含纳米颗粒的相变功能材料在外场下的响应研究

This project is to investigate the new functionalities of traditional precipitation hardened alloys that are two-phase nano-dispersions consisting of precipitates of a low-symmetry phase embedded into a cubic matrix. These functionalities are giant low-hysteretic strain responses generated by the displacive lattice rearrangements of nano-precipitates under external stimuli such as stress, electric and/or magnetic fields. This is a new concept for obtaining a remarkable combination of giant low-hysteretic responses and good mechanical properties in physically distinct material systems. Due to the difficulty of considering the heterogeneous effects associated with the complex nanostructures, the study of such an idea and its applications is, however, still at a very beginning stage. In this project, we, as pioneers of this field, propose to systematically study the prototyping materials and promising real material systems. We will first develop an advanced version of phase-field methods to consider the microstructure formation and evolution. With the aid from experimental observations and other theoretical and computational tools, we will put emphases on the effects of thermodynamic, crystallographic and kinetic parameters on the formation and evolution of nanodispersive systems, the effects of various defects and inclusions on the macroscopic properties, and the possible means of optimizing the nanodispersive microstructure by the thermo-mechanical/electric/magnetic treatments. The success of this project will be a help on formulating a transformative approach to the discovery and development of a new class of advanced functional materials with excellent properties, and generating initiatives for developing high-performance devices to be used in high-technological applications.

拟研究含有纳米颗粒的相变材料在外力、电场或磁场的诱发下改变其颗粒的晶格取向，从而使材料具有低耗散大响应的新功能特性。这是一种能够同时获取优异功能特性和良好力学性能的响应机制，并且能适用于具有不同物理特性的材料系统。然而，由于这类材料中两相共存微结构的高度复杂性，相关研究在国际上才刚刚开始。作为这一机制的提出者，我们将发展能够考虑材料微结构的相场方法，将结合实验报道和其他计算方法系统地研究模型材料和几类有望实现低耗散大响应的真实材料系统。将重点研究材料的晶体学、热力学参量等材料本征属性对微结构的产生和演化的影响；研究非均匀夹杂颗粒和缺陷对材料性能的影响；探索改变温度、施加应力、电场或磁场等方法来调控材料微结构的途径。本课题的成功实施有望为开发性能卓越，但是价格低廉、环境友好的新型功能材料开辟一条新途径，促进广泛应用于国防、航空航天和医疗等重要领域的各种高性能器件的发展。

本项目发展了研究相变材料微结构的模拟计算方法，使其能够描述的材料系统中有更多的自由度（比如晶格取向），进而更真实地模拟材料微结构的形成和演化。结合实验观测和其他分析计算方法，本项目还研究了热力学、晶体学参量等材料本征特性对材料微结构的产生和演化的影响；各种非均匀夹杂（沉淀）和缺陷（如位错）对材料性能的影响；温度、应力、电场、磁场等外界刺激下材料微结构的形成和演化。此外，针对位移型相变材料在相变温度以上广泛存在的性能特异，我们提出了基于纳米胚胎颗粒的响应机制：相变产物的胚胎颗粒可由材料中的缺陷引起，并与基体材料形成一种新的热弹平衡，该平衡不同于传统的基于热扰动形核生长动力学过程的热弹性平衡，是一个热力学意义上的能量平衡。因此，该平衡可在外场作用下调整纳米胚胎的尺寸和百分比，进而解释预转变材料中的超弹性、模量软化、超磁致伸缩、弥散相变、因瓦和艾林瓦等效应。该机制为通过简单热处理加工大幅提升材料性能提供了一种新的可能性。项目相关部分成果已在 npj Computational Materials, Physical Review B 等 SCI 期刊上发表论文15篇。