The disproportionated structure of Sm2Fe17 observed by high resolution scanning electron microscopy

The hydrogenation, disproportionation, desorption and recombination (HDDR) processing technique used with Nd-Fe-B alloys has more recently been applied to Sm2Fe17 materials. Other researchers have used transmission electron microscopy to investigate the microstructure of Sm2Fe17 in the disproportionated state and have shown it to consist of approximately 20 nm diameter SmH2+/-x rods in an alpha-Fe matrix. Here the structure of disproportionated Sm2Fe17 is shown by high resolution scanning electron microscopy as well as the initiation and growth of disproportionated regions into the matrix phase. Comparisons with work by others on the microstructure of disproportionated Nd2Fe14B shows the materials to be similar. In as-cast Sm2Fe17 the disproportionation reaction is observed to have initiated at the alpha-Fe-matrix interface, indicating that this interface could be a rapid diffusion path for hydrogen in this material. This behaviour can be compared with observations on Nd-Fe-B materials with no alpha-Fe dendrites where the disproportionation reaction is shown to be initiated at the Nd-rich grain boundary phase.