Deep Insights into the Twinning Mechanism in High-Performance Al Alloys: A Comprehensive First-Principles Study

Abstract

The twinning mechanism of Al solid solutions is comprehensively investigated via the first-principles method. The relative stability of C and H atoms at tetrahedral and octahedral centers is discussed. Moreover, the interaction energies between solute atoms at different atomic layers and generalized stacking-fault structures are calculated. Results indicate that the stable occupation of C atom exists at the octahedral center rather than at the tetrahedral center. By contrast, the H atom stably exists at the tetrahedral center rather than at the octahedral center. Both atoms can effectively reduce the minimum energy barrier of dislocation nucleation, thereby promoting dislocation nucleation. The C atom more easily promotes dislocation nucleation than the H atom. Furthermore, both atoms are repelled by the stacking-fault plane. However, they are more likely to be segregated in the second neighboring layer of unstable stacking fault, intrinsic stacking fault (ISF), and unstable twinning fault (UTF) structures. Charge density measurements reveal that the twinning process is likely inhibited because of the strong local chemical bonding around the UTF layer from the ISF structure to the UTF structure. High concentrations of both atoms inhibit the twinning deformation at crack tips and grain boundaries, but they have almost no effect on the twinning deformation inside the grains. This study provides deep insights into the twinning deformation mechanism of face-centered-cubic alloy systems.