Grain size dependence of deformation behavior in Ti–15Mo alloy prepared by powder metallurgy

To the best of our knowledge, this is the first report demonstrating grain refinement to 4 μm via a mass-production method for the Ti–15Mo alloy. Grain sizes ranging from 4 to 38 μm were achieved by controlling thermomechanical processing in powder metallurgy, combined with heat treatment using recycled coarse powders for additive manufacturing. The critical grain size for deformation twinning was investigated, alongside an analysis of the deformation behavior and mechanical properties of the Ti–15Mo alloy with various grain sizes. Upon refining the grain size to 7 μm, deformation twinning is inhibited, shifting the plastic deformation mechanism from mechanical twinning to dislocation slip. The yield strength can be adjusted between 921 and 715 MPa, with elongation ranging from 18.4 % to 34.4 %, by varying the grain size distribution ratio of small to large grains relative to 7 μm from 1.5 to 0.42. This strengthening effect primarily arises from dislocation strengthening, Mo solid solution, texture strengthening, and modifications in the Hall-Petch constant due to changes in deformation behavior during grain refinement. • The grains of Ti–15Mo alloy are refined to 4 μm without severe plastic deformation via powder metallurgy. • The grain size ranging from 4 to 38 μm of Ti–15Mo alloy was adjusted via thermomechanical process and heat treatment. • The deformation twinning is suppressed with decreasing the grain size. • The critical grain size for deformation twinning in Ti–15Mo alloy is 7 μm. • A combination of 921 MPa yield strength and 18.4 % elongation is achieved by adjusting the grain size distribution ratio.