Microstructure and Low Temperature Tensile Properties in Cu–50 mass%Fe Alloy

Abstract

The temperature dependence of the mechanical properties of metals is closely related to its crystal structure. In bcc metals, the strength of the material increases with decreasing temperature, and the ductility decreases drastically at low temperatures. The mechanical properties of fcc metals hardly depend on temperature, and thus fcc metals exhibit large elongations even at low temperatures. In this study, the microstructure and low-temperature tensile properties of Cu–50 mass%Fe alloy consisting of fcc (Cu) and bcc (Fe) dual-phase structures were investigated. The Cu and Fe layers were aligned along the rolling direction. The deformation structures remained after annealing at 1023 K for 1.8 ks, while recrystallized ultra-fine grains were formed after annealing at 1123 K for 1.8 ks. At both annealing temperatures, Cu and Fe precipitated in the Fe and Cu layers, respectively. The elongation obtained when the alloy was annealed at 1123 K for 1.8 ks was higher than that at 1023 K for 1.8 ks. The recovery of strain and the formation of ultra-fine grain during annealing at 1123 K were largely responsible for the higher elongation. The tensile strength at 77 K was higher than that at 293 K for both annealing temperatures. Nevertheless, the elongation at 77 K was approximately equal to that at 293 K. Therefore, the fcc and bcc dual-phase structures has an excellent temperature dependence of mechanical properties: high strength in bcc structure and high elongation in fcc structure at low temperatures. A dimple fracture surface appeared at 77 K, indicating that ductile fracture occurred in both phases. Therefore, the Fe phase exhibited significant ductility even at 77 K. The excellent low-temperature tensile properties of the Cu–Fe dual-phase alloy may be due to strengthening by the Fe phase and suppressing of brittle fracture in the Fe phase by the ductile Cu phase.