Effect of initial orientation on subgrain formation in nickel single crystals during equal channel angular pressing

This study deals with the development of the microstructure and grain refinement of nickel single crystals during the Equal Channel Angular Pressing (ECAP) process. In the experimental study, the electron backscattered diffraction data reveal that during the forming process the microstructure is modified and subgrains are developed. The microstructure is characterized by both low and high angle grain boundaries. Also, the (111) pole figures show that after the ECAP process the orientation is scattered, and the deformation process is heterogeneous. In the numerical work, a rate-dependent elasto-viscoplastic material model based on the theory of materials with isomorphic elastic ranges is applied. The identification of the material parameters has been performed by using the least square method with the Levenberg-Marquardt algorithm. A three-dimensional model of the ECAP process has been implemented in the finite element software Abaqus/Standard. The initial and final orientations after a single pass of the ECAP process are evaluated to study the subgrain formation under large deformations. The agreement between the simulated and experimental response in terms of stress-strain response and (111) pole figures are investigated. The analysis of the misorientation distribution reveals that the grain fragmentation has occurred with both high and low angle grain boundaries. The reconstruction of the microstructure after the deformation shows that the initial orientation has a significant influence on the microstructural evolution and grain refinement after a single pass ECAP extrusion.