The Design And Research Of Fe-Mn-Si Shape Memory Alloy

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.