Surface modification of plasma spraying Al2O3–13 wt% TiO2 coating by laser remelting technique

Abstract

An Al2O3–13 wt% TiO2 composite ceramic coating was prepared on the TiAl alloy surface by plasma spraying and laser remelting combined technique. The morphology, microstructure, and phase composition of the prepared coating were analyzed by scanning electron microscopy, energy disperse spectroscopy, and x-ray diffraction. The bonding strength, microhardness, wear resistance, erosion resistance, and thermal shock resistance of the coating were also tested. Results demonstrated that after processing by laser remelting, the particles on the ceramic coating surface were refined, lamellar structure disappeared, and density increased. A remelting layer basically without crack and other defects was gained. Due to laser remelting, the metastable-phase γ-Al2O3 was converted into stable-phase α-Al2O3. Influenced by the low thermal conductivity of ceramic materials, remelting of the whole ceramic layer is impossible to realize during laser remelting. The remelted ceramic coating formed the isometric crystal remelting zone with small grain size, sintering zone, and lamellar residual plasma spraying zone. The bonding strength and microhardness of the coating improved significantly after laser remelting, and the wear resistance, erosion resistance, and thermal shock resistance were significantly superior to those of the original plasma spraying layer. Laser remelting specimens still represented typical brittle erosion characteristics. Cracks initiated and expanded on near surface, finally leading to breakage of the remelting layer, mainly manifested by grain peeling. With respect to thermal shock failure mode, the corner peeling is the major failure mode of the ceramic coating after plasma spraying. Differently, corner peeling and considerable local peelings were found at the center of the ceramic coating after laser remelting. The influences of laser remelting on the thermal shock performances of the coating are mainly manifested as the decreased initial failure resistance, decelerated crack expansion, and changes in failure modes of the coating.