Engineered Synthetic Diamond Film as a Protective Layer for Tribological and Machining Applications: A Review

Abstract

Cobalt-based tungsten carbide composite (WC-Co, with different grades) is the commonly used material for cutting tools and tribological components, because of its high hardness and high wear and corrosion resistance. The carbon fiber-reinforced plastics (CFRP) and Al-SiC metal-matrix composites (MMCS) are materials mostly used in aerospace and automobile industries due to their high strength-to-weight ratio. During the machining of these composite materials, the conventional WC-Co cutting tools are subjected to high abrasive wear because they contain constituent hard reinforced particles. Thus, these types of machining applications need super-hard coatings for better performance and durability. Nowadays, synthetic diamond coatings obtained by chemical vapour deposition (CVD) process play an important role in improving the performance of the carbide tools while machining these composite materials, because of their superior mechanical and tribological properties. CVD diamond coatings with good wear resistance, super hardness, and low friction coefficient are in demand for industrial applications. But, the main problem of these diamond coatings is the coating de-lamination under high mechanical loads experienced during the machining process. Presently, researchers concentrate on the improvement of the coating adhesion for their better performance. However, to achieve the desired synthetic diamond coating for industrial applications many characteristics of the coating-substrate system need to be considered like good adhesion, optimum coating thickness, and minimum thermal residual stresses. Therefore, the microstructure and architecture of the synthetic diamond coatings should be adjusted to achieve the basic practical requirements like high wear resistance, high hardness, enough adhesion strength, and low friction coefficient.