Morphological instabilities in thin films: Evolution maps

We consider morphological instabilities in binary multilayers and the post-instability evolution of the system. The alloys with and without intermediate phase are considered, as well as the cases with stable and meta-stable intermediate phase.Using the Galerkin finite element formulation for coupled Cahn–Hilliard – elasticity problem, maps of different evolution paths are developed in the parameter space of relative thicknesses of initial phases. We consider the relative importance of elastic and chemical energy of the system and develop maps for different cases.The systems exhibit rich evolution behavior. Depending on the initial configuration (which determines the mass conservation condition), the final equilibrium varies, but even greater variety is observed in evolution paths. The paths may consist of multiple evolution steps, which may proceed at different rates.Except for few special circumstances, the instabilities are to perturbations non-homogeneous in the film plane. Post-instability evolution is essentially two-dimensional, and cannot be reduced to the one-dimensional model.

Research highlights
► Maps of transformation and evolution of binary multilayer thin films are developed using Cahn-Hilliard-elasticity model.
► Effects of the growth of a meta-stable/stable intermediate phase and compositional strain on the instability of layers are investigated.
► Mixed order FEM is used to solve the governing equations of Cahn-Hilliard-elasticity problem.
► Instabilities are to perturbations non-homogeneous in the film plane.
► Post-instability evolution is essentially 2D and cannot be captured by 1D models.