Experimental investigations and thermodynamic calculations of the interface reactions between ceramic moulds and Ni-based single-crystal superalloys: Role of solubility of Y in the LaAlO3 phase

It is commonly recognised that more reactive elements contained in Ni-based superalloy result in more-severe interfacial reactions, and thus more inclusions formed at the interface. However, the present work revealed that with rare-earth elements, specifically 0.24 wt% La+Y added to Ni-based superalloys, the interfacial reaction (~5 µm in thickness) between the ceramics and metal was retarded compared to the case of 0.12 wt% Y (~10 µm in thickness). Scanning electron microscopy, focused ion-beam transmission electron microscopy, and X-ray photoelectron spectroscopy were used to characterise the microstructure at the interface. Thermodynamic calculations of the Gibbs free energies of interfacial reactions were conducted. Experimental and theoretical results show that the solubility of Y in the LaAlO3 phase (>3.4 at%) hinders interfacial reactions.