Ordering and phase separation in low supersaturated Ni–Cr–Al alloys: 3D atom probe and Monte Carlo simulation

The kinetics of ordering and unmixing in low supersaturated Ni–Cr–Al alloys have been studied by means of 3D atom probe, transmission electron microscopy and Monte Carlo simulation. The experimental results have been shown to validate the simulations. In both experiments and simulations, coarsening of ordered γ′ precipitates (Ni3Al type) is observed to begin in the early stages of growth. The experimental investigations strongly suggest a nucleation and growth regime. The study of the very early stages of ordering and of unmixing, by Monte Carlo simulation, suggests that after some short range ordering, a nucleation and growth process occurs. The nucleation of the γ′ precipitates seems to initiate from some small aluminium rich and ordered zones of about three unit cells which do not present any depletion in chromium.