  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.
