Investigation of microstructural and electrochemical behavior of chromized-doped layers with variant magnesium concentrations

Abstract

This study provides an innovative approach about chromized-doped layers by discovering the optimal proportion of Mg (1 wt.%, 2 wt.%, and 3 wt.%) used as doping elements in order to enhance diffusion and stabilize the formed chromium oxide during the diffusion process. Our main objective is to evaluate the effect of Mg doping on the microstructural and the electrochemical behavior of the doped layer, systematically evaluating the impact of simultaneous variation of NH₄Cl activator. The chromized-doped layers were analyzed by X-ray diffraction (XRD) and a scanning electron microscopy (SEM) equipped with EDX analysis. The doped layers were tested in 3.5% NaCl solution, and then were characterized by electron probe micro-analyzer (EPMA). The results revealed that doping contributed to the improvement of chromium diffusion for all the layers (≥ 96% Cr), stabilizing chromium oxide by forming a more stable oxide (MgCr₂O₄). However, Cr-Mg/1 wt.% showed the most homogenous crystalline structure and topography compared to the other layers, with the most insignificant defects. The Cr-Mg/1 wt.% presented an excellent corrosion resistance in the 3.5% NaCl solution, where its surface did not suffer any type of corrosion or damages. In addition, the balanced value of the activator (NH₄Cl) relative to the other doped layers may play a significant role. As a result, the Cr-Mg/1 wt.% (using 4 wt.% NH₄Cl) could be a robust and innovative surface, paving the way for new possibilities in the field of chromizing coatings.