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利用Fe-Mn-Si基合金凝固过程中固态转变残留的条状δ铁素体对奥氏体晶粒进行区域化分割, 实现应力诱发ε马氏体的区域化形成, 提高了合金的形状记忆效应. 根据Hammar铬镍当量公式制备了铬镍当量比为1.85的铸态Fe-18Mn-5.5Si-9.5Cr-4Ni合金. 利用OM和VSM(振动样品磁强计)研究了合金的室温组织和磁性能. 结果表明, 在铸态Fe-18Mn-5.5Si-9.5Cr-4Ni合金的室温组织中获得了条状δ铁素体. 这些条状δ铁素体将奥氏体晶粒分割成了若干小区域, 变形时能约束不同区域应力诱发ε马氏体的扩展, 使其以区域化的方式形成. 由于应力诱发ε马氏体的区域化形成减少了不同区域马氏体之间的碰撞, 在未经任何处理的铸态Fe-18Mn-5.5Si-9.5Cr-4Ni合金中获得了4.9%的可恢复变形量.

Low cost Fe-Mn-Si based shape memory alloys (SMAs) has not got widely applications because of their poor shape memory effect (SME) and the need of thermo-mechanical training, so developing training-free Fe-Mn-Si based SMAs with high memory property is significant. In the present study, it was put forth that the formation of stress-induced ε martensite in a domain manner could improve the SME of Fe-Mn-Si based SMAs and it could be realized through subdividing austenite γ grains into smaller domains using the residual lathy δ ferrite phase. According to Hammar's equivalents, a cast Fe-18Mn-5.5Si-9.5Cr-4Ni alloy with Cr/Ni equivalent ratio of 1.85 was prepared. OM and VSM (vibrating sample magnetometer) examination showed that the as-cast microstructure consists of γ austenite and lathy δ ferrite phase, and the lathy δ ferrite subdivided the austenite grains into smaller domains, which makes the stress-induced ε martensite bands form in a domain manner. Because the collisions between domain-like martensite bands were reduced, a high recovery strain of 4.9% was attained in the as-cast Fe-18Mn-5.5Si-9.5Cr-4Ni alloy. This result provides a novel way of developing training-free Fe-Mn-Si based SMAs. It can be expected that the SME of cast Fe-Mn-Si based SMAs will be further improved through modifying and optimizing alloy compositions, solidification parameters and heat treatment process.