# Microtwinning during intermediate temperature creep of polycrystalline Ni-based superalloys: mechanisms and modelling

Viswanathan, GB and Karthikeyan, S and Sarosi, PM and Unocic, RR and Mills, MJ (2006) Microtwinning during intermediate temperature creep of polycrystalline Ni-based superalloys: mechanisms and modelling. In: Philosophical Magazine, 86 (29-31). pp. 4823-4840.

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## Abstract

Deformation mechanisms, operative during intermediate temperature creep of Ni-based polycrystalline superalloys, are poorly understood. The creep deformation substructure has been characterized in Rene 88DT following rapid cooling from the super-solvus temperature, yielding a fine $\gamma^{\prime}$-precipitate microstructure. After creep to modest strain levels (up to 0.5% strain) at 650°C and an applied tensile stress of 838 MPa, microtwinning is found to be the predominant deformation mode. This surprising result has been confirmed using diffraction contrast and high-resolution transmission electron microscopy. Microtwinning occurs via the sequential movement of identical 1/6[11-2] Shockley partials on successive (111) planes. This mechanism necessitates reordering within the $\gamma^{\prime}$ precipitates in the wake of the twinning partials, so that the $L1_2$ structure can be restored. A quantitative model for creep rate has been derived on the basis that the reordering process is rate-limiting. The model is in reasonable agreement with experimental data. The results are also discussed in relation to previous studies under similar deformation conditions.

Item Type: Journal Article Copyright of this article belongs to Taylor and Francis. Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy) 30 May 2008 19 Sep 2010 04:45 http://eprints.iisc.ernet.in/id/eprint/14112