The formation mechanisms of growth twins in polycrystalline Al with high stacking fault energy

Growth twins are scarcely observed in metals with high stacking fault energy, such as pure Al. In this study, however, we report the observation of growth twins in sputtered polycrystalline Al films on amorphous substrates and a majority of these growth twins are inclined to the growth direction (inclined twins). Although the fraction of twinned grains is low in general, it increases monotonically with increasing film thickness, reaches a maximum at the film thickness of 80 nm, and decreases gradually thereafter in the thicker films. The nucleation mechanism for the inclined twins is compared with that of the parallel growth twins in Al. Different twin formation mechanisms are discussed. This study provides an alternative perspective to evaluate the formation of growth twins in metals with high stacking fault energy.