On the nucleation of planar faults during low temperature and high stress creep of single crystal Ni-base superalloys

Wu, X. and Dlouhy, A. and Eggeler, Y.M. and Spiecker, E. and Kostka, A. and Somsen, C. and Eggeler, G.

Volume: 144 Pages: 642-655
DOI: 10.1016/j.actamat.2017.09.063
Published: 2018

The present work studies the nucleation of planar faults in the early stages of low temperature (750 °C) and high stress (800 MPa) creep of a Ni-base single crystal superalloy (SX). Two families of 60° dislocations with different Burgers vectors were detected in the transmission electron microscope (TEM). These can react and form a planar fault in the γ′ phase. A 2D discrete dislocation model helps to rationalize a sequence of events which lead to the nucleation of a planar fault. First, one 60° channel dislocation approaches another 60° interface dislocation with a different Burgers vector. At a distance of 5 nm, it splits up into two Shockley partials. The interface dislocation is pushed into the γ′-phase where it creates a small antiphase boundary. It can only move on when the leading Shockley partial joins it and creates an overall 1/3<112> superdislocation. This process is fast and therefore is difficult to observe. The results obtained in the present work contribute to a better understanding of the processes which govern the early stages of low temperature and high stress primary creep of SX. © 2017 Acta Materialia Inc.

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