無酸素銅における低変形固相拡散接合

抄録

  Diffusion bonding requires loading relatively high pressures at elevated temperatures in order to advance an adhesion between surfaces. In the case of oxygen free copper, remarkable deformation occurs during the bonding process due to its poor mechanical strength at high temperatures. In the present study, the diffusion bonding of oxygen free copper under low pressures which enable the specimens to minimize deformation was attempted at 1073 K for 3.6 ks and 7.2 ks with other experimental factors. The process for increasing bonding areas consists of deformation and diffusion mechanisms. It was important to promote the latter because the former gets poorer under the low bonding pressures. Tensile strength of the specimens was increased with decreasing roughness on the bonding surfaces and comparable to that of the base metal in the specimens whose surfaces were polished with an emery paper #4000 and buffing. Furthermore, a fracture occurred at not the bonded interface but the base metal when contact between the bonding surfaces was delayed until a temperature was raised up to bonding condition. In the conventional procedure for diffusion bonding, the temperature has been generally raised with contact between the bonding surfaces so that copper oxides at the bonded interface are difficult to be decomposed due to depressed evacuation. The bonding surfaces were maintained as a free surface by the delayed contact procedure, which led to decomposing the copper oxides. Consequently, the tensile strength would be improved by reducing fracture origins. Grain boundary migration across the bonded interface was sufficiently generated only in the specimen prepared with buffing and prolonged for 7.2 ks in bonding time. In contrast, the fracture at the base metal was achieved in the specimens maintaining an original bonded interface. It was suggested that the grain boundary migration was not necessary to acquire superior joints.