CVD diamond films as protective coatings on titanium alloys

The solid particle erosion resistance of CVD diamond coated Ti-6Al-4V samples has been investigated in comparison with PVD hard coatings. In particular, diamond films grown with 4% methane gas concentration show excellent erosion resistance under both a 30 degrees and a 90 degrees incidence angle. Diamond coatings deposited applying 1% methane possess a somewhat lower particle impact resistance. The PVD coatings show almost no positive effect on the erosion behaviour of Ti-6Al-4V. Different failure mechanisms of diamond films grown with 1 and 4% methane gas concentration were identified: for the first an intercrystalline and for the latter a transgranular crack propagation was observed. This indicates relatively weak crystal boundaries for the diamond coatings grown with 1% methane concentration. Additional evidence for lower boundary strength was found when applying Rockwell C indents onto the films. (C) 1998 Elsevier Science Ltd. All rights reserved.