Effect of aging on martensitic transformation and microstructure in Ni-rich TiNiHf shape memory alloy

(Ti + Hf)3Ni4 particles precipitate in Ni-rich TiNiHf alloys aged at 823 K. The results show that the transformation temperatures of the alloys and their stability during thermal cycling increase noticeably because the (Ti + Hf)3Ni4 particles strengthen the matrix. In addition, the martensite variants are preferentially oriented in the 823 K/5 h aged Ti29.4Ni50.6Hf20 alloy.