EQUILIBRIUM OF SEGREGATION IN AG/CU - INFLUENCE OF THE ORIENTATION AND TEMPERATURE

We have used dissolution and segregation kinetics to investigate the equilibrium superficial segregation of silver on copper. The effect of surface orientation was deduced from dissolution kinetics at 450-degrees-C. A first-order phase transition occurs on a (111) surface; there is no evidence of such a transition on a (110) surface and, on a (100) surface, it is likely that a phase transition takes place at high coverage only. The effect of temperature was studied from segregation kinetics of silver on a (111)-oriented 0.45 at% Cu(Ag) solid solution at 450, 416 and 390-degrees-C. For theta < 0.6 the isotherms depicted a vertical part which was interpreted as a 2D phase transition; in this part a segregation enthalpy of about -100 kJ mol-1 was evaluated. For theta > 0.6 we found a slow-down in kinetics which is ascribed to the diminution of the relaxation energy with the silver superficial concentration.