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.

退火工艺对Ti-Ni-V形状记忆合金相变和形变行为的影响

利用差示扫描量热仪和拉伸试验研究了400℃×10~120 min和500℃×10~120 min退火态Ti-50.8Ni-0.5V合金的相变行为、拉伸性能和形状记忆行为。结果表明:随退火温度和时间变化,合金的相变类型、R相变温度T_(R)和热滞ΔT_(R)、马氏体相变温度T_(M)和热滞ΔT_(M)、抗拉强度R_(m)、伸长率A、应力诱发马氏体相变临界应力σ_(M)、加载-卸载残余应变ε_(R)和能耗W_(D)的变化规律如下:400和500℃退火态Ti-50.8Ni-0.5V合金皆发生B2→R→B19’/B19’→R→B2(B2-母相,CsCl型结构;R-R相,菱方结构;B19’-马氏体相,单斜结构)型相变;T_(R)^(400℃)>T_(R)^(500℃),T_(M)^(500℃)>T_(M)^(400℃),ΔT_(M)^(400℃)>ΔT_(M)^(500℃)≥ΔT_(R)^(400℃)≈ΔT_(R)^(500℃)≈4℃;R_(m)^(400℃)>R_(m)^(500℃),A^(500℃)>A^(400℃);400℃退火态合金的超弹性(SE)稳定性高于500℃退火态合金。随退火时间延长,T_(R)^(400℃)、T_(R)^(500℃)、T_(M)^(400℃)和T_(M)^(500℃)升高,ΔT_(M)^(400℃)和ΔT_(M)^(500℃)减小,ΔT_(R)^(400℃)和ΔT_(R)^(500℃)在3.5~4.6℃之间变化;400℃退火态合金保持SE,500℃退火态合金由SE向SE+SME(形状记忆效应)转变;σ_(M)^(400℃)和σ_(M)^(500℃)降低;W_(D)^(400℃)和W_(D)^(500℃)增加;ε_(R)^(500℃)先降后升;ε_(R)^(400℃)在0.64%~1.36%之间变化。要使Ti-50.8Ni-0.5V合金获得较高的T_(R),可对其进行400℃退火;要使该合金获得较高的T_(M),可对其进行500℃退火;要使该合金在室温下获得超弹性,可对其进行400℃×10~120 min或500℃×10~60 min退火。

Laser powder bed fusion additive manufacturing of NiTi shape memory alloys: a review

NiTi alloys have drawn significant attentions in biomedical and aerospace fields due to their unique shape memory effect(SME),superelasticity(SE),damping characteristics,high corrosion resistance,and good biocompatibility.Because of the unsatisfying processabilities and manufacturing requirements of complex NiTi components,additive manufacturing technology,especially laser powder bed fusion(LPBF),is appropriate for fabricating NiTi products.This paper comprehensively summarizes recent research on the NiTi alloys fabricated by LPBF,including printability,microstructural characteristics,phase transformation behaviors,lattice structures,and applications.Process parameters and microstructural features mainly influence the printability of LPBF-processed NiTi alloys.The phase transformation behaviors between austenite and martensite phases,phase transformation temperatures,and an overview of the influencing factors are summarized in this paper.This paper provides a comprehensive review of the mechanical properties with unique strain-stress responses,which comprise tensile mechanical properties,thermomechanical properties(e.g.critical stress to induce martensitic transformation,thermo-recoverable strain,and SE strain),damping properties and hardness.Moreover,several common structures(e.g.a negative Poisson’s ratio structure and a diamond-like structure)are considered,and the corresponding studies are summarized.It illustrates the various fields of application,including biological scaffolds,shock absorbers,and driving devices.In the end,the paper concludes with the main achievements from the recent studies and puts forward the limitations and development tendencies in the future.

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.

Tunable topological interface states and resonance states of surface waves based on the shape memory alloy

Topological interface state(TIS)of elastic wave has attracted significant research interest due to its potential prospects in strengthening acoustic energy and enhancing the signal accuracy of damage identification and quantification.However,previous implementations on the interface modes of surface waves are limited to the non-adjustable frequency band and unalterable mode width.Here,we demonstrate the tunable TIS and topological resonance state(TRS)of Rayleigh wave by using a shape memory alloy(SMA)stubbed semi-infinite one-dimensional(1D)solid phononic crystals(PnCs),which simultaneously possesses the adjustable mode width.The mechanism of tunability stems from the phase transformation of the SMA between the martensite at low temperature and the austenite at high temperature.The tunable TIS of Rayleigh wave is realized by combining two bandgap-opened PnCs with different Zak phases.The TRS with adjustable mode width is achieved in the heterostructures by adding PnCs with Dirac point to the middle of two bandgap-opened PnCs with different Zak phases,which exhibits the extraordinary robustness in contrast to the ordinary Fabry–Perot resonance state.This research provides new possibilities for the highly adjustable Rayleigh wave manipulation and find promising applications such as tunable energy harvesters,wide-mode filters,and high-sensitivity Rayleigh wave detectors.

Two-way Shape Memory Effect in a Ti-Ni-Nb Shape Memory Alloy with Wide Hysteresis

A two-way shape memory effect (TWSM E) in the Ti46.3Ni44.7Nb9 alloy has been systematically investigated by means of bending test and transmission electron microscopy (TEM ) observations. Based on the analysis of the microstructure after training. the mechanism of TWSME in the Ti46.3 Ni44.7Nb9 alloy has been discussed.

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.

Electrochemical behavior of Ti-Ni shape memory alloy in fibrinogen solution

Electrochemical behaviors of Ti Ni shape memory alloy in fibrinogen solution were studied by electrochemical techniques. The results indicate that the addition of the fibrinogen has no obvious effect on the corrosion potential, but decreases the pitting potential markedly and increases the passive current densities. The analysis of energy dispersive X ray for samples adsorbing fibrinogen exhibits that the elements of O, C and N exist on the surface of Ti Ni alloy. Furthermore, the scanning electron microscope micrographs confirm that the configuration of the adsorbing fibrinogen concentrating on surface defects is like cluster and the fibrinogen adsorption concentration is 96.67 mg/m 2 through ultroviolet ray absorption method. Fibrinogen combined with Ti Ni alloy surface by complex band and its electrochemical transfer accelerated the corrosion of alloy.

R-phase transformation of aged Ti-Ni shape memory alloy

Ti-50.6Ni（molar fraction, %） shape memory alloy solution treated at 850℃ for 1h followed by ageing treatment at 450℃ for 3h was studied with differential scanning calorimetry（DSC）, X-ray diffractometry（XRD） and transmission electron microscopy（TEM）. DSC measurement reveals two separate transformation peaks. XRD and TEM demonstrate that a three-stage transformation occurs. The Ti3Ni4 precipitates are coherent with the R-phase. The crystal structure of R-phase was analyzed by two diffraction patterns method. The diffraction patterns of R-phase were obtained in detail from the same region.

退火和时效工艺对富镍Ti-Ni形状记忆合金显微组织和相变行为的影响

为了给富镍Ti-Ni形状记忆合金热处理工艺的优化提供依据,以Ti-50.8Ni合金丝为对象,用光学显微镜、透射电子显微镜和示差扫描量热仪研究了退火和时效工艺对富镍Ti-Ni合金显微组织、相变类型、相变温度和相变热滞的影响规律。Ti-50.8Ni合金丝经350~800℃+5~120 min退火处理后,随退火温度和时间增加,合金发生回复、再结晶和晶粒长大过程,再结晶温度在600℃左右,显微组织形态由纤维状向等轴状变化;冷却/加热相变类型由B2→R→B19′/B19′→R→B2型向B2→R→B19′/B19′→B2型向B2→B19′/B19′→B2型转变(B2-母相,CsCl型结构;R-R相,菱方结构;B19′-马氏体相,单斜结构);R相变温度θ_(R)先升后降,极大值35.2℃在400℃退火态合金中取得;马氏体(M)相变温度θ_(M)升高,M相变热滞Δθ_(M)降低,R相变热滞Δθ_(R)约为4℃。该合金经300~500℃+0.5~50 h时效处理后,随时效温度和时间增加,合金中Ti3Ni4析出物形貌由细小颗粒状→针状→粗片状变化;300℃和500℃时效态合金的相变类型分别为B2→R→B19′/B19′→R→B2和B2→R→B19′/B19′→B2,400℃时效态合金的相变类型由B2→R→B19′/B19′→R→B2型向B2→R→B19′/B19′→B2型转变;θ_(R300)、θ_(R400)、θ_(R500)、θ_(M300)和θ_(M500)升高;θ_(M400)先降后升,极小值-121.4℃在400℃+1 h时效态合金中取得;Δθ_(M300)和Δθ_(M400)先升后降,极大值70.5℃和129.4℃分别在300℃+5 h和400℃+1 h时效态合金中取得;Δθ_(M500)降低,Δθ_(R300)和Δθ_(R400)约为4℃。

Zr掺杂对Ti-Ni形状记忆合金相变、拉伸性能和循环超弹性的影响

为了开发超弹性优异的Ti-Ni基形状记忆合金(SMA),以600℃退火态Ti-50.8Ni和Ti-50.8Ni-0.1Zr(摩尔分数)SMA为研究对象,用示差扫描量热仪、XRD、SEM和拉伸试验研究了Zr掺杂对Ti-Ni基SMA相组成、相变行为、拉伸性能和循环超弹性的影响。结果表明:掺杂0.1%Zr不影响Ti-Ni SMA的组成相和相变类型,但降低马氏体相变温度(t_(M)),增加相变热滞(Δt),提高抗拉强度(R_(m)),降低伸长率(A),增强非线性超弹性稳定性。600℃退火态Ti-50.8Ni和Ti-50.8Ni-0.1Zr合金的室温组成相主要为母相B2,冷却/加热时发生B2→B19′/B19′→B2一步可逆马氏体相变;掺杂0.1%Zr后,Ti-Ni SMA的t_(M)降低了34℃,Δt增加了22℃,R_(m)增加了79 MPa,A降低了22%。随应力-应变循环次数增加,Ti-50.8Ni合金由部分非线性超弹性转变为线性超弹性,Ti-50.8Ni-0.1Zr合金则始终保持稳定非线性超弹性,两种合金的超弹性残余应变(ε_(R))和能量耗散(W_(D))均先降低后趋于稳定。随着循环应变速率的增加,Ti-50.8Ni合金的W_(D)和等效阻尼比先降低后趋于稳定;Ti-50.8Ni-0.1Zr合金的W_(D)和等效阻尼比先升高后趋于稳定。随循环应变幅值的增加,Ti-50.8Ni和Ti-50.8Ni-0.1Zr合金的W_(D)和等效阻尼比皆升高。

CuZnAl Shape Memory Alloy Refined with Composite Rare Earths La+Ce

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.

Experimental Study on Characteristics of NiMnGa Magnetically Controlled Shape Memory Alloy

The static and dynamic magnetic controlling characteristics of NiMnGa magnetically controlled shape memory alloy （MSMA） were experimentally studied. The results show that the characteristics of induced strain with respect to the magnetic field are nonlinear with saturation nature, and dependent on the temperature as well as the load applied to the MSMA. The magnetic shape memory effect can be observed only in complete martensite phase at room temperature. The magnetic permeability of MSMA is not constant and reduces with the increment of magnetic field. The relative saturation magnetic permeability of MSMA is about 1.5.

Microstructures and properties of capacitor discharge welded joint of TiNi shape memory alloy and stainless steel

Microstructures and properties of capacitor discharge welded （CDW） joint of TiNi shape memory alloy （ SMA ） and stainless steel （SS） were studied. The fracture characteristics of the joint were analyzed by means of scanning electron microscope （ SEM）. Microstructures of the joint were examined by means of optical microscope and SEM. The results showed that the teusile strength of the inhomogeneous joint （ TiNi-SS joint） was low and the joint was brittle. Because TiNi SMA and SS melted, a brittle as-cast structure and compound were formed in the weld. The tensile strength and the shape memory effect （SME） of TiNi-SS joint were strongly influenced by the changes of composition and structure of the weld. Measures should be taken to prevent defects from forming and extruding excessive molten metal in the weld for improving the properties of TiNi-SS joint.

EFFECT OF MICROSTRUCTURE ON THE HARDENING AND SOFTENING BEHAVIORS OF POLYCRYSTALLINE SHAPE MEMORY ALLOYS PART Ⅰ:MICROMECHANICS CONSTITUTIVE MODELING

The effects of microstructure and its evolution on the macroscopic superelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)are studied by a microstructure-based constitutive model developed in this paper.The model is established on the following basis:(1)the transformation conditions of the unconstrained single crystal SMA microdomain(to be distinguished from the bulk single crystal),which serve as the local criterion for the derivation of overall transfor- mation yield conditions of the polycrystal;(2)the micro-to macro-transition scheme by which the connection between the polycrystal aggregates and the single crystal microdomain is established and the macroscopic transformation conditions of the polycrystal SMA are derived;(3)the quantitative incorporation of three microstruc- ture factors(i.e.,nucleation,growth and orientation distribution of martensite)into the modeling.These microstructural factors are intrinsic of specific polycrystal SMA systems and the role of each factor in the macroscopic constitutive response is quan- titatively modeled.It is demonstrated that the interplay of these factors will result in different macroscopic transformation kinematics and kinetics which are responsible for the observed macroscopic stress-strain hardening or softening response,the latter will lead to the localization and propagation of transformation bands in TiNi SMA.

Influences of 2.5wt%Mn addition on the microstructure and mechanical properties of Cu-Al-Ni shape memory alloys

The influences of 2.5wt%Mn addition on the microstructure and mechanical properties of the Cu-11.9wt%Al-3.8wt%Ni shape memory alloy（SMA） were studied by means of scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,and differential scanning calorimeter（DSC）.The experimental results show that Mn addition influences considerably the austenite-martensite transformation temperatures and the kind of martensite in the Cu-Al-Ni alloy.The martensitic transformation changes from a mixedβ1→β＇1＋γ＇1 transformation to a singleβ1→β＇1 martensite transformation together with a decrease in transformation temperatures.In addition,the observations reveal that the grain size of the Cu-Al-Ni alloy can be controlled with the addition of 2.5wt%Mn and thus its mechanical properties can be enhanced.The Cu-Al-Ni-Mn alloy exhibits better mechanical properties with the high ultimate compression strength and ductility of 952 MPa and 15%,respectively.These improvements are attributed to a decrease in grain size.However,the hardness decreases from Hv 230 to Hv 140 with the Mn addition.

Microstructure and corrosion behavior of NiTi shape memory alloys sintered in the SPS process

NiTi shape memory alloys(SMAs) was developed using the spark-plasma sintering(SPS) process with different average particle size(45 μm and 10 μm) under various temperature. The influence of particle size and temperature on the density, microstructure, and corrosion behavior of the NiTi in simulated body fluid was examined. The porosity decreased with increasing sintering temperature and decreasing particle size, which resulted in an increase in density of the alloy. Increasing the sintering temperature led to the formation of Ni-and Ti-rich intermetallic such as Ni3Ti and NiTi2. The formation of these secondary phases influenced the corrosion behavior of NiTi by changing its chemical composition. The planar structure of NiTi was transformed into a dendritic structure at 900℃, which resulted in the formation of uniform oxide and phosphate layers on the entire surface. A high corrosion potential and low corrosion current density were achieved with NiTi prepared with 10 μm particles at 900℃, which exhibited superior corrosion resistance.