基于应变玻璃相变的应力调控热膨胀行为研究

Most materials expand or contract with increase or decrease in temperature; this effect is known as the normal "thermal expansion" behavior. In order to control the thermal expansion behavior of materials, two common approaches are widely used. One is combining materials with different thermal expansion behavior. However, this method may leads to local stresses and strains that often enhance materials fatigue and thus shorten the component lifetime. The other is altering the composition or thermal treatment of some special single, uncombined materials, which has attracted much attention in recent years... Different from the above two methods, in this proposal, the applicant intends to propose a new way, i.e., tune the thermal expansion behavior of a strain glass alloy by external stress. This idea is based on the strain glass transition and the heterogeneity of micro-structures in strain glass alloys. During strain glass transition on cooling, one portion of the high temperature phase transforms into nanodomains with larger volume; this transformation causes volume expansion. The remaining portion of the high temperature phase keeps unchanged and undergoes normal volume contraction. Thus, these two opposite effects will compensate each other to some extent. Furthermore, previous studies indicate that applying external stress will promote the population of these nanodomains. Therefore, by altering external stress, the proportion of the above two opposite effects will be changed, and consequently the thermal expansion behavior of the whole alloy can be adjusted. With increasing external stress, the thermal expansion coefficient is expected to vary linearly from positive through zero then to negative. .. This study will involve both experiment and computer simulation to achieve the final goal. On one hand, experimentally the applicant intends to prove the feasibility of tuning thermal expansion behavior by external stress in strain glass alloys, then to check whether such effect is universal by studying different strain glass systems and finally obtain the relationship between thermal expansion coefficient and external stress. On the other hand, with the help of Landau-Ginzburg simulation, the underlying mechanism of such effect is expected to be clarified, by probing the dynamic evolution of nanodomains under different external stress on cooling. This study can offer a new idea to control the thermal expansion behavior of a material precisely and also provide important implications in understanding the properties and structure of glassy materials.

为了满足不同领域对材料热膨胀性能的需求，一般通过复合材料或者成分调整等手段来实现对材料热膨胀行为的调控。本申请项目基于渐进式应变玻璃相变及其合金微结构的不均匀性，提出一种通过外加应力来调控材料热膨胀行为的新思路：即通过应力控制应变玻璃相变过程中纳米应变畴的数量和尺寸，进而减小、抵消、甚至逆转基体的正热膨胀行为，使得同一个材料在不同的应力作用下能呈现正热膨胀，零热膨胀，甚至负热膨胀。本项目拟首先从实验上探明应力调控热膨胀行为的可行性，普遍性和规律性；进而通过理论模拟与实验相结合的方式揭示其内在物理机制。本项目的工作可望为实现人为实时精确调控材料的热膨胀行为提供原理性基础；同时关于玻璃态材料微结构及其新功能性的探索也具有重要的理论研究价值。

热胀冷缩是材料本征的一种物理性能，因此为了调控材料的热膨胀性能，一般采用调整材料的成分或者进行材料复合的手段来实现。本项目研究基于应变玻璃合金中母相和纳米马氏体畴共存的天然复合结构，利用外加应力来调控纳米马氏体畴的大小和体积分数，进而达到调控合金宏观热膨胀行为的目的。本项目研究主要得到了以下结论：.（1）通过原位高分辨电镜观察，首次为应变玻璃的局域对称破缺及玻璃相变过程提供了直接证据，发现纳米马氏体畴在降温过程中出现、长大直至冻结的过程。基于这种不均匀微结构，研究了外加拉应力下，Ti-40Pd-10Cr合金的热膨胀行为的演变，随着拉应力的增加，热膨胀系数从正数逐渐变为零，甚至变为负数。Landau-Ginzburg模拟分析表明，热膨胀系数的变化主要归功于外加拉应力作用下，纳米马氏体畴在应力方向上的尺寸长大。.（2）研究发现随着C掺杂含量的增加， MnCu基合金的马氏体相变温度点急剧降低，同时相变伴随的热膨胀行为逐渐从负热膨胀变为在260-300K之间的近乎零热膨胀行为。该研究结果提供了一种利用缺陷掺杂改变合金的马氏体相变行为，进而调控材料的热膨胀行为的思路。.（3）开发了一系列的Fe，Mn掺杂的TiPd基应变玻璃合金，其应变玻璃化转变温度在室温附近。研究还发现掺氢的TiPd基马氏体合金在室温附近宽温域（250-400K）呈现出极高的阻尼性能（Q-1~0.02-0.09）。同时兼顾室温和高阻尼性能使得该合金远远超过现有的高阻尼合金，具有潜在的应用价值。. 本项目共在国际SCI期刊上发表学术论文9篇，其中包括Physical Review Letters 1篇，Acta Materialia 1篇, Physica Status Solidi B-Basic Solid State Physics 邀请论文 2篇，Materials Science and Engineering A 1篇，Journal of Applied Physics 1篇，Journal of Physics: Condensed Matter1篇, Applied Physics Letters 1篇,EPL1篇。项目组成员工参加国际会议2次，并作口头报告。本项目研究为有效调控应变玻璃合金的热膨胀行为提供了一种新的思路，同时拓展了应变玻璃合金可能的应用领域。