Critical Grain Size at Meso-Level after Deformation of Polycrystalline Metals and Alloys in Low-Stability State

Abstract

The paper deals with the dislocation and dislocation-disclination substructures of polycrystalline FCC alloys Cu–Al and Cu–Mn modified by tensile deformation. Observations are performed using the transmission electron microscopy. It is shown that the grain size of the alloy structure ranging from 10 to 240 μm, can serve as a critical parameter in the low-stability state during the deformation and transition from one stage of hardening to another. The dependences are obtained for the parameters describing the defect substructure and the mean grain size. These dependences are compared with the structure and phase composition of the alloys. The critical grain size of about 100 μm is found at a meso-level. When the grain size exceeds 100 μm, the main role in defect accumulation play intracrystalline processes. At stage II, the strain-hardening coefficient does not depend on the grain size of >100 μm and rapidly increases at a grain size of <100 μm.