Microstructural Evolution and Tensile Properties of Direct Energy Deposited Ti-4Al-5Co-0.25Si Alloy During Heat Treatment

Additive manufacturing (AM) stands as an advanced manufacturing process, successfully utilized for the fabrication of high-value titanium components. However, these components have yet to find widespread use in industrial applications due to their inadequate performance when compared to conventionally processed parts. Consequently, there is a pressing demand to develop new alloys and microstructural control strategies to overcome this limitation. Here, we have designed a cost-effective Ti-4Al-5Co-0.25Si alloy for use in laser-based direct energy deposition additive manufacturing. The selection of solute elements has resulted in both solute strengthening and grain refinement. Additionally, the implementation of a heat-treatment schedule has allowed for control over the phase constituents and their stability. The as-fabricated alloy exhibits a prior-β grain size of ~50 μm, α plate thickness of ~0.6 μm, and tensile strength of 1145MPa. Subsequent heat treatment induces the formation of subgrains, discontinuous grain boundary α and metastable β phases, and ultrafine martensitic features ranging from 40 to 100nm. Moreover, this heat treatment improved the tensile strength of the alloy to 1500MPa while maintaining an elongation of ~5%. Importantly, the proposed hierarchical structured alloy offers an economical alternative, outperforming commercially available titanium alloys. This study presents a new direction for further research into alloy and microstructural design, aiming at the development of low-cost, high-performance titanium alloys suitable for additive manufacturing.