Masaaki Tsukamoto, Takuya Kajiura and Atsushi Yamamoto
Division of Materials Science and Chemistry, Graduate School of Engineering, University of Hyogo, Himeji 671-2201
Diffusion bonding is an appropriate method for chromium copper which is difficult to weld due to its high thermal conductivity. However, there have been few reports on diffusion bonding of chromium copper. In the present study, diffusion bonding conditions for chromium copper were investigated to obtain excellent joint strength. The bonded specimens were scarcely deformed because grain growth was suppressed by chromium precipitations. The bonding could be achieved above a temperature of 1073 K and the tensile strength was increased with increasing bonding temperature and pressure. Bonding time had a small influence on the tensile strength. Grain boundary migration across the bonded interface did not occur in all the specimens. Voids and oxides remaining at the bonded interface would play a role of barrier to the migration. The specimens could not be bonded with decreasing roughness on the bonding surfaces. Chromium oxide layer as well as copper one is formed on the bonding surfaces of chromium copper and is not removed with chemical polishing. The oxide layer would be broken by deformation of irregularities on the bonding surfaces. The tensile strength was reduced when contact between the bonding surfaces was delayed until temperature was raised up to bonding condition. Copper oxides are decomposed at 1073 K under a high vacuum of 4.0×10-3 Pa on a free surface of copper, while chromium is segregated to the bonding surfaces and is oxidized. Consequently, chromium oxide layer is strengthened, which inhibits diffusion between the bonding surfaces.
chromium copper, diffusion bonding, temperature, pressure, surface roughness, deformation, contact timing, chromium oxide
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