Nano-lamination in amorphous carbon for tailored coating in micro-dry stamping of AISI-304 stainless steel sheets

Nano-lamination is a new way to make full use of multi-layered structure for coating instead of the mono-layered coating system. Different from the conventional nano-lamination approach, where two different kinds of material system are deposited in layers, the amorphous carbon layer, a-C:H, is alternatively deposited with graphite-like cluster layer, resulting in an amorphous carbon base nano-laminated coating. In this nano-lamination, the pulse bias voltage and the pulse duration time are programmed to control the bi-layer thickness and number of laminates. Furthermore, the mechanical properties are also controllable by varying the bi-layer thickness and sub-layer ratio. In this paper, the effect of number of layers and bi-layer thickness on the mechanical properties is investigated by the nano-indentation technique. Higher hardness and Young's modulus is attained with reduction of bi-layer thickness. The scratching test of this nano-laminated coating is made to demonstrate that it has sufficient scratch load above 100 N. Furthermore, a dry micro stamping test is performed to prove that this nano-laminated coating has sufficient wear-toughness enough to make dry stamping in 10,000 times in practice even if it has nearly the same Young's modulus and hardness as the mono-layered coating. No delamination or break-away occurs on the ironed surface of coated tools while severe delamination is observed in the conventional mono-layered coating.