Following ECAP, the billets were sectioned perpendicular
to their longitudinal axes and then mounted and carefully
polished to a mirror-like finish. Microhardness measurements
were taken using an FM-1e microhardness tester
equipped with a Vickers indenter. A series of individual measurements
was recorded on each polished section whereby
the Vickers indenter was moved over the surface and measurements
of the Vickers microhardness, Hv, were recorded
in a regular grid pattern with spacings between each separate
measurement of ∼0.5 mm. This procedure gave a total
of ∼220 individual values of Hv on each polished section.
These individual values of Hv were then plotted in the form
of color-coded contour maps depicting the variation of the
local microhardness over the cross-sectional plane for each
sample.