Effect of low temperature aging on superelastic Behavior in Biocompatible β TiNbSn alloy

Superelasticity of beta Ti-16 at%Nb-4.8 at%Sn alloy consisting of non- (or minimal-) cytotoxic elements was investigated for biomedical applications as functions of,deformation temperature and aging heat treatment after quenching. As-quenched Ti-16Nb-4.8Sn having A(f) (the reverse martensitic transformation finish temperature) of 266K exhibits superelasticity at human body temperature (310K) with an elastic recovery strain of 3.2%. Af decreases with increasing aging temperature in the range of 353 to 423 K or with increasing aging time at 423 K. It is confirmed from TEM observation and Young's modulus measurements that omega) transformation occurs on aging at 423 K for 500 h. Stress for inducing martensitic transformation, am, increases with aging. Stress-strain curves showing superelasticity are quite similar to each other when as-quenched or aged samples are deformed at such temperatures that they have the same sigma M. It is concluded that maximum superelastic recovery strain can be obtained at intended temperature, e.g. human body temperature, in beta Ti-Nb-Sn alloys by aging at relatively low temperatures.