Monitoring of the hydrogen decrepitation process by acoustic emission.

Abstract Acoustic Emission Testing (AT) was applied to monitor the Hydrogen Decrepitation (HD) process for two different NdFeB-type materials: sintered NdFeB magnet and annealed NdFeB ingot alloy. Acoustic signals of clearly different characteristics were acquired for these two materials, indicating different course of the HD process. Acoustic waves of high signal strength and high peak amplitude were generated for the sintered NdFeB magnet whereas acoustic signals of low energy and low intensity were registered for the annealed NdFeB alloy. These findings were supported by real-time visual observation of the HD process. The sintered NdFeB magnet decrepitates rapidly and its particles spatter for a longer distance comparing to the ingot NdFeB alloy. Different behavior of the investigated materials can be explained in relation to their structural properties and manufacturing history. Fine microstructure, homogenously distributed thin layer of the Nd-rich grain boundary phase and stress accumulated after fabrication process can be responsible for more intense characteristic of the HD process in case of the sintered NdFeB magnets. Graphical abstract Image 1 Highlights • Monitoring of the Hydrogen Decrepitation via Acoustic Emission. • Various acoustic waves generated during the HD process. • Waves are influenced by distribution of the Nd-rich phase and accumulated stress. • Incubation time can be determined by AE. [ABSTRACT FROM AUTHOR]