GRAIN REFINEMENT AND MECHANICAL PROPERTIES IMPROVEMENT FOR ALLOYS PROCESSED BY ECAE

EQUAL-CHANNEL angular extrusion (ECAE) is now an accepted processing technique for the development of an ultrafine-grained structure in bulk materials. The grain sizes produced by ECAE processing are typically in the sub-micrometer range and this leads to high strength at ambient temperatures. In addition, and provided by the ultrafine grains which are reasonably stable at elevated temperatures, there is a potential for developing superplastic characteristics in tensile testing, with the superplastic flow occurring both at rapid strain rates and at relatively lower temperatures by comparison with conventional superplasticity. Processing by ECAE entails pressing a sample, generally in the form of a bar or rod, through a die constrained within a channel which is bent through an abrupt angle usually equal to, or very close to, 90 deg. Since the cross-sectional dimensions of the workpiece remain unchanged when it is pressed through the die, repetitive pressings may be conducted to introduce very high strains. It has been shown that, for a die having an angle of 90 deg between the two parts of the channel, a strain of similar to 1 is introduced on each separate pass through the die.