材料状态对NiTi形状记忆合金相变行为的影响

用金相显微镜观察了冷加工和固溶状态的显微组织形貌,用示差热量扫描法(DSC)系统研究了冷加工、固溶和时效处理对近等原子比的NiTi形状记忆合金的相变温度的影响。试验结果表明,冷加工态NiTi合金组织形态呈纤维状,固溶处理后组织形态呈等轴状。冷加工带来的大量变形缺陷抑制了热弹性马氏体的相变;冷加工态NiTi合金直接进行时效发生了P→M相变;经固溶处理后再进行时效则发生了P→R→M相变。NiTi合金在不同的热处理条件下发生了不同类型的热弹性马氏体相变。分析认为,应力、位错密度及析出相对NiTi合金热弹性马氏体的相变行为有重要的影响。

Effect of Material State on the Phase Transformation of NiTi Shape Memory Alloy

The effects of cold-working,solution treatment and aging on the phase transformation of near-equi-atomic NiTi shape memory alloy have been investigated systematically by means of DSC.The results show that the microstructure of the cold-worked NiTi wire is fibrous structure and the microstructure of solution treated NiTi alloy is equi-axial grains.The defects induced during cold-working restrained the phase transformation of thermoelastic martensite.When aging treatment was taken immediately after cold-working,the transformation process of NiTi alloy was P→M.When aging treatment was taken after solution,the transformation process of NiTi alloy was P→R→M.Different types of thermoelastic martensite transformation of the NiTi alloy took place under different treatment conditions.It is recognized that the stress,dislocation density and precipitates have big influence on the phase transformation behavior of thermoelastic martensite of NiTi alloy.