Oxidation behaviour of a CrCoNiAlTi multicomponent alloy

Multi-component metallic alloys, such as high-entropy alloys (HEAs), have recently attracted scientific and industrial interest due to their capacity to be used in a variety of applications, especially as potential candidates for high-temperature services. In this study, the oxidation behavior of CrCoNiAlTi alloy was investigated at different temperatures and exposure times.

Oxidation tests were carried out in a tubular furnace in atmospheric air. Samples were tested at 800°C, 900°C and 1000°C and subjected to exposure times of 5 h, 24h and 48 h at each temperature. Microstructural characterization was performed by X-Ray Diffraction (XRD) scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS).

XRD revealed the presence of a hexagonal close-packed corundum-type phase, which might consist of both alumina and/or chromia, as both oxides present similar trigonal crystal structures. SEM analysis, supported by EDS, indicated the presence of an inner layer of Al2O3 and an external layer of Cr2O3. Mass gain calculations investigated the oxidation rate law. In this case, a parabolic rate law was observed in all tested samples, which suggests a diffusion-controlled process along the different time intervals and the possibility of formation of stable oxide scales. The observed mass gain for the 48 h time interval (which was the most significant oxide scale production interval), for example, included values ranging from 0,228 mg/cm² (at 800°C) to 0,679 mg/cm² (at 900°C) to 1,941mg/cm² (at 1000°C), showing a notable enhancement in scale production at the higher temperature of 1000°C. In fact, that significant increase in scale formation can be determined by the calculated equilibrium constant (Kp) when one compares the Kp at 800°C = 1,20 x 10^-3 mg²cm^-4h^-1 and the Kp at 1000°C = 4,59 x 10^-3 mg²cm^-4h^-1.

These results present a starting point for understanding the oxidation kinetics of CrCoNiAlTi multicomponent alloys.