形变热处理制备的纳米晶NiTi形状记忆合金的超弹性行为

来源期刊:中国有色金属学报(英文版)2018年第3期

论文作者:E. MOHAMMAD SHARIFI A. KERMANPUR

文章页码:515 - 523

关键词:纳米晶材料;形状记忆合金;超弹性;形变热处理

Key words:nanocrystalline material; shape memory alloy; superelasticity; thermomechanical processing

摘    要:研究冷轧和后续退火形变热处理对Ni50Ti50形状记忆合金超弹性行为的影响。采用铜坩埚真空感应熔炼法制备样品。将成分均匀的样品进行热轧后在900 °C退火,然后再进行冷轧,冷轧后样品的厚度有不同程度的减少,最大可达 70%。透射电镜检测结果显示严重的冷轧导致Ni50Ti50合金中形成了纳米晶和非晶的复合显微组织。400 °C 下退火1 h后,冷轧样品中的非晶发生晶化形成纳米晶组织。随着冷轧变形量的增加,在超弹性实验中Ni50Ti50 合金的弹性应变增加,变形量为70%的冷轧-退火样品其弹性应变为12%。此外,随着变形量的增加,应力诱导马氏体相变的临界应力提高。值得注意的是,70%变形量的冷轧-退火样品的阻尼容量值为28 J/cm3,明显高于商业NiTi合金。

Abstract: Effects of thermomechanical treatment of cold rolling followed by annealing on microstructure and superelastic behavior of the Ni50Ti50 shape memory alloy were studied. Several specimens were produced by copper boat vacuum induction melting. The homogenized specimens were hot rolled and annealed at 900 °C. Thereafter, annealed specimens were subjected to cold rolling with different thickness reductions up to 70%. Transmission electron microscopy revealed that the severe cold rolling led to the formation of a mixed microstructure consisting of nanocrystalline and amorphous phases in Ni50Ti50 alloy. After annealing at 400 °C for 1 h, the amorphous phase formed in the cold-rolled specimens was crystallized and a nanocrystalline structure formed. Results showed that with increasing thickness reduction during cold rolling, the recoverable strain of Ni50Ti50 alloy was increased during superelastic experiments such that the 70% cold rolled-annealed specimen exhibited about 12% of recoverable strain. Moreover, with increasing thickness reduction, the critical stress for stress-induced martensitic transformation was increased. It is noteworthy that in the 70% cold rolled-annealed specimen, the damping capacity was measured to be 28 J/cm3 that is significantly higher than that of commercial NiTi alloys.

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