Concentration gradients near heterophase boundaries in crept single crystal nickel base superalloys

Abstract

This paper presents the results of an atom-probe analysis of γ/γ′ interfaces in a nickel base superalloy single crystal which was crept for 5 h at 1050°C, under a 100 MPa compression stress applied along one 〈001〉 direction. Subtle chemistry variations are detected near the two types of interfaces, namely parallel and perpendicular to the stress direction. They are interpreted as evidence for the early stage of precipitate shape evolution as the origin of "rafting". The driving force for migration of solute elements is discussed in the light of local stress field calculations using finite element modelling.