Application of ultrasonic methods to determine elastic anisotropy of polycrystalline copper processed by equal-channel angular pressing

Anisotropy of elastic properties of ultrafine-grained polycrystalline copper after one, two and four passes of equal-channel angular pressing (ECAP) is investigated by means of ultrasonic methods. For each material, Young's and shear moduli in the principal processing directions are evaluated and the symmetry and orientation of the anisotropy are identified. The relation between the determined symmetry and the processing mechanisms is discussed. It is shown that the material after one and two passes of ECAP exhibits a measurable anisotropy, while the material after the fourth pass behaves isotropically. Within the discussion, it is shown that the origin of the observed anisotropy may be attributed to the spatial arrangement of grain boundaries rather than to the crystallographic texture. In the light of this conclusion, the obtained results correspond well with optical and transmission electron microscopy observations of the microstructures of ECAPed materials documented in the literature.