Effects of thermomechanical process on the microstructure and mechanical properties of a fully martensitic titanium-based biomedical alloy

Thermomechanical treatments have been proved to be an efficient way to improve superelastic properties of metastable β type titanium alloys through several studies. In this paper, this treatment routes, already performed on superelastic alloys, are applied to the Ti–24Nb alloy (at%) consisting of a pure martensite α′′ microstructure. By short-time annealing treatments performed on the heavily deformed material, an interesting combination of a large recoverable strain of about 2.5%, a low elastic modulus (35 GPa) and a high strength (900 MPa) was achieved. These properties are shown to be due to a complex microstructure consisting of the precipitation of nanoscale (α+ω) phases in ultra-fine β grains. This microstructure allows a superelastic behavior through stress-induced α′′ martensitic transformation. In this study, the microstructures were characterized by X-ray diffraction and transmission electron microscopy and the evolution of the elastic modulus and the strain recovery as a function of the applied strain was investigated through loading–unloading tensile tests.

► Recent thermomechanical treatments are performed on a pure martensitic α′′ Ti–24Nb alloy. ► Ultra-fine β grains of 100 nm with nano-precipitates are achieved for this material. ► High superelasticity with low elastic modulus (35 GPa) and high strength is achieved.