Mechanical and tribological properties of Ti/TiAlN duplex coatings on high and low alloy tool steels

In this research work, different steels were hardened using plasma nitriding process in an Arc-PVD device. Afterwards, on both non-nitrided and plasma nitrided substrates, different Ti/TiAlN multilayer coatings were deposited by a magnetron sputtering device. Scratch tests were performed on the duplex systems in order to characterize their adhesive properties. The failure modes of individual coating systems under various normal loads were described using light optical microscope. Furthermore, to study the effect of plasma nitriding on the friction coefficient and wear rate of the systems, ball-on-disc tests were carried out. It was shown that high and low alloy tool steels obtained different levels of hardness after plasma nitriding process. The results of scratch tests showed that both Ti/TiAlN multilayer coatings have a higher adhesion to plasma nitrided steels compared to non-nitrided steels. In addition, plasma nitriding of the substrates resulted in an increase in the wear rates of multilayer coatings. It was also revealed that the adhesion and the tribology of multilayers depend strongly on the amount of titanium interlayers. An increase of the thickness of titanium interlayers enhanced the adhesion of multilayers. However, increasing the thickness of titanium interlayers decreased the hardness and wear resistance of multilayers.