Effect of microstructural heterogeneity on the mechanical behavior of nanocrystalline metal films

Conventionally, mean grain size is considered the most critical microstructural parameter in determining the mechanical behavior of pure metals. By systematically controlling the distribution of grain orientations in aluminum films, we show that microstructural heterogeneity alone induces large variation in the mechanical behavior of nanocrystalline metal films. Aluminum films with relatively homogeneous microstructure (all grains with identical out-of-plane orientation) show substantially less early Bauschinger effect compared to films with heterogeneous microstructure, irrespective of film thickness or grain size. On the other hand, the films with homogeneous microstructure show relatively higher yield stresses. A direct correspondence is found between the nonuniformity of plastic deformation and early Bauschinger effect, which confirms the critical role of microstructural heterogeneity.