Microstructure and water erosion resistance of in situ synthesized (TiBx+TiC)/Ti composite coatings produced by laser cladding

Abstract

(TiC + TiBx)/Ti composite coatings were prepared on a Ti6Al4V substrate by laser cladding to improve its microhardness and water erosion resistance. The 1 wt% Gr + 49 wt% Ni60 + 50 wt% Ti6Al4V composite powders were used as the precursor. The effects of laser energy density and powder deposition density on the geometric morphology, phase composition, microstructure, microhardness and water erosion resistance characteristics of the coatings were comprehensively studied through numerical simulation and experimental characterization. The results showed that the geometric morphology of the coating was determined by the laser energy density and powder deposition density; however, the microstructure of the coating was not completely understood. A high scanning speed was more conducive to grain refinement than a low scanning speed. In addition, the earlier precipitated hard phases provided heterogeneous nucleation sites for other grains and promoted their dispersion. Due to the dispersion strengthening and grain refinement effects of the in situ synthesized hard phases, the microhardness and water erosion resistance characteristics of the coatings significantly improved. With a laser energy density of 64 J mm−2 and a powder deposition density of 5 × 10−3 g mm−2, the microhardness of the coating reached 919.9 HV0.3, which was 2.8 times greater than that of the Ti6Al4V substrate. The water erosion resistance of the coating was the best.