具有弱一级马氏体相变Fe-Pd形状记忆合金的弹热效应机制研究

Shape memory alloy (SMA) exhibiting a stress-induced martensitic transformation (MT) is the most suitable material for the elastocaloric effect which was employed in the new refrigeration system. Compared with the SMA exhibiting a typical first-order MT, the Fe-Pd SMA exhibiting a weak first-order MT shows an elastocaloric effect with wide working temperature window (~160 K), high efficiency (~98%) and stable temperature change (the temperature attenuation is less than 0.2 K after 1000 times loading/unloading processes). Based on the previous study, this research will focus on: (1) the micro thermodynamics mechanism of elastocaloric effect in Fe-Pd SMA (the origin of the elastocaloric effect), in other words, the contribution of each factors to the elastocaloric effect; (2) the micro crystallography under the stress filed in the Fe-Pd single crystals with different crystal orientations, and the anisotropy of elastocaloric effect; (3) the influence of dislocation and domain boundary on the elastocaloric effect in Fe-Pd SMA. The purpose of this project is to perfect the micro mechanism of elastocaloric effect in the Fe-Pd SMA exhibiting a weak first-order MT, and to lay the groundwork for design and application of the new elastocaloric materials.

基于应力诱发马氏体相变的形状记忆合金（SMA）是呈现降温制冷弹热效应的首选材料。相比呈典型一级相变的SMA，具有弱一级马氏体相变的Fe-Pd SMA （[001]晶轴取向）呈现出宽温域（~160 K）、高能效（~98%）、温变稳定（1000次加卸载后温变衰减小于0.2 K）的特点。基于前期工作，本项目将研究：（1）Fe-Pd SMA弹热效应的热力学微观机制（本质起源），即各因素对弹热效应的定量贡献；（2）不同晶轴取向Fe-Pd单晶应力场下的微观晶体学，及弹热效应的各向异性；（3）位错与畴界对Fe-Pd单晶弹热效应的影响规律。以上研究旨在揭示具有弱一级马氏体相变Fe-Pd SMA弹热效应的机制，为新型弹热制冷材料的开发利用奠定理论基础。

本项目对具有弱一级马氏体相变的Fe-Pd SMA的弹热效应进行了深入研究，结果表明：（1）Fe-Pd SMA弹热效应的绝大部分贡献（约70%）来源于弹性变形（杨氏模量随温度的急剧变化），部分（约30%）来源于相变潜热。（2）Fe-Pd SMA弹热效应在[001]方向获得最大值，[111]方向最次之，且压缩所致弹热效应明显高于拉伸所致。其原因归咎于Fe-Pd SMA较大的弹性各向异性值（约4-10）。（3）Fe-Pd SMA在高周期疲劳实验中呈现出优异的力学性能，尤其是在[001]方向的压缩测试，且整体变形过程为均匀连续变化。其原因主要归咎于Fe-Pd SMA的马氏体变体呈现沿压缩方向的连续晶格变化，该过程类似弹性变形。（4）发现了两种异常的弹热效应，即反弹热效应与马氏体状态下的弹热效应，这两种特殊的弹热效应都与材料中特定的内应力场有紧密联系。综上所述结果，Fe-Pd SMA具有优异的疲劳性能且温度变化均匀，但其温度变化幅度相对较小。通过引入特定内应力场可以实现异常的弹热效应。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。项目资助发表SCI论文13篇（第一作者7篇，通讯作者5篇）。正在培养博士3名，硕士1名，完成本科毕设2人次。项目投入经费21万元，支出20.9745万元，各项支出基本与预算相符。