Current status of hard coating research

The emergence of hard coatings has improved tool productivity and service life and reduced machining costs while ensuring machining quality. In order to meet the development needs of difficult-to-machine materials and cutting processes, coating materials have been continuously developed and updated in terms of composition and structure, and the composition has developed from simple binary coatings (such as CrN, TiN) and ternary coatings (such as AlCrN, TiAlN, TiC) to multi-coatings, nanocomposite coatings and high-entropy alloy coatings, and the structure has changed from single-layer to multi-layer direction.