The Brazing Reaction of Iron Base Metal with Copper. II : Dissolution Reaction of Iron Base Metal and Migration of Molten Copper into Iron

An investigation was made of the reaction for dissolution of solid iron in liquid copper-iron solution of various concentrations and the migration of molten copper into solid iron. Cylindrical samples of base metal iron were rotated in liquid copper-iron alloys of various iron concentrations at a given rate in argon atmosphere in resistance furnace and further, a small quantity of copper was padded in the cylinder of the solid iron, which was then melted in vacuum in induction furnace. The rate of dissolution was dependent on the rotational speed, the temperature and the iron concentration. The reaction was found to be rate-controlled by the diffusion of solute from the iron-copper interface to the liquid bulk and the activation energy for the dissolution was about 14.3 kcal/mole. At high rotations and high temperatures, however, the transition from purely diffusion control to mixed control is likely to occur with increasing solute concentration. On the other hand, a small amount of the molten copper migrates through the copper-iron interface into the solid iron and a thin layer of the base metal adjacent to the interface appears to be saturated with molten copper. The principal mechanism of the transfer of molten copper into solid iron was shown to be volume diffusion and grain-boundary diffusion, without grain-boundary penetration of liquid metal. The mechanism of the migration was thought to be varied with interfacial energy, grain-size and temperature. The structure of the solidified iron-copper interface was metallographically examined