EVALUATION OF MPCVD DIAMOND FILM ADHESION ON HARD METAL SUBSTRATES BYMICRO-RAMAN SPECTROSCOPY

Diamond films produced by CVD are an attractive approach for lifetime improvement of conventional hard metal wear parts and cutting tools. H owever, the presence of the cobalt binder catalyses the formation of a weak graphite layer between the film and the substrate which compromi ses adhesion. This problem is minimised by acid leaching of the hard m etal surface to remove the cobalt a few microns deep. Diamond films we re grown on WC-6% Co and WC-10% Co substrates by MPCVD technique using different surface pretreatments and deposition conditions. Adhesion s trengths were evaluated using the scratch test. Micro Raman spectra in adherent zones show deviation on the diamone peak to higher wave numb ers (1333-1339 cm(-1)) compared to the characteristic value of the det ached film (1332 cm(-1)), as a result of high compressive residual str esses up to 3.9 GPa. Diamond line deviation on micro Raman spectra alo ng the scratch worn tracks could be used to trace the length of the pr eserved region before film damaging, as a complementary method to SEM and acoustic detection. (C) 1997 Elsevier Science S.A.