Periodic Solute Segregation Weakens Chemically Stabilized Grain Boundaries

Here, atomic-resolution HAADF-STEM and atomistic modeling identify a periodically Nd-decorated asymmetric [12̅10] tilt GB in a deformed Mg–Nd alloy. Voronoi analysis and segregation-energy calculations show that Nd occupies distorted boundary-core sites and reduces local interfacial strain energy.

Contrary to the common expectation that rare-earth segregation strengthens magnesium interfaces, shear simulations show that periodic Nd segregation substantially reduces the mechanical resistance of this boundary. Under loading, the segregated regions undergo amorphization-like structural rearrangement, redirecting stress relaxation from the intrinsic direction-dependent modes of the pure boundaryinterfacial twinning or localized interfacial dislocation activityto premature grain-boundary sliding.