基于马氏体区域化形成的免训练铸造Fe-Mn-Si-Cr-Ni形状记忆合金 Ⅱ.退火对形状记忆效应的影响

A TRAINING-FREE CAST Fe-Mn-Si-Cr-Ni SHAPE MEMORY ALLOY BASED ON FORMATION OF MARTENSITE IN A DOMAIN MANNER Ⅱ.Influence of annealing on shape memory effect

采用OM和铁素体测量仪研究了铸态Fe-18Mn-5.5Si-9.5Cr-4Ni合金的微观组织随退火温度的改变及其对合金形状记忆效应的影响.结果表明,在773-1173 K之间退火处理能进一步提高合金的形状记忆效应.经973 K退火30 min后,合金的可恢复变形量达到了6.4%,比训练4次的常规Fe-14Mn-5Si-8Cr-4Ni合金高1.2%.当铸态合金在低于1173 K退火30min后,δ铁素体仍为条状,变形时能使应力诱发ε马氏体以区域化的方式形成,合金具有良好的形状记忆效应;当退火温度高于1273 K时,δ铁素体将固溶到奥氏体中,体积分数减少.当退火温度进一步升高到1423 K时,δ铁素体的体积分数显著增加,形态由条状演变为岛状.条状δ铁素体体积分数的减少和岛状δ铁素体的形成导致δ铁素体不能有效分割奥氏体晶粒,合金的形状记忆效应显著下降.

The microstructure and memory property evolutions of as-cast Fe-18Mn-5.5Si- 9.5Cr-4Ni alloy with annealing temperature were investigated using OM,ferrite measuring instrument and bending method.The results showed that when the as-cast Fe-18Mn-5.5Si-9.5Cr-4Ni alloy was annealed between 773 and 1173 K,its shape memory effect（SME） was further improved.A high recovery strain of 6.4%was obtained only through annealing the as-cast alloy at 973 K for 30 min,which is 1.2%higher than that of the conventional Fe-14Mn-5Si-8Cr-4Ni alloy after four times thermo-mechanical training.When the as-cast Fe-18Mn-5.5Si-9.5Cr-4Ni alloy was annealed below 1173 K for 30 min,the morphology ofδferrite phase was still lathy and it could make the stress-inducedεmartensite form in a domain manner during deformation,which is the reason why the good SME was obtained in the as-cast alloy annealed below 1173 K for 30 min.When the annealing temperature was above 1273 K,theδferrite phase would dissolve in the austenite and its amount decreased. When the annealing temperature was further increased to 1423 K,the amount ofδferrite phase remarkably increased and its morphology evolved into the island from the lath.The austenite grains could not be well subdivided into smaller domains due to the decrease of lathyδferrite phase or the formation of islandδferrite phase.The SME of this as-cast alloy dramatically decreased when annealed above 1273 K.