Some applications of crystal plasticity modeling in equal channel angular extrusion（ECAE） of face-centered cubic metals were highlighted.The results show that such simulations can elucidate the dependency of grain refinement efficiency on processing route and the directionality of substructure development,which cannot be explained by theories that consider only the macroscopic deformation behavior.They can also capture satisfactorily the orientation stability and texture evolution under various processing conditions.It is demonstrated that crystal plasticity models are useful tools in exploring the crystallographic nature of grain deformation and associated behavior that are overlooked or sometimes erroneously interpreted by existing phenomenological theories.
A new die design for equal channel angular pressing （ECAP） of square cross-section billet was proposed by a 45° rotation of the inlet and outlet channels around the channel axes. ECAP utilizing the rotated and conventional dies was simulated in three dimensions using the finite element method. Conditions with different material properties and friction coefficients were studied. The billet deformation behavior was evaluated in terms of the spatial distribution of equivalent plastic strain, plastic deformation zone and load history. The results show that the rotated die appears to produce billets with a smaller deformation inhomogeneity over the entire cross- section and a greater average of equivalent plastic strain at the cost of a slightly larger working load. The billet deformdtion enters into a Steady s^ate earlier in the case of the rotated die than the conventional die under the condition of a relatively large friction coefficient.
An experimental study of the microstructures in pure copper billets processed by 8 passes of equal channel angular extrusion （ECAE） via an extended range of processing routes with a 90° die is carried out. Each processing route is defined according to the inter-pass billet rotation angle （χ）, which varies from 0° to 180°. According to the generation of high-angle boundaries and reduction of grain size by electron backscatter diffraction （EBSD） measurements, the grain refinement is found to be most efficient for route with χ=90°and least efficient with χ=180°, among the seven routes studied. This trend is supported by supplementary transmission electron microscopy （TEM） measurements. Comparison of the EBSD and TEM data reveals the importance of considering the non-equiaxity of grain structures in quantitative assessment of microstructural differences in ECAE-processed materials.
The development of texture during plastic deformation plays an important role in determining the stretch formability of magnesium alloy sheets.In this study,the orientation stability during equibiaxial tension of magnesium was analyzed based on three dimensional lattice rotations calculated by using a rate-dependent crystal plasticity model and assuming five different combinations of slip modes.The results show that no orientations can satisfy the stability criteria with both zero rotation velocity and convergent orientation flow in all dimensions.However,relatively stable orientations with zero rotation velocity and an overall convergence are found.They are featured by characteristic alignments of specific crystallographic directions in the macroscopic axis of contraction,depending on the slip modes involved in the deformation.It is also shown that the orientation stability varies significantly with the deviation of deformation mode from equibiaxial tension.The simulation results are briefly discussed in comparison with pre-existing experiments.
