Dynamic scaling of phase separation in CuCo alloys

Abstract

The Langer-Bar-Miller (LBM) theory and the non-linear Cahn theory on phase separation dynamics in alloys have been reviewed briefly and applied to calculate dynamics of phase separation of homogenized CuCo alloys. The three-parameter technique of the LBM theory for evaluating compositional fluctuations is applicable only in a narrow range of alloy composition. In this narrow range, the as-calculated equal time structure function S(k,t), where k is the wave vector and t is time, does not follow the universal scaling hypothesis in the late stage of phase separation: km3S(k/km) = f(k/km), where f is a scaling function and km is the peak position of S(k,t). The kinetic growth exponent, defined by km as a power function of time, does not agree with prediction of the scaling analysis. The non-linear Cahn approach has been applied to evaluate the profile and amplitude spectra of the compositional fluctuations during phase separation in both meta-stable and non-stable regions. Overall range of alloy composition, the structure function S(k,t) in the late stage of phase separation shows scaling behaviours quite well consistent with the universal scaling hypothesis. The kinetic growth exponent equals to 0.22 in the non-stable region, well consistent with prediction of the scaling analysis. In the meta-stable region, this exponent increases up to 0.28 as the alloy composition decreases down to 0.01, exhibiting good agreement with theory of coarsening kinetics.