Effects of TiB2 Particles Content on Microstructure, Mechanical Properties and Tribological Properties of Ni-Based Composite Coatings Reinforced with TiB2 Particles by Laser Cladding

The effect of TiB2 particles content (10–40 wt.%) on the microstructure, mechanical properties and tribological properties of TiB2-reinforced Inconel 718 alloy composite coatings by laser cladding was investigated. From the perspective of solidification thermodynamics and dynamics, when the TiB2 particles content increases from 10 to 30 wt.%, the cooling rate increases for the increase in thermal conductivity and thermal diffusion coefficient, leading to the decrease in dendrite size, and the uniformity of TiB2 particles becomes better for the decrease in the critical capture speed of the solid–liquid interface, causing the improvement of microhardness and tribological properties. However, when the TiB2 particles content is too high (40 wt.%), the cooling rate decreases for the increase in heat released by solidification, so the dendrite size increases, and the Marangoni convection is too weak to drive the rearrangement of TiB2 particles, leading to the heterogeneous microstructure, large fluctuation of microhardness and the deterioration of tribological properties. When the TiB2 particles content is 30 wt.%, the composite coating has the finest and densest dendrites and evenly distributed TiB2 particles, the bonding strength is as high as 1.714 GPa, the microhardness is up to 844.33 HV0.2, which is 2.98 times that of Inconel 718 alloy coating, and the friction coefficient and the wear rate are 0.355 and 9.12 × 10−7 g/(N·m), which are 22.99% and 83.86% lower than those of the Inconel 718 alloy coating.