Environment-assisted crack nucleation in La(Fe,Mn,Si)13-based magnetocaloric materials

TL;DR

This study investigates how environmental factors cause crack formation in La(Fe,Mn,Si)13-based magnetocaloric materials, revealing that reactions with moisture lead to microstructural degradation and crack nucleation.

Contribution

The paper provides new insights into the environmental-assisted crack nucleation mechanism in La(Fe,Mn,Si)13 materials, highlighting the role of La-rich particles and moisture-induced reactions.

Findings

Cracks form around La-rich particles after air exposure.

Water/moisture reacts with La2O3, causing volume expansion and degradation.

Minimizing La-rich phases can improve long-term stability.

Abstract

Cracking in La(Fe,Si)13-based magnetocaloric materials has been observed to predominantly form around La-rich (La2O3) particles and pose a threat to their long-term structural integrity. To understand the formation of these cracks, FIB cross-sectional polishing followed by SEM characterisation was employed to study local microstructural evolution after air exposure. Results suggest that volume expansion and internal degradation associated with a chemical reaction between La2O3 particles and water/moisture can lead to crack nucleation in the 1:13 phase adjacent to La-rich particles. This observation indicates that the formation of La-rich phase should be suppressed, or their size minimised during material processing to ensure the long-term structural integrity of La(Fe,Mn,Si)13 magnetocaloric materials.