Studies of HDDR processes in Sm 2Fe 17, Sm 10.2Fe 85.8Nb 4 and Sm 9.5Fe 80.5Nb 10 alloys

Abstract

The hydrogenation, disproportionation, desorption and recombination (HDDR) process in Sm 2Fe 17, Sm 10.2Fe 85.8Nb 4 and Sm 9.5Fe 80.5Nb 10 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 Sm 2Fe 17 matrix phase. Differences in reaction rates of disproportionation and recombination during solid-HDDR processing for the alloys with various Nb contents at T = 800°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 α-Fe matrix; the distribution of the paramagnetic NbFe 2-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.