Short-range atomic order in f.c.c-Ni-9 at.% Al solid solution

Abstract

The short-range atomic order for a single crystal of f.c.c.—Ni-9 at.% Al solid solution quenched from 1073 K, as well as the short-range order transformations initial stages during isothermal annealing at 373 K have been investigated using the diffuse X-ray scattering method. Specific features of the thermal two-phonon diffuse scattering have been analyzed. It is shown that in quenched state, the short-range order corresponds to the presence of concentration waves in the alloy with ordering vectors kₛ = X(001) and kₛ = (000.2). The initial ordering kinetics stages are accompanied by a considerable increasing of the short-range order diffuse intensities for vectors close to the structural one. The time dependence of the Warren-Cowley short-range order parameters, as well as local atomic configurations simulation results (using the Monte-Carlo technique), have shown that such transformations correspond to the nucleation and growth of the two short-range ordered regions: clustered (decomposing) and L1₂-type weakly ordered (Ni₃AI) ones.