Analysis of temperature distribution in shell mould during thin-wall superalloy casting and its effect on the resultant microstructure

Abstract

This work focuses on the influence of temperature distribution in a shell mould during investment casting of thin wall parts on macrostructure, chemical composition of microstructural constituents and γ/γ′ misfit parameter. A reduction of production costs is associated with the optimization of precision casting technology of aircraft engine critical parts, including control of the solidification front in thin-walled castings of nickel superalloys.Appropriate lost-wax casting parameters lead to the creation of coarse grained structure, desired for high-temperature service applications. As a result of non-equilibrium solidification, substantially large chemical inhomogeneities in the dendrite core and interdendritic spaces are formed. Interdendritic spaces are occupied by constituents formed as a consequence of segregation of alloying elements, namely eutectic islands γ/γ′, borides, carbides, and an intermetallic compound of Ni and Zr. Dendrite cores consist of cubic-shaped γ′ precipitates surrounded by Ni-rich γ channels. Low lattice misfit influences cubic morphology of γ′ precipitates, which is favourable for jet engine application because it can guarantee good creep resistance.