Microstructure, Mechanical and Tribological Properties of Functionally Graded Ti-6Al-4 V/SiC Coatings Fabricated by Laser-directed Energy Deposition

In this study, Ti-6Al-4 V/SiC functionally graded material (FGM) coatings were fabricated on Ti-6Al-4 V substrates using laser-directed energy deposition (L-DED), and their microstructure, phase composition, hardness, and tribological properties were compared with those of the Ti-6Al-4 V substrate and SiC-Only coatings. The FGM coatings exhibited a gradual Ti–Si compositional gradient, mitigating residual stresses and suppressing crack formation, whereas the SiC-Only coatings showed abrupt compositional transitions and high crack density. X-ray diffraction and SEM/EDS analyses revealed TiC, TiSi₂, and SiC as the primary phases in the FGM coating, and rapid solidification induced partial transformation of SiC from hexagonal to cubic structure. The FGM coatings demonstrated significantly enhanced hardness and wear resistance due to the formation of hard phases and dispersion strengthening within a supersaturated matrix, while the gradual compositional and property gradient further alleviated local thermal and mechanical stress concentrations. Pin-on-disk tests indicated that mixed protective oxide layers (TiO₂, SiO₂, TiCₓO_y) formed on the FGM surface, suppressing adhesive wear and enhancing lubrication, resulting in lower friction and stable tribological behavior. These results confirm that L-DED-based FGM coatings outperform SiC-Only coatings in terms of hardness, wear resistance, and friction performance, highlighting the potential of compositional gradient design and optimized processing conditions for industrial applications.