Recent developments in the new generation of hard coatings applied on cemented carbide cutting tools

The main requirements of cemented carbides as cutting, machining, and drilling tools are wear resistance, chemical stability at high temperatures, and proper mechanical properties. However, some studies have indicated that the surface temperature of these tools increases locally during the cutting or machining process, which leads to oxidation, compositional change, and tool degradation over time. In addition, these tools are sometimes used in corrosive media such as saline water, etc. Cemented carbides contain carbide and metallic phases; therefore, there is a possibility of severe galvanic corrosion in these composites, which leads to the preferential dissolution of the metallic phase and the remaining carbide skeleton. On the other hand, the corrosion rate of hardmetals depends on the pH of the electrolyte. In alkaline electrolytes, Co passivation occurs; in contrast, WC actively dissolves. This behavior is vice versa in acidic electrolytes. Deposition of hard protective CVD coatings is an appropriate way to protect cemented carbides from environmental damage and oxidative wear. In past studies, it has been mentioned that using single-component coatings such as TiN is unsuitable for improving the cutting performance of such tools due to oxidative degradation of the coating. But the use of modified multilayer coatings has shown a significant improvement in the proficiency and lifespan of these cutting tools. In recent years, CVD TiAlN coatings have replaced the previous generation of hard coatings due to their unique properties. Much research has been carried out on the properties of these coatings, and the effect of different contents of Al and dopants have been reported. Recently, CVD TiSiCN coatings have been introduced as a new generation of hard coating that has attracted the attention of researchers. These composite coatings are one of the promising options for the next generation of wear-resistant coatings due to their ultra-high hardness, wear and oxidation resistance, and excellent performance in the cutting/machining process.