Fractal morphologies from decomposition of Fe-Ni-Invar alloys

Small angle neutron scattering investigations performed on Fe-1-x-Ni-x alloys with 0.26 less than or equal to x less than or equal to 0.45 revealed a thermodynamically driven decomposition below 800 degrees C. The miscibility gap extends at least from 30 at. % Ni to 45 at. % Ni. The diffusion-controlled 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 less than or equal to d(m) less than or equal to 3) to surface fractals with 2 less than or equal to d(s) less than or equal to 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.