On the assessment of creep damage evolution in nickel-based superalloys through correlative HR-EBSD and cECCI studies

Sulzer, S. and Li, Z. and Zaefferer, S. and Hafez Haghighat, S.M. and Wilkinson, A. and Raabe, D. and Reed, R.

Volume: 185 Pages: 13-27
DOI: 10.1016/j.actamat.2019.07.018
Published: 2020

The evolution of dislocation density with creep strain in single-crystal superalloys is studied quantitatively using high-resolution electron backscatter diffraction (HR-EBSD) and electron channelling contrast imaging under controlled diffraction conditions (cECCI). Data regarding dislocation density/structure is measured for deformation at 900 °C and 450 MPa up to ≈ 1% plastic strain. Effects of chemical composition are elucidated via three purpose-designed superalloys of differing rhenium and ruthenium contents. The evidence indicates that dislocation avalanching is already prevalent at plastic strains of ≈ 0.1%; thereafter, an exponential decay in the dislocation multiplication rate is indicative of self-hardening due to dislocation constriction within the matrix channels, as confirmed by the imaging. The results are rationalised using discrete dislocation dynamics modelling: a universal dislocation evolution law emerges, which will be useful for alloy design efforts. © 2019

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