镍钛形状记忆合金在特定内应力场下异常弹热效应的机制研究

Due to the large entropy change during the stress-induced martensitic transformation (MT) and good mechanical property, Ni-Ti shape memory alloy (SMA) has become the most potential candidate for the elastocaloric materials. Associated with the aging under stress, the Ti3Ni4 precipitate or deformation dislocation can introduce special internal stress field into Ni-Ti SMA, and induce two types of abnormal elastocaloric effect: the inverse elastocaloric effect (where loading process causes the specimen temperature decrease and unloading process causes the temperature increase); and the martensite elastocaloric effect (where the elastocaloric effect can be obtained even in the martensite phase). The present research will focus on: (1) indicating the internal stress filed caused by the Ti3Ni4 precipitate, observing the microstructural evolution during the stress-induced inverse R-B2 MT, revealing the mechanism of the inverse elastocaloric effect; (2) analyzing the formation process of the internal stress field caused by deformation dislocation, indicating the pseudoelasitc behavior of R phase, revealing the mechanism of the martensite elastocaloric effect; (3) associated with different aging factors, controlling the Ti3Ni4 precipitate by using Ni-Ti single crystals and the dislocation by employing cold-drawn and cold-rolled methods, in order to control the internal stress field and abnormal elastocaloric effects. The purpose of this project is to perfect the mechanism of two types of abnormal elastocaloric effects in the Ni-Ti SMA and effectively control them, in order to lay the groundwork for design and application of the new elastocaloric materials.

镍钛形状记忆合金（Ni-Ti SMA）以其应力诱发马氏体相变（MT）伴随的巨大熵变及优异的力学性能成为弹热制冷材料的首选。通过Ti3Ni4析出相或大变形位错结合应力时效，在Ni-Ti SMA中引入特定内应力场，从而获得两类异常弹热效应：反弹热效应（材料温度随加载降温、卸载升温）；马氏体弹热效应（马氏体相仍具有弹热制冷效应）。本课题将：（1）表征Ti3Ni4析出相所形成的特定内应力场，观测应力诱发逆R-B2 MT的微观结构演化，揭示反弹热效应起源；（2）分析变形位错形成特定内应力场的过程，阐明R相赝弹性行为，揭示马氏体弹热效应机制；（3）采用Ni-Ti单晶实现Ti3Ni4析出相的精确调控，利用冷拔、冷轧两类大变形实现位错的有效控制，结合不同的时效因素调控内应力场及异常弹热效应。以上研究旨在揭示Ni-Ti SMA中两类异常弹热效应的机制并有效调控，为新型弹热制冷材料的开发利用奠定理论基础。

本项目对镍钛形状记忆合金在特定内应力场下异常弹热效应进行了深入研究。（1）表征了Ti3Ni4析出相所形成的特定内应力场，观测了应力诱发逆R-B2 MT的微观结构演化，揭示了反弹热效应起源；（2）分析了变形位错形成特定内应力场的过程，阐明了R相赝弹性行为，揭示了马氏体弹热效应机制；（3）采用Ni-Ti单晶实现了Ti3Ni4析出相的精确调控，利用冷拔、冷轧两类大变形实现了位错的有效控制，结合不同的时效因素有效调控了内应力场及异常弹热效应。相关研究丰富了弹热效应理论并为今后的实际应用奠定了基础。在该项目资助下，以第一/通讯作者发表论文16篇，其中包括金属领域权威期刊Acta Materialia三篇，Scripta Materialia六篇，Physical Review Materials两篇。相关工作得到国内外学者的充分肯定，在国内外做邀请报告七次。项目帮助培养两名博士生一名硕士生，直接经费预算60万元，支出60万元，各项支出基本与预算相符。