A duplex treatment to improve the sliding behavior of AISI 316L: Low-temperature carburizing with a DLC (a-C:H) topcoat

Low-Temperature Carburizing (LTC) is a thermochemical treatment that improves the wear resistance of austenitic stainless steels without decreasing their corrosion resistance. However, LTC does not contribute to the decrease in the coefficient of friction in steel-to-steel contacts, which take place in many tribological applications involving LTC-treated parts. Therefore, in this work the dry sliding behavior of a duplex system consisting of PA-CVD hydrogenated amorphous carbon (a-C:H) topcoat on LTC-treated AISI 316L, was investigated by a flat-on-cylinder tribometer, at room temperature and in laboratory air, so as to evaluate the influence of (i) the polishing procedure before a-C:H deposition, (ii) the LTC interlayer and (iii) the type of countermaterial (untreated or LTC-treated AISI 316L). The results showed that (i) the polishing step prior to a-C:H deposition to obtain low roughness and therefore low friction (and also low wear of the countermaterial) must be carried out before LTC, otherwise the thickness of the layer is modified uncontrollably. (ii) LTC improves the load bearing capacity of the substrate, thus leading to increased adhesion and longer coating life. (iii) Finally, the a-C:H topcoat proved to be effective in reducing both friction and wear compared to the uncoated LTC-treated steel (up to the transition load).