【作者】 刘俊峰；

【导师】 程晓敏；

【作者基本信息】 武汉理工大学 ， 材料学， 2005， 硕士

【摘要】 形状记忆合金利用应力诱发马氏体相变或温度诱发马氏体相变实现形状记忆效应,是一种新兴的功能材料。Fe-Mn-Si合金是一种实用性能优良、造价低廉的形状记忆合金材料,近年来成为人们研究的热点。尽管该合金研究起步较晚,但其在紧固件等方面应用的优越性使得对其研究进展迅速。 本文对Fe-Mn-Si合金进行了化学成分设计与分析、显微结构观察与分析、硬度测试、不同回复退火温度下形状记忆回复率测试、不同预变形量下形状记忆回复率测试以及形状记忆训练等试验研究。Mn、Si含量对合金的尼耳转变点、奥氏体转变终了温度、马氏体转变开始温度等参数有很强烈的影响,且由此影响合金的形状记忆效应。另外,Si的固溶强化作用提高了合金硬度。因此,合金成分选择至关重要。要产生应力诱发马氏体相变及逆相变,避免全位错滑移的引入,实现优良的形状记忆效应,合金中Mn的含量要控制在20%～30%,Si的含量要控制在4%～6%。本文采用工业纯铁、电解锰及纯硅通过真空熔炼制备得到Fe-22.72Mn-5.01Si合金。 Fe-22.72Mn-5.01Si合金高温淬火后得到单一奥氏体相。在外加应力作用下合金从面心立方结构奥氏体转变为密排六方结构马氏体。卸去外应力,对其进行回复退火,合金发生逆转变,从马氏体转变为奥氏体。合金的马氏体相变是层错形核机制,由Shockley不全位错的运动产生。同时由于层错能较低,两个Shockley不全位错和一片层错产生的新组态不易滑移,决定了其可逆运动途径的唯一性,从而实现形状回复。 在一定的变形范围内,Fe-22.72Mn-5.01Si合金的形状记忆回复率随着预变形量的增大而提高;随着回复退火温度升高而增加,且在600℃附近获得峰值。在训练过程中,合金的记忆回复率先逐渐上升,然后稳定。训练合金的显微组织为奥氏体和马氏体,可以观察到较清晰的奥氏体晶界;马氏体分布比较均匀,相互平行,交叉现象较少,有利于合金中马氏体逆转变的发生。更多还原

【Abstract】 Shape memory effect of alloy is obtained by making use of martensitic phase transformation induced by stress or temperature. Shape memory alloy is a new kind of function materials. And Fe-Mn-Si alloy is developed as shape memory alloy for its better practicability, lower cost and superiority when used as fastening pieces. As focus of recent research, Fe-Mn-Si alloy is researched widely and is progressed rapidly.In this dissertation, Fe-22.72Mn-5.01Si alloy was designed; its chemical constitution was anglicized, related microstructures were observed, its hardness was tested and shape memory restoring ratio of samples with same deformation annealed at different temperature and samples with different deformation annealed at the same temperature were measured based on experiments.. Some parameters such as Neel transition temperature, finishing temperature of austenitic phase transformation and starting temperature of martenstic phase transformation of the alloy are affected intensively by the content of Mn, Si. Hardness of the alloy is increased through solution strengthening. Thus, shape memory effect of the alloy is affected intensively by the content of Mn, Si, too. For these reasons, design of the alloy’s chemical constitution is critical. To gain stress induced martensitic phase transformation , martensitic reverse phase transformation and abstain slipping of perfect dislocation to obtain better shape memory effect, the content of Mn should be fixed in 20%~30% and the content of Si should be fixed in 4%~6%. Fe-22.72Mn-5.01Si alloy was obtained in this dissertation by vacuum melting industrial pure iron, electrolytic Manganese and pure Silicon.Fe-22.72Mn-5.01Si alloy is simple austenite after hot quenched. Austenite to martensite transformation takes place in the alloy when it is applied to external stress and the microstructure of predeformed samples is lath-shaped martensite distributed on austenite base. Martensite to austenite reverse transformation takes place when the alloy is annealed after the external stress is unloaded and the microstructure of annealed samples is austenite with relict martensite. Compared with the corresponding microstructure of predeformed samples, martensite is decreased, whichauthenticates martensitic reverse phase transformation has taken place. The alloy’s martensitic phase transformation is based on fault nucleation system and induced by the moving of Shockley imperfect dislocations. At the same time, the new formed configuration made up of two Shockley imperfect dislocations and a piece of fault can’t be slid easily because of low fault energy of the alloy, so the way of reverse transformation is determined exclusively.shape memory restoring ratio of Fe-22.72Mn-5.01Si is decreased when the predeformation of samples is increased in certain extent and increased when the annealing temperature is increased, better shape memory restoring ratio of the alloy can be obtained when the alloy is annealed at 600°C. In course of being trained, shape memory restoring ratio of the alloy is increased gradually at first, then stabilized slowly. The microstructure of trained samples is austenite and martensite, distinct grain boundary of austenite can be observed and martensite is distributed evenly, paralleled with each other except for fewer intercrossing.更多还原