Cavitation erosion behaviour and mechanism of HVOF-sprayed NiCrBSi-(Cr3C2-NiCr) composite coatings

NiCrBSi-(Cr3C2-NiCr) coatings were prepared by high velocity oxy-fuel (HVOF) thermal spraying technique, and their cavitation erosion behaviour was investigated by a magnetostrictive cavitation method. It was observed that in the initial 8 h, cavitation occurred at higher rate, and cumulative mass loss of the two coatings was apparently higher than that of the substrate. Conversely, beyond 12 h, the former was lower than the later, indicating that the coatings depressed the cavitation erosion effectively. This study verified that the cavitation is due to mechanical shock, turbulence of liquid with bubbles and residual stresses, and therefore the formation of cracks and the delamination of coating are induced. Furthermore, an increase in the number of pores results in an increase in damage to the coatings, taking this into account distributions of pores can be termed as a key factor in determining the resistance of cavitation damage.