Kinetic Roughening of Interfaces and Mixing in Alloys Under Shear or Irradiation

Abstract

AbstractBoth irradiation and plastic deformation can induce the stabilization of non-equilibrium phases in alloys. A simple kinetic atomistic model is used for describing these two situations, when the external forcing is acting in competition with thermally activated diffusion. Monte Carlo simulations are performed on alloys with positive heats of mixing. Both situations share common features : random solid solutions are stabilized at high enough forcing intensity (i.e. irradiation flux or shearing rate), while at moderate forcing intensities interfaces exhibit kinetic roughening. However, major differences are observed : alloys under irradiation undergo dynamical transitions between steady-states, such as a dynamical roughening transition at interfaces and a precipitation-dissolution transition in the bulk ; in alloys under shear such transitions are not observed ; instead the steady-state microstructure of a two-phase alloy is continuously refined on increasing the shearing rate. These differences originate from the size of the perturbation induced by the external forcing : the perturbation is of microscopic size for alloys under irradiation, while it is of macroscopic size for alloys under shear. Results obtained for the shearing case provide a rationalization scheme of ball milling experiments showing chemical mixing of immiscible elements. The fact that such systems consist of nanograins should also contribute to prevent the existence of 1st order phase transitions on varying the milling conditions.