LOW-TEMPERATURE COPPER SOLUBILITIES AN FE-CU-NI

An atom probe characterization of the copper concentration in the matr ix of a model Fe-1.1at.%Cu-1.4% Ni alloy has been performed after isot hermal ageing for various extended times at low temperatures. The matr ix copper concentrations from material annealed at 500, 550 and 600 de grees C are approximately 10% lower than the equilibrium values predic ted from the Thermocalc(TM) program with the Kaufman database. Isother mal annealing for 4000 h at either 400 or 300 degrees C was not suffic ient to attain the equilibrium copper concentration. The kinetics of c opper precipitation was investigated with the Starink-Zahra model deri ved for nucleation and growth reactions and a good fit with the atom p robe data was found for an activation energy of 250 kJ mol(-1). (C) 19 98 Elsevier Science S.A. All rights reserved.