CONCENTRATION GRADIENTS NEAR HETEROPHASE BOUNDARIES IN CREPT SINGLE-CRYSTAL NICKEL-BASE SUPERALLOYS

This paper presents the results of an atom-probe analysis of gamma/gam ma' interfaces in a nickel base superalloy single crystal which was cr ept for 5 h at 1050 degrees C, under a 100 MPa compression stress appl ied along one [001] direction. Subtle chemistry Variations are detecte d near the two types of interfaces, namely parallel and perpendicular to the stress direction. They are interpreted as evidence for the earl y stage of precipitate shape evolution as the origin of ''rafting''. T he driving force for migration of solute elements is discussed in the light of local stress field calculations using finite element modellin g.