Microstructure tailoring of Ti-15Mo alloy fabricated by selective laser melting with high strength and ductility

In this study, selective laser melting (SLM) of Ti-15Mo alloy was systematically investigated, especially in its densification, microstructure and mechanical properties. At low scanning speed, the formation of spherical holes are mainly due to gas porosity brought about by residual gases. At high scanning speed, the lack of fusion (LOF) defects are presented because of the insufficient energy density, which is very detrimental to the ductility. Owing to the difference of the temperature gradient, the transition from the cellular crystals to equiaxed crystals has been observed in XY plane while the XZ plane are mainly consist of columnar crystals which are radiating along the edge of the molten pool. As a result of the retention of a reasonable level of omega phase, high dislocation density, finer grains, the twinning-induced plasticity (TWIP) and the changes of texture orientation, the Ti-15Mo samples processed by the SLM achieve a greater combination of high tensile strength of 840.41 MPa and a high elongation of 32.37%, which are higher than those reported so far. The twins become denser and thicker with increasing strain, and the average of twin widths with various strains were calculated to 7 mu m at strain of 10%, 4 mu m at strain of 15% and 2 mu m at strain of 20%.