Microstructure and properties of in situ TiC/Ni functionally gradient coatings by powder-fed laser cladding

Powder-fed laser cladding with layer-by-layer deposition characteristics offers the unique advantages in the fabrication of ceramic/metal functionally gradient coatings (FGC). However, the inability of the size to vary with the content of the ceramics usually results in limited wear resistance or non-uniform mechanical properties of ceramic/metal FGC fabricated by the ex-situ process. Therefore, in this study, in situ synthesis of titanium carbide/nickel (TiC/Ni) FGC was carried out on ductile cast iron by powder-fed laser cladding using Ni45, Ti, and Ni-coated graphite (C). Seven groups of gradient compositions from 0 to 50% Ti + Ni-coated C with a Ti to C atomic ratio of 1:1 were designed. The phase composition, microstructure, interfacial characteristics between the consecutive layers, microhardness, and wear rate from the bottom to the top of the in situ synthesized TiC/Ni FGC were systematically studied. The results indicated that the phase composition was subjected to the desired evolution with the increase in the deposition height. Besides, the relative length and area fractions of ceramic compounds also gradually increased, following the quadratic and linear functions, respectively. The microhardness increased from the bottom to the top following a quadratic function: Y=2.961E−6X2+0.0217X+530.30 with an R-square of 97.97%, and the wear rate decreased following a linear function: Y=4.873E−9X+5.077E−5 with an R-square of 94.04%. The maximum microhardness of 1036.25 HV and minimum wear rate of 4.872E−6 mm3·N-1·m-1 were obtained at the top of the in situ TiC/Ni FGC. Besides, the wear mechanism also varied with the relative length and area fraction of the in situ TiC. This study confirms the feasibility of the fabrication process of the ceramic/metal FGC involving the size varies with the content of ceramics by in situ process.