High-Temperature Oxidation Behavior of an As-Cast γ-TiAl Alloy: Oxidation Kinetics, Multilayer Scale Evolution, and Interfacial Chemical Redistribution

γ-TiAl-based alloys are promising lightweight materials for high-temperature applications, but their insufficient oxidation resistance near 800 °C remains a major limitation. This study aims to clarify the short-term oxidation behavior and associated scale/interface evolution of an as-cast Ti-44Al-4Nb-1.5Cr-0.5Mo-0.1B (at.%) alloy. This composition was selected because the Nb, Cr, and Mo containing TiAl system enables alloying-element redistribution to be examined together with oxide-scale evolution. Isothermal oxidation was conducted in static air at 800 °C for 1–48 h, followed by oxidation-kinetics measurements and multiscale characterization. The mass gain increased continuously with a kinetic exponent of n = 1.77, indicating deviation from ideal parabolic behavior. After 48 h, a porous and chemically heterogeneous multilayered scale formed, comprising a TiO2-dominated outer region, locally distributed Al-rich oxides, and nitride-containing interfacial regions. TiN and Ti2AlN were identified together with pronounced interfacial N enrichment and localized Nb/Cr enrichment. The results indicate that a continuous compact Al-rich protective layer was not established during short-term oxidation, highlighting the importance of scale continuity and compactness in limiting oxidation of TiAl alloys near 800 °C.