3D DDD modelling of dislocation–precipitate interaction in a nickel-based single crystal superalloy under cyclic deformation

Bing Lin,Minsheng Huang,Liguo Zhao,Anish Roy,Vadim Silberschmidt,Nick Barnard,Mark Whittaker,Gordon Mccolvin

doi:10.1080/14786435.2018.1447159

Abstract

Strain-controlled cyclic deformation of a nickel-based single crystal superalloy has been modelled using three-dimensional (3D) discrete dislocation dynamics (DDD) for both [0 0 1] and [1 1 1] orientations. The work focused on the interaction between dislocations and precipitates during cyclic plastic deformation at elevated temperature, which has not been well studied yet. A representative volume element with cubic γ′-precipitates was chosen to represent the material, with enforced periodical boundary conditions. In particular, cutting of superdislocations into precipitates was simulated by a back-force method. The global cyclic stress–strain responses were captured well by the DDD model when compared to experimental data, particularly the effects of crystallographic orientation. Dislocation evolution showed that considerably high density of dislocations was produced for [1 1 1] orientation when compared to [0 0 1] orientation. Cutting of dislocations into the precipitates had a significant effect on the plastic deformation, leading to material softening. Contour plots of in-plane shear strain proved the development of heterogeneous strain field, resulting in the formation of shear-band embryos.

Highlights

Nickel-based superalloys are widely applied as rotating turbine blades and discs in the hottest sections of gas turbine engines
Using the 3D discrete dislocation dynamics (DDD) framework given in the above section, numerical analyses were conducted for three representative volume element (RVE), consisting of 1, 8 and 27 precipitates with randomly
Cyclic deformation of a nickel-based single crystal superalloy has been modelled by 3D DDD at high temperature (850 °C)

Summary

Introduction

Nickel-based superalloys are widely applied as rotating turbine blades and discs in the hottest sections of gas turbine engines. Their exceptional mechanical properties at high temperature are due to the coherent double-phase microstructure, i.e. a L12-ordered ′-precipitate phase and a ductile -matrix phase. In order to achieve further improved mechanical properties, new development of nickel-based superalloys is normally pursued by increasing the ′ volume fraction. Nickel-based superalloys are often subjected to severe cyclic or sustained loads in harsh environments, a reliable characterisation and prediction of their mechanical behaviour at high temperature, such as plastic deformation under low cycle fatigue, is critical in order to accurately assess damage tolerance of their components

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