Ti-50.8Ni合金的相变、形状记忆和超弹性特性

用热重分析仪、X射线衍射仪、光学显微镜、示差扫描热分析仪和拉伸试验研究了Ti-50.8Ni形状记忆合金的组织、相变、形状记忆效应(SME)和超弹性(SE)特性。结果表明,Ti-50.8Ni合金在600℃以下退火后组织呈纤维状,在该温度以上退火后组织呈等轴状。加热温度超过600℃后合金氧化加剧。随退火温度Ta升高,合金冷却/加热过程中的相变类型由A→R→M/M→R→A型向A→R→M/M→A型再向A→R/R→A型转变(A—奥氏体,R—R相,M—马氏体),合金的M相变温度升高,R相变温度降低,M相变热滞降低,合金室温特性由SME+SE向SE转变。形变温度Td<20℃时,合金弹簧呈SME+SE,Td>30℃时,合金弹簧呈SE。随Td升高,合金弹簧的应力诱发M应力升高。

Transformation, Shape Memory and Superelasticity Characteristics of Ti-50.8Ni Alloy

The microstructure,transformation,shape memory effect (SME) and superelasticity (SE) characteristics of Ti-50.8Ni shape memory alloy were investigated by thermal gravimetry,X-ray diffraction,optical microscopy,differential scanning calorimetry and tensile testing.The results show that the microstructure of Ti-50.8Ni alloy is fibrous after annealing below 600 ℃,while it is equiaxed after annealing over 600 ℃.The alloy oxidation speeds up when the heating temperature is over 600 ℃.With the annealing temperature Ta increasing,the transformation types of Ti-50.8Ni alloy change from A→R→M/M→R→A to A→R→M/M→A to A→R/R→A (A—parent phase,R—R phase,M—martensite),the M transformation temperature increases,the R transformation temperature decreases,the M transformation temperature hysteresis decreases,and the alloy’s characteristics at room temperature change from SME+SE to SE.Ti-50.8Ni alloy spring shows SME+SE with deforming temperature Td<20 ℃,and it shows SE with Td>30 ℃.The stress-induced martensite stress of the alloy spring increases with increasing Td.