Characterization and Accelerated Erosion Testing of WC-Co-Cr- and CoNiCrAlY-Coated CA6NM Turbine Steel

In the present study, in-depth characterization of the high-velocity oxy-fuel (HVOF)-spray WC-Co-Cr and CoNiCrAlY coatings deposited on CA6NM turbine steel was done using scanning electron microscope (SEM), x-ray diffraction (XRD), roughness tester, microhardness tester, and optical image analyzer. Further, these coatings were tested under accelerated slurry erosion conditions using a high-speed erosion test rig. The effects of three different parameters related to actual operating conditions, namely erodent velocity relative to target surface, average erodent particle size, and slurry concentration on erosion behavior of these coatings, were investigated. SEM images on the specimen surface taken before and after erosion tests were carefully examined to understand the possible erosion mechanism. The study revealed that HVOF-sprayed WC-Co-Cr coating was found to impart higher erosion resistance in comparison with CoNiCrAlY coating under all the slurry erosion conditions. The reason for this behavior may be attributed to the higher hardness of HVOF-sprayed WC-10Co-4Cr coating in comparison with CoNiCrAlY coating.