Study of superior strength in Ti15Mo alloy manufactured using selective laser melting

Abstract

A biomedical Ti15Mo (wt%) alloy with a relative density of 99.9% was successfully fabricated using selective laser melting. Characterization of its microstructure revealed that it possessed a β phase with embedded nanometer-sized isothermal ω precipitates, accompanied by a large number of dislocations. The formation of isothermal ω precipitates was ascribed to the effect of in-situ heat treatment, and resulting to a superior strength of the as-built Ti15Mo. The existence of isothermal ω precipitates triggered a dislocation slip instead of {332}<113> twins, and the interaction between gliding dislocations with ω precipitates significantly enhanced the yield strength of as-built Ti15Mo to 1000–1200 MPa, which is significantly higher than that of solution-treated Ti15Mo with about 400–700 MPa. The grain size, amount of isothermal ω precipitates increased with decreasing scanning speed, but the number of defects was just opposite. The defects, as potential sites for crack initiation, had a significant influence on the elongation but a negligible influence on the yield strength of the as-built Ti15Mo alloy.