In pursuit of imperfection: can modelling help?

David J. Bacon

The beauty of the perfection of crystals grabs attention, but materials scientists know that it is the imperfection in crystalline materials that can hold the interest. Whilst most of the basic properties of crystal defects were established long ago, important details have lain undiscovered. Not all are amenable to experimental investigation, but, with the aid of modern computing power, modelling by simulation can be a powerful aid to the researcher. This paper will review a few topics in an attempt to justify this claim. It will focus on radiation damage, dislocation-obstacle interactions and interfaces in metals.

Displacement cascades are the primary source of radiation damage in fast neutron- and ion-irradiated metals. Atomic-scale computer simulation has revealed details of the population and clustering of defects in cascades and their dependence on parameters such as the energy and mass of the primary knock-on atom. Simulation is also being used to investigate the interaction of dislocations with defects in irradiated metals under external stress. Processes such as defect absorption and transformation have been identified, and parameters associated with the obstacle strength of defects have been determined. This information is required for reliable modelling at the continuum level in the multi-scale framework. Finally, simulation can provide information of defect processes in boundaries to supplement conventional models based on crystallography. Examples include absorption of a crystal dislocation by a moving twin boundary and its transformation into a defect source of twinning dislocations, and the interaction between a moving boundary and point defect clusters that leads to either defect absorption by the boundary or boundary pinning.