INTERLAYERS FOR DIAMOND DEPOSITION ON TOOL MATERIALS

The direct deposition of diamond on such tool materials as hard metals and steels is difficult because graphitization occurs and adhesion is poor. The following hard coatings have been investigated concerning t heir suitability as interlayers for diamond growth: TiN, TiC, Si3N4, S iC, SiCxNy, (Ti, Si)N-x and pulsed are deposited a-C (laser-are). The diamond deposition was performed by hot-filament CVD. A sufficient dia mond nucleation density was only reached by ultrasonic pretreatment wi th diamond powder. The nucleation density further depends on interlaye r materials and substrate temperature. The determined nucleation densi ties were 10(5)-10(8) cm(-2) for the titanium- and silicon-containing interlayers. The ultrasonic-pretreated a-C layers had a nucleation den sity of about 10(10) cm(-2) compared with 4-6 x 10(7) cm(-2) for untre ated samples. No dependence of the nucleation density on a-C layer thi ckness was found. Raman spectroscopic results show that diamond films with low non-diamond quantity grew on interlayers of TiC, SiC and SiCx Ny. In addition stress and adhesion were investigated. The poorest adh esive strength resulted for diamond on TiN and a-C. Silicon-containing interlayers such as Si3N4 and SiC showed good adhesion with critical loads up to 22 N measured by scratch test.