Microstructure and mechanical properties of TC4 titanium alloy remanufactured by laser powder bed fusion

Objective This study aims to elucidate the microstructural evolution mechanism of TC4 titanium alloy remanufactured by laser powder bed fusion (LPBF) and its subsequent impact on mechanical properties. Methods LPBF deposition was performed on a forged TC4 substrate. The microstructural characteristics of both the substrate and the deposited zone were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). Additionally, the tensile properties and fracture mechanisms at room and elevated temperatures were evaluated. Results The LPBF-deposited zone exhibited epitaxial columnar grains indicative of directional solidification, containing a substantial amount of acicular α′ martensite. This unique microstructure imparted high strength but poor ductility; consequently, the ultimate tensile strength (UTS) of the deposited alloy at room and elevated temperatures exceeded 1000 MPa, with corresponding elongations of merely 0.5% and 2.5%. The tensile fracture surfaces lacked macroscopic necking, displaying typical brittle fracture features. Furthermore, a sound metallurgical bond was achieved at the interface between the forged substrate and the deposited alloy. For the remanufactured TC4 samples, the UTS and elongation at both testing temperatures fell intermediate to those of the substrate and the deposited alloy. Deformation and ultimate fracture predominantly occurred in the softer forged substrate zone. Conclusion Defect-free TC4 parts with excellent forming quality can be successfully remanufactured via LPBF. The interfacial bonding strength surpasses that of the forged substrate, demonstrating the vast potential of LPBF for the high-precision repair and remanufacturing of complex components.