Condition–dependent wetting and interfacial degradation of Ni–Fe–Co–Cr and Ni–Fe–Co–Cr–Ti–Al high entropy alloys on industrial Al2O3–SiO2 refractories

This research investigates the high-temperature interactions between Ni–Fe–Co–Cr and Ni–Fe–Co–Cr–Ti–Al high-entropy alloys and industrial ceramic refractories with high alumina content (approximately 68–85 wt%) and silica as a secondary component. The primary objective is to quantitatively assess wettability and elucidate the interfacial reactions that led to the formation of reaction layers, non-metallic inclusions, and surface contamination during melting and casting. Sessile-drop wetting experiments were conducted using a CLASIC high-temperature observation furnace/heating microscope capable of operating up to 1600 °C. To mitigate oxidation and isolate interactions between the refractory materials and metals, the experiments were conducted either in a vacuum or under a controlled overpressure of ultra-high-purity argon (≥99.9999%). Post-experimental analysis of the metal–ceramic interfaces was performed using scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) microanalysis, along with X-ray powder diffraction (XRD), to examine interfacial morphology, elemental distribution, and reaction products. The central finding is that the testing environment plays a crucial role in determining the transition from minimal interfacial reactions to significant refractory degradation. Specifically, the application of argon overpressure has been found to suppress capillary infiltration. In contrast, when subjected to low-pressure argon, phenomena such as capillary infiltration, aluminum transfer, the formation of aluminum-oxide-rich scales, and the development of titanium-rich nitride/oxynitride products were promoted. Moreover, stable droplets exhibited apparent contact angles exceeding 110°, indicating a macroscopically non-wetting configuration under the conditions investigated. In contrast, the substrate with the highest alumina content demonstrated optimal performance under argon overpressure.