Engineered CVD Diamond Coatings for Machining and Tribological Applications

Diamond is an allotropes of carbon and is unique because of its extreme hardness (similar to 100 GPa), low friction coefficient (< 0.05), high thermal conductivity (similar to 2000 Wm(-1) K-1), and high chemical inertness. Diamond is being synthesized artificially in bulk form as well as in the form of surface coatings for various engineering applications. The mechanical characteristics of chemical vapor deposited (CVD) diamond coatings such as hardness, adhesion, friction coefficient, and fracture toughness can be tuned by controlling the grain size of the coatings from a few microns to a few nanometers. In this review, characteristics and performance of the CVD diamond coatings deposited on cemented tungsten carbide (WC-Co) substrates were discussed with an emphasis on WC-Co grade selection, substrate pretreatment, nanocrystallinity and microcrystallinity of the coating, mechanical and tribological characteristics, coating architecture, and interfacial adhesion integrity. Engineered coating substrate architecture is essential for CVD diamond coatings to perform well under harsh and highly abrasive machining and tribological conditions.