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 [ $20\bar{2}\bar{1} $] of a { $10\bar{1}4 $}< $20\bar{2}\bar{1} $> 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.