Corrosion and tribo-corrosion enhancement of SS301 and Ti–6Al–4V substrates by amorphous hydrogenated SiN/SiC/a-C multilayer coating architecture

Amorphous hydrogenated silicon-based multilayer coatings were deposited on 301 stainless steel (SS301) and Ti–6Al–4V alloy substrates using plasma enhanced chemical vapor deposition (PECVD), in order to integrate the advantages of the respective layers. Corrosion and tribo-corrosion behaviors of the complete coating/substrate system on different substrates were investigated. The SiN/SiC double-layer coating substantially improved the corrosion resistance of the metals: For SS301, the corrosion current, icorr, was reduced by more than three orders of magnitude, and the breakdown voltage was increased from 0.34 to 1.37 V. For Ti–6Al–4V, the icorr was decreased by a factor of ~ 50. Particularly, the Ti–6Al–4V/SiN/SiC multilayer system exhibited excellent anti-corrosion properties according to potentiodynamic polarization measurements, due to the superior corrosion resistance of both the Ti–6Al–4V substrate and the silicon-based coatings. Further enhancement of the tribo-corrosion resistance has been achieved by applying an amorphous hydrogenated carbon (a-C) coating as a top layer in the three-layer system. In the tribo-corrosion test in 1 wt.% NaCl solution, the SiN/SiC/a-C coating reduced the wear rate and the friction coefficient by a factor of ~ 175 and ~ 4, respectively, compared with the bare Ti–6Al–4V. The Ti–6Al–4V/SiN/SiC/a-C multilayer system integrates in synergy the advantages of the respective layers, and its versatility makes it a particularly attractive candidate for applications in different harsh working environments.