Mesoscopic Investigation of the Heterogeneities Induced by Channel-Die Compression

Experimental techniques were applied to study the heterogeneities of deformation of metals at the mesoscopic scale (typically 100 μm in the present case). The first are fiducial carbon grids that are transferred on to the surface of the test-pieces. Here, they were used on single and polycrystals deformed in channel-die compression. They prove efficient for strains above 1. They bring out the role of the corners of the samples, which trigger bands of deformation that grow in importance as the compression goes on. They put in evidence the mesoheterogeneities that appear in the mechanical behavior of a few highly symmetric orientations such as cube. The second technique is the use of microfocused X-rays, which give the crystallographic orientation at the same scale of 100 μm and can work in the presence of the carbon grids even when there is considerable strain hardening. The gradients found in the lattice rotations are far less pronounced than the sharp localizations in the displacement field. This highlights the importance of the rotations due to the activity of the slip systems.