Comprehensive structural, nanomechanical and tribological evaluation of silver doped DLC thin film coating with chromium interlayer (Ag-DLC/Cr) for biomedical application

Silver (Ag) doping in carbon matrix have shown promising results in anti-bacterial potency. Adhesion of diamond-like-coating (DLC) on steel substrates is inferior; however, this can be circumvented by employing interlayers to it. In the present study, Ag incorporated DLC coating with chromium interlayer (Ag-DLC/Cr) was deposited on surgical SS using cathodic arc deposition technique. The topographical, morphological and structural analysis of the coating was performed using AFM, XRD, Raman spectroscopy and FTIR studies. The nanomechanical and wear performance of the coating was evaluated using nanoindentation, nanoscratch, dry sliding simulated tribotest and Vickers microhardness tests. Depositing chromium interlayer to DLC film resulted in improved hardness, adhesion and elastic modulus of the substrate due to sp(3) content and formation of transmittal chromium carbide in the coating. Moreover, Ag doping causes formation of ductile bridges in carbon matrix enabling it to absorb more energy during deformation. While the coating exhibited higher strain hardening exponent and lower plastic work contributing to higher scratch hardness, lower deformation and no pileup; the coating simultaneously resulted in reduction of wear rate by four orders of magnitude. SEM micrographs suggest emanation of lubricious film during tribotests due to dispersion of soft Ag clusters on the top layer, resulting in lower friction coefficient. Also, the sticky nature of DLC particles on the counter-face acted as an anti-adhesive agent thereby preventing transfer of material from the counterbody during tribotest. Lastly, the friction dynamics during dry sliding and Vickers microhardness test post tribotests highlights enhanced durability of Ag-DLC/Cr coated substrates.