Study On Magnetic Materials Of Sm-Fe And Sm-Fe-M(M=Ti,Nb) Alloys And Their Nitrides

Sm-Fe-N matrix compounds have excellent magnetic properties such as high saturationmagnetization, high magnetic anisotropy and relatively high Curie temperature. These propertiesmake the materials highly promising for permanent magnet applications. In this paper, Sm-Feand Sm-Fe-M (M=Ti, Nb) alloys and their nitrides were prepared by means of powdermetallurgy processes appending HDDR (hydrogenation-disproportionation-desorption-recombination ), mechanical grinding, high-enenrgy ball-milling and disc milling, and themicrostructure, phase composition and magnetic properties were investigated in detail. It wasshown that the host phases of annealed Sm-Fe and Sm2Fe17-xNbx (x<4) alloys retained therhombohedral Th2Zn17-type structure. The host phase of Sm2Fe17-xTix alloys with x less than 1quickly cooling from annealing temperature still retain Sm2(Fe,Ti)n, when x is equal to 1.0, thehost phase behaves Sm3(Fe,Ti)29, and when x is equal to or more than 2.0, the host phase finallybecames Fe9.5SmTi1.5. But when slowly cooling from annealing temperature, the host phases ofSm2Fe17-xTix alloys with x no more than 2 retain Th2Zn17-type structure. Nb and Ti addition canreduce the a-Fe content in as-cast and annealed Sm-Fe matrix alloys. The interactions betweenhydrogen and Sm-Fe alloys at different temperature were investigated by means of XRD, it wasfound that the interaction was composed of hydrogenation, disproportionation, desorption andrecombination, and the desorption and recombination processes maybe carried out according tothe reaction SmHy + a-Fe-Sm2Fe17 + H2 above 700C contrary to disproportionation. Thehydrogenation and disproportionation processes had finished when the samples werecontinuously heated up to 800C at the heating rate of 400C/h and the desorption andrecombination processes would reach equilibrium with disproportionation process on the basis ofSmHy+a-Fe-Sm2Fen+H2 and only pumping-vacuum could facilitate the reaction to right.The surface of the powder particles treated by HDDR processes was not smooth and consist ofcracks, honeycomb holes, closed packed small particles and dispersed fine particles with the sizeof dozens to 200 nanometers. When nitrogenated in closed pure N2 atmosphere with constantinitial pressure of 0.13 MPa, all Th2Zn17-type phases can exist stably, Sm3(Fe,Ti)29 becamesunstable when the lattice stress is much larger, SmFe11Ti and Fe9.5SmTi1.5 are disappear, thephases rich in Fe, such as a-Fe, Fe2Ti or Fe2Nb are increased. Nitrogenation mechanism inclosed N2 of Sm-Fe and Sm-Fe-M alloys by HDDR treatment is essentiallyas same as that of those alloys nitrogenated in closed or circulated N2 but not treated by HDDR processes, and nitrogenation is composed of two stages: N reacts with Sm-Fe matrix powders and N diffuses homogeneously in nitrides, but the reaction rate between N and Sm-Fe matrix powders treated by HDDR was slower than that not treated by HDDR. When nitrogenated in circulated pure N2 the 2:17-type nitride phases will be supersaturation and the expansion of unit cell volume could exceed 10%. Ti and Nb addition improve nitrogetion rate and increase nitrogen content of nitrides, moreover, Ti, Nb and HDDR process all improve the coercivity of Sm-Fe-N alloys but decrease the magnetization. Besides the anisotropy bonded magnets of Sm-Fe-N and Sm-Fe-M-N compounds not treated by HDDR were obtained, the anisotropy bonded magnets of Sm-Fe-N and Sm-Fe-M-N treated by HDDR processes were also prepared successfully, and Sm2Fe16.5Ti0.5Ny magnet exhibits the peak coercivity of 2900 Oe under the applied magnetic field of 15000 Oe. The size of particles or grains of the alloys not treated by HDDR are basically more than 100 nm, so the nanocomposite magnets through exchange coupling were not prepared. Howerer, the intergranular exchange-coupling interaction in the nonocrystalline Sm-Fe-N and Sm-Fe-M-N nitrides treated by HDDR was partially formed, and a-Fe can be embedded in 2:17-type matrix phases or dispersed w...