Distributions of Stretch and Rotation in Polycrystalline OFHC Cu

Abstract

High resolution experimental characterization of material stretch and rotation fields in relatively fine-grained polycrystals has been limited, inhibiting direct comparison with predictions of crystal plasticity theory. In this study, micron scale grids used more commonly in etching of substrates for microelectronic circuits were deposited on specimens of Oxygen Free High Conductivity Copper (OFHC Cu) subsequently subjected to uniaxial compressive deformations to effective strain levels up to unity. Material stretch and rotation fields were assessed for fields of view encompassing on the order of 20 grains. Some rather striking features emerge, including the apparent relative lack of deformation in regions sized on the order of large grains, and the apparent concentration of stretch and rotation in bands surrounding these relatively undeformed areas. Comparisons are drawn with results of 3D crystal plasticity calculations performed on digitized grain structures that conform to representative microstructures in terms of initial grain size and shape distributions. The crystal plasticity simulations predict regions of relatively large rotation and relatively localized stretch traversing multiple grains. The numerical solutions also exhibit slightly higher local stresses in the vicinity of grain boundaries and triple points than in grain interiors, a phenomenon attributed to local lattice misorientation among neighboring grains. However, the crystal plasticity calculations do not, in an average sense, predict larger-than-average maximum stretch or rotation in the grain boundary regions. The numerical solutions are also quite sensitive to initial lattice orientations assigned to the grains. Comments are made regarding the segmentation of slip within the grains and its implications for modeling, based upon direct comparison of results from experiments and simulations.