Scratch adhesion characteristics of PVD TiAlN deposited on high speed steel, cemented carbide and PCBN substrates

Modern tool materials, ranging from powder metallurgical high speed steel to super hard materials such as polycrystalline cubic boron nitride and diamond, are used as cutting tools in the metal cutting industry. In order to further improve the cutting performance, these tools are frequently coated by thin, hard PVD coatings such as TiN, TiAlN, AlCrO3, etc. In order to develop and design new PVD coatings it is important to characterize the mechanical properties of the coatings and understand the coating/substrate deformation mechanisms in a tribological contact, e.g. metal cutting. For example, it is important to be aware that the mechanical properties of the substrate (tool material) have a significant impact on the practical coating adhesion and the coating failure mechanisms. In the present study scratch testing has been used in order to evaluate to increase the understanding of the mechanical response and potential coating failure modes of cathodic arc evaporated TiAlN deposited on high speed steel, cemented carbide and polycrystalline cubic boron nitride. Post-test characterization of the scratched samples using optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy were performed and the cohesive and adhesive surface failure mechanisms are described and related to the substrate material properties. The results clearly show that, although all substrate materials can be regarded as hard, they result in completely different coating failure mechanisms at the normal load corresponding to substrate exposure. Also, coating failure resulting in substrate exposure does not necessarily correspond to interfacial cracking resulting in adhesive fracture along the coating–substrate interface.