Microstructural evolution and tensile properties of direct energy deposited Ti-4Al-5Co-0.25Si alloy during heat treatment

• Published in: Journal of alloys and compounds 2024-07, Vol.993, p.174657, Article 174657
• Main Authors: Narayana, P.L., Kim, Jae H., Hong, Jae-Keun
• Format: Article
• Language: English
• Subjects: Additive manufacturing; Cost-effective alloys; High-strength materials; Microstructure control; Novel titanium alloy
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2024.174657

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 1145 MPa. Subsequent heat treatment induces the formation of subgrains, discontinuous grain boundary α and metastable β phases, and ultrafine martensitic features ranging from 40 to 100 nm. Moreover, this heat treatment improved the tensile strength of the alloy to 1500 MPa 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. •A novel low-cost and high-strength Ti-4Al-5Co-0.25Si alloy was designed for additive manufacturing.•As-fabricated alloy showed equiaxed prior-β grains (∼50μm) with fine α plates.•Sub-transus heat treatment for various time intervals significantly alters the alloy's phase stability and microstructure.•After heat treatment for 24 h, the β phase mostly transformed to the ultrafine α'.•The maximum strength of >1.5 GPa was attributed by various strengthening mechanisms.