Diamond coatings on cemented tungsten carbide tools by low-pressure microwave CVD

Diamond coatings were deposited on commercial, cemented tungsten carbide to ols of various cobalt content (3%, 6% and 12% Co) by low-pressure microwave CVD to assess the role of cobalt on the quality and adhesion (reliability) of diamond coatings. The samples were characterized by micro-Raman spectro scopy, scanning electron microscopy, and low angle X-ray diffraction. Probl ems associated with the detrimental effects of cobalt on the quality and ad hesion of diamond coatings as well as the effect of cobalt at low and high substrate temperatures were investigated. Micro-Raman spectroscopy was used to assess the quality of the diamond coatings (phase purity as well as the amount of amorphous carbon associated with the sp(2) structure with increa se in the concentration of Co in the WC tools) and the residual stresses on the tools. The presence of surface cobalt on the cemented tungsten carbide tools was established for the first time using the glancing angle X-ray di ffraction technique. Various surface pretreatment techniques (removal of su rface cobalt with aqua regia, Murakami treatment, and Murakami followed by ultrasonic microscratching with fine diamond suspension) were investigated with a view to enhance the mechanical adhesion of diamond coatings on to th e cemented tungsten carbide. The morphology of diamond coatings was assesse d using an SEM. Etching by Murakami followed by ultrasonic seeding with dia mond particles generated isotropically rough surface which facilitated a st rong mechanical anchoring in all directions of the diamond coating to the s ubstrate. The diamond films deposited were qualitative assessed for adhesio n using the Rockwell hardness tester with a Brale indenter. Significant imp rovement in the adhesion of diamond coatings on WC-3%, 6% and 12% Co tools were obtained by proper surface treatment and processing conditions. (C) 19 99 Elsevier Science S.A. All rights reserved.