A Kinetic Model for Oxide–Carbonitride Inclusion Heterogeneous Nucleation and Precipitation during Superalloy Solidification

Abstract

Complex oxide–carbonitrides (MgO-Ti(CN), Al2O3-Ti(CN), and MgO·Al2O3-Ti(CN)) are the most common non-metallic inclusions presented in cast and wrought superalloys. In this work, a coupled kinetics model was proposed to predict the complex oxide–carbonitride inclusion’s precipitation behavior during the solidification of superalloys. This model takes into account thermodynamics, micro-segregation, heterogeneous nucleation in the inter-dendritic liquid, and growth controlled by the diffusion of solute elements and kinetics of interfacial reaction. The results demonstrated that both the cooling rate and nitrogen content take significant effects on the final size of complex oxide–carbonitride inclusions, as the former controls the total growth time and the latter determines the initial precipitation temperature. In comparison, the particle size of primary oxides shows a negligible impact on the final size of complex inclusions. The practice of an industrial vacuum arc remelting confirmed that the inclusion size variation predicted by the present model is reasonably consistent with the experimental results.

Keywords

• non-metallic inclusion
• nucleation and growth
• kinetics model
• superalloy