采用OM, EBSD, XRD, TEM和SQUID研究了3种不同Mn含量的固溶态Fe-(14~21)Mn-5.5Si-8.5Cr-5Ni合金在马氏体转变开始温度M_s以上10 K (M_s+10 K)变形前后的形状记忆效应和微观组织. 结果表明, 固溶态Fe-(14~21)Mn-5.5Si-8.5Cr-5Ni合金的形状记忆效应随Mn含量增加而增加. 这是由于: 一方面, 奥氏体屈服强度与应力诱发e马氏体临界应力的差值随着Mn含量的增加而增大, 即提高Mn含量增强了奥氏体抵抗塑性变形的能力; 另一方面, Mn含量的提高减小了应力诱发e马氏体的宽度, 抑制了α' 马氏体的引入, 从而提高了应力诱发e马氏体的可逆性。

Fe-Mn-Si base shape memory alloys (SMAs), as compared with Ni-Ti and Cu base SMAs, have attracted much attention since the 1980s due to their promising advantages, such as low cost, good workability and weldability. However, the recovery strain of polycrystalline Fe-Mn-Si base SMAs is only about 2%~3% except single crystals and ribbons ones. At the present time, in order to enhance the recovery strain of this kind of alloys, some methods such as thermo-mechanical training, ausforming and thermo-mechanical treatment are used. In recent years, the research group had prepared training-free cast Fe-Mn-Si base alloys showing an excellent shape memory effect (SME). Unfortunately, the grains of cast Fe-Mn-Si base alloys are coarse, certainly leading to low yield strength and recovery stress. Many factors affecting the shape memory effect, such as alloy elements, the amount of pre-strain, deformation temperatures, annealing treatments and the training, have been studied. However, there is a debate on the effect of Mn contents on the shape memory effect of Fe-Mn-Si base alloys. The aim of this work is to clarify the debate, shape memory effect and microstructures of solution treated Fe-(14~21)Mn-5.5Si-8.5Cr-5Ni alloys were investigated by OM, EBSD, XRD, TEM and SQUID before and after deformation at 10 K higher than their start temperature of martensitic transformation (M_s+10 K). The result showed that the shape memory effect of solution treated Fe-(14~21)Mn-5.5Si-8.5Cr-5Ni alloys increased with the Mn contents. There are two reasons for this result. One is that the difference value between austenitic yield strength and critical stress of stress-induced e martensite increased with the Mn contents. In other word, the ability resisting plastic deformation was improved by increasing the Mn contents. The other is that the reversibility of e martensite reverse transformation was enhanced by increasing the Mn contents because the width of stress-induced e martensite decreased while the α' martensite was difficult to be introduced with increasing the Mn contents。