X-ray Diffraction Study of Deformational Evolution of Stacking Faults in Nanocrystalline Metals

Abstract

The evolution of stacking faults (SF) during the mechanical activation (MA) of metals with a different energy of SF (γ): Co (7 mJ/m2), Cu (45 mJ/m2), Ni (125 mJ/m2),—was studied by X-ray diffraction analysis using (i) a complex for processing diffraction patterns and (ii) simulation of crystal diffraction patterns (DIFFaX). The study was performed to understand the connection of the evolution mentioned with plastic deformation mechanisms and depending on grain size. The values ​​of the energy yields of stacking faults (G) upon MA for nanocrystalline Co and Cu are in agreement with the values of ​​ γ for these metals in the coarse crystalline state (the lower the γ, the higher the G). The increased G for nanocrystalline nickel is associated with the effect of impurities. When decreasing the sizes of Co, Cu, and Ni crystallites in the course of MA to 30, 77, and 60 nm respectively, the maximum G are observed, which is a consequence of deformation by the mechanism of the generation of partial Shockley dislocations by nanograin boundaries and their sliding in the grain body with the formation of SF. A scheme of the deformation-induced shear transformation in nanocrystalline cobalt is proposed.