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In this study, the effects of stress-assisted heat treatment on the microstructure and phase transformation of a Ti-rich (Ti-49.52 at.% Ni) shape memory alloy were investigated. For this purpose, the alloy was heat treated at temperature of 500 °C for 10 h under applied stresses of 100 and 200 MPa. XRD, TEM, and repeated thermal cycling were employed to study the microstructure and transformation behavior of the heat-treated materials. Room temperature XRD diffractogram of the stress-free heat-treated material showed a weak reflection of austenite (B2), while that for the stress-assisted heat-treated materials had a high intensity implying the presence of residual austenite in the microstructure. TEM observations confirmed the presence of residual austenite and revealed mechanical twins as another constituent of the microstructure in the stress-assisted heat-treated materials. Moreover, with increasing the value of applied stress the size of mechanical twins was increased and a high density of structural defects was observed at the interfaces of the twins. DSC results demonstrated two-stage transformation in the initial cycles of transformation in the stress-assisted heat-treated material. After about eight cycles of transformation, the two-stage transformation has vanished, and a single-stage transformation remained up to 100 cycles. It was suggested that the accommodation of stresses at Ti2Ni/matrix interface provides a suitable condition for local transformation of B2 to B19′ that is manifested by a two-stage phase transformation. Introduction of structural defects during repeated thermal cycling may counteract the stress field at Ti2Ni/matrix interface leading to a single-stage transformation. 相似文献
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以多孔NiTi合金为研究对象建立了B2-R的相场模型,分析了孔隙率、孔隙尺寸以及孔隙形状对R相生长动力学行为的影响。结果表明,R相尺寸和尺寸分布均匀性都随孔隙率的增加而增大,然而R相的分布特征和尺寸均匀性对孔隙大小以及孔隙形状不敏感。 相似文献
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Superelastic NiTi shape memory alloy (SMA) has high recoverable strain and outstanding damping capacity, and has been used as a damping material for many applications. When subjected to displacement-controlled cyclic deformation, the material exhibits distinctive temperature and stress oscillations due to the release of latent heat and hysteresis heat and the heat transfer with the ambient. In this paper, we establish a model to predict the temperature variation of NiTi SMA wire specimen under the cyclic phase transition by lumped heat transfer analysis. Closed-form solution on the evolution of the temperature is obtained. It is shown that, for all the test frequencies, steady-state cyclic thermal response of the specimen can be reached after a certain number of loading cycles in a transient stage, exhibiting a kind of ??thermal shake down.?? In the steady state, the temperature profile oscillates around a mean temperature plateau. We show that the temperature oscillation is mainly due to the release/absorption of latent heat during cyclic phase transition, while the mean temperature rise of the specimen is caused by the accumulation of the hysteretic heat of the phase transition. The model predictions agree well with the experimental results. 相似文献
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《金属学报(英文版)》2017,(8)
Based on equiatomic nickel and titanium, three kinds of NiTiFe alloys with a nominal chemical composition of Ni_(49)Ti_(49)Fe_2, Ni_(48)Ti_(48)Fe_4 and Ni_(47)Ti_(47)Fe_6(at.%), respectively, have been designed to investigate the influence of the addition of Fe element on phase transformation, microstructure and mechanical property of equiatomic NiTi shape memory alloy. The microstructures of three kinds of NiTiFe alloys are characterized by the equiaxed grains instead of the dendrites.Consequently, some Ti_2Ni precipitates are found to distribute in the grains interior and at the grain boundaries. The content of Fe element has an important influence on mechanical property of NiTiFe alloy. With increasing content of Fe element,the strength of NiTiFe alloy increases substantially, but the plasticity decreases sharply. It can be concluded that precipitation strengthening and solution strengthening play a significant role in enhancing the strength of NiTiFe alloy. In the case of three NiTiFe alloys, neither martensitic transformation nor reverse transformation can be observed in the range from-150 to 150 ℃. On the one hand, the phase transformation temperature is probably out of the scope of the present experimental temperature. On the other hand, the addition of Fe element probably suppresses first-order martensitic transformation or reverse transformation, and consequently the second-order-like phase transformation from an incommensurate stage to a commensurate stage can probably take place. 相似文献
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研究了近等原子比NiTi形状记忆合金在阴极充氢后时效过程中表面的相变与破坏,认为时效裂纹的产生与奥氏体不锈钢类似,为氢释放和氢致马氏体分解导致表面收缩产生较大张应力所致,时效过程中裂纹扩展持续时间超过5天。氢致马氏体微观形貌与应力诱发马氏体相似,二者形貌上不可区分。氢化物与基体的界面和氢致马氏体与奥氏体相界面在时效过程中可能成为裂纹源。 相似文献
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Z. Lekston M. Zubko K. Prusik D. Stróż 《Journal of Materials Engineering and Performance》2014,23(7):2362-2367
Processing of NiTi shape memory alloys strongly influences their microstructure, phase transformations, mechanical, and shape memory properties. Hot forging, hot swaging, or hot rolling are efficient techniques for obtaining the desired shape, but during multiple operations the material must be heated and worked in the temperature range from 700 to 900 °C. During these processes, intense oxidation takes place. In order to reduce it, the hot-pack working is applied. The hot extrusion is more effective for reduction of ingot, billet, and rod diameters than hot forging, hot swaging, or hot rolling. Also, during hot extrusion the material surface undergoes considerably less oxidation. In the present work, results of the characterization by differential scanning calorimetry, low-temperature x-ray powder diffraction, and three-point bending and free recovery ASTM F2082-06 tests of the samples after hot direct extrusion and heat treatment are presented. The obtained alloy after hot direct extrusion exhibits desired shape memory effect. The phase transformations during cooling and heating cycle occur with the presence of the R phase. The range of the characteristic temperatures for the obtained material gives possibility for further medical applications. After annealing at 400 and 500 °C, the characteristic temperatures shift to higher values. 相似文献
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NiTi合金的显微组织和双程形状记忆效应 总被引:1,自引:0,他引:1
通过弯曲试验和透射电镜分析系统研究了热处理工艺、形变量、形变温度对NiTi合金双程形状记忆效应和显微组织的影响。结果表明 ,冷轧变形试样经不同温度退火后 ,双程可逆应变量随退火温度的升高而增大 ,退火温度超过 550℃后 ,温度继续升高 ,双程可逆应变量基本不变。同一温度退火的试样 ,双程可逆应变量随弯曲形变量的增加而增加 ,至形变量εt=12 %时达到最大值 ,εt 进一步增加 ,双程可逆应变量呈下降趋势。弯曲形变量相同时 ,弯曲温度升高 ,双程可逆应变量εt 减小 ,形变温度超过Mσs 时基本不再呈现双程记忆效应。马氏体再取向形成的位错可以产生有效内应力场 ,诱发双程形状记忆效应 相似文献
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Metals and Materials International - In the present work, Ni32-x-Ti-Ta18+x (x?=?0, 2, 3, 4, 5, 6, 7, 8) shape memory alloys, produced by arc-melting method. Then, differential scanning... 相似文献
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Z. H. Wu D. Vokoun C. C. Leu C. T. Hu 《Journal of Materials Engineering and Performance》2017,26(12):5801-5810
Ni4Ti3 precipitates are formed in Ni-rich NiTi shape memory alloys (SMAs) after a certain heat treatment. Such a treatment then results in the changed phase transformation behavior of the alloy switching from the one-step reversible phase change B2 ? B19′ to the two-step, B2 ? R ? B19′, phase change. The present study reports a two-way shape memory (TWSM) due to an all-round treatment followed by an R-phase constraint aging at room temperature. The enhanced TWSM behavior was observed upon temperature cycling between 273 K (R-phase) and 77 K (B19′ phase). The effect of various constraint strains in R-phase aging by employing different diameters of the constraint ring was studied. However, the TWSM effect due to constraining the R-phase will be eliminated after a temperature rise of specimen to the fully parent phase (373 K). 相似文献
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Shuilin Wu Xiangmei Liu K. W. K. Yeung Z. S. Xu C. Y. Chung Paul K. Chu 《Journal of Materials Engineering and Performance》2012,21(12):2622-2627
Porous NiTi shape memory alloy (SMA) scaffolds have great potential to be used as orthopedic implants because of their porous structure and superior physical properties. Its metallic nature provides it with better mechanical properties and Young??s modulus close to that of natural bones. Besides allowing tissue ingrowth and transfer of nutrients, porous SMA possesses unique pseudoelastic properties compatible to natural hard tissues like bones and tendons, thus expediting in vivo osseointegration. However, the nickel release from debris and the metal surface may cause osteocytic osteolysis at the interface between the artificial implants and bone tissues. Subsequent mobilization may finally lead to implant failure. In this study, the wear properties of porous NiTi with different porosities processed at different treatment temperatures are determined. The results of the study show that the porosity, phase transformation temperature, and annealing temperature are major factors influencing the wear characteristics of porous NiTi SMA. 相似文献
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合金元素对CuAlMnTi形状记忆合金组织和相变点的影响 总被引:2,自引:2,他引:0
利用扫描电镜、能谱仪、金相显微镜和差热分析仪等研究了用非自耗真空电弧炉熔制的不同成分的Cu-Al-Mn-Ti形状记忆合金的成分、组织和性能,综合分析合金的成分、组织和相变点之间的关系.结果表明:Al含量为9.5%、11.5%左右时,Ms点随Mn含量的增加而降低;当w(Al)=12.5%时,由于合金在降温过程中发生共析转变,使得热弹性马氏体大量减少甚至完全消失,形状记忆效应受到很大的影响. 相似文献
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利用差示扫描量热法研究了两种CuZnAlMnNi记忆合金以两种不同速率升温时的相变过程。发现升温速率为10℃/min时,DSC曲线为单一大峰,而以0.1℃/min的速率升温时出现许多连续或不连续的小峰。微观机理分析表明,诸多小峰是由合金内各微区相变点略有差异、相变不同步所形成的;单一大峰是在升温速率较快的条件下,各微区在较短时间内相继发生相变而形成的单一合成波。但相变热焓与升温速率无关。 相似文献
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TiNi形状记忆合金薄膜的位借与相变 总被引:2,自引:1,他引:1
用X射线衍射线形的傅里叶分析及电阻法,研究了溅射Ti-49.37at%Ni合金薄膜的位错组态及相转变温度随退火条件的变化规律,以及位错密度与相变温度的关系。研究结果表明:随退火温度升高和保温时间增加,平均位错密度下降,马氏体相变温度升高。位错密度的变化受析出相粒子的大小和分布制约。随位错密度增加,马氏体相变温度下降,R相变温度基本保持不变。 相似文献
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F. Chen Y. X. Tong X. L. Lu B. Tian L. Li Y. F. Zheng 《Journal of Materials Engineering and Performance》2012,21(12):2509-2514
This article studies the dependence of martensitic transformation on Mn:Sn ratio in Ni43Co7Mn50?x Sn x alloy and the shape memory behavior of Ni43Co7Mn43Sn7 in detail. The results show that all the transformation temperatures show a linear decrease with the decrease of Mn:Sn ratio. The similar tendency is also found in the change of T c. Ni43Co7Mn43Sn7 alloy exhibits a moderate shape memory effect and the maximum shape recovery strain is 2.96%. Temperature memory effect is also observed in Ni43Co7Mn43Sn7 alloy. 相似文献
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采用差示扫描量热法研究了时效处理对NiTi形状记忆合金加热相变过程的影响规律。结果表明:当时效温度低于瓦(特征转折温度)时,相变温度(As和Af)随时效温度的升高而升高;当时效温度高于瓦时,相变温度随时效温度的升高而下降。对于As,当时效15min时,T0=500℃,当时效30rain时,T0=400℃;对于Af,T0均为400℃。在300℃、400℃和500℃时效15min,加热相变过程为M→R和R→P两阶段,在600℃和700℃时效15min时,加热相变过程为M→P一阶段;当时效时间延长至30min时,加热相变过程由M→R和R→P两阶段相变过程变为M→P一阶段。时效温度为500℃和700℃时,体积转变率与温度关系曲线的斜率较大。 相似文献