Phase transformation and precipitation in aged Ti–Ni–Hf high-temperature shape memory alloys
Phase transformation and precipitation in aged Ti–Ni–Hf high-temperature shape memory alloys
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DOI：
10.1016/j.msea.2006.01.099
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发表时间：
2006-11
期刊：
影响因子：
6.4
通讯作者：
Xianyu Meng;W. Cai;Yufeng Zheng;L. C. Zhao
中科院分区：
文献类型：
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作者：
Xianyu Meng;W. Cai;Yufeng Zheng;L. C. Zhao
Ti-Ni-Hf三元高温形状记忆合金因其相变温度高、热稳定性好、成本低而受到人们的广泛关注。然而，Ti-Ni-Hf合金的塑性较差，形状记忆效应仅为3%左右，限制了其应用。众所周知，提高高温形状记忆合金形状记忆性能的方法有三种：（a）冷轧+退火;（B）向合金中添加另一种元素;（c）时效。这些方法不适合于改善Ti-Ni-Hf合金的性能。本文提出了一种通过时效处理将富镍Ti-Ni-Hf合金作为高温形状记忆合金的方法。对于富镍的Ti 80 − xNixHf 20合金（数字以.%表示）在823 K时效2 h后，合金的相变温度平均提高100 K以上。特别是对于Ni含量小于50.6at.%的合金，时效后马氏体相变开始温度高于473 K。透射电子显微镜显示时效后存在（Ti+Hf）3 Ni 4沉淀。与富Ni Ti-Ni合金中Ti 3 Ni 4颗粒的析出相比，富Ni Ti-Ni-Hf合金中（Ti+Hf）3 Ni 4颗粒的析出需要更高的温度和更长的时间。
More attention has been paid to ternary Ti–Ni–Hf high-temperature shape memory alloys (SMAs) due to their high phase transformation temperatures, good thermal stability and low cost. However, the Ti–Ni–Hf alloys have been found to have low ductility and only about 3% shape memory effect and these have hampered their applications. It is well known that there are three methods to improve the shape memory properties of high-temperature SMAs: (a) cold rolling+annealing; (b) adding another element to the alloy; (c) aging. These methods are not suitable to improve the properties of Ti–Ni–Hf alloys. In this paper, a method of conditioning Ni-rich Ti–Ni–Hf alloys as high-temperature SMAs by aging is presented. For Ni-rich Ti80−xNixHf20alloys (numbers indicate at.%) the phase transformation temperatures are on average increased by more than 100K by aging at 823K for 2h. Especially for those alloys with Ni contents less than 50.6at.%, the martensitic transformation start temperatures (Ms) are higher than 473K after aging. Transmission electron microscopy shows the presence of (Ti+Hf)3Ni4precipitates after aging. Compared with the precipitation of Ti3Ni4particles in Ni-rich Ti–Ni alloys, the precipitation of (Ti+Hf)3Ni4particles in Ni-rich Ti–Ni–Hf alloys needs higher temperatures and longer times.