Effect of Coating Thickness on the Slurry Erosion Resistance of HVOF-Sprayed WC-10Co-4Cr Coatings

High-velocity oxy-fuel (HVOF)-sprayed WC-10Co-4Cr coatings were deposited with thickness of 150, 300 and 450 mu m in the present work. The structural and mechanical properties, adhesion strength and residual stress were analyzed as a function of coating thickness. With increasing coating thickness, an increase in hardness and a drop in fracture toughness were observed. The compressive residual stresses decreased by a factor of two with increased coating thickness from 150 to 450 mu m. The elastic modulus of the coatings was influenced by their porosity. The results of the slurry erosion tests indicated a brittle erosion response of the coatings, and the ratio of the erosion rate at 90 degrees impact angle to that at 30 degrees impact angle increased with increasing coating thickness. The slurry erosion resistance of the coatings was governed by the impact angle, residual stresses and mechanical properties of the coatings. The main material removal mechanisms were plastic grooving of the binder phase, carbide pullout, micro-cracking and brittle fracture.