S-HDDR INDUCED CAVITATION IN NDFEB

Previous resistivity studies have shown that, when cycling a sample of Nd16Fe76B8 in hydrogen and in vacuum at 800 degrees C, the rate of di sproportionation and recombination increased considerably after the fi rst cycle. A schematic model has been proposed to explain this behavio ur. It has been shown by metallographic investigations that, during th e first recombination stage, there is a substantial redistribution of the Nd-rich grain boundary phase along the grain boundaries of the new ly formed, fine grained Nd2Fe14B regions produced by the S-HDDR proces s. This allows the rapid transport of hydrogen into and out of the str ucture on subsequent cycles. As a consequence of this redistribution, significant cavitation occurs on the first cycle, confirmed by density measurements. This increases the effective surface area and enhances the diffusion of hydrogen within the bulk of the sample, thus also inc reasing the rate of the subsequent disproportionation and recombinatio n cycles.