Microstructures of the ultra-fine grained nickel produced by equal channel angular processing, pressed 12 times through the BC route to impart a strain of about 12, were investigated using transmission electron microscopy and electron back-scattering diffraction. The average grain size obtained from orientation imaging microscopy was 0.23μm, for a tolerance angle of 5° and 0.24μm from transmission electron microscopic investigations. The microstructure of equal channel angular processed nickel was not homogeneous. The grain refinement was more extensive after 12 passes as in the present investigation than 8 passes (studied earlier), when processing in both the cases was via equal channel angular processing using route BC. The grain boundary character distribution was determined in the 12-pass equal channel angular processed Ni. The details changed depended upon whether the cut-off angle was 5° or 2°. It was found here that a 5° cut-off gave physically more meaningful results. The Vickers micro-hardness depended upon the location in the extruded sample and varied between 1.56 and 2.47GPa, for an applied load of 25g. When the load was increased to 50g, it ranged from 1.6 to 2.3GPa.

Grain Size and Grain Boundary Character Distribution in Ultra-Fine Grained (ECAP) Nickel. K.S.Raju, M.G.Krishna, K.A.Padmanabhan, K.Muraleedharan, N.P.Gurao, G.Wilde: Materials Science and Engineering A, 2008, 491[1-2], 1-7