Erosion of thermal spray MCr-Cr3C2 cermet coatings

High velocity oxy fuel (HVOF) cermet coatings have been used to reduce the damage caused by solid particle erosion (SPE). The current work investigated the erosion resistance of FeCrAIY-Cr3C2 and NiCr-Cr3C2 cermet coatings with carbide levels ranging from 0-100% (in the pre-sprayed powder) in order to determine the optimum ceramic content for the best erosion resistance. The as sprayed coating microstructures were analyzed using light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray diffraction, and microprobe techniques. Erosion testing was carried out using a particle accelerator apparatus set at a velocity of 40 m/s, a mass flow of 80 g/min, and 400 degrees C with 450 mu m Al2O3 particles at 30 degrees and 90 degrees impact angles. Image analysis revealed the carbide levels in the pre-sprayed powder are much higher than in the final as sprayed coating. The lower carbide levels in the coatings are caused by a combination of poor carbide spray efficiency and reduction/oxidation of the carbide particles in the HVOF jet, resulting in the formation of various oxides and metal rich carbides. Erosion testing of the sprayed coatings found that decreasing the carbide content, and overall hard phase content (oxides and carbides), decreased the erosion rate for 90 degrees impact. In addition, for 30 degrees impact the erosion rate remained fairly constant regardless of carbide or hard phase content. (C) 1999 Published by Elsevier Science S.A. All rights reserved.