Strengthening effect of Mo in biocompatible titanium alloys

Abstract

Metastable titanium alloys containing molybdenum (Mo) are promising for biomedical applications due to their superior mechanical properties. To investigate the influence of Mo content on thermomechanical processing, the deformation mechanisms in Ti-Mo alloys were analysed using hot compression experiments performed on Ti-12Mo and Ti-18Mo. Tests were carried out in both the alpha+beta-and beta-phase regions over a temperature range of 610 degrees C-910 degrees C and at strain rates from 0.01 s(-1)-10 s(-1), up to a true strain of 0.80, followed by immediate water quenching. Microstructural characterisation of samples tested in the alpha+beta-and beta-phase regions was performed using scanning electron microscopy images and electron backscatter diffraction measurements, respectively. Flow curves in the beta-phase region display pronounced work hardening, a behaviour rarely observed in beta-Ti alloys, which is likely attributed to suppressed dynamic recovery influenced by Mo. In alpha+beta-phase deformation, flow curves exhibit softening after reaching peak values, corresponding to morphological changes in the alpha phase. Due to the slow diffusivity of Mo, subgrain formation and alpha-phase globularisation were primarily confined to prior beta grain boundaries, resulting in a heterogeneous deformed microstructure. The extent of dynamic recovery, subgrain size, and dynamic alpha-phase globularisation were quantified and compared between the investigated alloys. Mo retards dynamic recovery and alpha-phase globularisation, increasing strength in the beta-phase region but reducing it in the alpha+ beta region.