Structure change in Sm-Fe-B-Ti permanent magnet materials induced by HDDR process

The structures of Sm8.3Fe85.2B2.0Ti4.5 and Sm9.4Fe84.1B2.0Ti4.5 alloys, whi ch show superior properties as isotropic permanent magnets after a hydrogen ation-disproportionation-desorption-recombination (HDDR) process followed b y a nitridation, have been investigated by transmission electron microscopy , and electron and X-ray diffraction, paying particular attention to the st ructural changes induced by the HDDR process. It is found that a hexagonal Th2Ni17-type structure, observed in both alloys, with an approximate compos ition Sm(Fe,Ti)(9.5) before the HDDR process, transforms to a rhombohedral Th2Zn17-type structure with a composition Sm(Fe,Ti)(8.5) after the HDDR pro cess. The Ti content in the hexagonal Th2Ni17-type structure is higher than that in the rhombohedral structure. The hexagonal Th2Ni17-type and rhomboh edral Th2Zn17-type structures in the Sm9.4Fe84.1B2.0Ti4.5 alloy have lattic e parameters a=0.85103(3) nm and c=0.83820(5) nm, and a=0.85549(3) nm and c =1.24826(9) nm, respectively, and show the relationship a(hex) <a(rhomb) bu t 1/2c(hex) > 1/3c(rhomb). (C) 1999 Elsevier Science S.A. All rights reserv ed.