Dislocation dynamics modelling of the creep behaviour of particle-strengthened materials.

F X Liu,E Tarleton,A C F Cocks

doi:10.1098/rspa.2021.0083

F X Liu, E Tarleton + Show 1 more

Open Access

https://doi.org/10.1098/rspa.2021.0083

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Abstract

Plastic deformation in crystalline materials occurs through dislocation slip and strengthening is achieved with obstacles that hinder the motion of dislocations. At relatively low temperatures, dislocations bypass the particles by Orowan looping, particle shearing, cross-slip or a combination of these mechanisms. At elevated temperatures, atomic diffusivity becomes appreciable, so that dislocations can bypass the particles by climb processes. Climb plays a crucial role in the long-term durability or creep resistance of many structural materials, particularly under extreme conditions of load, temperature and radiation. Here we systematically examine dislocation-particle interaction mechanisms. The analysis is based on three-dimensional discrete dislocation dynamics simulations incorporating impenetrable particles, elastic interactions, dislocation self-climb, cross-slip and glide. The core diffusion dominated dislocation self-climb process is modelled based on a variational principle for the evolution of microstructures, and is coupled with dislocation glide and cross-slip by an adaptive time-stepping scheme to bridge the time scale separation. The stress field caused by particles is implemented based on the particle–matrix mismatch. This model is helpful for understanding the fundamental particle bypass mechanisms and clarifying the effects of dislocation glide, climb and cross-slip on creep deformation.

Highlights

As a reliable, low-emitting and cost-competitive source of electricity, nuclear energy has become the second-largest source of low-carbon electricity production globally, which is playing an expanded role in creating a sustainable future energy system
We present here the first three-dimensional discrete dislocation dynamics (DDD) framework for particle strengthened materials that account for dislocation glide, cross-slip and self-climb mechanisms
Coupled with a superposition method, it provides an effective model to predict the creep behaviour of particle-strengthened materials within a finite domain at relatively high temperature, by revealing the collective dislocation behaviour in the presence of particles

Summary

Introduction

Low-emitting and cost-competitive source of electricity, nuclear energy has become the second-largest source of low-carbon electricity production globally, which is playing an expanded role in creating a sustainable future energy system. As a significant amount of new dislocation line has to be created in the course of ‘local climb’, extra energy must be supplied, resulting in a relatively large threshold stress This gives an appropriate order-ofmagnitude estimate for creep thresholds measured in particle-strengthened materials, it can be argued [16] that ‘local climb’ represents an extremely unstable process; in practice, the sharp change in profile of the dislocation could be rapidly relaxed by diffusion, leading to a more ‘general climb’ profile. We have developed a new method which incorporates atomic diffusion into the nodal-based DD method and bridges the time scale separation between dislocation glide and self-climb [4,35] This method acts as a steppingstone for the modelling of a new class of physical problems.

Methodology

Dislocation–particle interactions

Creep test during compression of micropillars

Conclusion