Experimental analysis of the orientation dependence of deformation laminates.

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The aim of the project is the experimental investigation of the local deformation-induced patterning of the crystallographic orientation in metals and the quantitative comparison of the observed microstructures with theoretical models. In the previous funding period, we made significant progress in uniting lamination theory and experiments. We quanti- tatively correlated the orientation patterning observed in shear deformed copper single crystals using orientation microscopy EBSD (electron back scatter diffraction) with a model of kinematically compatible laminates using a technique developed within this re- search initiative. The specification of the experimentally observed patterning phenomenon as a laminate the formation of which is predicted to be based on strong latent hardening is novel in the research fields of microscopy and microplasticity. However, the ”energy landscape” provided by the model for energetic favorable laminate variations is not yet explored. Therefore, for the applied funding period, we propose the experimental in- vestigation of the orientation phase space of patterning phenomena supported by the correlation to the lamination model (P6, Dondl/M¨uller). Shear experiments for well con- trolled frictionless homogeneous loading will be performed on single crystals of copper and B2 ordered NiAl. Both materials will be plastically deformed in several orientations so that single, double, and triple slip activity can be studied. A small number of poten- tial slip systems in case of B2 ordered NiAl allows precise activation of the slip systems and should lead to more pronounced orientation patterning. Furthermore, study on opti- mal microstructures to free surface boundary conditions provided in bending experiments will be performed in cooperation with P6. Study of the dynamic processes such as the initial steps of lamination and subsequent microstructure evolution are of particular in- terest within the microplasticity. To study the microstructure dynamics, we will perform experiments on the evolution of laminated microstructures which will be accompanied by time-continuous finite crystal plasticity calculations (P3, Hackl/Kochmann/Wagner). The energetic reasons and the mechanisms for the initiation and evolution of the laminate formation will be explored. Moreover, experiments regarding formation and evolution of rank-two laminates and crystallographic analysis of these structures will be performed. This investigations will be supported by further development of the finite plasticity model for high-order laminates (P3). Beside the study of the progress of the lamination, we will investigate the evolution of the dislocation structures within the laminated microstruc- ture. These investigations provide insights into the mechanisms of dislocation trapping and generation of dislocation walls in correlation with the laminate formation. For this reason, we will apply the electron channeling contrasts technique which allows the ob- servation of the dislocation structures and the simultaneous analysis of the surrounding microstructure by using EBSD. Thus, we can explore the impact of the dislocation rear- rangements on the formation of laminated microstructure. This way, we can answer one of the open questions existing in lamination theory, such as whether cell structures may be understood as compatible arrangements of regions of single slip.