Publications

On the diffusive phase transformation mechanism assisted by extended dislocations during creep of a single crystal CoNi-based superalloy

Makineni, S.K. and Kumar, A. and Lenz, M. and Kontis, P. and Meiners, T. and Zenk, C. and Zaefferer, S. and Eggeler, G. and Neumeier, S. and Spiecker, E. and Raabe, D. and Gault, B.

ACTA MATERIALIA
Volume: 155 Pages: 362-371
DOI: 10.1016/j.actamat.2018.05.074
Published: 2018

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.

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