Grain refinement of pure nickel using equal-channel angular pressing

Nickel of 99.9% purity, with an initial grain size of ∼80 μm, was subjected to equal-channel angular pressing (ECAP) to a strain of ∼8 at room temperature. After ECAP, there was a homogeneous microstructure of very fine grains separated by high-angle boundaries. The average grain size was measured as ∼0.30 μm. Annealing of samples after ECAP revealed an abrupt increase in the grain size, to ∼4–5 μm, at temperatures in the range of 473–573 K: it is shown this behavior is analogous to conventional recrystallization. The results for pure Ni are compared with data obtained when ECAP is applied to pure Al and pure Cu. It is concluded that pure Ni is an ideal model material for use in ECAP because the stacking fault energy, which is intermediate between that of pure Al and pure Cu, leads to a much smaller grain size than in pure Al but a more homogeneous microstructure than in pure Cu.