Reaction of a Molten Cr-Si-Base Alloy with Ceramics and a High Entropy Oxide

Abstract Due to their higher thermal and chemical stability than other high-temperature materials, chromium-silicon-base (Cr-Si-base) alloys are among the most promising materials for future gas turbines and other high-temperature applications operating under harsh conditions. To enable near-net-shape casting of Cr-Si-base alloys, a compatibility of the alloy melt with the ceramic crucibles and molds is necessary. Additionally, a metal-ceramic contact exists at the interface between thermal barrier coating (TBC) and alloy, where metallic may melts play a role in the case of coating failure and overheating. In this study, molten Cr₉₂Si₈ (in at. %) alloy is brought into contact with powders of ceramics commonly used for casting molds or crucibles (e.g. ZrSiO₄, Al₂O₃, 3YSZ), to investigate liquid metal corrosion, interdiffusion, and stabilities. Additionally, the high entropy oxide (Sm0.2Gd0.2Dy0.2Er0.2Yb0.2)₂Zr₂O₇ (HEO), a potential future TBC material, is investigated. Before melting using an electric arc furnace the powders of the investigated ceramics were mixed with pulverized Cr₉₂Si₈ and pressed to alloy-ceramic pairs, to maximize the contact area between molten metal and ceramic. For microstructural investigations and phase analysis the materials were assessed using scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The widely used mold material ZrSiO₄ and the coating BN were found to decompose, while reaction products of SiO₂ and CoAl₂O₄ with the melt were detected. Al₂O₃, 3YSZ, and the HEO did not show decomposition or corrosion by the melt. Al₂O₃, 3YSZ, and the HEO are therefore considered as promising crucible, mold, and TBC materials for Cr-Si-base alloys.