Additive manufacturing of a novel alpha titanium alloy from commercially pure titanium with minor addition of Mo2C

In this study, a fully dense and crack-free alpha titanium alloy was fabricated using selective laser melting (SLM) of commercially pure titanium (CP Ti) blended with 1 vol.% micrometre-sized Mo2C powder. The microstructure and mechanical properties of the fabricated Ti alloy were systematically investigated. It was found that the fabricated Ti alloy consisted of both alpha (alpha) and beta (beta) phases and exhibited a nest-like inhomogeneous microstructure with graded local phase formation, composition and crystallographic texture. This novel microstructure was formed through melting and rapid solidification of CP Ti and Mo2C during SLM, assisted by the high laser absorptivity and resultant high temperature rise of the Mo2C powder. The fabricated Ti alloy exhibited higher tensile strength (similar to 1250 +/- 50 MPa) and improved ductility (elongation similar to 17 +/- 1%) when compared to CP Ti fabricated using the same SLM process. The underlying reasons were mainly attributed to (i) the nest-like in-homogeneous microstructure consisting of fine grained alpha-Ti and beta-Ti, (ii) the overall solid solution strengthening of the Ti matrix by interstitial C, and (iii) the high dislocation density in the Ti matrix arising from the mismatch between alpha-Ti and beta-Ti phases. This study not only provides a fundamental knowledge about the modification of CP Ti with minor addition of secondary particles through SLM but also provides insight into the fabrication of in-homogeneous Ti alloys with graded microstructure and local composition through SLM for enhanced mechanical properties.