Effect of graphene addition on the performance of in-situ (TiC+TiBx)/Ti composite coatings by laser cladding: Microstructure and water droplet erosion resistance

In this study, different amounts of graphene (Gr, 0–2 wt%) were added into Ni60/Ti6Al4V powder mixtures to prepare (TiC+TiBx)/Ti composite coatings on Ti6Al4V substrates by laser cladding. By means of XRD, SEM, EDS, and TEM, the effects of Gr content on the dilution rate, phase composition, microstructure, microhardness and water droplet erosion (WDE) resistance of the coatings were comprehensively analyzed. The results showed that the coatings comprised phases of Ti2Ni, TiC, TiB, TiB2, α-Ti and β-Ti. The increased Gr content precipitated more TiC, providing more heterogeneous nucleation sites for other grains and suppressing the grain growth. The TiC-TiB2 and TiB-TiC intergrowth structures exhibited high load-bearing capacity and contributed to the synergistic hardening and strengthening effects. When the Gr content was 1 wt%, the coating had the highest microhardness of 886.3 HV0.3 and showed the best WDE resistance. The excellent performance of the hard phases, the existence of a large number of grain boundaries and the effect of the skeleton improved the WDE resistance of the coatings.