形变温度对FeMnSiCrNiC合金第二相方向性析出及记忆效应的影响

基于控制第二相方向性析出提高铁基合金形状记忆效应的构想,研究了不同形变温度对Fe13.53Mn4.86Si8.16Cr3.82Ni0.16C合金γ/ε界面(母相丫与诱发马氏体ε之间界面)的数量和结构及随后时效第二相析出的数量和方向性的影响,以及第二相析出的数量和方向性对马氏体相变和形状记忆效应的影响.扫描电镜分析显示,形变温度远高于Ms时,无γ/ε面产生,时效后第二相析出少;形变温度接近Ms时,产生大量γ/ε面,时效后析出第二相数量很多,且方向性良好;形变温度进一步接近Ms时,γ/ε界面交叉,导致时效后方向性的第二相也交叉.透射电镜分析显示,析出方向性Cr23C6第二相的合金再次进行预变形时,产生的应力诱发马氏体具有单一方向.原因在于方向性Cr23C6及其产生的应力场对马氏体相交产生约束作用,避免马氏体片之间的交叉,使其具有更好的可逆转变性.     

Substructures of lenticular martensites with different martensite start temperatures in ferrous alloys

This study investigated the substructures of lenticular martensites with different martensite start temperatures (Ms) by transmission electron microscopy. Observation of Fe–33Ni revealed a substructural change from fine transformation twins in the midrib and twinned region to several sets of screw dislocations in the untwinned region during growth. Tangled and curved dislocations also appeared near the martensite–austenite interface of the untwinned region, as the martensite inherited the dislocations in the surrounding austenite. In contrast, curved and tangled dislocations appeared in the entire untwinned region in Fe–31Ni and in the whole martensite plate in Fe–20.5Ni–35Co, as the higher Ms temperatures facilitated the plastic deformation of the surrounding austenite. Thermally transformed thin plate martensite in Fe–31Ni–10Co–3Ti grew into a lenticular shape accompanied by a substructure with dislocations after deformation at temperatures above the Ms temperature. The change in the substructure of lenticular martensite presumably resulted from the local temperature rise in the martensite plate.     

低应力／应变幅控制的对称拉压疲劳对Ti—49.6Ni合金相变行为的影响

采用电阻法研究了TiNi形状记忆合金在对称拉压应力或应变疲劳条件下的相变行为,结果表明,经过低应力/应变疲劳,材料发生R相变,试样的相变温度变得稳定,马氏体相变温度Ms和逆相变温度As低于未疲劳试样,随着循环次数的增加,应变疲劳后材料的Ms点、As点与循环次数无明显关系,材料具有良好的相变稳定性。     

Ni2MnGa铁磁形状记忆合金开裂的原位研究

对Ni2MnGa铁磁形状记忆合金的缺口试样,通过在微分干涉相衬显微镜下原位拉伸,研究了裂纹形核、扩展和马氏体相变以及塑性变形的关系．结果表明,拉伸时首先形成马氏体,当裂尖应力集中足够大时就会在裂尖产生局部塑性区,微裂纹易于沿马氏体界面形核,但也可在塑性区中形核．随载荷升高,微裂纹沿马氏体不连续形核,通过韧带剪切连接,从而导致裂纹扩展阻力也随裂纹扩展而增大．     

EFFECTS OF HEAT TREATMENT ON THE MICROSTRUCTURE OF Cu-Zn-Al (RE) SHAPE MEMORY ALLOYS

1. Introduction Cu-Zn-Al shape memory alloys have extensive application prospects because of their unique properties and low cost. However, some elements have to he added into Cu-Zn- Al shape memory alloys in order to refine their grains and to improve their mechanical properties. Some works indicated that adding rare earth (RE) elements or mixed RE (La+Ce) could improve the related properties remarkably[13]. The effects of RE addition are as the following: (1) refining grains of the al…     

Transformation behaviors of Ti48.5Ni48Fe2Nb1.5 dependence of annealing and thermomechanical cycling

The effect of annealing treatments and thermomechanical cycling on the transformation behaviors and shape memory effect of Ti48.5Ni48Fe2Nb1.5 shape memory alloys were investigated using electrical resistivity measurement and tensile testing. It is found that the transformation behaviors are influenced considerably by the annealing treatments. Both Ms and As increase with increasing annealing temperature and cooling rate. Martensite stabilization occurs during thermomechanical cycles, thus resulting in lower...     

马氏体相变

对前人所下的马氏体相变定义和所作的分类进行了总结,将马氏体相定义为：替换原子经无扩散切变位移（均匀的和不均匀的形变）由此产生形状改变和表面浮突,呈不变平面应变特征的一级,形核一长大型的相变,马氏体要变按动力学分为变温相变和等温相变,按热力学和界面动态分为弹性相变,近似（半）热弹性相变和非热弹性相变,热弹性相变的判据为（１）临界项相变动动力小,热滞小;（２）相界面能往复（正,逆）运动;（３）形状应变     

Cu-Zn-Al合金中马氏体穿晶界生长过程的动态观察

合金中的马氏体是晶体点阵切变的产物,对于多晶材料,马氏体通常在各个晶粒中形核长大,但不跨越晶界,然而在Cu-Zn-Al形状记忆合金的研究中,我们观察到了马氏体穿晶界生长现象。记忆合金中的马氏体相变具有热滞后和驱动力小等特点,称为热弹性马氏体相变,马氏体穿晶界生长可能也是这类相变的一个特征。该现象既涉及马氏体相变理论本身,又与晶界问题密切相关,应该成为一个有趣的研究课题。     

Study of Thermal Scanning Rates on Transformations of Ti-19Nb-9Zr (at.%) by Means of Differential Scanning Calorimetry Analysis

Differential scanning calorimetry (DSC) thermal analysis is a well-accepted technique used to measure the transformation temperatures of shape memory alloy and its thermoelastic transformation energies. In this study, both forward and reverse transformation temperatures of a nickel-free Ti-19Nb-9Zr (at.%) SMA were investigated using DSC technique with different cooling and heating scanning rates in a range of 10 to 100 °C/min. The results showed that the transformation temperature intervals vary substantially with respect to the thermal scanning rates. It is found that the martensitic start (M _s) temperature decreases with decreasing the cooling rates. The optimal scanning rate was found to be 40 °C/min for obtaining the maximum thermoelastic transformation energies stored between the forward and the reverse martensitic transformations. It is believed that the thermoelastic transformation energy increases with the increase in the volume fraction of martensite. Based on these measurements, these thermoelastic transformation energies between the forward and the reverse martensitic transformations were estimated to be ~21 and ~27 J/g, respectively. The appropriate selection of scanning rate for SMA analysis will be discussed.     

Influence of the post-deformation annealing heat treatment on the low-cycle fatigue of NiTi shape memory alloys

Shape memory alloys (SMA) suffer from the same impairing mechanisms experienced during cycling loading by classic alloys. Moreover, SMA fatigue behavior is greatly influenced by thermomechanical cycling through the zone of thermoelastic phase transformation, which is the basis of shape memory and superelasticity effects. Since the fatigue resistance of any material can be improved by an appropriate thermomechanical treatment, in the present work combined differential scanning calorimetry and microhardness testing were used to determine an optimum annealing temperature for the cold-worked Ni-50.1%Ti alloy. The optimization is based on the assumption that latent heat of transformation is proportional to the mechanical work generated by SMA upon heating, while material hardness is related to the yield stress of the material. It is supposed that an optimum trade-off in these two properties guarantees the best dimensional and functional stability of SMA devices. The level and stability of the mechanical work generated by the material during low-cycle fatigue testing are considered criteria for the material performance and thus of the validity of the proposed optimization procedure.     

Cu-Zn-Al形状记忆合金在模拟宫腔液中的腐蚀行为

采用化学失重法、电化学方法和原子吸收光谱法研究了紫铜、Cu-Zn-Al形状记忆合金和Cu-Zn-Al合金在模拟宫腔液中的腐蚀行为.结果表明, 模拟宫腔液中紫铜、Cu-Zn-Al形状记忆合金和Cu-Zn-Al合金的腐蚀历程受阴极氧去极化步骤控制.Cu-Zn-Al形状记忆合金和Cu-Zn-Al合金由于铝的表面离子化倾向比锌的大, 优先形成致密坚固的保护性氧化铝膜, 降低了腐蚀速率.在模拟宫腔液中发现Cu-Zn-Al形状记忆合金和Cu-Zn-Al合金发生脱铝腐蚀, Cl-参与腐蚀反应历程, 促进脱铝腐蚀的进行.白蛋白与氧的竞争吸附加速了阳极溶解, 使紫铜、Cu-Zn-Al形状记忆合金和Cu-Zn-Al合金的阳极活性电流密度随白蛋白浓度的上升而增加.     

Study of anisothermal ageing of CANTiM shape memory alloys by positron annihilation

The thermal-elastic property of high temperature CuAlNiMnTi shape memory alloys was found strongly affected by anisothermal ageing. With slow cycling (cycled at low heating and cooling rates), the transformation temperatures increase with the number of thermal cycle while the transformation enthalpy decreases and finally drop to zero, which indicated a total deterioration of the shape memory effect. Martensite stabilisation was found to be the cause of such deterioration. Positron Annihilation technique was employed to study the properties of the vacancies during the anisothermal ageing process. This was compared with the isothermal aged results. We propose that the changes in the quantity and characteristics of vacancies during anisothermal ageing are only responsible for the kinetics of the martensitic transformation. The result is the shift of transformation temperatures. However, the presence of vacancy agglomerations may have assisted the diffusion of atoms during ageing. Other factors like microstructural changes and atomic reordering will lead to the irreversible martensite stabilisation and make the transformation thermodynamically unfavourable.     

Electrochemical behavior of Cu-Zn-Al shape memory alloy after surface modification by electroless plated Ni-P

The electrochemical behavior of Cu-Zn-Al shape memory alloy (SMA) with and without electroless plated Ni-P was investigated by electrochemical methods in artificial Tyrode‘s solution. The results showed that Cu-Zn-Al SMA engendered dezincification corrosion in Tyrode‘s solution. The anodic active current densities as well as electrochemical dissolution sensitivity of the electroless plated Ni-P Cu-Zn-Al SMA increased with NaC1 concentration rising, pH of solution decreasing and environmental temperature uprising. X-ray diffraction analysis indicated that after surface modification by electroless plated Ni-P, an amorphous plated film formed on the surface of Cu-Zn-Al SMA. This film can effectively isolate matrix metal from corrosion media and significantly improve the electrochemical property of Cu-Zn-Al SMA in artificial Tyrode‘s solution.     

Cu-Zn-Al合金热弹性马氏体稳定化机理的探讨SCIEI

本文研究了快速凝固Cu-Zn-Al合金热弹性马氏体稳定化的机理,认为该合金马氏体稳定化实际上是一个原子组态由有序向无序、马氏体结构由M18R向b/a=1/3^(1/2)的N9R转变的过程,这一过程是由马氏体固有的分解趋势所决定的。     

Transformation Sequence Rule of Martensite Plates and Temperature Memory Effect in Shape Memory Alloys

In thermoelastic martensitic transformation, it is well established that the first martensite plate appearing upon cooling becomes the final one during reverse transformation to austenite upon heating. The results obtained from this work show that the transformation sequence of the martensite appears to be random. Newly formed martensite plates can modify the elastic strain energy level stored in the already existing martensite. Additionally, the elastic strain energy stored in newly formed martensite is not necessarily to be higher than the remaining martensite. The obtained results may assist in understanding phenomena related to partial transformation of shape memory alloys, such as temperature memory effect.     

INFLUENCE OF Mn CONTENT ON THERMOELASTIC MARTENSITE TRANSFORMATION AND SHAPE MEMORY EFFECT IN Cu-AI-Zn-Mn-Ni ALLOYS

用电阻法、光学显微镜和透射电镜研究了Mn含量对Cu-Al-Zn-Mn-Ni合金的相变点、马氏体形态和亚结构以及形状记忆效应的影响.结果表明:Mn含量增高导致相变温度显著降低,弹性马氏体相变温度范围变宽,并使马氏体形态由平行排列的长条状向自协作形态不断完善,马氏体亚结构由孪晶型向层错型过渡.马氏体的自协作完善程度和变体大小及淬火空位对合金的形状记忆效应有显著影响.     

化学镀镍磷表面改性Cu-Zn-Al形状记忆合金的腐蚀行为

采用电化学方法研究了Cu-Zn-Al形状记忆合金(SMA)及其化学镀镍磷表面改性试样在Tyrode's人工体液中的腐蚀行为.结果表明，在Tyrode's人工体液中Cu-Zn-Al SMA发生脱锌腐蚀.化学镀镍磷Cu-Zn-Al SMA随NaCl浓度增加、pH值降低、环境温度升高，阳极活性电流密度增大，电化学溶解敏感性增强.X-射线衍射分析结果表明，Cu-Zn-Al SMA表面化学镀镍磷后，形成了非晶态镀层，其在Tyrode's人工体液中的耐蚀性显著提高；这是由于改性表面形成均匀、稳定的阻碍性镀层，有效地将基体金属和外界腐蚀介质隔绝而达到防护作用. 镀镍磷      

THERMODYNAMICS OF MARTENSITIC TRANSFORMATION IN β-Cu BASE ALLOYS

An approach for the thermodynamics of the thermoelastic martensitic transformation in β-Cu base alloys is suggested.Driving forces for martensitic transformation,T_0 and M_s tempera- tures in Cu-Zn,Cu-Al and Cu-Zn-Al alloys were calculated and the calculated M_s are in good agreement with the experimental ones.Ordering of the parent phase lowers M_s(T_0)in Cu-Zn and Cu-Zn-Al alloys,but raises M_s(T_0)in Cu-Al alloys.Two methods for the es- timation of the critical driving force for the thermoelastic martensitic transformation are also introduced.     

Thermodynamic analysis of shape memory phenomena — I. Effect of transformation plasticity on elastic strain energy

The effect of plastic strains accompanying the thermoelastic transformation on shape memory phenomena is evaluated. It is shown that transformation plasticity can be formally included in Eshelby's macroscopic elastic analysis by defining a net transformation strain equal to the difference of the crystallographic transformation strain and the associated plastic strain. A two variant analysis for a thermoelastic martensite transformation is developed which enables calculation of the variant structure along the path of minimum elastic energy. It is shown that plastic strain accompanying the formation of a martensitic plate reduces the elastic energy stored during the forward transformation. The equilibrium variant structure is shown to be determined by both the applied stress and the fraction of martensite. If the plastic strains accompanying the forward and reverse transformations do not cancel, residual elastic stress fields remain after completion of the reverse transformation. The residual elastic strain fields influence subsequent transformation behaviour and provide the driving force for two-way shape memory behaviour.     

Thermodynamics of martensite transformation hysteresis in Ni-Ti shape memory alloys

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