Carbon based coatings deposited on stainless steel : study of thermal degradation

Abstract

Amorphous hydrogenated carbon (DLC) coatings have a high hardness depending on the relative amount of sp3/sp2 bondings. They also exhibit an extremaly low friction coefficient and are chemically inert. However, these coatings have some disadvantages which limit their applications. For instance, adhesion is poor when are deposited on metallic substrates and they are also unstable at high temperatures, degrading into graphite and loosing hardness. in this work, DLC coatings were deposited on presipitation hardening stainless steel (PH Corrax) which was plasma nitrided before the coating deposition. The samples were submitted to annealing treatments for an hour at different temperatures from 200 to 600ºC, together with a control group, wich was only coated but not nitrided. After each annealing cycle, Raman Spectroscopy, nanoindentation and microscopy were used to check fil properties. It was demonstrated that the nitriding pretreatment improved not only adhesion but also the thermal stability of the DLC, slowing degradation and preventing delamination.