Efeito da temperatura na estrutura físico-química de intercamadas depositadas a partir de HMDSO para adesão de DLC em aço

Abstract

Diamond-like carbon thin films (DLC) show a unique combination of properties such as high wear resistance and ultra-low friction. However, a widespread use regarding energy efficiency issues in the automobile industry is neglected due to the poor adhesion of DLC on steel and/or expensive technologies. DLC adhesion on steel can be achieved by nanometric bonding interlayers containing silicon, which are particularly beneficial to mitigate the high compressive stress and the thin film mismatching, promoting stronger chemical bonds between the interfaces. The Si interlayers were deposited at different temperatures from 50 °C to 500 °C from a hexamethyldisiloxane (HMDSO)/Ar mixture and the DLC was deposited at 80 °C by a low-cost pulsed DC-PECVD technique assisted by electrostatic confinement. The microstructure and chemical mapping was analyzed by SEM and EDS. The chemical depth profiling was performed by GD-OES. Hardness and critical loads were analyzed by nanoindentation and nanoscratch tests. Results show better adhesion as substrate temperature is raised during the SiCx:H interlayer deposition process. As the deposition temperature is raised, H and O are removed from the structure, making the interlayer more inhomogeneous, with C concentrated on the outermost interface, a- C:H/SiCx:H and Si on the innermost interface, SiCx:H/Steel. This restructuring allows the formation of a higher quantity of C-C bonds at the outermost interface, which are stronger than Si-C bonds. Also, the removal of H and O allows C atoms to diffuse into the interlayer during the a-C:H coating deposition process. Consequently, more Si-C bond are formed on the bulk of the interlayer, reducing compressive stress and, thus, improving the adhesion of the a-C:H film. Finally, an atomistic model is proposed in order to explain the DLC bonding and debonding mechanisms.