Effect of powders recycling on microstructure evolution and wear mechanism of plasma sprayed Ni625-WC composite coating

The utilization rate of metal powders during the preparation of plasma-sprayed coatings is typically below 70 %, which has raised significant concerns regarding efficiency. The microstructure evolution and wear mechanism of plasma-sprayed Ni625-WC composite coatings with received powders (C-p₁) and recovered powders (C-p₂) were studied to investigate the feasibility of powder recycling. The results showed that the boundary layer at WC particles in C-p₂ was 2.84 μm thicker than that in C-p₁. Decarburized WC products were dispersed nucleation to form block M₂₃C₆ at the boundary of WC particles and within Inconel 625 matrix in C-p₁. In contrast, the larger contact area of block M₂₃C₆ after initial heating promoted the nucleation and growth of acicular M₂₃C₆ in C-p₂. In addition, the wear rate of C-p₂ is 9.1 % lower than that of C-p₁. Although the higher elastic modulus (E) of C-p₁ caused the Inconel 625 matrix to adhere more strongly to WC particles, resulting in higher degree adhesive wear rather than exfoliations and less adhesion in C-p₂, the presence of harder and more uniformly distributed acicular M₂₃C₆, and higher microhardness (H)/E ratio in C-p₂, improved the wear resistance.