EROSION RESISTANCE OF DIAMOND COATINGS

Preliminary solid particle erosion testing of 10 mum thick diamond films on silicon substrates showed excellent erosion resistance. The application of diamond coatings to materials that are commonly used in erosive environments should result in significant improvement over other erosion-resistant coatings. Diamond films were applied to silicon, tungsten and Ti-6Al-4V using a high-pressure microwave-assisted plasma deposition system and were determined to have a high degree of sp3 bonding using Raman spectroscopy. Erosion tests were performed on diamond-coated silicon, tungsten and Ti-6Al-4V, as well as on uncoated substrates and alternative coatings. The erosion resistances of the target materials were compared using volume loss versus erodent mass plots and steady-state erosion-rate data. Diamond-coated silicon showed the highest erosion resistance. Diamond-coated Ti-6Al-4V also showed high erosion resistance when compared with uncoated materials. Erosion mechanisms were identified by examination of eroded surfaces using scanning electron microscopy. Diamond coatings on Ti-6Al-4V substrates fail by delamination of the coating from the substrate. This is believed to be a result of high residual stresses and stress concentrations at the coating-substrate interface. Diamond coatings on silicon and tungsten substrates are gradually removed by a brittle erosion process.