Hot deformation mechanisms of a metastable Ti-18Mo alloy

Metastable molybdenum (Mo)-based titanium alloys exhibit a low Young’s modulus, along with excellent biocompatibility, corrosion resistance, and mechanical properties, making them ideal for biomedical applications. The microstructure of Ti-Mo alloys can be tailored through thermomechanical processing, where Mo diffusion significantly influences microstructural evolution. To investigate the deformation mechanisms of a Ti-18Mo alloy, hot compression tests were performed using a Gleeble® 3800 in both the α+β- and β-phase regions at temperatures ranging from 610 °C to 910 °C and strain rates between 0.01 s^-1 and 10 s^-1, reaching final strains of 0.50 and 0.80, followed by an immediate water quench. Scanning electron microscopy images and electron backscatter diffraction measurements were used to examine the microstructure of the deformed samples in the α+β- and β-phase regions, respectively. In the β-phase region, the flow curves exhibit a broad work hardening, uncommon in various β-Ti alloys, representing a slowing of dynamic restoration processes, likely due to the influence of Mo on the softening kinetics. Flow curves from α+β-phase deformation show a softening after the peak value, attributed to the globularisation of the α phase. Heterogeneous microstructures were observed during deformation in both regions, indicating that the subgrain formation and α phase globularisation primarily occurred near the previous grain boundaries. Dynamic recovery, dynamic recrystallisation, subgrain size, and α phase globularisation were quantified and correlated with deformation parameters and the influence of Mo.