Solid particle erosion of CVD diamond coatings

This paper reports solid particle erosion studies of 10-47 mu m chemical va pour deposited (CVD) diamond coatings deposited on W and SIC substrates. Tw o erosion test facilities were used: a water-sand slurry rig and a high-vel ocity air-sand rig. The erodent used was silica sand with average diameters of 135 mu m, 194 mu m and 235 mu m with the velocities in the range of 16- 268 ms(-1) and 90 degrees nominal impingement angle. The erosion rates were plotted against particle kinetic energy and compared with those for cement ed tungsten carbide and stainless steel. The samples were examined both pre - and post-test by scanning electron microscopy in order to determine the m echanisms of degradation suffered by the coating during the erosion process ; the effects of thickness and microstructure were also examined. The time to failure of the coatings at 268 ms(-1) was found to increase from 5 to 18 5 min over the range of coating thickness tested. The erosion mechanism at high-velocity conditions is thought to be a three-stage process consisting of micro-chipping, development of pin-holes and interfacial debonding, foll owed by catastrophic failure. However, it should be noted that, at particle velocities of 268 ms(-1), 46 mu m CVD diamond coatings on tungsten display ed approximately six times the erosion resistance of cemented tungsten carb ide. (C) 1999 Elsevier Science S.A. All rights reserved.