Incoherent tilt grain boundaries stabilized by stacking faults and solute-cluster segregation: a case-study of an Mg-Gd alloy

Despite their wide presence in hcp metals, incoherent tilt grain boundaries (ITGBs) are rarely studied. In this work, first-principles calculations were combined with atomic-resolution HAADF-STEM analyses to investigate the structure and formation of one special type ITGB in an Mg-Gd alloy featured with a unique Gd-rich cluster segregation pattern. Our results suggested this ITGB as a mirror-glide boundary formed by gliding the atoms along [] of a {}<> coherent twin boundary due to its interaction with stacking faults. The ITGB can be further stabilized by partial-column Gd substitution, leading to the observed unique segregation pattern. [GRAPHICS] . IMPACT STATEMENT A strategy of combining first-principles calculations with atomic-resolution HAADF-STEM has been developed and showed great promises for interpreting complex ITGB structures with solute-cluster segregation in hcp crystals.