Experimental study on the regulation of microstructure and properties of SLM-formed TC4 titanium alloy by heat treatment

This study addresses the strength-ductility trade-off in selective laser melting fabricated TC4 titanium alloy caused by the formation of a nonequilibrium martensitic α′-phase during rapid solidification. Specimens were solution-treated at 950 to 1000 °C, followed by water quenching, and aged at 500 or 550 °C. Microstructure was analysed using deep learning for α-phase quantification. Mechanical and corrosion properties were assessed through tensile tests, Vickers hardness measurements, and electrochemical testing in 3.5 wt% NaCl solution. Results demonstrate that the 990 °C solution treatment followed by 500 °C ageing produced a high fraction of 86.2% equiaxed primary α-phase. This refined structure led to a remarkable 126% improvement in elongation, increasing from 4.9% in the as-fabricated state to 11.1%, while maintaining high tensile strength of 870 MPa and hardness of 312 HV. Corrosion resistance was also significantly enhanced, evidenced by a 68 percent reduction in corrosion current density, along with increases of 0.25 volts in pitting potential and 0.32 volts in breakdown potential of the passive film. In contrast, increasing the solution temperature to 1000 °C reduced the primary α-phase fraction to 80.4% and resulted in inferior mechanical and corrosion performance, confirming 990 °C as the optimal solution temperature. This work demonstrates that solution treatment and ageing heat treatment effectively optimise the microstructure of selective laser melting processed TC4 alloy, achieving simultaneous improvement in both ductility and corrosion resistance without strength compromise. The strategy provides a viable processing route for manufacturing critical components in aerospace and biomedical applications that demand complex geometries, superior damage tolerance, and excellent corrosion resistance.