The effect of hydrogen pressure on the kinetics of the HDDR-process of bulk Nd-Fe-B-type alloys

The HDDR (hydrogenation, disproportionation, desorption, recombination)-process of bulk Nd-Fe-B-type alloys has been investigated by in-situ electrical resistivity measurements. The effect of hydrogen pressure on the rate of the disproportionation reaction, in which the Nd/sub 2/Fe/sub 14/B phase forms Fe, Nd-hydride and Fe/sub 2/B, was studied in detail on a Nd/sub 14.68/Dy/sub 0.94/Al/sub 0.62/Fe/sub 76.47/Nb/sub 0.5/B/sub 6.79/ alloy, which is used for the production of commercial permanent magnets. Experimental data reveal a strong dependence of the HDDR-kinetics on the hydrogen pressure which was varied between p(H/sub 2/)=0.1-1.0 bar at T=750/spl deg/C. Optical micrographs suggest that the Nd-rich grain boundary phase acts as a diffusion path for the hydrogen in the HDDR-process. The 2-14-1 matrix phase subsequently disproportionates from the grain boundary phase inwards.<
>