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

Hard coatings such as titanium nitride are currently used in many appl ications, e.g. metal cutting, metal forming, plastic moulding and deco rative fields. For a coating to be successfully functional, it should possess good adhesion to the substrate. The adhesion of a coating depe nds on factors which include, inter alia, surface preparation methods, affecting surface cleanliness, condition and roughness. The present s tudy describes some results concerning the influence of surface roughn ess on the adhesion of titanium nitride coatings to high speed steel s ubstrates. A scratch adhesion measuring unit was used to evaluate the adhesive strength of the coatings. Scanning and optical microscopes we re 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 especi ally in the broader context of quality assurance and manufacturing eff iciency.