Microstructure and oxidation resistance of Al50(Fe–Cr)(50-x)(SiC)x composite coated low-carbon steel prepared by mechanical milling

Abstract

In this study, the influence of silicon carbide (SiC) content on microstructure and oxidation behavior of the Al50(Fe–Cr)(50-x)(SiC)x composite coating on low-carbon steel was studied for the first time. The correlation between the microstructure and oxidation behavior of the Al50(Fe–Cr)(50-x)(SiC)x composite coating at different SiC content was determined using X-ray diffraction (XRD), optical microscope, and scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The result confirms that the phase and microstructure of the coating is a composite structure consisting of highly densified and porous regions. The addition of SiC (5 at.%) on the composite coating improves the microstructure quality, but increasing SiC more than 5 at.% causes the increment of micro-porosity. The high-temperature cyclic oxidation results at 800 °C for 200 h revealed that all composite coating followed a parabolic rate law. The best oxidation resistance is shown by the addition of 5 at.% SiC on the Al50(Fe–Cr)(50-x)(SiC)x composite coating. It indicated a lower Kp of 0.84 × 10−3 mg2/cm4.s than the other samples. Moreover, the protective oxides of Al2O3 were formed on the composite coating surface. This oxide scale is dense and fully adhered to the coating, thus improving oxidation resistance.