High velocity sand impact damage on CVD diamond

This paper describes a recent study of the damage mechanisms generated by high velocity-sand impact on diamond coatings deposited on tungsten substrates by chemical vapour deposition (CVD). The coatings were erosion tested using 90-355-mum diameter sand at a velocity of 268 m s(-1) and the eroded coatings examined by scanning electron and acoustic microscopy. The images indicate that the circumferential cracks and pinholes are the main erosion features and are only located on debonded areas of the coating. This suggests that they could be formed by stress waves reflected from the coating-substrate interface, which interact with surface waves to generate circumferential cracks, the precursor to pinholes. The high spatial resolution of scanning acoustic microscopy enables the resolution of individual pinholes, thus, providing important evidence for identifying the mechanism responsible for the formation of circumferential cracks, the precursor to the pinholes. However, the acoustic images must be interpreted with care; in particular, it is important to compare microstructural features observed by acoustic microscopy with other techniques. (C) 2001 Elsevier Science B.V. All rights reserved.