This is a copy of the slides presented at the meeting but not formally written up for the volume.

Grain size reduction induced by severe plastic deformation (SPD) and the resulting mechanical properties have been widely investigated for pure metals but less is known and reported about multi-phase materials. To study the grain size reduction mechanisms in multiphase structure subjected to SPD, two copper based composites (Cu-10%Fe and Cu-43%Cr) were severely deformed by torsion under high pressure. The grain size achieved with these composite materials is much smaller than in pure metals. It is for example in a range of 10 to 20 nm for the Cu-43%Cr composite, e.g. one order of magnitude lower than in pure Cu processed by SPD. Three dimensional atom probe data show also the formation of non equilibrium supersaturated solid solutions. The mechanisms of the deformation induced intermixing are discussed together with its influence on the mechanical properties.