A process by which a nickel-based superalloy substrate prone to deleterious reactions with an aluminum-rich coating can be stabilized by carburization. The process generally entails processing the surface of the substrate to be substantially free of oxides, heating the substrate in a non-oxidizing atmosphere to a carburization temperature, and then contacting the surface of the substrate with a carburization gas mixture comprising a diluted low activity hydrocarbon gas while maintaining the substrate at the carburization temperature. While at the carburization temperature and contacted by the carburization gas, carbon atoms in the carburization gas dissociate therefrom, transfer onto the surface of the substrate, diffuse into the substrate, and react with refractory metals within the substrate to form refractory metal carbides within a carburized region beneath the surface of the substrate. The substrate is then cooled in a non-oxidizing atmosphere to terminate carbide formation.