Discontinuous coarsening of lamellar cellular precipitate in an austenitic Fe-30 wt.%Ni-6 wt.%Ti alloy—II. Growth kinetics

Abstract The growth kinetics of discontinuous coarsening of lamellar cellular precipitate in an austenitic Fe-30 wt.%Ni-6 wt.%Ti Alloy aged at temperatures ranging from 400 to 900°C have been studied by light and electron microscopy measurements of cell growth rate and lamellar spacing. Analysis of the growth kinetics shows that the Livingston-Cahn [1] model is not obeyed with the reason being that not all of the available volume free energy is used in the first reaction. A theory which considers the volume free energy remaining after the first reaction is presented. According to this theory, the growth rate of the coarsening reaction in this system is controlled by grain boundary diffusivity, Db. and depends on the growth rate, V1, and lamellar spacing, λ1, of the first cellular precipitation reaction according to the following equation: V 2 = − V 1 λ 1 2 λ 2 2 + 8D b δ RTλ 2 2 (ΔF 0 + 2σv λ 2 ) .