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

• Published in: Acta materialia Vol. 155; pp. 362 - 371
• Main Authors: Makineni, Surendra Kumar, Kumar, Ankit, Lenz, Malte, Kontis, Paraskevas, Meiners, Thorsten, Zenk, Christopher, Zaefferer, Stefan, Eggeler, Gunther, Neumeier, Steffen, Spiecker, Erdmann, Raabe, Dierk, Gault, Baptiste
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.08.2018
• Subjects: Atom probe tomography (APT); Creep deformation and stacking faults; Electron channeling contrast imaging (ECCI); Superalloys; Transmission electron microscopy (TEM); Superalloys; Electron channeling contrast imaging (ECCI); Creep deformation and stacking faults; Transmission electron microscopy (TEM); Atom probe tomography (APT)
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2018.05.074

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. [Display omitted]