Anneal hardening in cold rolled PM Cu-Au alloy

Pure copper and Cu-11.4 wt%Au alloy were obtained by a powder metallurgy (PM) technique and subjected to thermomechanical treatment that was used to produce the conditions that led to an anneal hardening effect in the alloy. The results showed that low-temperature annealing of cold-rolled alloy caused a two-stage increase in hardness, microhardness and electrical conductivity. The mechanism of anneal hardening in this alloy was studied using differential thermal analysis (DTA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The analysis of the DTA curve showed the presence of one endothermic and three exothermic reactions during the linear heating, which confirmed the occurrence of both short-range ordering and solute segregation. A decrease in the lattice parameter of the cold-rolled alpha Cu-Au solid solution at the annealing temperature, which corresponded to the second hardness peak, was explained by solute clustering. Formation of precipitates in the copper-based matrix during annealing was not observed by TEM. It was confirmed that the dominant hardening mechanism during annealing was solute segregation towards lattice defects. (C) 2016 Elsevier B.V. All rights reserved.