Growth, structure and properties of TiN coatings on steel substrates

Abstract

Titanium nitride, (TiN) coatings have achieved a large interest due to in particularly the commercial success as wear protective coatings on various type of cutting tools. In this paper the growth and resulting microstructure of TiN coatings deposited by reactive magnetron sputtering on steel substrates are reviewed. The microstructure of the films and of the film‐substrate interface region is also correlated to the hardness and adhesion of the films. It is shown that not only parameters such as substrate temperature and substrate bias influences the growth and microstructure but also the structure and chemical composition of the substrate surface is of high importance. For example, on the MC phase (M is primarily vanadium) in high‐speed steel substrates TiN grows epitaxially if the substrate surface is cleaned thoroughly. This epitaxial growth results in large grains and a low energy interface, the latter promoting a high adhesion. However, during the formation of these large grains on top of the MC phase, voids are created in the grain boundaries, resulting in films with a low hardness. The formation of these voids can be suppressed by using a substrate bias during growth. This give rise to dense hard films but still films with a high adhesion to the high speed steel substrate.