Ti–30Nb–10Ta–5Zr–0.3O (TNTZO) alloy, which is simplified chemical composition similar to that of biomedical Ti–29Nb–13Ta–4.6Zr alloy, and the same system alloys of TNTZO with different oxygen (O) and niobium (Nb) contents such as Ti–30Nb–10Ta–5Zr–0.5O, Ti–30Nb–10Ta–5Zr–0.6O alloys, and Ti–27Nb–10Ta–5Zr–0.3O, Ti–28Nb–10Ta–5Zr–0.3O and Ti–29Nb–10Ta–5Zr–0.3O alloys are fabricated by powder metallurgy processing, in which it undergoes severe deformation during swaging. Changes in the deformation behaviors of these alloys caused by small changes in the O and Nb contents are investigated in this study. The stress–strain curve of TNTZO changes nonlinearly with the strain and is characterized by a small stress hysteresis, indicating that TNTZO shows a nonlinear recovery behavior during unloading. This deformation in the alloy is a result of a typical elastic deformation as well as stress-induced martensitic transformation. However, with an increase in the O content, as in the case of alloys with 0.5O and 0.6O, the stress–strain curves change almost linearly with the strain and exhibit a linear recovery behavior during unloading without stress hysteresis. In such alloys, deformation is mainly caused by the typical elastic deformation. On the other hand, with a decrease in the Nb content, the stress–strain curves show two steps with an increase in the strain, and deformation is accompanied by stress hysteresis during both loading and unloading. This deformation is mainly caused by stress-induced martensitic transformation and reverse transformation.
