2020 Volume 59 Issue 1 Pages 289-293
The temperature dependence on mechanical properties in a metal material relates to its crystal structure. In a bcc metal, the strength increases with lowering temperature though the ductility decreases drastically at a low temperature. While mechanical properties in an fcc metal hardly depend on temperature, and thus the fcc metal exhibits high elongation even at low temperatures. In this study, the microstructure and low temperature tensile properties in Cu–50mass％Fe alloy consisting of fcc （Cu） and bcc （Fe） dual phase structure were investigated. Cu and Fe layers were aligned along the rolling direction. The microstructure after annealing at 1023 K for 1.8 ks maintained a deformation structure, while it after annealing at 1123 K for 1.8 ks was the recrystallized ultra–fine grain. In both annealing temperature, Cu and Fe precipitated in Fe and Cu layers, respectively. The elongation in the specimen annealing at 1123 K for 1.8 ks was higher than that of the specimen annealing at 1023 K for 1.8 ks. The recovery of strain and ultra–fine grains should improve the elongation in the specimen annealing at 1123 K. The tensile strength at 77 K was higher than that at 293 K in both specimens annealing at 1023 K and 1123 K. Nevertheless, the elongation at 77 K was nearly equivalent to that at 293 K. Therefore, the fcc and bcc dual phase structure has a superior temperature dependence on mechanical properties： high strength in bcc structure and high elongation in fcc structure at low temperature. A dimple fracture surface appeared at 77 K, meaning that the ductile fracture occurs in both phases. Hence, the Fe phase has enough ductility even at 77 K. The superior low temperature tensile properties may be due to strengthening by the Fe phase and suppressing brittle fracture of the Fe phase by the ductile Cu phase.
