Direct observations of nucleation in a nondilute multicomponent alloy

The chemical pathways leading to γ^'(L1₂) nucleation from nondilute Ni-5.2 Al-14.2 Cr at. %, γ(fcc), at 8730.3em0exK 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⟩0.60.3em0exnm, results from Al diffusion during quenching. Domain site occupancy develops as their number density increases leading to Al-rich phase separation by γ^'-nucleation, ⟨R⟩=0.750.3em0exnm, after SRO occurs.