Machine learning-assisted efficient design of Cu-based shape memory alloy with specific phase transition temperature

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.

Effects of thermomechanical cycling on the shape memory behavior and transformation temperatures of a Ni50.2Ti49.8 alloy

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.

Phase Transformation and Thermal Stability of Aged Ti-Ni-Hf High Temperature Shape Memory Alloys

The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys （SMAs） through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased more than 100 K by aging at 823 K for 2 h. Especially for the alloys with Ni-content of 50.4 at. pct and 50.6 at. pct, their martensitic transformation start temperatures （Ms） are more than 473 K after aging. TEM observation confirmed that some fine particles precipitate from the matrix during aging. The aged Ni-rich TiNiHf SMAs show the better thermal stability of phase transformation temperatures than the solutiontreated TiNiHf alloys. The fine particles precipitated during aging should be responsible for the increase of phase transformation temperatures and its high stability.

Effect of Training on Two-way Shape Memory Effect and Its Stability in a Ti-Ni-Hf High Temperature Shape Memory Alloy

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.

The Reverse Transformation Behavior of TiNi Shape Memory Alloy Wires Prestrained at Different Temperatures

The reverse transformation behavior of TiNi alloy wires prestrained at different temperatures is studied in this paper. Experimental results show that prestrain at different temperatures obviously affects the reverse transformation behavior of the TiNi alloy wire. A single peak appears on the DSC curves of wires prestrained at 253-313K (in the martensite state). However deformed at 333K, three consecutive peaks appear on the DSC curves of wires with a smaller prestrain and a single peak appears on the DSC curves of the wires with a larger prestrain. The recovery strain ratio of the wires prestrained at 253-313K are very similar. However, the ratio of the wire predeformed at 333K is obviously smaller than that of the wire prestrained in the martensite state.

Martensite Aging Effect and Thermal Cyclic Characteristics in Ti-Pd and Ti-Pd-Ni High Temperature Shape Memory Alloys

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.

Factors Affecting Transformation Temperatures in Fe-Mn-Si-Cr-Ni Shape Memory Alloy

The effects of prestrain and annealing temperature on phase transformation temperatures in Fel4Mn5Si8Cr4Ni shape memory alloy have been studied. The results showed that when the annealing temperature was 673 K, both the At and the Ms temperatures increased appreciably as the prestrain increased, the As temperature increased slightly with increasing prestrain; the resistivity difference at 303 K between the heating and cooling curve also increased with increasing prestrain, which agreed with the recovery strain. The shape memory effect in Fe-Mn-Si-Cr-Ni shape memory alloy is caused by the stress-induced γ→ε martensite transformation and its reverse transformation. When the prestrain was 10%, the Ms temperature decreased remarkably as the annealing temperature increased.

High temperature strain glass in Ti–Au and Ti–Pt based shape memory alloys

Strain glass is a frozen short-range strain ordered state found in shape memory alloys recently, which exhibits novel properties around the ideal glass transition temperature T_(0). However, the T_(0) of current strain glass systems is still very low, limiting their potential applications and experimental studies. In this paper, we reported two new strain glass systems with relatively high T_(0). In Ti_(50)Au_(50-x)Cr_(x) alloys, the strain glass appears at x = 25, and exhibits a T_(0) of 251 K, while in Ti_(50)Pt_(50-y)Fey alloys, the strain glass takes place at y = 30, and shows a T_(0) of 272 K. Both of them are comparable with the highest T_(0) value reported so far. Moreover, the phase diagrams of main strain glass systems in Ti-based alloys were summarized. It is found that the influence of the martensitic transformation temperature of the host alloy on the T_(0) of the strain glass is limited. This work may help to design new strain glass systems with higher T_(0) above ambient temperature.

Thermal stability and high-temperature shape memory characteristics of Ti-20Zr-10Ta alloy

The microstructure, martensite transformation behavior, thermal stability and shape memory behavior of Ti–20Zr– 10Ta high temperature shape memory alloy were investigated. The Ti–20Zr–10Ta alloy exhibited a reversible transformation with the high martensite transformation temperature of 500oC and good thermal stability. The alloy displayed the elongation of 15% and a maximum recovery stain of 5.5% with 8% pre-strain.

LOW VELOCITY RESPONSE CHARACTERISTICS OF COMPOSITE PLATE WITH EMBEDDED SHAPE MEMORY ALLOY

This paper analyzes the characteristics of utilizing shape memory e?ect (SME) of shape memory alloy (SMA) in improving the low velocity impact resistance performance of com- posite plate by using ?nite element method. The constitutive relation for SMA hybrid composite plates is presented. The analytic model of ?nite element for SMA composite plate subjected to low velocity impact is established. The modi?ed Hertz’s contact law is used to determine the impact contact force. The computing procedures for solving the ?nite element equation using Newmark direct integration method are given. The numerical modelling results show that the SMA can e?ectively improve the low velocity impact resistance performance of composite plate.

STUDY ON THE RESPONSE TO LOW-VELOCITY IMPACT OF A COMPOSITE PLATE IMPROVED BY SHAPE MEMORY ALLOY

Improvement from the pseudo-elastic effect of shape memory alloy （SMA） on the low-velocity impact （LVI） resistance of a composite plate is investigated by the finite element method （FEM）. The stiffness matrix of the dynamic finite element equation is established step by step and the martensite fraction is obtained at each time step. The direct Newmark integration method is employed in solving the dynamic finite element equation, while the impact contact force is determined using the modified Hertz＇s law. It is found that SMA can effectively improve the performance of a composite structure subjected to low-velocity impact. Numerical results show that the deflection of a SMA-hybrid composite plate has been reduced approximately by thirty percent when the volume fraction of the embedded SMA reaches 0.3.

Microstructure and high-temperature shape-memory effect in Ni_(54)Mn_(25)Ga_(21) alloy

Ni54Mn25Ga21 alloy was prepared to investigate the microstructure, martensitic transformation and high-temperature shape-memory effect. Ni54Mn25Ga21 alloy exhibits single phase of non-modulated martensite with tetragonal structure at room temperature. Its martensitic start temperature Ms, martensitic finish temperature Mf on cooling, and austenitic start temperature As, austenitic finish temperature Af on heating are 260.2, 237.8, 262.5 and 287.8 ℃, respectively. The compressive strength and strain of Ni54Mn25Ga21 single crystal were measured to be 845 MPa and 20.5%, respectively, with compressive axis along the growth direction of the rods. An excellent shape-memory strain of 6.1%, which is the best performance among high-temperature shape-memory alloys up to the present, is obtained when prestrained to 8%.

HYSTERESIS OF PHASE TRANSFORMATION TEMPERATURE IN NiTi SHAPE MEMORY ALLOY

The relationship between structure and hysteresis of phase transformation temperature in NiTi shape memory alloy has been investigated by means of TEM observation,positron an- nihilation and electrical resistivity measurement.The sequence of hysteresis for the alloy aged under different regimes was found to be:plate martensite>R-phase>tie-like martensite. The reversible displaeement of phase boundaries of these transformations is blocked by the co- herent stress field around Ti_(11)Ni_(14)phase particles.A linear relationship between S paramet- er of positron annihilation and maximum values of temperature hysteresis showed that the mismatch dislocation and elastic stress field established by Ti_(11)Ni_(14)phase precipitation are the main factor to determine the temperature hysteresis of phase transformation in NiTi shape memory alloy.

Influence of cooling rate on phase transformation and microstructure of Ti-50.9%Ni shape memory alloy

Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence of cooling rate on transformation behavior and microstructures of NiTi shape memory alloy. The experimental results show that three-stage phase transformation can be induced at a very low cooling rate such as cooling in furnace. The cooling rate also has a great influence on the phase transformation temperatures. Both martensitic start transformation temperature （Ms） and martensitic finish transformation temperature （Mf） decrease with the decrease of the cooling rate, and decreasing the cooling rate contributes to enhancing the M→A austenite transformation temperature. The phase transformation hysteresis （Af-Mf） increases with the decrease of the cooling rate. Heat treatment is unable to eliminate the textures formed in hot working of NiTi sample, but can weaken the intensity of them. The cooling rate has little influence on the grain size.

Temperature Dependent Work-hardening Behaviour in an Fe-Mn-Si-Cr-Ni Shape Memory Alloy

The work-hardening behaviour in an Fe-Mn-Si-Cr-Ni alloy has been investigated using tensile test at different temperatures and TEM observation. It was found that besides the intersection of εmartensite, the intersections of ε martensite with stacking fault and the cross-slip of dislocation which is difficult to occur in the alloy with low stacking fault energy are also important factors to the temperature dependent work-hardening behaviour.

Two-way shape memory effect and its stability in Ti-Ni-Hf high temperature shape memory alloy

The two-way shape memory effect（TWSME） in a Ti36Ni49Hf15 high temperature shape memory alloy（SMA） was systematically studied by bending tests. In the TiNiHf alloy, the martensite deformation is an effective method to get two-way shape memory effect even with a small deformation strain. The results indicate that the internal stress field formed by the bending deformation is in the direction of the preferentially oriented martensite variants formed during the bending deformation. Upon cooling the preferentially oriented martensite variants form under such an oriented stress field, which should be responsible for the generation of the two-way shape memory effect. Proper training process benefits the formation of the oriented stress field, resulting in the improvement of the two-way shape memory effect. A maximum TWSME of 0.88% is obtained in the present alloy.

DSC study on temperature memory effect of NiTi shape memory alloy

A systematic study on the temperature memory effect (TME) in a polycrystalline NiTi shape memory alloy was presented. The investigation was carried out through a series of differential scanning calorimeter (DSC) tests. Two types of tests were conducted, namely single-step test and multi-step test. The influence of the step temperature on the peak/trough temperatures in the subsequent heating process and the associated energy absorption/release in the phase transformations was investigated. Using a simple theoretical model, the exact mechanism behind TME was studied.

Transformation behavior and shape memory effect of Ti_(50-x)Ni_(48)Fe_2Nb_x alloys by aging treatment

The influence of aging treatment on transformation behavior and shape memory of the Ti 50_x Ni_(48) Fe_2 Nb_x(x=0,0.6,0.8,1.0,and 1.2) alloys was investigated using differential scanning calorimeter(DSC),mechanical drawing machine,and microhardness tester in this paper.It is indicated that the aging treatment has a significant effect on the phase transformation temperatures(M_s,M_f,M_p,A_s,A_f,and A_p) and microhardness of the samples.The phase transformation temperatures are found to decrease initially with the increasing aging temperature from 300 to 500 ℃ and increase with further increase of the aging temperature.The aging treatment at intermediate temperature between 400 and 500 ℃ results in an improved shape memory effect.In addition,the highest microhardness value is also obtained.

PREPARATION OF TiNi SHAPE MEMORY ALLOY POROSINT BY SHS

TiNi shape memory alloy porosint, a promising artificial bone material, was prepared by self propagating high temperature synthesis method. It is found that the key technical parameter affecting the porosity, the shape and distribution of the bores in the synthesized product is the pre heating temperature of green compact. While the pre heating temperature varies between 523 K and 673 K, the TiNi shape memory alloy porosint with wholly homogeneously distributing bores will be gained. The porosity of the porosint is 70% when the pre heating temperature is near 673 K, which is maximal under different pre heating temperatures. The compressive strength of TiNi SMA porosint with a porosity of 70% manufactured by SHS is up to 100 MPa and the percentage recovered is 92%.

EFFECT OF γ-IRRADIATION ON CuZnAl SHAPE MEMORY ALLOY

Effect of γ-irradiation on the shape memory alloy CuZnAl has been studied by the techniques of TEM,positron annihilation etc..The martensitic transformation temperature of the alloy increases obviously ofter γ-irradiation at a dose of 2×10~7 Gy but not for a dose of 1× 10~7 Gy.The shape memory effect in both irradiated alloys remains unaffected.