The Reaction of Solid Cobalt with Molten Copper. II : On the Migration of Molten Copper into Solid Cobalt and the Structure of Copper-Cobalt Interface

A basic investigation in brazing was made of the migration or the penetration of molten copper into solid cobalt and of the structure of copper-cobalt interface in the temperature range 1100°-1300°C for the reaction time from 0 to 30 min. The principal mechanism of the migration of molten copper into solid cobalt was shown to be volume diffusion. Initial rate of the penertation of molten copper into cobalt is 0.4-1.1×10-3 mm/min. The thickness of Cu-penetrated layer ranged from 5.4 to 50.4μ and it increase in proportion to the square root of the reaction time. The obtained value of the penetration-rateconstant is 2.57.3×10-3 mm/min1/2 and from the temperature dependence of the rate-constant the value of the activation energy for the penetration, 23.5 Kcal/mole was obtained. In copper-cobalt interface, a cobalt dendrite layer which had been crystallized on the copper side of the interface during solidification was recognizedand on the opposite side of this interface, a thicker copper-enriched cobalt solid solution.