Developing ultrafine grain sizes using severe plastic deformation

Severe plastic deformation may be used as a processing tool to achieve a refinement in grain size in metallic alloys to the submicrometer or nanometer range. This paper describes recent developments using the procedure of equal-channel angular pressing (ECAP) in which samples are pressed through a die containing a channel bent into an L-shaped configuration. The shearing associated with passage through the die introduces bands of subgrains which evolve, with additional pressings, into arrays of grains separated by boundaries having high angles of misorientation. The process of ECAP is a useful tool for both increasing the strength and toughness of an alloy at ambient temperatures and achieving a potential for superplastic forming of the alloy at rapid strain rates at elevated temperatures.