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

Dr Fengxian Liu, with colleagues from the Department of Materials and the  Department of Engineering, ​​​​has developed a model for understanding fundamental particle bypass mechanisms and for clarifying the effects of dislocation glide, climb and cross-slip on creep deformation

The research article, published by The Royal Society, explains how plastic deformation in crystalline materials occurs through dislocation slip, and that 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.

In the research article, the dislocation-particle interaction mechanisms were systematically examined.  The analysis was 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.