Studies of HDDR processes in Sm2Fe17, Sm10.2Fe85.8Nb4 and Sm9.5Fe80.5Nb10 alloys

The hydrogenation, disproportionation, desorption and recombination (HDDR) process in Sm2Fe17, Sm10.2Fe85.8Nb4 and Sm9.5Fe80.5Nb10 alloys has been investigated by means of hydrogen absorption and desorption studies, electrical resistivity measurements and microstructural observations. Thermopiezic analysis (TPA) shows that the addition of Nb increases the disproportionation temperature of the Sm2Fe17 matrix phase. Differences in reaction rates of disproportionation and recombination during solid-HDDR processing for the alloys with various Nb contents at T = 800 degrees C and p(H-2) = 1.0 bar have been revealed, showing that the 4 at% Nb-containing alloy has the lowest reaction rates. The disproportionated mixture consists of rods of Sm hydride embedded in an alpha-Fe matrix; the distribution of the paramagnetic NbFe2-type Laves phase remains unchanged during the overall process. A coarsening of the eutectic mixture was observed during recombination. The 2/17-matrix phase of the fully recombined material exhibits a uniform, submicron grain size.