On the development of microstructure and texture heterogeneity in ECAE via route C

Deformation in every two passes of route C by equal channel angular extrusion (ECAE) is commonly viewed as severe forward and reverse shearing. Contrary to predictions by standard polycrystal models, microstructural observations and texture measurements of a variety of ECAE materials consistently show that the initial state of the material is not recovered after even-numbered passes in this route. For the first time, the factors governing the microstructural and texture evolutions during two passes of route C are investigated using orientation imaging microscopy (OIM) and multi-scale modeling. For a two-pass pure copper sample processed by a 90° die, a useful model example, the OIM measurements reveal that the variation in microstructure and texture across the sample thickness is significant and all the textures show shear-type characteristics. Using finite element simulations for the macroscopic deformation, self-consistent modeling for polycrystals, and a latent hardening model for single crystals, it is shown that the deviation from idealized simple shear deformation and the difference in the deformation between successive passes due to changes in material behavior play a primary role, while anisotropy in single-crystal hardening plays a relatively minor one. Textures predicted, considering the two main factors, are in good agreement with the measurements.