Corrosion Properties of a Novel FeCrMoNbB Thin Film Metallic Glass Deposited by DC Magnetron Sputtering
Authors: Capute Batalha Weverson , Roche Virginie , Champion Yannick , Mantel Marc , Moreira Jorge Junior Alberto 
Published: February 2024

The application of amorphous alloys as thin-film coatings with good corrosion properties has drawn attention in the last years since overcoming the typical limitations of these materials, such as the critical size and brittleness. Techniques based on Physical Vapor Deposition, like DC magnetron sputtering, are interesting once it allows parameter optimization to achieve the desired microstructure [1,2,3]. This study aims to characterize the electrochemical properties of a novel FeCrMoNbB (low Cr content – 11at%) alloy as a coating.

Thin-film coatings were produced in a DC magnetron sputtering PVD system with 0.5 Pa Ar working pressure, 92 W of sputtering power, and 200°C deposition temperature. The substrate was 316L stainless steel. Corrosion tests were performed in a three-electrode cell in a Gamry 600+ potentiostat using the following sequence: two hours of open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) from 100kHz to 0,02 Hz, 20 minutes of OCP, and potentiodynamic polarization test from -0,03 to 1,2V (vs. OCP). The solution was a 0,6M NaCl (Cl- content equivalent to seawater), natural pH of 5.5. Measurement Model software, developed by Orazem et al. [4], was used for data regression. X-ray photoelectron microscopy (XPS) was performed to obtain complementary information about the passive film. An XR3E2 apparatus from Vacuum Generator with an Mg-Kα source was used. The analysis was performed after stabilization in an open circuit for two hours.

Fully amorphous thin films of about 400 nm were obtained. Outstanding corrosion behavior was observed for the coating, which presented a corrosion current (icorr) around 5 x10-9 Acm-2 and a corrosion potential of 127 mV. The icorr value is more than two decades lower when compared to the 316L of the substrate, indicating a higher corrosion resistance after applying the coating. EIS results showed a high impedance modulus at low frequency was |Z|LF = 3.7 MΩ.cm2. XPS analysis showed that all the alloying elements were in the oxidized form on the surface. Metallic species from the underlying surface could also be detected, meaning the oxide layer has less than 10 nm. Regression with Measurement Model software found a global capacitance C = 5.7 μF.cm2, a typical value for a compact passive layer. From the value of C, the film thickness was estimated to be around 2 nm, corroborating with the XPS analysis. A compact, thin layer of oxide composed of Cr, Nb, and Mo can be associated with high protectiveness of the passive film, hence, good corrosion resistance. Furthermore, the pitting phenomenon typical of 316L near 500mV was not observed in the coating. In summary, the results are promising for using these alloys as coatings for marine applications, potentially replacing conventional stainless steels.

[1] M. Panayotova, Y. Garbatov, C. Guedes Soares, Corrosion of Steels in Marine Environment, Monitoring and Standards, Safety and Reliability of Industrial Products, Systems and Structures, Taylor & Francis Group, 2008.p.370.

[2] WOOD Maureen; VETERE ARELLANO Ana Lisa; VAN WIJK Lorenzo. Publications Office of the European Union; 2013. JRC84661

[3] Chu, J. P. et al. Thin film metallic glasses: Unique properties and potential applications. Thin Solid Films 520, 5097–5122 (2012).

[4] M.E.O. W. Watson, EIS: Measurement Model Program., ECSarXiv. (2020). https://doi.org/10.1149/osf.io/kze9x.