The effect of hydrogen on the multiscale mechanical behaviour of a La(Fe,Mn,Si)13-based magnetocaloric material

TL;DR

This study investigates how hydrogen affects the mechanical properties and failure mechanisms of La(Fe,Mn,Si)13-based magnetocaloric materials, revealing anisotropic weakening and atomic-level hydrogen arrangements.

Contribution

It provides new insights into hydrogen-induced mechanical degradation and the atomic-scale mechanisms in magnetocaloric materials, aiding their durability assessment.

Findings

Hydrogen weakens the material by promoting transgranular fracture.

Strength depends on crystal orientation, with significant weakening along {111} planes.

Hydrogen's effect is anisotropic, negligible on {001} planes.

Abstract

Magnetocaloric cooling offers the potential to improve the efficiency of refrigeration devices and hence cut the significant CO2 emissions associated with cooling processes. A critical issue in deployment of this technology is the mechanical degradation of the magnetocaloric material during processing and operation, leading to limited service-life. The mechanical properties of hydrogenated La(Fe,Mn,Si)13-based magnetocaloric material are studied using macroscale bending tests of polycrystalline specimens and in situ micropillar compression tests of single crystal specimens. The impact of hydrogenation on the mechanical properties are quantified. Understanding of the deformation/failure mechanisms is aided by characterization with transmission electron microscopy and atom probe tomography to reveal the arrangement of hydrogen atoms in the crystal lattice. Results indicate that the intrinsic strength of this material is ~3-6 GPa and is dependent on the crystal orientation. Single crystals under compressive load exhibit shearing along specific crystallographic planes. Hydrogen deteriorates the strength of La(Fe,Mn,Si)13 through promotion of transgranular fracture. The weakening effect of hydrogen on single crystals is anisotropic; it is significant upon shearing parallel to the {111} crystallographic planes but is negligible when the shear plane is {001}-oriented. APT analysis suggests that this is associated with the close arrangement of hydrogen atoms on {222} planes.