大可逆应变Ni-Mn-In多晶的形变及回复机理研究

脆性大、可逆应变量小是目前制约Ni-Mn-In磁性形状记忆合金实际工程应用的重要因素。而纳米孪晶独特的微结构使得金属材料具有优异的综合力学性能、物理性能和使役行为。本项目拟通过掺杂Co元素和改变急冷甩带工艺参数获得具有纳米尺寸马氏体孪晶变体的Ni-Mn-In合金薄带，并将薄带有序堆叠采用放电等离子烧结的方法制备纳米孪晶Ni-Mn-In多晶块材，探究纳米孪晶提高形状记忆可回复应变的原因。在力学性能显著提高的基础上，考察纳米孪晶马氏体的应力应变行为特征，查明不同尺寸纳米孪晶在形变各阶段和卸载后回复过程中的迁动方式与特点，建立纳米孪晶尺寸与热致形状记忆可回复应变及磁致应变量的关系，观察纳米孪晶界面与位错等缺陷的相互作用，阐明纳米孪晶提高Ni-Mn-In多晶热致可回复应变的内在机理及对磁致应变的影响规律，为获得大可逆应变、高韧性的Ni-Mn-In磁性形状记忆合金提供理论及实验指导。

Brittleness and small reversible strain are the factors which restrict the engineering application of Ni-Mn-In magnetic shape memory alloy. Excellent mechanical property, physical property and driving behavior can be provided by the nanotwin in metals. This proposal plans to obtain Ni-Mn-In ribbons with martensitic twin variants in nanometer dimension by means of Co doping and melt-spinning technology, and prepare bulk polycrystals by spark plasma sintering the ordered piled melt-spun ribbons. The increase of shape recovery due to the nanotwins is needed to be found out. On the improvement of mechanical properties, the stress-strain behavior as well as the movement of nanotwin with different dimension during each stage of the deformation and recovery process are managed to be detected. The relationship between the dimension of nanotwin and recovery strain induced by heat or magnetic field will be built. The interaction of twin boundaries and dislocations are also needed to be investigated. Thus, based on the results obtained above, the mechanisms of improvement on shape recovery induced by.heat and the influence of nanotwin on magnetic field induced strain will be clarified. The aim of this proposal is to provide theoretical and practical guide for the application of magnetic shape memory alloy with large mangnetic field induced strain and high ductility.