TiC-TiSi2-Al2O3 composite coatings prepared by spray drying, heat treatment and plasma spraying

Highlights: • Density and cohesive strength of Al-TiO₂-SiC powder were improved by heat treatment. • Al-TiO₂-SiC powders were plasma sprayed to prepare TiC-TiSi₂-Al₂O₃ composite coatings. • Coating obtained by heat-treated Al-TiO₂-SiC powder had higher hardness and toughness. -- Abstract: An innovative approach to improve the quality of TiC-TiSi₂-Al₂O₃ composite coating was demonstrated. In-situ synthesis is one of the most economical methods for preparing refractory composite coatings, but the problems of low reaction degree and poor quality of the as-prepared coatings still exist. In the present investigation, TiC-TiSi₂-Al₂O₃, Al-TiO₂-SiC and heat-treated Al-TiO₂-SiC composite powders were plasma sprayed on the surface of TC4 titanium alloy to prepare TiC-TiSi₂-Al₂O₃ composite coatings, respectively. The phase composition and microstructure of the three kinds of composite powders and as-prepared coatings were analyzed, and the porosity, microhardness and fracture toughness of the coatings obtained by the three kinds of composite powders were comparatively studied. The results show that the heat-treated Al-TiO₂-SiC composite powders had higher density and smoother surface than that of Al-TiO₂-SiC composite powders. The pre heat treatment of Al-TiO₂-SiC feedstock could avoid the inadequate reaction during the plasma spraying process. The coating obtained by plasma spraying heat-treated Al-TiO₂-SiC composite powders had the highest bonding strength, microhardness (51.8% higher than Al-TiO₂-SiC coating) and fracture toughness among the three coatings.