Influence of grain size and film composition on wear resistance of ultra fine grained AISI 304 stainless steel coated with amorphous carbon films

The tribological properties of the ultra fine microstructure (down to 1.0 μm) of austenitic stainless steels obtained by means of a martensitic transformation and subsequent austenite reversion are reported. The effects of the grain size on the wear resistance of such materials is, for the first time, investigated and compared to those measured for the same samples coated with amorphous hydrogenated carbon (a-C:H) films deposited by means of plasma enhanced chemical vapour deposition (PECVD). Ball on disk (BoD) sliding friction tests are performed in order to investigate wear behaviour of coated and uncoated substrates with different grain sizes. For the uncoated samples the BoD test results show a strong dependence of the wear track volume as a function of grain size. Furthermore, a strong improvement of the wear resistance is found in a-C:H coated specimens with respect to the uncoated ones with the same substrate microstructure. The effects of nitrogen incorporation into the films are also investigated showing an increase of the tribological and adhesion strength between substrate and coatings.