In vitro corrosion resistance of Si containing multi-principal element carbide coatings

Three types of multi-principal carbide coatings - (HfNbTaTiSi)C, (HfTaTiZrSi)C, and (NbTaTiZrSi)C - containing, apart from carbon and silicon, four elements selected from five transition metals known as biocompatible (Hf, Nb, Ta, Ti, Zr), were investigated as possible candidates for biomedical applications. The coatings were deposited on 316L stainless steel substrate through reactive co-sputtering of pure element targets in an Ar+CH4 gas mixture. In vitro corrosion behavior of the coatings was studied in simulated body fluid (pH=7) at 37 degrees C. Additionally, the coatings were investigated for elemental and phase composition, crystalline structure and morphology. The coatings, with almost equiatomic concentrations of metals (8.2-10.9at%), with Si content of 6.9-7.0at% and with carbon/(metal+Si) ratio of about 1.1, were found to consist of single FCC solid solution phases. Smooth surfaces and columnar cross-sectional morphologies were observed. Compared to the bare 316L substrate, all coatings showed significant better corrosion behavior in terms of open circuit, corrosion and breakdown potentials, corrosion current density, polarization resistance, and weight loss. Among the coatings, (NbTaTiZrSi)C proved to be the most resistant to the corrosive attack.