The mechanical and microstructural behavior of heat treated, texture-controlled Ti-10%Mo alloys manufactured by laser powder bed fusion

Abstract

The crystallographic texture of additively manufactured metals can change significantly depending on process parameters, which in turn affects mechanical performance. Titanium with 10 wt% molybdenum (Ti-10Mo) displays a significant oriented-to-misoriented transition (OMT) when laser scan speed is increased from 500 mm/s to 2000 mm/s at a constant volumetric energy density of 130 J/mm3. This alloy showed no significant ductility as-printed or when solution treated and air quenched due to ω nanoprecipitates and α’’ martensite but had an elongation to failure of 14.3% when heat treated for 3 h at 700 °C into a duplex α+β microstructure. Comparison of heat treated oriented, semi-oriented, and misoriented microstructures showed an increase in yield strength isotropy but a decrease in strength hardening rate isotropy with decreasing texture. Tensile plastic deformation was found to occur preferentially in the β-phase along the close packed {110} slip system, but also in the α-phase via the pyramidal slip system. Decreasing texture suppressed grain rotation towards these slip systems, leading to greater strain hardening. Fracture was shown to occur at the α-β interfaces, particularly at grain boundary nucleated α grains.