Low temperature copper solubilities an Fe-Cu-Ni

An atom probe characterization of the copper concentration in the matrix of a model Fe-1.1at.%Cu-1.4% Ni alloy has been performed after isothermal ageing for various extended times at low temperatures. The matrix copper concentrations from material annealed at 500, 550 and 600 degrees C are approximately 10% lower than the equilibrium values predicted from the Thermocalc(TM) program with the Kaufman database. Isothermal annealing for 4000 h at either 400 or 300 degrees C was not sufficient to attain the equilibrium copper concentration. The kinetics of copper precipitation was investigated with the Starink-Zahra model derived for nucleation and growth reactions and a good fit with the atom probe data was found for an activation energy of 250 kJ mol(-1). (C) 1998 Elsevier Science S.A. All rights reserved.