Mechanical properties of Ti-Nb biomedical shape memory alloys containing Ge or Ga

Mechanical properties of Ti-24 mol% Nb-based shape memory alloys (SMA) containing 3 mol% Ga or Ge were characterized in this paper as a part of our systematic work for the development of beta-Ti based biomedical shape memory alloys. The alloys, called TiNbGa and TiNbGe, were produced by severe cold-rolling followed by a solution treatment at 1273 K for 1.8 ks. The apparent phase was beta (bcc) at RT in both the alloys. It was revealed by X-ray diffraction pole figure analysis that a {112}(beta)< 110 >(beta) recrystallization texture was well developed in TiNbGa. However, a {00.1}(beta)< 110 >(beta) deformation texture still remained in TiNbGe even after the solution treatment. Martensite transformation temperatures were significantly lowered by the addition of Ge, compared to Ga and Al additions. TEM-EDX observation revealed that (Ti, Nb)(5)Ge-3 particles are formed in TiNbGe regardless of the solution treatment. The (Ti, Nb)(5)Ge-3 particles were judged to be an ineffective strengthener, because significant hardening was not recognized in the flow-stress of TiNbGe. TiNbGa exhibited a large shape recovery of about 2% above RT in the strain-temperature curves during thermal cycles under external stress. The TiNbGe alloy exhibited superelasticity of 3.5% at RT. (c) 2005 Elsevier B.V. All rights reserved.