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

Fracture properties of La(Fe,Mn,Si)13 magnetocaloric materials

“…In contrast, plates without observable pre-existing cracks broke into three nearly even pieces, where the two cracks were both within the region between the loading/inner pins for all the plates (Figure 2(e)). The fracture mode is mainly intragranular as evidenced by Figure 2(f), in agreement with our prior work on hydrogenated La(Fe,Mn,Si)13 [6]. We found previously that hydrogenation changes the fracture mode of this material upon bending tests [6], but we note that in-service fracture mode may also be affected by factors such as corrosive media [7] and/or external stress state [8].…”

“…A key challenge in its commercialisation arises from the poor mechanical stability of the La(Fe,Mn,Si)13 magnetocaloric materials when subjected to simultaneous action of several generalised forces during processing and service, leading to limited lifetime [3,4]. Understanding the mechanical properties of these materials is therefore of high demand, yet studies are limited [5,6]. We found previously that although the intrinsic strength of La(Fe,Mn,Si)13 is up to ~6 GPa, strength of the actual materials in use is reduced by a factor of ~20 likely due to cracks/pores in the microstructure [6,7] and potentially (pre-existing) dislocations and grain boundaries.…”

“…Understanding the mechanical properties of these materials is therefore of high demand, yet studies are limited [5,6]. We found previously that although the intrinsic strength of La(Fe,Mn,Si)13 is up to ~6 GPa, strength of the actual materials in use is reduced by a factor of ~20 likely due to cracks/pores in the microstructure [6,7] and potentially (pre-existing) dislocations and grain boundaries. While complete removal of the cracks is difficult because of technical limitations and service environment requirements, it is important to understand the tolerance of cracks in the material for prolonged stable performance, thereby establishing a guideline for quality control before device production.…”

“…The plate thickness is in the sub-mm scale, and the thickness to width ratio is ~1:30. Microstructure of the plates was characterised using scanning electron microscopy (SEM) imaging and electron backscatter diffraction (EBSD), on a FEI Quanta 650 SEM with a Bruker eFlashHR (v2) EBSD camera using a beam voltage of 20 kV [6]. As shown in Figure 1, the material consists of two main phases: the La(Fe,Mn,Si)13 (also termed main/1:13) phase and the α-Fe phase.…”

“…In (b) and (c), grain boundaries of the 1:13 phase, and phase boundaries between La(Fe,Mn,Si)13 and α-Fe are highlighted with black and white lines, respectively. MUD denotes multiples of the uniform density [6]. Note that the image in (a) shows the cross sections of the pores, of which the 3D shapes could be revealed by X-ray or focussed ion beam tomography.…”