Laser directed energy deposition of TA15/TiAl bimetallic structure: laser power optimization, microstructure evolution and mechanical performance

Abstract

This study explores the fabrication of crack-free TA15/TiAl bimetallic structures prepared by laser directed energy deposition (LDED) for high-temperature applications. By employing laser power (800−1600 W) for S1–S5 (1600, 1400, 1200, 1000, 800 W, respectively), defect-free interfaces were achieved, with sample S2 (1400 W) exhibiting the lowest porosity (0.19 %) and finest microstructure. The transition zone exhibited a composition gradient of Al/Ti, driven by atomic diffusion and Marangoni convection, resulting in a heterogeneous multi-gradient structure. Notably, the uniform distribution of FCC phase in the transition zone reduced stress concentration from Al₃Ti hard phase, while the absence of cracks and lack-of-fusion defects confirmed robust metallurgical bonding. Room-temperature tensile tests showed that sample S2 fractured near the TiAl side, achieving an ultimate tensile strength of 780 ± 25 MPa and elongation of 1.41 ± 0.11 %, attributed to stress redistribution facilitated by ductile α-Ti and gradient strain accommodation. These findings demonstrated that LDED-fabricated TA15/TiAl bimetallic composites exhibited enhanced interfacial strength and thermal stability, promising for aerospace components in extreme environments.