Planar defect formation in the gamma' phase during high temperature creep in single crystal CoNi-base superalloys

Eggeler Y, Müller J, Titus MS, Suzuki A, Pollock TM, Spiecker E (2016)

Publication Type: Journal article

Publication year: 2016

Journal

Acta Materialia Elsevier

Book Volume: 113

Pages Range: 335-349

DOI: 10.1016/j.actamat.2016.03.077

Abstract

The structure and formation mechanism of extended planar defects in the \textgreekg/\textgreekg$\prime$ microstructure of creep deformed CoNi-base single crystal superalloys have been studied by conventional and advanced transmission electron microscopy (TEM). Planar defects in numerous isolated as well as contiguous \textgreekg$\prime$ precipitates on (111) planes reveal a characteristic configuration whereby superlattice intrinsic stacking faults (SISF) are fully embedded within antiphase boundaries (APB). Detailed analysis revealed that a leading 1/3[112] superpartial dislocation first creates an SISF. The SISF is then transformed into an APB by a trailing 1/6[112] partial dislocation. The partial is left inside the precipitate and remains as a dislocation loop. Thus, the entire shearing process constitutes a crystallographic slip of type 1/2[112]. A force balance analysis indicates that the initial APB energy exceeds the SISF energy. However, energy-dispersive X-ray spectroscopy (EDXS) indicates pronounced local reordering and diffusion processes near both types of planar defects. The APB qualitatively adopts the composition of the \textgreekg phase whereas the SISF locally changes its composition towards that of the Co3W--D019 phase. We propose that these atomic diffusion processes determine the formation and shrinkage of the loops. A post mortem in situ TEM heating experiment shows that with increasing temperature the APBs exhibit complete faceting into [100] planes followed by coarsening, eventually leading to disintegration of the \textgreekg$\prime$ precipitate. This indicates a detrimental impact of APBs as potential nuclei for fragmentation of the \textgreekg/\textgreekg$\prime$ microstructure in CoNi-base superalloys.

Authors with CRIS profile

Yolita Eggeler Lehrstuhl für Werkstoffwissenschaften (Mikro- und Nanostrukturforschung) Julian Müller Lehrstuhl für Werkstoffwissenschaften (Mikro- und Nanostrukturforschung) Erdmann Spiecker Lehrstuhl für Werkstoffwissenschaften (Mikro- und Nanostrukturforschung)

Additional Organisation(s)

Exzellenz-Cluster Engineering of Advanced Materials (EAM) Interdisziplinäres Zentrum, Center for Nanoanalysis and Electron Microscopy (CENEM) Lehrstuhl für Werkstoffwissenschaften (Mikro- und Nanostrukturforschung)

Involved external institutions

GE Global Research US United States (USA) (US) University of California US United States (USA) (US)

How to cite

APA:

Eggeler, Y., Müller, J., Titus, M.S., Suzuki, A., Pollock, T.M., & Spiecker, E. (2016). Planar defect formation in the gamma' phase during high temperature creep in single crystal CoNi-base superalloys. Acta Materialia, 113, 335-349. https://doi.org/10.1016/j.actamat.2016.03.077

MLA:

Eggeler, Yolita, et al. "Planar defect formation in the gamma' phase during high temperature creep in single crystal CoNi-base superalloys." Acta Materialia 113 (2016): 335-349.

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