Compositional softening and non-basal slip in off-stoichiometric Ca–Mg–Al C14 Laves phases

The effect of off-stoichiometric alloying on the mechanical behaviour of the hexagonal C 14 Ca-Mg-Al Laves phase was investigated through a combined atomistic modelling and experimental approach. Atomistic simulations were used to explore the compositional space and characterise the resulting transitions in elastic and plastic properties. The calculations reveal that partial substitution of Mg by Ca significantly reduces elastic stiffness and unstable stacking fault energies, indicating enhanced dislocation mobility in Ca enriched compositions. A ternary C 14 Ca 37 Mg 61 Al 2 phase was synthesised and analysed to validate these predictions. Nanoindentation yielded an average hardness of 2.4 ± 0.3 GPa and modulus of 50.0 ± 1.9 GPa, representing a ∼32 % hardness reduction relative to binary Ca 31 Mg 69 . Slip trace analy-sis and transmission electron microscopy confirmed dominant non-basal deformation involving prismatic and pyramidal ⟨ a ⟩ dislocations, as well as the occurrence of cross-slip. The agreement between simulations and experiments demonstrates that the enrichment with larger Ca atoms induces lattice dilation and facilitates dislocation activity. This compositional softening mechanism provides a route to tune the plasticity of Laves phases through controlled off-stoichiometric alloying.