Unraveling the self-annealing behavior of cryo-rolled Cu-Fe-P alloy sheets: Evidence and implications

Deformation of Cu-Fe-P alloys at cryogenic temperature (CT) leads to the evolution of a complex microstructure, which includes deformed and recrystallized grains, strain localizations (SLs), and heterogeneous deformation. In this study, specimens of Cu-Fe-P alloy were subjected to cryogenic rolling (CR) at reduction ratios (RR) of 20, 40, 60, and 80%. The microstructural evolution of the CR specimens was characterized using electron back-scattered diffraction (EBSD) and high-resolution transmission electron microscopy (HR-TEM). Severely deformed CR specimens showed SLs, which formed predominantly in the Copper and S oriented grains. After deformation, the CR specimens exhibited self-annealing behavior, which is also referred to as static recrystallization (SRX). Self-annealing at room temperature (RT) caused grain nucleation at the deformed grain boundaries (GBs) and at the SLs. The nucleation of new grains was attributed to both discontinuous SRX (DSRX) and continuous SRX (CSRX) phenomena. The characteristics of DSRX and CSRX grains were analyzed based on transmission Kikuchi diffraction (TKD) and HR-TEM investigations. DSRX grains were surrounded by high-angle GBs, whereas CSRX grains showed sub-boundaries with no dislocations inside. The as-received Cu-Fe-P specimen showed a weak plane-strain texture that intensity increased with an increase in the RR. The CR-80 specimen showed the highest-intensity for plane-strain texture components. SRX at the SLs showed preferential formations of Copper, Brass and S-nucleated grains in the CR-80 specimen. In this study, crystal plasticity finite element method (CPFEM) was used to calculate the stored energy, relative slip activity and texture fractions for the CR specimens. Copper and S oriented grains showed the occurrence of predominant single-slip systems near the severely deformed regions which was the primary cause of SLs formation.