The strain distribution in heterostructured wurtzite InAs/InP nanowires is measured by a peak finding technique using high resolution transmission electron microscopy images. We find that nanowires with a diameter of about 20 nm show a 10 nm strained area over the InAs/InP interface and the rest of the wire has a relaxed lattice structure. The lattice parameters and elastic properties for the wurtzite structure of InAs and InP are calculated and a nanowire interface is simulated using finite element calculations. Both the method and the experimental results are validated using a combination of finite element calculations and image simulations.

A cellular automaton algorithm with probabilistic cell switches is employed in the simulation of dynamic discontinuous recrystallization. Recrystallization kinetics are formulated on a microlevel where, once nucleated, new grains grow under the driving pressure available from the competing processes of stored energy minimization and boundary energy reduction. Simulations of the microstructural changes in pure Cu under hot compression are performed where the influence of different thermal conditions are studied. The model is shown to capture both the microstructural evolution in terms of grain size and grain shape changes and also the macroscopic flow stress behavior of the material. The latter gives the expected transition from single-to multiple-peak serrated flow with increasing temperature. Further, the effects on macroscopic flow stress by varying the initial grain size is analyzed and the model is found to replicate the shift towards more serrated flow as the initial grain size is reduced. Conversely, the flow stress is stabilized by larger initial grain sizes. The extent of recrystallization as obtained from simulations are compared to classical JMAK theory and proper agreement with theory is established. In addition, by tracing the strain state during the simulations, a post-processing step is devised to obtain the macroscopic deformation of the cellular automaton domain, giving the expected deformation of the equiaxed recrystallized grains due to the macroscopic compression.

a b s t r a c tA constitutive model for polycrystalline metals is established within a micromechanical framework. The inelastic deformation is defined by the formation and annihilation of dislocations together with grain refinement due to continuous dynamic recrystallization. The recrystallization studied here occurs due to plastic deformation without the aid of elevated temperatures. The grain refinement also influences the evolution of the dislocation density since the recrystallization introduces a dynamic recovery as well as additional grain and subgrain boundaries, hindering the movement of dislocations through the material microstructure. In addition, motivated by experimental evidence, the rate dependence of the material is allowed to depend on the grain size. Introducing a varying grain size into the evolution of the dislocation density and in the rate dependence of the plastic deformation are believed to be important and novel features of the present model. The proposed constitutive model is implemented in a numerical scheme allowing calibration against experimental results, which is shown using commercial-purity aluminum as example material. The model is also employed in macroscale simulations of grain refinement in this material during extensive inelastic deformation.

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