Atomistic simulations of grain coalescence

Grain coalescence has been proposed as a mechanism for tensile stress generation in deposited films. The present work investigates this mechanism using atomistic simulations performed over a wide range of grain boundary configurations. Surface, grain boundary, and elastic strain energies are measured and correlated with the stress generated during coalescence. Strain accommodation at the atomic scale is shown to depend on the details of grain boundary structure, and the magnitude of stress developed is found to scale inversely with grain boundary energy. The results are compared with a popular continuum-level model that overestimates the maximum stress observed in the present simulations and also in experiments in the literature in general. It is concluded that grain coalescence is governed by the maximum range of atomic interaction across the coalescence gap, and the stress generated depends on the apparent stiffness of the coalescence reaction. These results have important implications in understanding the tensile stress developed in experiments and continuum-level models.