Erosion wear behavior of NiCr+Cr3C2–NiCr coating under multi–impact angle and novel coating structure design

Abstract

Despite advances in NiCr + Cr 3 C 2 –NiCr coating improving the erosion wear resistance at low impact angles, the deterioration at medium and high impact angles has not been solved for the impeller subjecting to multi–impact angle. Herein the conflict is circumvented by combining the erosion performance of the NiCr and Cr 3 C 2 –NiCr under different impact angles and proposing a novel coating structure. First, the NiCr + Cr 3 C 2 –NiCr coating specimens with different NiCr content were prepared using the plasma spraying system. Second, the erosion rate of NiCr + Cr 3 C 2 –NiCr coatings in relation to the impact angle and the concentration of NiCr was measured by an air jet erosion test system, the microhardness was measured on the polished cross-section, and the erosion morphology was observed by SEM and analysed. Erosion behavior analysis showed that the NiCr + Cr 3 C 2 –NiCr coatings exhibited the coupling erosion wear mechanism of high toughness and high hardness, where the dominant characteristic was depending on the concentration of NiCr. Then, a tangential functional gradient coating structure was proposed by combining the excellent erosion wear resistance of ductile and brittle materials at varying impact angles, and a semi-theoretical erosion rate model considering the influence of the NiCr concentration was established based on the deformation wear theory. The erosion rate model was validated by experiments which showed the error was within 9.15%. Consequently, the erosion rate can be regulated on demand along the entire eroded surface, which significantly improves the erosion resistance of cermet at medium and high impact angles, thus prolonging the residual life of remanufactured impeller.