無酸素銅とオーステナイト系ステンレス鋼における低変形拡散接合

抄録

  Achieving good tensile strength and low deformation in the case of diffusion bonding of dissimilar materials is difficult because different materials vary in mechanical properties at high temperatures. In the present study, diffusion bonding of OFC (oxygen-free copper) to austenitic stainless steel SUS304 was carried out under pressures that are suitable for suppressing any deformation of the specimens. The specimens could be bonded above 1073 K, and the bonding time slightly influenced the tensile strength. Convex areas on the bonding surfaces of SUS304 were scarcely deformed, and quite large voids were formed at the bonding interface. The void size decreased with decreasing roughness of the bonding surfaces. However, the specimens polished with emery papers #1000 and #4000 could not be bonded. The tensile strength of the specimens did not change when a nickel film was used as a metallic insert. The fracture occurred at the interface between SUS304 and the nickel film. Bonding could not be realized when the bonding surfaces were not in contact while the temperature increased. Copper and chromium oxide layers exist on the bonding surface of OFC and SUS304, respectively. Bonding was inhibited by the latter layer. The tensile strength was significantly improved when the bonding temperature was raised from 1073 K to 1173 K. Chromium inclusions were observed at the bottom of dimples on the fractured surface, which indicated that the chromium oxide layer cohered at 1173 K. Consequently, the fracture at the base metal of OFC was attained in the specimen obtaining sufficient adhesion between the bonding surfaces. Grain boundaries of the specimen did not migrate across the bonded interface, which suggested that the grain boundary migration was not necessarily required to acquire superior joints.