Effects of WC Particles on the Microstructure of IN718/WC Composite Coatings Fabricated by Laser Cladding: A Two-Dimensional Phase-Field Study

Abstract

During the process of laser cladding IN718/WC composite coatings, the dissolution and metallurgical reaction of WC particles significantly influence the microstructures of the coatings. However, the limited experimental methods restrict direct observation and prevent a deep understanding of this complicated process. Therefore, a novel numerical model for the solidification process of IN718/WC composite coatings was proposed. The model was established with the coupled multi-phase-field model and lattice Boltzmann method. Different kinds of microstructure around WC particles were simulated by the model and verified by experiments. Subsequently, microhardness and wear tests were carried out to investigate the improved mechanical properties of IN718 coatings reinforced by WC particles. The results show that the cellular alloy reaction layer, IN718 grains, and eutectic structure are formed, in turn, around WC particles. The convection in the laser molten pool can induce double-tail-like or spindle-like WC convection diffusion bands. The hardness of these bands is higher than that of the IN718 matrix. More importantly, WC convection diffusion bands can inhibit the growth of columnar crystals, because the dissolved WC can decrease the freezing temperature of the melt. Finally, mechanical property tests show that WC particles increase the hardness of the coating and significantly improve its wear resistance.