取向Ni-Mn-In基合金的马氏体相变行为及磁致应变研究

The maximum recoverable strain is related to the crystallographic orientation of the shape memory alloy. Thus, it is crucial to .obtain polycrystals with prefered orientation and favorable mechanical property from the viewpoint of pratical application. This .project proposes a new idea to produce Ni-Mn-In based magnetic shape memory alloy with high density, good mechanical property .and preferred orientatation by means of spark plasma sintering the ordered piled melt-spun ribbons, in order to improve the small.recoverable strain due to the isotropy of the polycrystals, self-collaboration between grains and the intergranular fracture due to .the intrinsic brittleness of intermetallics. The texture type, martensitic transformation behavior, magnetic property, charactoristics .of magnetic field induced reverse martensitic transformation as well as the recoverable strain caused by this process will be investigated. .The relationship between the texture and recoverable strain, and the influence mechanism of texture on the mangetic field induced shape memory effect will also be clarified.The aim of this project is to provide theory guidelines for the application of magnetic shape memory alloy.

形状记忆合金的最大可回复应变量与晶体学取向密切相关，因此，从工程实际应用出发，具有择优取向且机械加工性能良好的多晶材料是获得大可回复应变量的关键。本项目提出采用等离子放电烧结(SPS)有序堆叠的具有择优取向合金带材的方法制备致密度高、力学性能优异、且具有一定择优取向的多晶Ni-Mn-In基磁性形状记忆合金的新思路。解决由于多晶材料各向同性和晶粒间相互协调导致的可回复应变量小及金属间化合物易沿晶开裂的本征脆性。考查SPS烧结制备取向Ni-Mn-In基磁性形状记忆合金的织构类型、马氏体相变行为、磁性能、磁场驱动马氏体逆相变特征及此过程可回复应变量的大小，查明合金织构类型与可回复应变量的关系及织构对可回复应变量的影响规律，阐明织构影响Ni-Mn-In基合金马氏体相变行为和磁致形状记忆效应的内在机制，为磁性形状记忆合金的工程实际应用提供理论指导。

本项目通过单辊急冷甩带的方法制备具有强择优取向的Ni-Mn-In合金薄带，研究表明，单辊转速对带材的择优取向有较大影响，单辊转速为15m/s时，织构强度最高，织构类型为(001)<100> 及 (001)<350>。将晶粒具有明显择优取向的带材有序堆叠，经放电等离子烧结（SPS）后块材的致密度与铸锭接近，织构强度与烧结前带材相近，而力学性能较之铸锭有大的提高。600℃烧结后断裂强度和断裂应变分别为1200MPa和14%（普通铸锭分别为950MPa和7%）。研究表明，通过改变温度和压力等烧结条件，可在一定程度上控制烧结后块体材料的织构强度。低温烧结（600℃）后块体材料的晶粒仍具有较强的择优取向，而较高温度烧结后（700℃以上），晶粒长大，择优取向变弱。.烧结制备的块体材料具有磁场驱动马氏体逆相变现象，且逆相变过程伴随着应变回复。目前实验表明，600℃烧结的块体材料温度驱动的形状记忆可回复应变量最大为6%。本项目的研究表明，带材堆叠烧结制备取向多晶成为在合金中获得织构的一种有效方法，并且在取向多晶中实现大的应变回复（形状记忆效应）对于Ni-Mn-In合金的工程实际应用具有重要的意义。