SEM-ECC Investigation of Dislocation Arrangements in Cyclically Deformed Copper Single Crystals with Different Crystallographic Orientations

Abstract

The dislocation arrangements induced by cyclic deformation in some differently oriented copper single crystals were investigated using electron channelling contrast (ECC) technique in scanning electron microscopy (SEM). It is shown that the ECC technique can well be used to examine dislocation arrangements in fatigued copper single crystals, especially at higher imposed plastic strain amplitudes. The typical dislocation structures in the cyclically deformed copper single crystals detected by this technique are in good agreement with those found by transmission electron microscopy (TEM). Furthermore, the SEM-ECC technique shows some attractive advantages compared to TEM. For instance, ECC observation clearly reveals an evolutional process of dislocation structure from the vein structure of matrix formed at lower strain amplitude to the labyrinth structure formed st higher strain amplitude. Moreover, the exact observations of dislocation arrangements within cyclic deformation bands (DBs), which are rather difficult to achieve by TEM, are successfully accomplished using the ECC method. The DBs formed in cyclically strained copper single crystals may exhibit quite different microstructures, depending upon their crystallographic orientation and accumulated plastic strain, such as PSB ladder, wall and labyrinth structures. Finally combining the existing TEM results with the present SEM-ECC observations, we can state with certainty that the crystallographic orientation has a strong effect on the saturation dislocation features of copper single crystals.