Grain coalescence and its effect on stress and elasticity in nanocrystalline metal films

An approach based on the grain coalescence mechanism is developed to explain and predict the elastic behavior (and stress) of nanocrystalline films. The model explains how, under an external strain, coalescence and decoalescence at grain boundaries alter the stress state of the film, thereby reducing the film's effective Young's modulus. An assessment of the effect of coalescence at grain boundaries could be made on the basis of the analysis of the contributions of grain boundary and strain energies. The estimations of Young's modulus and stress based on the model are in agreement with the data experimentally observed for sputtered iron nanocrystalline films.