Influence of heat treatment on the tensile properties of Ti–15Mo additively manufactured by laser metal deposition

Abstract

A bidirectional powder deposition strategy was employed to additively manufacture Ti–15Mo wt% using laser metal deposition. The as-built alloy was subsequently subject to post-fabrication heat treatment. Microstructural characterisation was conducted in the heat-treated state and also after uniaxial tensile deformation. X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy were employed in the heat-treated state. Electron backscatter diffraction was used in investigating the deformed microstructure. Columnar β grain refinement was achieved by fragmentation from a combined contribution from precipitated phases and deformation induced products. The three distinct microstructural zones, namely the fusion, remelted and heat affected zones, observed in each deposited layer of the as-built microstructure were retained after sub-β-solvus heat treatment but completely erased in the super-β-solvus microstructure. Accommodation of plastic deformation in β matrix was by a combination of slip and primary α′′ martensite which formed preferentially at grain boundaries. Elastic modulus decreased from 86.85 ± 0.45 GPa in the as-built alloy to 72.8 ± 0.65 GPa after heat treatment. Ultimate tensile strength of 1168± 1.12 MPa from the heat-treated sample represents only a marginal increase from that of the as-built sample of 1099± 2.3 MPa. This was accompanied by a small decrease in total elongation.