Advanced fracture mechanics design of diamond-like carbon coating against delamination behavior

Ceramic, diamond-like carbon and diamond coatings have been widely used as a protective medium to prevent the structural parts and members from severe erosion, corrosion, or wearing and to significantly save the oil consumption by maintenance of low frictional state both in sliding mechanism and in manufacturing. Delamination is one of the most important issues of nuisance for these protective coatings; once the delamination occurs even in local, the whole functions of tools or parts must be diminished. In the present chapter, linear fracture mechanics and damage mechanics are applied to describe various delamination behavior in practice. Design of laminated coating is introduced to improve the engineering durability with comparison to a mono-layered coating. Linear fracture mechanics with consideration of cracking path is also applied to explain the feasibility of laminated coating to erosion and severe wearing conditions. On the basis of this understanding, nano-lamination in the diamond like carbon coating is proposed to have sufficient toughness against wearing or erosion and to advance the engineering steps toward the green manufacturing with less use of lubricating oils. Further difficulties related to the endurance of coating are also discussed to find a new direction leading to advanced coating design.