Overview of experiments on microcrystal plasticity in FCC-derivative materials: selected challenges for modelling and simulation of plasticity

An important frontier in both metallurgy and mechanics is the development of a modelling framework that accurately represents length-scale effects and dislocation structure. Emerging mechanics formulations incorporate a length scale tied to distortion gradients aimed at modelling the effects from geometrically necessary dislocations (GND). However, recent experimental studies show important intrinsic size effects exist separately from an evolving GND structure at a mesoscopic scale. The present studies probed for intrinsic size effects at this scale using experimental methods that more closely approach the size scales accessible via discrete dislocation simulation (DDS) in 3d. Uniaxial compression tests of single crystals of pure Ni, Ni3Al alloys, Ni superalloys and fine grained polycrystalline Ni showed material-unique size-dependent responses. Notable among these are a range of strengths and clear intermittency of flow that reveals self-organization. Mechanistically self-consistent simulation of such results, by either discrete dislocation or continuum methods, stands as an unsolved challenge for emerging materials modelling approaches.