Low-temperature tensile properties of Cu-Fe laminated sheets with various number of layers

Abstract

The Cu-Fe laminated sheets with various number of layers were produced by the accumulative roll bonding process, and the effects of the number of layers on the microstructure and low-temperature tensile properties of the sheets were elucidated. Then the reason for the excellent low-temperature tensile properties in dual-phase materials of Cu and Fe was discussed. The tensile properties of the pure Cu and Fe sheets used for fabricating the Cu-Fe laminated sheets exhibited the typical temperature dependence seen in the case of face-centered cubic (fcc) and body-centered cubic (bcc) metals. The layered structure of the laminated sheets was maintained till the number of layers was 100 but broke in the case of the 1000-layer sheet, which showed a network-like structure. The electrical conductivity of the sheets was independent of the number of layers and significantly higher than that of a Cu-Fe alloy, indicating that Fe had neither dissolved nor precipitated in the Cu layers of the laminated sheets. In the case of the 50-, 100- and 1000-layer sheet, the strength increased with lowering the temperature, while its elongation remained constant. A facet fracture surface was observed until the number of layers was 7, while in the case of the sheets consisting of more than 50-layers, fine dimples were observed on the fracture surfaces of both layers, indicating that ductile fracturing occurred. The strain in the Cu layers around the strain concentration sites of the Fe layers was high in the 50-layer laminated sheet when it was subjected to tensile deformation at 77 K. The strain concentration in the Fe layers might be accommodated by the surrounding soft Cu layers, resulting in the suppression of the nucleation of cleavage cracks in the Fe layers. This should be one of the reasons that the Cu-Fe layered sheets exhibited excellent elongation at low temperatures. Thus, the Cu-Fe layered structure take an important role for the excellent low-temperature tensile properties in the fcc and bcc dual-phase materials.