Additively manufactured Ti–6Al–4V alloy by high magnetic field heat treatment

Abstract

This work reports the use of a novel strategy, high magnetic field (HMF, 3T) heat treatment (HT), to modify the microstructure of Ti–6Al–4V (Ti64) alloy fabricated by laser-powder bed fusion (L-PBF) to improve mechanical properties. Applying an HMF-HT to L-PBF Ti64 at 800–900 °C increased the sub-grain boundaries in the α-phase from ∼7% to ∼21%. The distribution of high kernel average misorientation (KAM) values is consistent with the distribution of the sub-grain boundaries in the α-phase. This finding was further supported by analysis using the modified Williamson-Hall approach and transmission electron microscopy (TEM) characterization. HMF-HT accelerated the coarsening and globularization of the α-phase, resulting in thick α-laths (3.40 μm) and the formation of globular α-phase particles. The HMF-HT at 900 °C further increased the β-phase volume fraction from 6.5% to 13.4% with a larger lattice parameter of 3.2143 Å due to the resulting lower average V content (confirmed by TEM analysis). In addition, the HMF-HT rendered the α-variants to better align with the <11–20>α direction, where the prismatic and basal slips in the <11–20>α direction are the easiest slip modes to activate in the α-variants. These combined effects enhanced the tensile ductility of Ti64 to 15.4 ± 1.3%. HMF-HT can be used to effectively tune the microstructure and mechanical properties of L-PBF α-β titanium alloys.