Improved adhesion and tribological properties of fast-deposited hard graphite-like hydrogenated amorphous carbon films

Graphite-like hard hydrogenated amorphous carbon (a-C:H) was deposited using an Ar-C2H2 expanding thermal plasma chemical vapour deposition (ETP–CVD) process. The relatively high hardness of the fast deposited a-C:H material leads to high compressive stress resulting in poor adhesion between the carbon films and common substrates like silicon, glass and steel. A widespread solution to this problem is the use of an adhesion interlayer. Here we report on the changes in adhesion between the graphite-like a-C:H films and M2 steel substrates when different types of interlayers are used. Insignificant to very small improvements in adhesion were observed when using amorphous silicon oxide (a-SiOx), amorphous organosilicon (a-SiCxOy:Hz) and amorphous hydrogenated silicon carbide (a-SiCx:Hy) as adhesion layers. However, when sputtered Ti was used as an interlayer, the adhesion increased significantly. The dependence of the adhesive properties on the deposition temperature and interlayer thickness, as well as on the thickness of the a-C:H layer is presented and discussed. The low wear rates measured for the a-C:H/Ti/M2 stack suggest that these films are ideal for tribological applications.

► a-C:H can be deposited with good adhesion on steel substrates by ETP–CVD technique. ► Using a Ti interlayer with a controlled structure adhesion improves drastically. ► The measured wear rates of such a a-C:H/Ti/steel stack are very promising.