SAND EROSION PERFORMANCE OF DETONATION GUN APPLIED TUNGSTEN CARBIDE COBALT-CHROMIUM COATINGS/

Sand erosion studies of thermally sprayed WC-Co-Cr (Denotation-Gun LW4 5) have been undertaken using a sand/waterjet impingement rig. Results are presented which show that the erosion rate of sprayed compared to sintered tungsten carbide-cobalt-chrome is similar for low energy imp arts but the sintered material outperforms by 4 times the sprayed mate rial for high energy impacts. This reflects the anisotropic microstruc ture of the thermally sprayed coating with a preferred crack propagati on parallel to the coating surface followed by crack interlinking and spalling. This is the dominant erosion mechanism present. A minor eros ion mechanism consists of micro-cutting and ploughing at low angles of particle impact. The coatings have a relatively high density of defec ts including thermal stress induced transverse cracks, voids, oxides, and grit blasting remnants. Such defects are shown to accelerate the e rosion process considerably because they aid crack initiation and grow th leading to partial, mono or multi-splat spalling of loose material. The influence of slurry jet angle was found to be more pronounced und er low energy conditions where maximum erosion occurred at 90 degrees and the minimum at 30 degrees in contrast to the high energy erosion r ates which were independent of jet angle. This is a result of the lowe r levels of fluctuating stresses imparted to the coating during low en ergy impacts leading to the impact angle having a greater effect on su b critical growth rate than for the high energy conditions. (C) 1997 E lsevier Science S.A.