Study of the coating thickness of silicon carbide on MgAZ31 alloy in a CVD reactor as a function of operating time

Abstract

In this study, the effect of the silicon carbide (SiC) coating thickness deposited via a plasma process was investigated as a function of operating time, using a Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor on a magnesium alloy (MgAZ31). The objective was to determine the optimal thickness that ensures good corrosion resistance. Samples were subjected to different deposition times, using methane (CH4) and hexamethyldisilazane (HMDS) as precursors, resulting in four distinct thicknesses varying the deposition time (30, 60, 90, and 120 minutes).

The characterization of the samples was performed using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and polarization curves in a simulated body fluid (SBF) to evaluate the corrosion resistance of the coating. The results obtained by SEM showed a linear relationship between the coating thickness and deposition time. The sample with a thickness of 3.68 μm, corresponding to 90 minutes of deposition, presented the optimal coating. In contrast, in samples with thinner coatings, the substrate material was detected. On the other hand, in the sample with a thickness of 5.13 μm, obtained after 120 minutes of deposition, the presence of the substrate was observed due to coating failures. These failures were due to an excessive coating thickness, which generated internal stresses and led to structural failure of the material. In terms of corrosion rate, the sample with a 3.68 μm deposition thickness showed the lowest corrosion rate, in accordance with the SEM images. The FTIR characterization confirmed that the coating was indeed SiC.