Effect of Oxide Film on the Early Process of Diffusion Welding : Study of the Early Process of Diffusion Welding by Means of Electric Resistance Measurement (Report I)
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The early bonding process of diffusion welding of metals has been investigated by means of electric resistance measurement of bonding zone with particular reference to the behavior of oxide film on faying surfaces ; a couple of base metals were placed in a vacuum with their faying surfaces in contact, and the electric resistance across bonding interface was measured in a process of heating the bonding zone from room temperature to a temperature below melting point at a constant rate. The base metals used were commercially pure aluminum, titanium, iron, copper and silver. The electric resistance across bonding interface ρ for each metal was higher than the resistivity ρM of base metal at room temperature before heating and approached ρM^<as> the bonding zone was heated. The initial values of the electric resistance ρ (at room temperature before heating) except for silver were considerably higher than that estimated using the constriction resistance theory on the assumption that the faying surfaces were perfectly clean metallic surface. In particular, those of aluminum and titanium bonding zone were extremely higher. As the thickness of these oxide films of aluminum, titanium and copper was increased by oxidation treatment in air at a high temperature before welding, the electric resistance ρ increased evidently in its initial value, and approached the resistivity of the base metal at considerably higher temperature. These results indicate that the oxide film on the faying surface except for silver is one of the most important factor which prevents the attainment of true metal-to-metal contact at the bonding interface.
- Transactions of JWRI
Transactions of JWRI 10(2), 173-181, 1981-12