M. Kubis

Highly coercive SmCo5 magnets prepared by a modified hydrogenation-disproportionation-desorption-recombination process

The hydrogenation-disproportionation-desorption-recombination (HDDR) process was applied to SmCo5 using extreme conditions, namely high hydrogen pressures and reactive milling under hydrogen. Investigations on the hydrogen absorption behavior of SmCo5 by differential scanning calorimetry under hydrogen pressures between 1 and 7 MPa showed absorption events due to an interstitial absorption at about 100 °C and a disproportionation reaction at about 600 °C. X-ray diffraction showed the disproportionation of SmCo5 into Sm hydride and fcc-Co. A favorable effect of high hydrogen pressures on the disproportionation reaction was observed which can be explained by a decrease of the free enthalpy of the samarium hydride for increasing hydrogen pressures. Reactively milled SmCo5 showed also the products of the disproportionation reaction. The recombination to the original SmCo5 phase on hydrogen desorption in a subsequent heat treatment in vacuum was successful for both methods. However, Sm2O3, Sm2Co17, and Sm2Co7 ...

Hydrogenation and disproportionation of Sm2Fe17−xGax at high hydrogen pressures

In order to apply the hydrogenation-disproportionation-desorption-recombination process for the preparation of highly coercive Sm2Fe15Ga2Cy, which exhibits excellent magnetic properties together with a high thermal stability, the disproportionation of Sm2Fe17−xGax was investigated. A systematic study of the hydrogen absorption behavior of Sm2Fe17−xGax (x=0, 0.5, 1, and 2) at hydrogen pressures between 0.5 and 8 bar by means of hydrogen differential thermal analysis (HDTA) showed that increased hydrogen pressures promote the disproportionation of the stabilized 2:17 phase. X-ray diffraction investigations of the HDTA samples showed a decreasing content of the 2:17 phase for increasing hydrogen pressures. It was possible to achieve a nearly full disproportionation even for the most stable compound Sm2Fe15Ga2 by applying a pressure of 8 bar. Microstructural changes within the disproportionated mixture as a result of the applied pressure have been documented in detail by high resolution scanning electron micr...

Permanent magnets prepared from Sm10.5Fe88.5Zr1.0Ny without homogenization

Abstract In as-cast Sm 2 Fe 17 the high amount of α-Fe caused by a peritectic reaction can be considerably reduced by a small addition of about 1 at% Zr. X-ray diffraction showed that as-cast Sm 10.5 Fe 88.5 Zr 1.0 mainly consists of a phase with the Th 2 Zn 17 -type structure and SmFe 3 . Non-homogenized Sm 10.5 Fe 88.5 Zr 1.0 was milled and (i) annealed in vacuum or (ii) treated with a hydrogenation-disproportionation-desorption-recombination (HDDR) process. The annealed and subsequently nitrogenated powder is magnetically anisotropic and has a coercivity μ O J H C up to 2.0 T and an energy product ( BH ) max up to 136 kJ/m 3 . HDDR-treated and nitrogenated powder is isotropic and exhibits values of μ O J H C = 3.1 T and ( BH ) max = 103 kJ/m 3 . Consequently, Sm 10.5 Fe 88.5 Zr 1.0 N y ( y ≈ 16) permanent magnets with very good properties can be prepared without the time-consuming homogenization procedure.

Modified HDDR procedures applied to NdFeB alloys

The magnetic properties of Nd/sub 16.2/Fe/sub 78.2/B/sub 5.6/, Nd/sub 12.6/Fe/sub 81.4/B/sub 6.0/ and Nd/sub 12.6/Fe/sub 69.4/Co/sub 11.0/Ga/sub 1.0/B/sub 6.0/ alloys after the application of modified HDDR (hydrogenation-disproportionation-desorption-recombination) procedures have been investigated and particular emphasis has been given to the development of magnetic anisotropy and high coercivity in these different types of materials. Conventional HDDR processing leads to anisotropic material only in the case of the Nd/sub 12.6/Fe/sub 69.4/Co/sub 11.0/Ga/sub 1.0/B/sub 6.0/ alloy. Combining solid-disproportionation with a controlled recombination under partial hydrogen pressure at 900/spl deg/C, a significant degree of anisotropy and a good coercivity were achieved for the two ternary alloys. These findings indicate the possibility of more than one mechanism and the relevance of the rod-like solid-disproportionated structure for the inducement of anisotropy. Another modification of the standard procedure, the reactive milling technique, leads to isotropic Nd/sub 16.2/Fe/sub 78.2/B/sub 5.6/ powder with grain sizes, both in the disproportionated and recombined states, significantly smaller than those of conventional powder and a very high coercivity of /spl mu//sub 0J/H/sub c/=1.88T.

Microstructure and HDDR-processing of as-cast Sm10.5Fe88.5Zr1.0

Abstract Microstructure and hydrogen absorption behaviour of as-cast Sm 10.5 Fe 88.5 Zr 1.0 were investigated. The as-cast sample consists mainly of Sm 2 Fe 17 main phase, SmFe 3 and (Sm,Zr)Fe 3 , with Zr contents of 0.6, 1 and 20 at%, respectively. The Zr addition leads to a higher onset of hydrogen absorption and a sluggish disproportionation.

Effect of small Zr additions on the microstructure of Sm/sub 2/Fe/sub 17/

Microstructure and phase composition of Sm/sub 10.5+/spl delta//Fe/sub 89.5-/spl delta/-/spl infin//Zr/sub /spl infin// samples with /spl delta/=0, 1.5 and x=0, 1, 2 were investigated. The Zr addition reduces the amount of Sm-rich phase and free /spl alpha/-Fe in as-cast materials, whereas the Sm addition (only investigated for Zr-containing alloys) reduces the amount of free /spl alpha/-Fe on cost of a higher amount of Sm-rich phase. The Zr is not uniformly distributed in the as-cast materials, forming Zr-rich (Sm, Zr)Pes phase (10-20 at% Zr) besides 1:3 and 2:17 phases with lower Zr content (/spl les/1 at% Zr). However, after homogenization, these Zr- rich regions disappeared and the Zr was then uniformly distributed in the 1:3 phase regions. The hard magnetic properties of all samples were studied after milling and nitrogenation. The highest energy product (BH)/sub max/ of 146 kJm/sup -3/ was obtained for the homogenized Zr-free sample. However, the properties of the as-cast materials are improved by the Zr-addition, with the optimum composition of Sm/sub 12/Fe/sub s/spl tau//Zr/sub 1/N/sub y/ showing a (BH)/sub max/ of 125 kJm/sup -3/.

Intrinsic magnetic properties of Sm/sub 2/Fe/sub 17-x/M/sub x/N/sub y//C/sub y/ [M=Al, Ga, or Si]

The partial substitution of Fe by AI, Ga or Si enhances the thermal stability of the interstitial Sm,Fe,,-carbides making possible the application of high temperature processes for the preparation of highly dense magnets [l-4]. The intrinsic magnetic properties of the compounds investigated in the present work play an important role for the assessment of their potential for possible applications. SmzFe,,.,M, samples with M = Al (x = I, 2, 31, M = Ga (x = 0.5, 1, 2), and M = Si (x = 0.25,0.5, I ) were prepared by arc melting, induction melting and homogenization treatment. The samples were pulverized by crushing and milling to mean particle sizes mainly below 10 pm and nitrogenated at 500OC for 6hrs in 800mbar N, or carhurized at 500°C for 16hrs in 600 mbar CH,. Alternatively, a melt-carburized Sm,Fe15Ga2C,.B sample was prepared. The powders were aligned in a magnetic field of 2 T, cold compacted with a pressure of about 500MPa and resin-bonded. The Curie temperatures were obtained fmm M’(T)-Plots of thermomagnetic measurements. Demagnetization curves were measured in a vibrating sample magnetometer. The saturation polarization I, and the anisotropy field Ha were determined by a numerical fining procedure of the demagnetization curves in the region of the reversible rotation magnetization processes [5]. The obtained values of Curie temperatures, saturation polarizations and anisotropy fields for the Sm2Fe,,.,M,N,/C, samples are given in Fig. I . For comparison, the intrinsic magnetic properties of Sm,Fe,,N,/C, taken from ref. [6] were added to the graphs. Curie temperature and saturation polari2ation decrease monotonically for increasing content of substitution M. The nonmagnetic dilution by the substitution atoms seems to be the dominating effect. The nitrides exhibit always larger values than the corresponding carbides. The drop of the saturation polarization 1, is very strong. For example. J, of Sm2Fe,,GazC, is only 0.81 T and with that much lower than the reported value of 1.05 T for melt-carburized Sm2Fe,,Ga2C, [2]. On the other hand, the I,-value of 1.0 T obtained for the melt-carburized Sm,Fe,,Ga2C18 sample corresponds very well with ref. [2]. It can he concluded, that the gas-carburization has an unfavourable effect on the saturation polarization compared to melt-carburization. The anisotropy fields increase significantly for small M contents x 4 1 (e.g. Sm,Fe165Ga, 5CyR”y with Ha = 25.0126.6 T compared to Ha = 16122 T for Sm,Fe,,CylN,). For M contents x 2 1 the anisotropy fields start to decrease. The decrease of H, for the carbides is weaker than that for the nitrides, leading finally to comparahle or even higher Ha values for ‘the carbides (e.g. Sm,Fe,,AI,C/”, with Ha= 17.3115.2 T). The gas-carburized SmzFe,,Ga,C, sample shows a much higher H,value (17.8 T) than the melt-carburized Sm2FelrGa2CiR y n p l e (Ha= 10.1 T, which corresponds well with the reported Ha-value for melt-carburized Sm2Fe,,GazC2 of 13 T [2]). In this case, a favourable effect of the gas-carburization on the anisotropy field compared lo melt-carburization can be stated. Regarding the intrinsic magnetic properties of the investigated compounds (x t O), the samples with small Ga-addition show the hest potential for permanent magnet applications.