the microhardness increased quickly in the first
pass and then the rate of increase was low in the subsequent
passes, which was common for both cases of route A and
route BC. The sudden increase in strength was also marked
in the yield stress (65% increase in the first pass), as shown
in Fig. 7. Further passes of ECA pressing increased the yield
stress by 75% and 84% from those of the starting material in
four passes by route A and route BC, respectively. The higher
efficiency of the route BC in strengthening the material is attributed
to the more effective grain refining. In Fig. 8, the