Study of the microstructure and texture heterogeneities of Fe–48wt%Ni alloy severely deformed by equal channel angular pressing

Abstract

A Fe–48wt%Ni alloy was processed by severe plastic deformation using equal channel angular pressing process. A stacking of 9 sheets was introduced and pressed up to two passes into die with an inner angle of Φ = 90o and outer arc of curvature ψ = 17° at room temperature following route A. The same material in bulk form was also ECAPed up to one pass. The microstructure and the texture were investigated by means of electron backscattered diffraction and X-ray diffraction, respectively. To evaluate the mechanical response, Vickers microhardness was carried out. The given analyses concern the as-received sample, the peripheral and the central plates of the pressed stacks and the upper, the middle and the lower parts of the pressed bulk material. The deformation was heterogeneous, and variations in texture and microstructure, resulting from different efficiencies in the shearing process, were locally noted. For the stacks samples, the microstructure evolved from equiaxed grains of 9 μm with high fraction of high-angle grain boundaries (around 90%) to a heterogeneous fine grain structure with an average grain size of 3 μm after two passes. On the contrary, for the bulk sample, the evolution was to a banded structure after one pass. Results of mechanical property show that microhardness increased significantly from 147 Hv before deformation to mean values of 244 (after one pass) and 235 Hv (after two passes) for the bulk and stacked samples, respectively. The Hall–Petch effect and dislocation density were evaluated as most responsible in material strengthening.