Direct observations of nucleation in a nondilute multicomponent alloy

The chemical pathways leading to gamma(')(L1(2)) nucleation from nondilute Ni-5.2 Al-14.2 Cr at. %, gamma(fcc), at 873 K are followed with radial distribution functions and isoconcentration surface analyses of direct-space atom-probe tomographic images. Although Cr atoms initially are randomly distributed, a distribution of congruent Ni3Al short-range-order domains (SRO), < R >congruent to 0.6 nm, results from Al diffusion during quenching. Domain site occupancy develops as their number density increases leading to Al-rich phase separation by gamma '-nucleation, < R >=0.75 nm, after SRO occurs.