Growth twins in high stacking fault energy metals: Microstructure, texture and twinning

This work explores the formation of twin boundaries in high stacking fault energy metals (SFE >125 mJ/m2) by synthesizing thick films (>10 µm) of Al, Al-5.3 wt%Mg, and Ni using magnetron sputtering. We report the observation of twin boundaries that are inclined with respect to the film growth direction across the entire thickness of the films. The formation of these inclined twin boundaries results in localized changes in the texture of the columnar grains. Microstructural analysis revealed that the fraction of twinned grains in the Al film (46%) is four times higher compared to other similar studies in Al, while the Al-5.3 wt% Mg and Ni films can be considered highly twinned since the fraction of twinned grains is 70% and 90%, respectively. The experimental observations provide an explanation on the formation of twin boundaries during the synthesis of the films, and emphasize that, in addition to stacking fault energy restrictions, high grain boundary mobility is a limiting factor on the nucleation of twin boundaries.