回复应变退火温度对铁锰硅合金形状记忆效应的影响

结果表明，预应变后的合金经回复应变退火后，组织转变分为三个阶段，形状记忆效应主要产生于４７５℃以前第一阶段的应力诱发ε马氏体向奥氏体转变，４７５℃以后的各阶段组织转变对形状记忆的效应不产生贡献。适宜的回复应变退火温度为５００℃。     

形变时效对FeMnSiCrNi合金形状回复率和相变温度的影响

为了进一步提高Fe-14Mn-6Si-8Cr-5Ni合金的形状记忆效应,对固溶态合金采用了形变时效的方法处理,并利用光学显微分析、X射线衍射分析和透射电子显微分析的测试手段分析了时效温度和时效时间对合金形状回复率和相变温度的影响.结果表明,固溶态合金经10%拉伸和600℃时效10 min时,形状回复率提高幅度最大,由固溶态的48%提高到84.7%,并且合金γ→ε马氏体转变的起始温度Ms由固溶态的34℃降低到13.2℃.合金的形状回复率得到提高的主要原因是合金中热诱发ε马氏体已经消失,组织为奥氏体和大量定向α’马氏体,这样的组织特征有利于应力诱发γ→ε马氏体相变以及它们的逆相变.     

不同固溶处理温度下的FeMnSiCrNi合金的微观组织分析

利用金相显微镜、X射线衍射仪和力学测试等手段研究了Fe30Mn6Si4Cr5Ni形状记忆合金在不同固溶处理温度的金相组织和形状记忆机制。试验结果表明，形状恢复率随着固溶处理温度的升高而提高，固溶处理温度约为1000℃时达到最大值，随后恢复率随着固溶处理温度的进一步升高而降低。研究结果还表明，形变过程中产生的形变孪晶是铁基合金形状记忆效应产生的来源之一。     

回复应变退火对铁锰硅合金形状记忆效应的影响

结果表明，预应变后的合金经回复应变退火后，组织转变分为三个阶段，形状记忆效应主要产生于４７５℃以前第一阶段的应力诱发ε马氏体向奥氏体转变，４７５℃以后的各阶段组织转变对形状记忆的效应不产生贡献。适宜的回复应变退火温度为５００℃。     

预变形温度对Fe-Mn-Si-Ni-Cr合金形状记忆效应及Υ ε转变的影响

研究了不同预变形温度下Ｆｅ－２５Ｍｎ－４Ｓｉ－２Ｎｉ－Ｃｒ合金的形状记忆效应和Υ　ε转变。结果表明，在２０３Ｋ进行预变形可以获得最大形状恢复率；适当降低预变形温度有利于应力诱发发马氏体转变和形状记忆效应；但在７７Ｋ进行６％的预变形会使ε马氏体交割处产生全位错，不利于逆转变和形状记忆效应     

热机械处理中退火时间对Fe-Mn-Si基合金形状记忆效应的影响

热机械处理能显著改善Fe-Mn-Si基合金的形状记忆效应。本工作中，对铸态Fe-Mn-Si基合金进行热锻、20%冷轧变形及固溶处理，随后在1073 K对部分经10%室温拉伸变形的试样进行不同时间退火处理。借助背散射电子显微分析(EBSD)、RGM-4300型万能试验机、示差四端电阻法及弯曲法研究热机械处理中退火时间对Fe-Mn-Si基合金微观组织和形状记忆效应的影响规律。结果表明：固溶态Fe-Mn-Si基合金的可恢复应变为4.1%;当经过退火时间为10 min的热机械处理后，合金的可恢复应变显著提高至5.3%;当进一步延长热机械处理的退火时间，合金的可恢复应变随之下降；当热机械处理的退火时间为180 min时，合金的可恢复应变下降至4.9%。随着热机械处理的退火时间延长，退火孪晶分数增加，堆垛层错密度下降，从而导致Fe-Mn-Si基合金促进应力诱发ε马氏体相变和抑制塑性滑移的能力变弱。这是Fe-Mn-Si基合金的可恢复应变随着热机械处理的退火时间延长而降低的主要原因。     

淬火温度对Fe-Mn-Si-C合金形状记忆效应及显微结构的影响

研究了淬火温度对Fe-18.1Mn-5.5Si-0.32C舍金形状记忆效应的影响,采用透射电子显微镜观察了合金经700℃淬火后的显微结构,并通过能谱仪对其进行微区成分分析.结果表明合金经700℃淬火后,其形状回复率最高,达到94%;奥氏体基体内含有大量的层错及一些平直的热诱发ε马氏体,层错微区出现了碳的富集,这些碳原子对奥氏体基体起强烈固溶强化的作用,有利于合金的形状记忆效应的提高.     

热-机械循环处理对FeMnSiCrNi 合金 记忆效应的影响

采用电子拉伸试验机考察了不同预变形量热-机械循环处理对FeMnSiCrNi合金形状记忆效应的影响,并利用光学及透射电子显微分析方法研究了经热-机械循环处理后母相γ及应力诱发ε马氏体的组织变化.结果表明:在预变形量为4%、5%、和6%的情况下,经2次循环训练后具有最高的应变恢复率;适当的热-机械循环处理能促进母相γ中形成大量按一定取向分布的晶体缺陷,为择优取向ε马氏体的成长打开通道,显著降低ε马氏体的几何尺寸,提高其逆相变的晶体学可逆性;若热-机械循环次数过多,母相γ中会形成位错缠结,阻碍γ→ε相变过程中层错扩展,从而不利于形状记忆效应.     

预变形温度对Fe—Mn—Si—Ni—Cr合金形状记忆效应及γ←→ε转变的影响

研究了不同预变形温度下Ｆｅ－２５Ｍｎ－４Ｓｉ－２Ｎｉ－Ｃｒ合金的形状记忆效应和γ←→转变。结果表明，在２０３Ｋ进行预变形可以获得最大形状恢复率；适当降低预变形温度有利于应国诱发马氏体转变和形状忘儿应；但在７７Ｋ进行６％的预变形会使ε马氏体交割处产生全位错，不利于逆转变和形状记忆效应。     

NiTiHf高温形状记忆合金的相变行为和形状记忆效应

利用透射电镜、X射线衍射仪和示差热分析仪系统分析了Ni49Ti36Hf15合金的相变行为及其形状记忆效应。结果表明，Ni49Ti36Hf15合金的热马氏体变体间构成典型的自协作组态，主要呈矛头状、镶嵌块状和楔状3种形态，亚结构主要为（001）复合孪晶。随着热循环次数的增加，相变温度降低，经50次热循环后，相变温度随热循环次数增加变化趋势不明显。固溶处理Ni49Ti36Hf15合金在20－184℃范围内弯曲变形时，呈现良好的形状记忆效应，其最大可恢复应变可达3％。形状恢复率随着弯曲变形温度的增加而下降，当弯曲变形温度大于317℃时，形状恢复率下降为0。     

The microstructure and shape memory effect of Ti-16 at.%Nb alloy

The microstructure, phase composition, mechanical properties and shape memory effect of the Ti-16 at.%Nb alloy were investigated by means of TEM, XRD, bending test and tensile test. The XRD results showed that the Ti-16 at.%Nb alloy is mainly composed of two phases: α″ phase and β phase at room temperature. TEM observation proved that there is also a little amount of ω phase in the Ti-16 at.%Nb alloy solid solution treated at 750 °C for 0.5 h. The martensite lath with a sub-structure of (111) type I twin was found in the Ti-16 at.%Nb alloy solid solution treated at 750 °C for 0.5 h by TEM observation. While solid solution treated at 750 °C, the Ti-16 at.%Nb alloy has the best combination of mechanical properties. The Ti-16 at.%Nb alloy has a certain shape memory effect. When the pre-strain is less than 2%, the deformed alloy can completely recover to the original shape. The SME of the Ti-16 at.%Nb alloy has an acceptable reproducibility, because when pre-deformed with 3.26% strain, after more than 20 times deformation cycling, the recovery ratio is still more than 40%.     

Characteristics of Deformation and Recovery in Shape Memory Alloy

The mechanical behavior and the effect of pre-strain on recovery behavior of Ti50Ni47Fe3 (at. pct) alloy were investigated systematically by tensile and recovered tests accompanied by electrical resistance measurement. Ti50Ni47Fe3 alloy has different deformation behaviors at different temperature ranges, the deformation curves in different temperature range can be classified into four kinds. The start temperature of recovery increases with the increase of pre-strain. There exists an optimal deformation condition, at which the specimen exhibits maximum free recovery strain. With increasing pre-strain the recovery stress increases and reaches the maximum at 8% pre-strain. R-phase to parent transition offered about 0.2% recovery strain. With pre-strain increasing the recovery stress increases and reaches to the maximum at 8% pre-strain. The recovery stress is corresponding with the critical stress of stress-induced martensitic transformation.     

Characteristics of Deformation and Recovery in Ti50Ni47Fe3 Shape Memory Alloy

The mechanical behavior and the effect of pre-strain on recovery behavior of Ti50Ni47Fe3 (at. pct) alloy were investigated systematically by tensile and recovered tests accompanied by electrical resistance measurement. Ti50Ni47Fe2 alloy has different deformation behaviors at different temperature ranges, the deformation curves in different temperature range can be classified into four kinds. The start temperature of recovery increases with the increase of pre-strain.There exists an optimal deformation condition, at which the specimen exhibits maximum free recovery strain. With increasing pre-strain the recovery stress increases and reaches the maximum at 8% pre-strain. R-phase to parent transition offered about 0.2% recovery strain. With pre-strain increasing the recovery stress increases and reaches to the maximum at 8% pre-strain. The recovery stress is corresponding with the critical stress of stress-induced martensitic transformation.     

Fe—Mn—Si—Cr—Ni—C形状记忆合金回复应力的研究

研究了预应变量、加热和冷却工艺对FeMn－Si-Cr－Ni－C形状记忆合金回复应力的影响。结果表明，当预应变量小于3％～4％时，随应变量的增加，回复应力增加。大于3％～4％后，则下降。同一温度下，冷却过程的回复应力大于加热过程的回复应力。停止加热时的温度越高，冷却过程中的回复应力越大。     

FeMnSiCrNiCo合金记忆性能的研究

针对具有良好耐蚀性的FeMnSiCrNiCo系合金 ,确定了合理的热加工及固溶处理温度 ,研究了预变形量、退火温度及记忆训练对合金记忆性能的影响 ,并分析了微观组织。结果表明 ,随着预变形量增加 ,记忆回复率 (ηm)下降 ,但记忆回复应变量 (εm)有一个最佳值。合金的记忆性能和微观组织随训练退火温度变化而不同 ,训练退火温度对训练效果起十分关键的作用 ,母相亚结构是决定合金记忆性能的根本因素     

Shape Memory Effect of an Aged Fe-Mn-Si-Co-Mo Alloy

The effect of ageing on the microstructure, mechanical properties and shape memory effect (SME) in a newly developed Fe-24Mn-5Si-8Co-4Mo shape memory alloy has been studied. It was found that Fe2Mo particles precipitate during ageing and thereby increase hardness and strength of the alloy The SME of the alloy can be remarkably improved by ageing and a maximum SME can be obtained when aged at 873 K. When the ageing temperature is over 873 K, the SME decreases with increasing ageing temperature. The reason for the improvement of SME by ageing in the Fe-Mn-Si-Co-Mo alloy is discussed     

Effect of Pre-strain on the Transformation and Recovery Behaviours of a Ti44Ni47Nb9 Shape Memory Alloy

The recovery strain, stress and transformation temperature of different pre-strained specimens of Ti44Ni47Nb9 were investigated by tensile test and electrical resistance measurement. The results indicated that pre-strain increases the reverse martensitic transformation temperature (A ' (s)) and hysteresis (A(s) - M-s). The recovery strain and stress are higher if the specimens are pre-strained between M-s and A(s) temperature than outside this temperature range. There exists an optimal pre-strain value, about 10%, at which the specimen exhibits maximum recovery strain and stress.     

Effect of pre-strain on shape memory characteristics in a Ti-17Nb-6Zr-1.0at.%O biomedical alloy

The effect of pre-strain on the shape memory characteristics of a biomedical alloy, Ti-17Nb-6Zr-1.0at.%O, was investigated using various tensile tests. A 3% cyclic test on a solution-treated (ST) specimen showed that the critical stress for inducing martensitic transformation (σ_SIM) decreases with an increase in the number of cycles. From the 9th cycle, the shape perfectly recovers after unloading. In the case of the 4% pre-strained specimen, a 3% cyclic test showed that σ_SIM dramatically decreases with increase in the number of cycles, and the shape perfectly recovers from 4th cycle. For the 5% pre-strained specimen, 3% and 4% cyclic tests showed superior superelasticity from the 5th cycle. The ST specimen and pre-strained specimens showed similar values of the critical stress for slip and maximum superelastic recovery strain. These results indicate that pre-strain has a small effect on the basic shape memory characteristics of the alloy.     

Experimental investigation on the debonding strength in shape memory alloy wire reinforced polymers

The interfacial shear strength between the shape memory alloy (SMA) wire and epoxy matrix was evaluated experimentally using a single wire pull-out test. Moreover, the effect of pre-strain in SMA wires on the interfacial behavior was studied by pre-straining the SMA wires to 2% and 4% pre-strains. Experiments were conducted in both martensite and austenite phases of SMA. Results showed that pre-straining SMA wire in the martensite phase caused enhancement in interfacial shear strength due to recovery force generation. Further, 9.7% and 33% improvements in the interfacial shear strength were achieved at 2% and 4% of SMA pre-strain, respectively. However, the enhancement of interface behavior did not occur, when the SMA wires were subjected to pre-strain in the austenite phase.