Modelling plastic deformation in a single-crystal nickel-based superalloy using discrete dislocation dynamics

Abstract

Background: Nickel-based superalloys are usually exposed to high static or cyclic loads in non-ambient environment, so a reliable prediction of their mechanical properties, especially plastic deformation, at elevated temperature is essential for improved damage-tolerance assessment of components. Methods: In this paper, plastic deformation in a single-crystal nickel-based superalloy CMSX4 at elevated temperature was modelled using discrete dislocation dynamics (DDD). The DDD approach was implemented using a representative volume element with explicitly-introduced precipitate and periodic boundary condition. The DDD model was calibrated using stress-strain response predicted by a crystal plasticity model, validated against tensile and cyclic tests at 850°C for <001 > and <111 > crystallographic orientations, at a strain rate of 1/s. Results: The DDD model was capable to capture the global stress-strain response of the material under both monotonic and cyclic loading conditions. Considerably higher dislocation density was obtained for the <111 > orientation, indicating more plastic deformation and much lower flow stress in the material, when compared to that for <001 > orientation. Dislocation lines looped around the precipitate, and most dislocations were deposited on the surface of precipitate, forming a network of dislocation lines. Simple unloading resulted in a reduction of dislocation density. Conclusions: Plastic deformation in metallic materials is closely related to dynamics of dislocations, and the DDD approach can provide a more fundamental understanding of crystal plasticity and the evolution of heterogeneous dislocation networks, which is useful when considering such issues as the onset of damage in the material during plastic deformation.

An efficient algorithm of dislocation-precipitate interactions for single crystal nickel-based superalloys within discrete dislocation dynamics and its application

“…However, when the sample becomes larger, especially for D = 1140 nm as shown in figure 5(d), a significant hardening stage can be readily observed. The [001] tensile stress-strain curve of bulk SCNBSs consists of three stages: elastic stage, plastic hardening stage and ideal plasticity stage [38,53]. This hardening stage is consistent with that in stress-strain curve of bulk SCNBSs under [001] tensile loading.…”

“…According to the limitation of DDD method, it is necessary to choose such high strain rate achieve a reasonable strain level. In fact, according to the experimental study [53], the response of SCNBSs is strain-rate dependent. It should be addressed that although the present DDD results may not be quantitatively comparable to experimental results due to different strain rates, both the size effect of SCNBSs and their associated dislocation mechanisms can still be captured.…”