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 their suitability as interlayers for diamond growth: TiN, TiC, Si3N4, SiC, SiCxNy, (Ti, Si)N-x and pulsed are deposited a-C (laser-are). The diamond deposition was performed by hot-filament CVD. A sufficient diamond nucleation density was only reached by ultrasonic pretreatment with diamond powder. The nucleation density further depends on interlayer materials and substrate temperature. The determined nucleation densities were 10(5)-10(8) cm(-2) for the titanium- and silicon-containing interlayers. The ultrasonic-pretreated a-C layers had a nucleation density of about 10(10) cm(-2) compared with 4-6 x 10(7) cm(-2) for untreated samples. No dependence of the nucleation density on a-C layer thickness was found. Raman spectroscopic results show that diamond films with low non-diamond quantity grew on interlayers of TiC, SiC and SiCxNy. In addition stress and adhesion were investigated. The poorest adhesive 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.