Microstructural evolution during processing by severe plastic deformation

The procedure of equal-channel angular (ECA) pressing may be used to subject a material to severe plastic deformation by pressing repetitively through a special die without any concomitant change in the cross-sectional dimensions of the sample. This processing method gives grain refinement in polycrystalline materials with as-pressed grain sizes typically in the submicrometer range. This paper describes the factors influencing the development of a homogeneous microstructure through ECA pressing including the influence of the pressing speed and the angle contained within the special die, the effect of rotating the sample between consecutive pressings and the significance of pressing to a high total strain. An experimental example is presented to illustrate the potential for using ECA pressing to achieve a superplastic forming capability at very rapid strain rates.