Microstructure characterization and tensile properties of Ti–15Mo alloy formed by directed energy deposition

Laser additive manufacturing of titanium (Ti) alloys results in a microstructure that differs from traditional manufacturing, affecting the subsequent alloy's performance. This paper details the correlation between the complex thermal cycles during directed energy deposition (DED) and the microstructure formation of a typical metastable β-titanium alloy Ti–15Mo, and elucidates its strengthening and toughening mechanisms. Relative to the forging standard, the yield and tensile strengths of the DED Ti–15Mo alloy increased by 51.4% and 28.7%, respectively, while retaining its elongation. Combined with experimental observation and finite element (FE) simulation, it was proven that the complex thermal cycles generated in the layer-by-layer stacking process of DED resulted in the presence of sub-structure in the Ti–15Mo alloy, precipitating the metastable ω phase, thereby improving its strength. Furthermore, the formation of {332}<113> twins in the tensile process was verified by SEM and EBSD, and the excellent elongation of the Ti–15Mo alloy was confirmed. This work is expected to lay the foundation for manufacturing excellent performing DED metastable β-titanium (Ti) alloys.