Microstructural simulation of phase decomposition in Cu-Ni alloys

The microstructure simulation of spinodal decomposition was carried out in the aged Cu-70 and 90 at.% Ni alloys, based on a solution of the non-linear Cahn-Hilliard partial differential equation by the finite difference method. The calculated concentration profiles were compared with the experimental ones determined by atom-probe field ion microscope analyses of the solution treated and aged Cu-70 at.% Ni alloy samples. Both the numerically simulated and experimental results showed a good agreement for the concentration profiles and microstructure evolution in the aged Cu-Ni alloys. A very slow growth kinetics of phase decomposition was observed to occur in this type of alloy. The morphology of decomposed phases consists of an irregular shape with no preferential alignment in any crystallographic direction. The wavelength of composition modulation was determined numerically to be about 2 nm and it remained constant after aging at 573 K for times as long as 8889 h. No phase decomposition was observed to occur for the numerical simulation of aging at temperatures lower than 523 K for a time as long as 1 year.