Redefining Plasticity in a Cubic Intermetallic: Dislocation Dynamics in the CaAl2 Laves Phase

Abstract

In the realm of materials design, understanding and manipulating the behaviour of dislocations — key drivers of plastic deformation — is a cornerstone. However, while dislocations are well-explored in simple crystalline materials, their structure and mechanisms of motion remain largely enigmatic for complex crystals, such as topologically closed-packed phases. This vast class of materials contains many intermetallics ranging from high-temperature structural materials to functional crystals that can act as superconductors, magnets, magneto-caloric or hydrogen storage materials. In all of these applications, structural integrity and therefore controlled plasticity is essential. This study bridges our current knowledge gap in plasticity of complex crystals by delving into the most prevalent among them, the Laves phase. Utilizing transmission electron microscopy, we unveil previously unreported defect structures in the cubic CaAl2 Laves phase. Complementing these observations, atomistic simulations elucidate the underpinning mechanisms, revealing novel deformation behaviours. We spotlight the role of full dislocations traversing multiple {1 1 n} slip planes, a departure from the conventional confinement to {1 1 1} planes. This multi-plane dislocation activity, including frequent cross-slipping, emerges as a pivotal factor in accommodating plastic deformation. Our findings not only challenge an existing paradigmin intermetallic plasticity but also propose a tangible path-way to understand the ductility of brittle complex alloys as a stride forward in phase selection and materials engineering.

Keywords: Topologically close-packed phase, dislocations, cross-slip, transmission electron microscopy, atomistic simulation