Improvement of adhesion force of hard coatings to cemented carbides by laser heating

Abstract

ABSTRACTLaser heating with different power densities was applied to hard coatings to improve their adhesion to cemented carbides substrate (cutting edges). The adhesion force was determined by critical load Lc in the scratch test using an automatic scratch tester constructed at Poznan University of Technology. The determination of adhesion force (the value of critical load, measured during the scratch test) was carried out based on the analysis of the vibration spectrum. Scanning electron microscopy, 3D surface profiling and X-ray mapping were used to verify the coating state after laser heating. The results indicate that significant increase of Lc can be achieved for the laser beam power density of up to 4100 W/cm2, for monolayer (single – Ti(C,N) and double – Ti(C,N)+TiN) coatings only. Higher beam power leads to coating cracking and decohesion of the substrate. Rapid laser heating is not recommended for the alumina layer in tri-layer coating (TiC+Al2O3+ Ti(C,N)) because alumina layer has low heat impact resistance. Also new in this article is the fact that as a result of laser heating, the chemical composition of the coating changes, which affects its adhesion to the substrate. Considerable increase in adhesion after laser heating of single and double coatings to substrate made of cemented carbides should contribute to better wear resistance of coated edges during machining.