Research Of Fe-Mn-Si Based Shape Memory Alloy And Its Coupler

The influence of chemical component, heat treatment process, microstructure and stacking fault energy on shape memory effect of Fe-Mn-Si, Fe-Mn-Si-Cr-Ni and Fe-Mn-Si-C alloys was investigated. The coupler of Fe-Mn-Si-C alloys was developed and the influence of bearizing rate of coupler, connection length and thickness of pipe wall on the connection strength and pressure resistance was analyzed. The results show that the addition of carbon, chrome and nickel elements into Fe-Mn-Si alloys improves the shape memory effect of the alloys greatly; proper heat treatment process helps to achieve the best shape memory effect of alloys; quenching temperature affects shape memory effect of alloys significantly; the maximum shape recovery ratio is achieved in alloys quenched from 700℃.Rapid cooling process can improve the shape recovery ratio. When heated to 50℃, shape recovery takes place in alloys subjected to predeformation. The velocity of shape recovery reaches a maximum at the range of 50-150℃ and nearly remains stable with further increasing of quenching temperature. The shape recovery decreases with the increasing of predeformation amount. The stacking fault probability of alloys at forged state and quenched state was measured by X-ray diffraction peak displacement method. It is found that the stacking fault probability of Fe-Mn-Si-Cr-Ni and Fe-Mn-Si-C alloys firstly increases with the increasing of quenching temperature, reaches a maximum at the range of 600-700℃, and then decreases with further increasing of quenching temperature; the stacking fault probability of Fe-Mn-Si alloys varies contrarily and slightly compared with that of above both alloys. The aggregation of Cr, Ni, C atoms and quenched-in vacancies is responsible for the influence of quenching temperature on the stacking fault probability of alloys.The optical microscope and transmission electron microscope were used to observe the microstructure of alloys subjected to different predeformation and quenched from different temperature. It is found that heat inducedε-martensite has double effect on shape memory effect of alloys. Porper quantities of heat inducedε-martensite benefit shape memory effect of alloys. The morphologies of stacking fault and martensite inquenched alloys may affect shape memory effect of alloys. Low stress induced ε-martensite laminar plates are liable to disappear due to the inverse phase transformation of ε→γ. When heated, high stress induced ε-martensite plates that are larger and intersected are difficult to be recovered.The coupler maded of Fe-Mn-Si-C shape memory alloys has very high connection strength and good pressure resistance. The connection strength increases with the increasing of bearizing rate of coupler and thickness of pipe wall, but decreases with the increasing of connection length. The addition of carbon atom doesn't reduce the corrosion resistance of alloys.