DESCRIPTION OF THE GROWTH AND DECOMPOSITION KINETICS OF SUPERSATURATED ALLOYS

A relation between the exponent m of the l = β0tm growth law and the total activation energy Eact is considered applying the Panseri‐Federighi formulae and with reference to special conditions. In cases when m = 1/2 and Eact = E XVM (migration energy of XV‐pairs) or Eact = E XVM + + E XVF (E XVF apparent formation energy of an XV‐pair) holds the growth should be volume diffusion controlled by XV‐pairs in thermal equilibrium at the annealing (Tq) or ageing temperature (Ta), respectively. In order to check these findings an Al‐‐‐Zn(15 at%) alloy is investigated in the Ta‐range between 130 and 200 °C by means of TEM and XSAS investigations. Analyzing the growth of the length of the partially coherent α R′‐particles by TEM yields m = 1/2 and Eact = = (1.02 ± 0.10) eV. Therefore this growth appears to be volume diffusion controlled by ZnV‐pairs in thermal equilibrium at the ageing temperature as E actDC = E ZnVM + E ZnVF = (0.45 + + 0.63) eV = 1.08 eV. Copyright © 1979 WILEY‐VCH Verlag GmbH & Co. KGaA