On the role and modelling of internal boundaries in size effects for metals (INVITED)

Abstract eng:
This paper focuses on the role of grain and phase boundaries in restricting dislocation motion, giving rise to size effects. Some essential features of a thermodynamically consistent model for a grain boundary are presented, which accounts for the grain boundary energy and defect structure and evolution. The role of a phase boundary is investigated with a dislocation transport driven crystal plasticity model, revealing the explicit role of the plastic phase contrast and phase boundary resistance. Interesting size effects are thereby recovered. Size effects can also be eliminated or inhibited by other microstructural mechanisms. Two cases are addressed to illustrate this. The first case reveals the role of dislocation climb and its effectiveness in dissolving dislocation pile-ups. The second case concerns a very thin austenitic phase in martensite, whereby the particular structure of the phase and its interface give rise to preferential sliding mechanisms that circumvent the common dislocation driven size effects.

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