The most attractive, and potentially the most useful,
SPD technique appears to be equal-channel angular pressing (ECAP)
in which a metallic rod or bar is pressed through
a die constrained within a channel which is bent through an
abrupt angle that is often equal to, or very close to, 90◦ [2–4].
Processing by ECAP leads to significant strengthening of
the material at ambient temperatures [5,6] and, provided the
ultrafine grains have a reasonable thermal stability, to the occurrence
of superplastic ductilities at very rapid strain rates
at elevated temperatures