Study On Microstructure And Adhesion Mechanism Of Graphite-Like Carbon Coating Deposited By Magnetron Sputtering

Graphite-like carbon coatings （GLC） with Cr/Cr（C）/C（Cr） bonding layers were prepared using the unbalanced magnetron sputtering system. The microstructures and phase constituents of the coating and adhesion interface behaviors of coatings on different substrates were observed and analyzed using scan electron microscope （SEM）, high resolution transmission electron microscope （HRTEM） and X-ray diffraction （XRD）, respectively. The micro-hardness was measured using a Fischerscope HVS-1000 micro-hardness tester, the adhesion strength was measured using a WS-2005 scratch tester, and the tribological properties of coatings were measured using the PoD- II pin-on-disc tester.The results of observation and analysis show that the GLC coating has three layers: Cr layer, Cr/C transition layer and C（Cr） working layer. Cr layer is columnar crystals structure. Cr/C transition layer is the structure of nanocrystal embed into amorphous phase, and with the decreasing of Cr content and the increasing of C content, the structure has the tendency transforming to amorphous. C（Cr） working layer is mainly amorphous structure. The microstructure of the coating is dense and grows as according to island growth mode. With the help of HRTEM images, we have observed different interfaces between coatings and Si, Mg and Cu substrates. The interface of the coating onto Si substrate is the amorphous-like layer. Interfaces of the coating onto Mg and Cu substrate are pseudo-diffusion layer. The testing results of properties show that GLC coatings have high hardness （>2600HV）, outstanding adhesion strength （>59N）, low friction coefficient （<0.1） and low specific wear rate (<6.0×10^-17m³ï¼ˆNm）^-1). Especially, lower friction coefficient is exhibited at high load than low load.Adhesion mechanism of the coating on M2 steel was analyzed. Eventually, the effects of the microstructure and bonding layers on properties were analyzed and discussed. The results show that the formation of pseudo-diffusion layer and occurrence of local area diffusion between M2 steel substrate and Cr layer result in that metallic bonds form. Moreover thermal expansion coefficient difference of M2 steel substrate and Cr layer is little, these factors assure that the coating and the substrate have better synergistic deformability. It is also the main adhesion mechanism of GLC coatings on M2 steel.Because of the working layer with amorphous structure and periodic lamellar structure, the coating has high hardness. Due to the disorder graphite planes reorientate and choose easy to slip orientation in the course of the rubbing, so the coating has low friction coefficient. Then the coating with low specific wear rate can be explained by the synthetical effects of high hardness, excellent adhesion strength and low friction coefficient.