基于记忆合金双晶片的新型热开关传热特性及其调控机制

热开关是指导热系数在温度、电场、磁场等环境刺激下发生较大变化的材料或器件。高性能热开关作为调控热流的新方法，在航空航天、能源环保等领域具有广泛应用。本项目选取其中最重要的类型之一——记忆合金型热开关，针对其尺寸大、装配复杂的主要缺点，提出一种基于记忆合金双晶片的新型驱动结构与开关机制，并重点研究其中关键传热过程的调控。测量镍钛记忆合金薄膜的主要热物性参数，探明组分、尺寸等因素对其传热特性的影响规律和作用机制；分析双晶片端部柔性接触界面的热导随表面粗糙度、化学态和残留水含量的变化，揭示其界面传热机理并发展调控方法；针对热开关的整体结构建立热-力耦合的唯象数值模型，为热开关的设计提供理论依据；选用并改良现有微纳加工工艺，制备热开关样品，并对其性能指标进行全面测试。项目成果将为此类热开关的设计制造提供关键依据，推动高性能热开关的研制和产业化应用。

Thermal switches are devices or materials that undergo large changes in thermal transport properties upon external thermal, electrical or magnetic stimuli. Enabling a new way to manipulate heat flow, high-performance thermal switches have wide potential applications in the aerospace industry as well as in developing sustainable energy technologies. Shape memory alloy actuated thermal switches is one of the most important existing types, but have drawbacks such as large size and complex assembly. The present project proposes a novel actuation concept based on shape memory alloy bimorphs that addresses these problems, and aims to study its key heat transfer characteristics. NiTi thin films are prepared and their thermal transport properties are measured to understand the influence of composition, size and other factors. The thermal interface conductance at the mechanical contact between the bimorph and the opposing surface is also experimentally determined and the roles of surface roughness, chemical termination and residual water molecules are clarified. A phenomenological model that combines thermal and mechanical effects is adopted to simulate the bimorph thermal switch numerically. Microfabrication processes are utilized and optimized to fabricate bimorph thermal switch samples, which are in turn characterized using a custom-built experimental setup. The outcome of this project will provide key insight in the development of thermal switches and ultimately accelerate their commercial application.