Microstructural influence on erosion behaviour of thermal spray coatings

The influence of structure on erosion performance of thermally sprayed Cr3C2–NiCr coatings under industrial turbine conditions has been investigated. Thermal spraying of these materials results in substantial variation in composition and microstructure due to exposure of the coating powders to the high temperature accelerating gas.Coatings were characterised using Back Scatter Electron imaging in conjunction with X-ray diffraction which showed carbide dissolution into the matrix of varying extent depending on deposition technique. Heat treatment at 900 °C caused carbide precipitation and matrix refinement. Erosion testing of as-sprayed and heat treated coatings was conducted at ambient and elevated temperature. Single impacts were characterised using Scanning Electron Microscopy in order to determine the erosion mechanism.At ambient temperature the single impacts caused a brittle response with both carbide grains and matrix being cleaved by the erodent particle. Brittle cracks surrounded each impact and intersected with splat boundaries leading to a significant contribution to erosion rate from splat structure. Following heat treatment the erosion response of the coatings was more ductile with mounds of plastically deformed material surrounding each impact, this significantly reduced erosion rate.