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Free keywords:
Creep; High resolution transmission electron microscopy; Phase transitions; Probes; Shearing; Single crystals; Stacking faults; Transmission electron microscopy, Atom-probe tomography; Creep deformations; Electron channeling contrasts; Extended dislocations; Partial dislocations; Phase transformation mechanisms; Structural contrasts; Superlattice intrinsic stacking faults, Superalloys
Abstract:
We propose here a deformation-induced diffusive phase transformation mechanism occurring during shearing of γ′ ordered phase in a γ/γ′ single crystalline CoNi-based superalloy. Shearing involved the creation and motion of a high density of planar imperfections. Through correlative electron microscopy and atom probe tomography, we captured a superlattice intrinsic stacking fault (SISF) and its associated moving leading partial dislocation (LPD). The structure and composition of these imperfections reveal characteristic chemical – structural contrast. The SISF locally exhibits a D019 ordered structure coherently embedded in the L12 γ′ and enriched in W and Co. Interestingly, the LPD is enriched with Cr and Co, while the adjoining planes ahead of the LPD are enriched with Al. Quantitative analysis of the three-dimensional compositional field in the vicinity of imperfections sheds light onto a new in-plane diffusion mechanism as the LPD moves on specific 111 planes upon application of stress at high temperature. © 2018 Acta Materialia Inc.