Martensitic Transformation Behavior and Shape Memory Effect of anAged Ni-rich Ti-Ni-Hf High Temperature Shape Memory Alloy

摘要

The martensitic transformation behavior and shape memory effect (SME) have beeninvestigated in a Ni-rich Ti_(29.6)Ni_(50.4)Hf_(20) high temperature shape memory alloy (SMA) in the present study. After aging, the transformation temperatures of Ti_(29.6)Ni_(50.4)Hf_(20) alloy increase obviously due to the precipitation of (Ti,Hf)_3Ni_4 particles. And the transformation sequence changes from one-step to two-step. When the experimental alloy is aged at different temperatures for 2h, the transformation temperatures increase rapidly with increasing the aging temperature and then change slightly with further increasing the aging temperature. Most of the martensite variants preferentially oriented in the ged Ti_(29.6)Ni_(50.4)Hf_(20) alloy. The aged Ti_(29.6)Ni_(50.4)Hf_(20) alloy shows the better thermal stability of ansformation temperatures than the solution-treated one because the precipitates depress theintroduction of defects during thermal cycling. In addition, the proper aged Ti_(29.6)Ni_(50.4)Hf_(20)alloy also shows the larger SME than the solution-treated one since the precipitates strengthen the matrix strongly.