Fractal morphologies from decomposition of Fe−Ni−Invar alloys

Abstract

Small angle neutron scattering investigations performed on Fe1−x–Nix alloys with 0.26 ≤ x ≤ 0.45 revealed a thermodynamically driven decomposition below 800 °C. The miscibility gap extends at least from 30 at.% Ni to 45 at.% Ni. The diffusioncontrolled decomposition produces fractal morphologies during the early stages of the process. During annealing the structure of the precipitated phase densifies continuously from mass fractals with small dimensionality (1 ≤ dm ≤ 3) to surface fractals with 2 ≤ ds ≤ 3. The results are compared with recent simulations of aggregation and growth as well as with a new analysis of spinodal decomposition, both predicting fractal morphologies.