INFLUENCE OF SUBSTRATE ROUGHNESS ON THE SCRATCH ADHESION OF TITANIUM NITRIDE COATINGS

Hard coatings such as titanium nitride are currently used in many applications, e.g. metal cutting, metal forming, plastic moulding and decorative fields. For a coating to be successfully functional, it should possess good adhesion to the substrate. The adhesion of a coating depends on factors which include, inter alia, surface preparation methods, affecting surface cleanliness, condition and roughness. The present study describes some results concerning the influence of surface roughness on the adhesion of titanium nitride coatings to high speed steel substrates. A scratch adhesion measuring unit was used to evaluate the adhesive strength of the coatings. Scanning and optical microscopes were employed to characterise the scratched surfaces. It has been shown that the critical load to failure decreases with increasing substrate roughness. The significance of these observations is considered especially in the broader context of quality assurance and manufacturing efficiency.