy. The valence electronic concentrations, size factor, L21 degree of order and strength of parent phase influence the martensitic transformation temperatures of the Ni-Fe-Ga-Si alloys. An understanding of the relationship between martensitic transformation temperatures and Si content will be significant for designing an appropriate Ni-Fe-Ga-Si alloy for a specific application at a given temperature.展开更多
The martensitic transformation temperature is the basis for the application of shape memory alloys(SMAs),and the ability to quickly and accurately predict the transformation temperature of SMAs has very important prac...The martensitic transformation temperature is the basis for the application of shape memory alloys(SMAs),and the ability to quickly and accurately predict the transformation temperature of SMAs has very important practical significance.In this work,machine learning(ML)methods were utilized to accelerate the search for shape memory alloys with targeted properties(phase transition temperature).A group of component data was selected to design shape memory alloys using reverse design method from numerous unexplored data.Component modeling and feature modeling were used to predict the phase transition temperature of the shape memory alloys.The experimental results of the shape memory alloys were obtained to verify the effectiveness of the support vector regression(SVR)model.The results show that the machine learning model can obtain target materials more efficiently and pertinently,and realize the accurate and rapid design of shape memory alloys with specific target phase transition temperature.On this basis,the relationship between phase transition temperature and material descriptors is analyzed,and it is proved that the key factors affecting the phase transition temperature of shape memory alloys are based on the strength of the bond energy between atoms.This work provides new ideas for the controllable design and performance optimization of Cu-based shape memory alloys.展开更多
The reverse transformation temperature and recovery strain ratio of the martensite formed during the cooling process under a constant stress in TiNi shape memory alloy wires are studied in this paper. Results sh...The reverse transformation temperature and recovery strain ratio of the martensite formed during the cooling process under a constant stress in TiNi shape memory alloy wires are studied in this paper. Results show that a higher level of the applied constant stress during the cooling process will induce martensite with a higher reverse martensitic transformation start temperature As and a smaller recovery strain ratio. Similarly, a prestrain at the room temperature elevates the As temperature and decreases the recovery strain ratio. However, the As temperature and the recovery strain ratio of the martensite formed during the cooling process under a constant stress are lower than those of the martensite formed by prestrain at the room temperature.展开更多
The present research aimed to analyze the influence that different contents of titanium(x=0.5,0.6 and 0.7 wt.%)have on the martensitic transformation temperature of a Cu-14Al-4Ni(wt.%)SMA(shape memory alloy).The Cu-14...The present research aimed to analyze the influence that different contents of titanium(x=0.5,0.6 and 0.7 wt.%)have on the martensitic transformation temperature of a Cu-14Al-4Ni(wt.%)SMA(shape memory alloy).The Cu-14Al-4Ni-xTi samples were casted in an arc-melting furnace and rapidly solidified.All samples underwent heat treatment in a tubular furnace at a temperature of 1,100°C for 30 min and water quenched at 25°C.Subsequently,samples were analyzed by SEM(scanning electron microscopy)with EDS(energy dispersive spectroscopy),XRD(X-ray diffraction)and DSC(differential scanning calorimeter).SEM images and XRD patterns showed that the presence of titanium modified the alloy’s microstructure,induced the formation of three titanium rich phases called“X”phase(CuNi2Ti,Cu3Ti and AlCu2Ti)and reduced the presence of the brittle phaseγ2(Cu9Al4)for samples with 0.6 and 0.7 wt.%Ti.The titanium added to the copper based SMA also functioned as a refiner,reducing GS(grain size)up to approximately 80%with the increase of Ti content.DSC results exhibited low enthalpy levels,hysteresis,as well as low start martensitic transformation temperatures.展开更多
A reversible martensitic transformation (MT) takes place during cooling and heating in the solution quenched and the solution quenched plus aged Ni59AlHMn30 alloy The MT temperature increases with increasing solution ...A reversible martensitic transformation (MT) takes place during cooling and heating in the solution quenched and the solution quenched plus aged Ni59AlHMn30 alloy The MT temperature increases with increasing solution temperature. The excellent MT characteristics can be obtained from a process of lOOCTC solution quenched plus 400 °C aged. Follow this process, the MT start temperature (Ms) and the reverse MT finish temperature (Af) are 469*C and 548"C, respectively. The martensitic stabilization effect in the solution quenched and aged Ni59AlnMn3o alloy is observed as an increase in the Af temperature of the first reverse MT during thermal cycles. This stabilization effect vanishes from the second thermal cycle. Thermal cycling can enhance the stability of the reversible MT. The microstructure of the quenched NisgAlnMnjo alloy consists of martensite (M) and gamma phase. The volume fraction of gamma phase is about 40%. The substructure of M and gamma phase is twins and dislocations, respectively. The hardness of M is higher than that of gamma phase. After aging treatment the basic phases of alloy do not change, but the hardness of the phases increases.展开更多
The martensitic transformation,mechanical,and magnetic properties of the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) (x=0.125,0.25,0.375,0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5)[(x=0.125,y=0.125,0.25,0.375,0.5) and (x=0.125...The martensitic transformation,mechanical,and magnetic properties of the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) (x=0.125,0.25,0.375,0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5)[(x=0.125,y=0.125,0.25,0.375,0.5) and (x=0.125,0.25,0.375,y=0.625)]alloys were systematically studied by the first-principles calculations.For the formation energy,the martensite is smaller than the austenite,the Ni–(Co)–Mn–Cu–Ti alloys studied in this work can undergo martensitic transformation.The austenite and non-modulated (NM) martensite always present antiferromagnetic state in the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) (y<0.625) alloys.When y=0.625 in the Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) series,the austenite presents ferromagnetic state while the NM martensite shows antiferromagnetic state.Cu doping can decrease the thermal hysteresis and anisotropy of the Ni–(Co)–Mn–Ti alloy.Increasing Mn and decreasing Ti content can improve the shear resistance and normal stress resistance,but reduce the toughness in the Ni–Mn–Cu–Ti alloy.And the ductility of the Co–Cu co-doping alloy is inferior to that of the Ni–Mn–Cu–Ti and Ni–Co–Mn–Ti alloys.The electronic density of states was studied to reveal the essence of the mechanical and magnetic properties.展开更多
The microstructure, martensitic transformation behavior, mechanical properties and shape memory effect of Ni54Mn25Ga15Al6 high-temperature shape memory alloy were investigated. By comparing with the Ni54Mn25Ga21 alloy...The microstructure, martensitic transformation behavior, mechanical properties and shape memory effect of Ni54Mn25Ga15Al6 high-temperature shape memory alloy were investigated. By comparing with the Ni54Mn25Ga21 alloy, the effect of Al addition on the properties of Ni-Mn-Ga alloys was analyzed. The results show that the Ni54Mn25Ga15Al6 alloy has a single-phase tetragonal non-modulated martensite structure with lamellar twins. The martensitic transformation start temperature of this alloy is up to 190 ℃, displaying the promising application as a high-temperature shape memory alloy. Al addition in Ni-Mn-Ga alloy can decrease the martensitic transformation temperatures due to the effect of size factor and improve the strength and plasticity. However, the shape memory effect is reduced remarkably with the Al addition.展开更多
The martensite transformation induced by tensile elongation and its effect onthe behavior of phase electrochemistry of AISI 304 and 316L in 3.5% NaCl solution were studied. Theresults show that the content of α′-mar...The martensite transformation induced by tensile elongation and its effect onthe behavior of phase electrochemistry of AISI 304 and 316L in 3.5% NaCl solution were studied. Theresults show that the content of α′-martensite in stainless steel 304 increases with the truestrain. As α′-martensite content increased, free corrosion potential and pitting potential ofstainless steel 304 in 3.5% NaCl solution appeared the change trend of a minimum. It was also foundthat pitting nucleated preferentially at the phase interfaces between martensite and austenite.There existed apparent difference between electrochemical properties of austenite and of martensitefor stainless steel 304 and 316L in 3.5% NaCl solution.展开更多
Complicated changns occur inside the steel parts during quenching process. The abruptly changed boundary conditions make the temperature field,micro - structure and stress field change dramatically in very short ti...Complicated changns occur inside the steel parts during quenching process. The abruptly changed boundary conditions make the temperature field,micro - structure and stress field change dramatically in very short time, and these variables take a contact interactions in the whole process. In this paper, a three dimensional non - linear mathematical model for queeching process has been founded and the numerical simulation on temperature field,microstructre and stress field has been realized.In the FEM analysis, the incremental iteration method is used to deal with such complicated nonlinear as boundary nonlinear, physical property nonlinear,transformation nonlinear etc.The effect of stress on transformation kinetics has been considered in the calculation of microstructure. In the stress field anal- ysis,a thermo- elasto - plastic model has been founded, which considers such factors as transforma- tion strain,transformation plastic strain, themal strain and the effect of temperature and transforma- tion on mechanical propertier etc. The transient temperature field, microstructure distribution and stress field of the roller on any time can be displayed vividly,and the cooling curve and the changes of stress on any position can also be given.展开更多
The effects of thermomechanical cycling on the shape memory behavior and transformation temperatures of a Ni50.2Ti49.8 alloy under a constant applied stress of 300 MPa were investigated, k is believed that thermomecha...The effects of thermomechanical cycling on the shape memory behavior and transformation temperatures of a Ni50.2Ti49.8 alloy under a constant applied stress of 300 MPa were investigated, k is believed that thermomechanical cycling induces defects such as dislocations, which evidently affect the shape memory behavior and transformation temperatures. The recovery strain decreases with increasing number of thermomechanical cycles, whereas the irreversible plastic strain increases, especially in the initial few cycles. The stored elastic strain energy has an important influence on transformation temperatures, the A5^σ decreases and the M5^σ increases with increasing number of thermomechanical cycles. The recovery strain, irreversible plastic strain, A5^σ , and M5^σ reach a saturation value after several cycles.展开更多
A three-dimensional transient heat transfer model for laser transformation hardening process has been developed in this paper. The finite size of the laser treated sample, the surface heat loss of the sample, the lat...A three-dimensional transient heat transfer model for laser transformation hardening process has been developed in this paper. The finite size of the laser treated sample, the surface heat loss of the sample, the latent heat of phase transformation and the temperature dependence of thermal properties of materials were considered. The heat source was considered as a moving Gaussian heat flux with a constant velocity. Three-dimension unequally spatial grid explicit finite difference equations, alternating direction implicit finite difference equations and implicit finite difference equations were deduced respectively. Three programs to calculate the temperature field were developed using Fortran language. The transient temperature fields of C22, 42CrMo, C60 steel samples during laser transformation hardening process were calculated using these programs, and the widths and depths of laser transformation hardening zones were also predicted. C22, 42CrMo, C60 steel samples were treated by CO_2 laser,the widths and depths of laser transformation hardening zones of these samples were also measured experimentally. The calculated widths and depths of laser transformation hardening zones are in good agreement with the experimental results.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No.11974184)。
文摘The thermal-elastic martensitic transformation from high-temperature Ni_(2)In-type hexagonal structure to low-temperature TiNiSi-type orthorhombic structure has been widely studied in MnMX(M=Ni or Co,and X=Ge or Si)alloys.However,the answer to how the orthorhombic martensite nucleates and grows within the hexagonal parent is still unclear.In this work,the hexagonal-orthorhombic martensitic transformation in a Co and Ge co-substituted MnNiSi is investigated.One can find some orthorhombic laths embedded in the hexagonal parent at a temperature above the martensitic transformation start temperature(M_(s)).With the the sample cooing to M_(s),the laths turn broader,indicating that the martensitic transformation starts from these pre-existing orthorhombic laths.Microstructure observation suggests that these pre-existing orthorhombic laths do not originate from the hexagonal-orthorhombic martensitic transformation because of the difference between atomic occupations of doping elements in the hexagonal parent and those in the preexisting orthorhombic laths.The phenomenological crystallographic theory and experimental investigations prove that the pre-existing orthorhombic lath and generated orthorhombic martensite have the same crystallography relationship to the hexagonal parent.Therefore,the orthorhombic martensite can take these pre-existing laths as embryos and grow up.This work implies that the martensitic transformation in MnNiSi_(1-x)(CoNiGe)_(x) alloy is initiated by orthorhombic embryos.
基金financially supported by the National Natural Science Foundation of China(No.U2102212)the Shanghai Rising-Star Program(No.21QA1403200)。
文摘Controlling the content of athermal martensite and retained austenite is important to improving the mechanical properties of high-strength steels,but a mechanism for the accurate description of martensitic transformation during the cooling process must be addressed.At present,frequently used semi-empirical kinetics models suffer from huge errors at the beginning of transformation,and most of them fail to exhibit the sigmoidal shape characteristic of transformation curves.To describe the martensitic transformation process accurately,based on the Magee model,we introduced the changes in the nucleation activation energy of martensite with temperature,which led to the varying nucleation rates of this model during martensitic transformation.According to the calculation results,the relative error of the modified model for the martensitic transformation kinetics curves of Fe-C-X(X = Ni,Cr,Mn,Si) alloys reached 9.5% compared with those measured via the thermal expansion method.The relative error was approximately reduced by two-thirds compared with that of the Magee model.The incorporation of nucleation activation energy into the kinetics model contributes to the improvement of its precision.
文摘Transformation induced plasticity (TRIP) and twinning induced plasticity (TWlP) effects had been widely studied in single austenite steel. But in duplex γ & α(δ) phase, such as welding materials of stainless steel, they had been less studied. Tensile shear loading experiment of resistance spot welding specimens prepared with 2 mm 301L sheets, was carried out at 15℃ and -50℃. Optical microscopy and scanning electron microscopy (SEM) as well as X-ray diffraction (XRD) were used to investigate the microstructure of weld nugget, and specimens fracture surface. The results showed that the initial weld nugget was composed of 8.4% α(δ) ferrite and 91.6% austenite. Tensile shear load bearing capacity of spot welding specimen at -50℃ was 24.8 kN, 17.7% higher than that at 15℃. About 78.5 vol. pct. martensite transformation was induced by plastic deformation at -50℃, while about 67.9 vol. pct transformation induced at 15℃. The plasticity of spot welding joint decreased with the decline of experimental temperature.
文摘A method of fuzzy identification based on T-S fuzzy model was proposed for predicting temperature Ms from chemical composition, austenitizing temperature and time for low alloy steel. The degree of membership of each sample was calculated with fuzzy clustering algorithm. Kalman filtering was used to identify the consequent parameters. Compared with the results obtained by empirical models based on the same data, the results by the fuzzy method showed good precision. The accuracy of the fuzzy model is almost 6 times higher than that of the best empirical model. The influence of alloying elements, austenitizing temperature and time on Ms was analyzed quantitatively by using the fuzzy model. It is shown that there exists a nonlinear relationship between the contents of alloying elements in steels and their Ms, and the effects of austenitizing temperature and time on Ms temperature cannot be neglected.
基金Project(51001035)supported by the National Natural Science Foundation of ChinaProject(LBH-Q14035)supported by the Postdoctoral Funds for Scientific Research Initiation of Heilongjiang Province,ChinaProject(HEUCF20151002)supported by the Fundamental Research Funds for the Central Universities,China
文摘The effect of annealing temperature on the martensitic transformation of a Ti49.2Ni50.8 alloy processed by equal channel angular pressing (ECAP) was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The as-ECAP processed and subsequently annealed Ti49.2Ni50.8 alloys consist of B2 parent phase, Ti4Ni2O phase and B19′ martensite at room temperature. Upon cooling, all samples show B2→R→B19′ two-stage transformation. Upon heating, when the annealing temperature is less than 400℃, the samples show B19′→R→B2 two-stage transformation; when the annealing temperature is higher than 500 ℃, the samples show B19′→B2 single-stage transformation. The B2-R transformation is characterized by wide interval due to the dislocations introduced during ECAP.
基金Project supported by the National Natural Science Foundation of China (Grant No 50471018).
文摘In this paper a first-principles study of the electronic structure and stability of B2 Ti1-xNiHfx (x = 0.2, 0.4, 0.6) and B19′ Ti1-xNiHfx(x = 0, 0.5) alloys is presented. The calculations are performed by the plane-wave pseudopotential method in the framework of the density functional theory with the generalized gradient approximation. This paper calculates the lattice parameters, density of states, charge density, and heats of formation. The results show that the electronic structure and stability of B2 Ti1-xNiHfx change gradually with Hf content. However, Hf content has little effect on the electronic structure and stability of B19′ Ti1-xNiHfx. The mechanism of the effect of Hf content on martensitic transformation temperature of TiNiHf alloys is studied from the electronic structure.
文摘Internal friction (IF) spectra during reverse martensitic transformation from 35 to 135°C at different temperature rates of 0.5,0.75,and 1°C/min for Ti50Ni27Cu23 shape memory alloy (SMA) samples were measured with a dynamic mechanical analyzer,respectively.The IF spectra were characterized by IF peak increasing progressively and peak shifting toward high temperature with an increase in temperature rate.An iterative approach was used to calculate the precise intrinsic and approximate transitory IF contributions to the normal IF spectrum.The quantitatively analyzed results indicate that the transitory IF of this alloy is nonlinearly dependent on the temperature rate and obeys a power law with a power coefficient of 0.55.The predicted and experimental IF spectra at different temperature rates of 0.75 and 1°C/min agree well with each other,respectively.
基金Project supported by the National Key Project of Fundamental Research of China(Grant No.2012CB932304)the National Natural Science Foundation of China(Grant No.U1232210)
文摘In order to study the relation between martensitic transformation temperature range AT (where AT is the difference between martensitic transformation start and finish temperature) and lattice distortion ratio (c/a) of martensitic transforma~ tion, a series of Ni46Mnz8_xGa22Co4Cux (x = 2-5) Heusler alloys is prepared by arc melting method. The vibration sample magnetometer (VSM) experiment results show that AT increases when x 〉 4 and decreases when x 〈 4 with x increasing, and the minimal AT (about 1 K) is found at x = 4. Ambient X-ray diffraction (XRD) results show that AT is proportional to c/a for non-modulated Ni46Mn28_xGa22Co4Cux (x = 2-5) martensites. The relation between AT and c/a is in agreement with the analysis result obtained from crystal lattice mismatch model. About 1000-ppm strain is found for the sample at x = 4 when heating temperature increases from 323 K to 324 K. These properties, which allow a modulation of AT and temperature-induced strain during martensitic transformation, suggest Ni46Mn24Ga22Co4Cu4 can be a promising actuator and sensor.
基金Project supported by the National Natural Science Foundation of China (Grant No. 50901026)the China Postdoctoral Science Foundation (Grant Nos. 20100471084 and 201104418)
文摘The effect of Fe on the martensitic transformation of TaRu high-temperature shape memory alloys has been investigated using first-principles calculations.The site preference of Fe in TaRu alloys has been clarified for the first time,and the results show that Fe is predicted to occupy Ru sites.The addition of Fe increases the stability of the Ta 50 Ru 50 x Fe x β phase,leading to a significant decrease in the β to β ' martensitic transformation temperature.In addition,the mechanism of the Fe alloying effect is explained on the basis of the electronic structure.
基金supported by the National Natural Science Foundation of China (Grant No. 10976007)the Fundamental Research Funds for the Central Universities (Grant Nos. ZYGX2009J046 and ZYGX2009X007)Royal Academy of Engineering-Research Exchanges with China and India Awards in UK
文摘This paper investigates the effects of substitution of Si for Ga on the martensitic transformation behaviours in Ni-Fe-Ga alloys by using optical metallographic microscope and differential scanning calorimetry (DSC) methods. The structure type of Ni55.5Fe18Ga26.5-xSix alloys is determined by x-ray diffraction (XRD), and the XRD patterns show the microstructure of Ni-Fe-Ga-Si alloys transformed from body-centred tetragonal martensite (with Si content x = 0) to body-centred cubic austenite (with x = 2) at room temperature. The martensitic transformation temperatures of the Ni55.sFelsGa26.5-xSi~ alloys decrease almost linearly with increasing Si content in the Si content range of x _~ 3. Thermal treatment also plays an important role on martensitic transformation temperatures in the Ni-Fe-Ga^Si alloy. The valence electronic concentrations, size factor, L21 degree of order and strength of parent phase influence the martensitic transformation temperatures of the Ni-Fe-Ga-Si alloys. An understanding of the relationship between martensitic transformation temperatures and Si content will be significant for designing an appropriate Ni-Fe-Ga-Si alloy for a specific application at a given temperature.
基金financially supported by the National Natural Science Foundation of China(No.51974028)。
文摘The martensitic transformation temperature is the basis for the application of shape memory alloys(SMAs),and the ability to quickly and accurately predict the transformation temperature of SMAs has very important practical significance.In this work,machine learning(ML)methods were utilized to accelerate the search for shape memory alloys with targeted properties(phase transition temperature).A group of component data was selected to design shape memory alloys using reverse design method from numerous unexplored data.Component modeling and feature modeling were used to predict the phase transition temperature of the shape memory alloys.The experimental results of the shape memory alloys were obtained to verify the effectiveness of the support vector regression(SVR)model.The results show that the machine learning model can obtain target materials more efficiently and pertinently,and realize the accurate and rapid design of shape memory alloys with specific target phase transition temperature.On this basis,the relationship between phase transition temperature and material descriptors is analyzed,and it is proved that the key factors affecting the phase transition temperature of shape memory alloys are based on the strength of the bond energy between atoms.This work provides new ideas for the controllable design and performance optimization of Cu-based shape memory alloys.
基金supported by the National Natural Science Foundation of the People’s Republic of China under grant No.50071037.
文摘The reverse transformation temperature and recovery strain ratio of the martensite formed during the cooling process under a constant stress in TiNi shape memory alloy wires are studied in this paper. Results show that a higher level of the applied constant stress during the cooling process will induce martensite with a higher reverse martensitic transformation start temperature As and a smaller recovery strain ratio. Similarly, a prestrain at the room temperature elevates the As temperature and decreases the recovery strain ratio. However, the As temperature and the recovery strain ratio of the martensite formed during the cooling process under a constant stress are lower than those of the martensite formed by prestrain at the room temperature.
基金The authors would like to thank the Federal Institute of Science and Technology of Bahia,the University of São Paulo,the University of Brasilia and the PRPGI for all the support to carry out this research.
文摘The present research aimed to analyze the influence that different contents of titanium(x=0.5,0.6 and 0.7 wt.%)have on the martensitic transformation temperature of a Cu-14Al-4Ni(wt.%)SMA(shape memory alloy).The Cu-14Al-4Ni-xTi samples were casted in an arc-melting furnace and rapidly solidified.All samples underwent heat treatment in a tubular furnace at a temperature of 1,100°C for 30 min and water quenched at 25°C.Subsequently,samples were analyzed by SEM(scanning electron microscopy)with EDS(energy dispersive spectroscopy),XRD(X-ray diffraction)and DSC(differential scanning calorimeter).SEM images and XRD patterns showed that the presence of titanium modified the alloy’s microstructure,induced the formation of three titanium rich phases called“X”phase(CuNi2Ti,Cu3Ti and AlCu2Ti)and reduced the presence of the brittle phaseγ2(Cu9Al4)for samples with 0.6 and 0.7 wt.%Ti.The titanium added to the copper based SMA also functioned as a refiner,reducing GS(grain size)up to approximately 80%with the increase of Ti content.DSC results exhibited low enthalpy levels,hysteresis,as well as low start martensitic transformation temperatures.
基金supported by the Science Foundation of Shaanxi University of Technology(No.SLG0332).
文摘A reversible martensitic transformation (MT) takes place during cooling and heating in the solution quenched and the solution quenched plus aged Ni59AlHMn30 alloy The MT temperature increases with increasing solution temperature. The excellent MT characteristics can be obtained from a process of lOOCTC solution quenched plus 400 °C aged. Follow this process, the MT start temperature (Ms) and the reverse MT finish temperature (Af) are 469*C and 548"C, respectively. The martensitic stabilization effect in the solution quenched and aged Ni59AlnMn3o alloy is observed as an increase in the Af temperature of the first reverse MT during thermal cycles. This stabilization effect vanishes from the second thermal cycle. Thermal cycling can enhance the stability of the reversible MT. The microstructure of the quenched NisgAlnMnjo alloy consists of martensite (M) and gamma phase. The volume fraction of gamma phase is about 40%. The substructure of M and gamma phase is twins and dislocations, respectively. The hardness of M is higher than that of gamma phase. After aging treatment the basic phases of alloy do not change, but the hardness of the phases increases.
基金financially supported by the National Natural Science Foundation of China(No.51771044)the Natural Science Foundation of Hebei Province(No.E2019501061)+3 种基金the Performance subsidy fund for Key Laboratory of Dielectric and Electrolyte Functional Material Hebei Province(No.22567627H)the Fundamental Research Funds for the Central Universities(No.N2223025)the State Key Lab of Advanced Metals and Materials(No.2022-Z02)Programme of Introducing Talents of Discipline Innovation to Universities 2.0(the 111 Project of China 2.0,No.BP0719037)。
文摘The martensitic transformation,mechanical,and magnetic properties of the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) (x=0.125,0.25,0.375,0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5)[(x=0.125,y=0.125,0.25,0.375,0.5) and (x=0.125,0.25,0.375,y=0.625)]alloys were systematically studied by the first-principles calculations.For the formation energy,the martensite is smaller than the austenite,the Ni–(Co)–Mn–Cu–Ti alloys studied in this work can undergo martensitic transformation.The austenite and non-modulated (NM) martensite always present antiferromagnetic state in the Ni_(2)Mn_(1.5-x)Cu_(x)Ti_(0.5) and Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) (y<0.625) alloys.When y=0.625 in the Ni_(2-y)Co_(y)Mn_(1.5-x)Cu_(x)Ti_(0.5) series,the austenite presents ferromagnetic state while the NM martensite shows antiferromagnetic state.Cu doping can decrease the thermal hysteresis and anisotropy of the Ni–(Co)–Mn–Ti alloy.Increasing Mn and decreasing Ti content can improve the shear resistance and normal stress resistance,but reduce the toughness in the Ni–Mn–Cu–Ti alloy.And the ductility of the Co–Cu co-doping alloy is inferior to that of the Ni–Mn–Cu–Ti and Ni–Co–Mn–Ti alloys.The electronic density of states was studied to reveal the essence of the mechanical and magnetic properties.
基金Project(51101057)supported by the National Natural Science Foundation of ChinaProject(12MS10)supported by the Fundamental Research Funds for the Central Universities of China
文摘The microstructure, martensitic transformation behavior, mechanical properties and shape memory effect of Ni54Mn25Ga15Al6 high-temperature shape memory alloy were investigated. By comparing with the Ni54Mn25Ga21 alloy, the effect of Al addition on the properties of Ni-Mn-Ga alloys was analyzed. The results show that the Ni54Mn25Ga15Al6 alloy has a single-phase tetragonal non-modulated martensite structure with lamellar twins. The martensitic transformation start temperature of this alloy is up to 190 ℃, displaying the promising application as a high-temperature shape memory alloy. Al addition in Ni-Mn-Ga alloy can decrease the martensitic transformation temperatures due to the effect of size factor and improve the strength and plasticity. However, the shape memory effect is reduced remarkably with the Al addition.
文摘The martensite transformation induced by tensile elongation and its effect onthe behavior of phase electrochemistry of AISI 304 and 316L in 3.5% NaCl solution were studied. Theresults show that the content of α′-martensite in stainless steel 304 increases with the truestrain. As α′-martensite content increased, free corrosion potential and pitting potential ofstainless steel 304 in 3.5% NaCl solution appeared the change trend of a minimum. It was also foundthat pitting nucleated preferentially at the phase interfaces between martensite and austenite.There existed apparent difference between electrochemical properties of austenite and of martensitefor stainless steel 304 and 316L in 3.5% NaCl solution.
文摘Complicated changns occur inside the steel parts during quenching process. The abruptly changed boundary conditions make the temperature field,micro - structure and stress field change dramatically in very short time, and these variables take a contact interactions in the whole process. In this paper, a three dimensional non - linear mathematical model for queeching process has been founded and the numerical simulation on temperature field,microstructre and stress field has been realized.In the FEM analysis, the incremental iteration method is used to deal with such complicated nonlinear as boundary nonlinear, physical property nonlinear,transformation nonlinear etc.The effect of stress on transformation kinetics has been considered in the calculation of microstructure. In the stress field anal- ysis,a thermo- elasto - plastic model has been founded, which considers such factors as transforma- tion strain,transformation plastic strain, themal strain and the effect of temperature and transforma- tion on mechanical propertier etc. The transient temperature field, microstructure distribution and stress field of the roller on any time can be displayed vividly,and the cooling curve and the changes of stress on any position can also be given.
文摘The effects of thermomechanical cycling on the shape memory behavior and transformation temperatures of a Ni50.2Ti49.8 alloy under a constant applied stress of 300 MPa were investigated, k is believed that thermomechanical cycling induces defects such as dislocations, which evidently affect the shape memory behavior and transformation temperatures. The recovery strain decreases with increasing number of thermomechanical cycles, whereas the irreversible plastic strain increases, especially in the initial few cycles. The stored elastic strain energy has an important influence on transformation temperatures, the A5^σ decreases and the M5^σ increases with increasing number of thermomechanical cycles. The recovery strain, irreversible plastic strain, A5^σ , and M5^σ reach a saturation value after several cycles.
文摘A three-dimensional transient heat transfer model for laser transformation hardening process has been developed in this paper. The finite size of the laser treated sample, the surface heat loss of the sample, the latent heat of phase transformation and the temperature dependence of thermal properties of materials were considered. The heat source was considered as a moving Gaussian heat flux with a constant velocity. Three-dimension unequally spatial grid explicit finite difference equations, alternating direction implicit finite difference equations and implicit finite difference equations were deduced respectively. Three programs to calculate the temperature field were developed using Fortran language. The transient temperature fields of C22, 42CrMo, C60 steel samples during laser transformation hardening process were calculated using these programs, and the widths and depths of laser transformation hardening zones were also predicted. C22, 42CrMo, C60 steel samples were treated by CO_2 laser,the widths and depths of laser transformation hardening zones of these samples were also measured experimentally. The calculated widths and depths of laser transformation hardening zones are in good agreement with the experimental results.