Interplay of chemistry and deformation-induced defects on facilitating topologically-close-packed phase precipitation in nickel-base superalloys

Topologically close packed (TCP) phases are often formed in nickel-base superalloys with high refractory elements during service, and they are detrimental for the high temperature performance of superalloys. The precipitation process of TCP phases is under scrutiny in particular for deformations that integrate strain and temperature but replicate the working conditions of superalloys. In this work, TCP phase precipitation is studied in nickel-base single crystal superalloys with or without Ru addition under thermomechanical fatigue deformation. Deformation twins on different {111} planes are observed intersecting with each other and forming large number of high angle boundaries. The structure of these high angle boundaries has high similarity to topologically close packed sigma phase, and the boundaries are enriched in Re, Ru, Co and Cr, thus it provides both structural origins and constituent elements for the formation of sigma phase. Ru is revealed intensely segregating to semi-coherent and incoherent interfaces between TCP phase and the matrix, this reduces the interface energies and leads to a dramatic change of the morphology of TCP phase precipitates. These results provide insight to effects of lattice imperfections and coevolution chemistry on TCP phase formation in superalloys, and shed light on inhomogeneous precipitation in alloys in general. (c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

This work investigates the precipitation process of topologically close packed (TCP) phases in nickel-base single crystal superalloys under thermomechanical fatigue deformation, with and without the addition of Ru. It is found that deformation twins on different {111} planes intersect and form high angle boundaries, which have a similar structure to topologically close packed sigma phase and are enriched in Re, Ru, Co, and Cr. The segregation of Ru to the interfaces between TCP phase and the matrix reduces interface energies and dramatically changes the morphology of TCP phase precipitates. These findings provide insights into the effects of lattice imperfections and coevolution chemistry on TCP phase formation in superalloys, as well as inhomogeneous precipitation in alloys in general.