Computer simulation of phase decomposition process generating precipitates harder than matrix

The Monte Carlo method combined with the static variational method is applied to a computer simulation on the phase decomposition process when a precipitate in a bcc binary alloy is elastically harder than the matrix. The present study is compared with our previous results that were obtained for the case of the same elastic constant of the precipitates as that of the matrix in our previous report. We have adopted the Jonson-type potentials as the interaction between the constituent elements, and have used three kinds of interaction potentials between solute atoms. We find an anisotropic structure in the alloy whose elastic constant of the precipitates is equivalent to the constant of the matrix. The alloy that has harder precipitates than the matrix shows an isotropic structure or a little anisotropic structure depending on the value of elastic constant of the precipitates. We presume that the isotropic structure is yielded because of the larger contribution of the interfacial energy than the elastic strain energy. Evidently the total energy of the alloy with isotropic clusters is lower than that with anisotropic clusters for every potential used in the present simulation. Therefore we conclude that the formation of anisotropic clusters is not due to the shape of precipitates with the minimum elastic energy but due to the dynamical process of phase decomposition concerned with nonlinear many body effect.