Large strain deformation structures in aluminium crystals with rolling texture orientations

An anisotropic, viscoplastic power law for face-centred cubic crystals: comparative evaluations in the Goss and Brass orientations of channel die compression

An anisotropic, viscoplastic power law is introduced and applied to analysis of the Goss and Brass orientations, and compared with predictions from rate-independent theory and experiment. The structure of the new power law is so chosen that it has the capability of approaching rate-independent results for lattice rotation and crystal shearing, after finite rotation about the load axis, in the range of unstable lattice orientations in (110) channel die compression. (Rate-independent predictions of shear and lattice rotation are in good to very good agreement with experiments on aluminium and copper in that range, whereas classicisotropicpower-law results are not.) It is established that, for sufficiently large power-law exponentn, the new anisotropic, elasto-viscoplastic theory predicts: (i) lattice stability in each of the Goss and Brass orientations, consistent with both experiment and rate-independent theory; (ii) zero crystal shear in the Goss orientation, also consistent with both; (iii) finite shear in the Brass orientation, in very good agreement with experiment and rate-independent theory; and (iv) a lateral-constraint stress that remains essentially elastic in both orientations, as predicted by rate-independent theory and close to experimental measurements for aluminium and copper in the Brass orientation.

Further investigation of crystal hardening inequalities in (110) channel die compression

A set of geometrically based FCC crystal slip-systems hardening inequalities is analytically investigated in (110) channel die compression for all lateral constraint directions between and , following previous analyses of the other two distinct orientation ranges in (110) compression. With all critical slip systems active, it is proved that these inequalities uniquely predict initial lattice stability and finite crystal shearing only in the horizontal channel plane, consistent with experiments for this range of orientations. (The earlier analyses had predicted load-axis stability in both orientation ranges, and lattice stability in one, also commonly found experimentally.) Moreover, it is established that the lateral constraint stress predicted by the hardening inequalities will be less than that given by classic Taylor hardening as this stress evolves with deformation. It is further shown, taking into account experimental stress–strain curves and latent hardening experiments for aluminium and copper, that lattice stability generally can be expected to very large deformations, except perhaps for lateral constraint orientations near the end of the range, which result is consistent with experiment. In appendix A, the possibilities of solutions with a critical slip system inactive are investigated, and predictions of a power law rate-dependent plasticity model are analysed for comparison with the results based on the hardening inequalities.

Global and Local Structural Evolution during Deformation and Annealing of FCC Metals

Deformation of metals from medium to high strain significantly affect the deformation structure as well as the recovery and recrystallization behaviour when deformed samples are annealed. This behaviour is illustrated for FCC metals of medium to high stacking fault energy, with emphasis on the behaviour of aluminium and aluminium alloys deformed by cold rolling to large strain. The analysis encompasses hardness testing, EBSD and TEM. The deformation microstructure is a lamellar structure of dislocation boundaries and high angle boundaries where the percentages of the latter increases to about 60-80% at large strain. The macrotexture is a typical rolling texture, which is composed of individual texture components present as micrometre and submicrometre size volumes. In the lamellar structure correlations have been established between microstructural parameters and local orientations showing for example variations in stored energy between the texture components and large variations in the spatial distributions of the high angle lamellar boundaries. Such local variations can affect the structural coarsening during recovery at low temperature leading to significant structural difference on a local scale. The local variations in the deformed structure can also significantly affect the structural changes taking place locally during high temperature annealing thereby affecting the evolution of the structure and texture on a macroscopic scale.

Watching the growth of bulk grains during recrystallization of deformed metals

We observed the in situ growth of a grain during recrystallization in the bulk of a deformed sample. We used the three-dimensional x-ray diffraction microscope located at the European Synchrotron Radiation Facility in Grenoble, France. The results showed a very heterogeneous growth pattern, contradicting the classical assumption of smooth and spherical growth of new grains during recrystallization. This type of in situ bulk measurement opens up the possibility of obtaining experimental data on scientific topics that before could only be analyzed theoretically on the basis of the statistical characterization of microstructures. For recrystallization, the in situ method includes direct measurements of nucleation and boundary migration through a deformed matrix.