Evolution of grain-scale microstructure during large strain simple compression of polycrystalline aluminum with quasi-columnar grains: OIM measurements and numerical simulations

Polycrystalline deformation and its modeling by currently used crystal plasticity models has been investigated by means of an experiment involving direct measurement of deformation induced orientation changes. The experiment used a polycrystalline aluminum sample with quasi-columnar grains, whose initial lattice orientations were mapped using the Orientation Imaging Microscopy (OIM) technique. The sample was then compressed 40% (along the axis of the columnar grains), and the lattice orientations after deformation were studied by OIM. It was found that most of the grains had significant in-grain misorientations in the form of deformation bands with two morphologies — either elongated on the grain scale or nearly equiaxed. In many, but not all cases, more than one similarly oriented deformation band was found in an individual grain. The deformation was then simulated using (i) a classical Taylor-type model, and (ii) a finite element model of the polycrystalline aggregate imposing equilibrium and compatibility between and within the constituent grains (in the weak numerical sense). A comparison of the predictions with the experimental results indicated that the Taylor-type model captured well the tendency to move towards a <110> fiber texture but failed to predict correctly which <110> pole was rotating towards the compression axis in the individual grains, and also by its implicit assumptions could not predict any in-grain misorientation. The finite element model predicted, reasonably well, grain rotations as well as the magnitude of the in-grain misorientations in most, but not all, of the individual grains, but failed completely to predict the morphology of the deformation bands that developed within the grains.