Effect of Fe content on tensile properties of TA15 alloy with equiaxed microstructure produced by laser directed energy deposition

The thermal gradient during laser directed energy deposition (LDED) makes avoiding columnar grains difficult. Columnar grains result in solidification defects and mechanical property anisotropy, which has become a significant challenge during additive manufacturing. Recently, various strategies have been explored to achieve the columnar-to-equiaxed transition (CET) process, including heat treatment, control of energy input, optimisation of processing parameters, incorporation of inoculants, and addition of solutes. This study explored the effect of Fe solute with low cost on the microstructure and tensile properties of LDEDed Ti-6.5Al-2Zr-Mo-V (TA15) alloys. The LDEDed TA15-xFe alloy from mixed powder widened the freezing temperature range by Fe addition and rapid solidification, achieving equiaxed β grain. Fe-modified TA15 alloy achieved higher strength (YS∼921 MPa, UTS∼1015 MPa) and better ductility (uniform elongation∼8.9%) than TA15, which enabled strength-ductility synergy. Compared with TA15 alloy, the strength and ductility of TA15-3Fe were improved by 27% and 37%, respectively, which mitigated the trade-off of strength and ductility. The strengthening mechanism and deformation mechanism of TA15-3Fe were systematically investigated. The findings provided a new insight for overcoming the strength-ductility trade-off in additively manufactured titanium alloys with equiaxed microstructure by alloy design.