Production of Functional Nanocrystalline Materials in Hydrogen

On the example of KS25 and KS37 samarium–cobalt-base commercial alloys and LaNi_4.5Al_0.5 alloy, we show the possibility, in principle, of obtaining functional materials in the nanocrystalline state with the help of a planetary mill in hydrogen medium. Milling with a rotational speed of 600 rpm during 24 h leads to the disproportionation of KS25 and KS37 alloys into samarium hydride and iron–cobalt (cobalt) and of LaNi_4.5Al_0.5 into Ni₃Al and amorphous products. After vacuum annealing up to 1181 K, the main phases of samarium–cobalt materials are recombined. The crystallite sizes after annealing are 58–72 and 70 nm for KS25 and KS37, respectively. We established that LaNi_4.5Al_0.5 alloy is not recombined in vacuum, and the nanocrystalline state in it can be reached by milling up to 30 min. The crystallite sizes constitute 45–78 nm.     

Specific features of the interaction of alloys of the didymium-iron-boron system with hydrogen

We study the interaction of alloys of the Dd-Fe-B system [M-82, M-83, M-84, and M-85 alloys with a mass content of 33–40% didymium, up to 0.5% aluminum, and 1–1.25% boron (the rest is iron)] with hydrogen using volumetric, X-ray phase, and differential thermal analysis. If the initial hydrogen pressure is 1.0 MPa, hydrides with 0.4–0.6 mass % of hydrogen are formed. The saturation of these alloys with hydrogen is accompanied by an increase in the spacing a of an elementary cell by 1.2–1.4% and in c by 0.8–1.1% (the general increase in volume is 3.2–3.9%). If the initial pressure is 0.15–0.2 MPa, the time of complete saturation with hydrogen is 15–20 min for most alloys. At 973–1033 K, the alloys under study in hydrogen disproportionate into DdHx didymium hydride (a = 0.5449 – 0.5458 nm), -iron (a = 0.2864 – 0.2866 nm), and Fe2 B iron boride (a = 0.5112 – 0.5117 nm, c = 0.4228 nm). An increase in the initial hydrogen pressure from 0.1 to 5.0 MPa is accompanied by a decrease in the disproportionation temperature to 930 K.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 2, pp. 105–112, March–April, 2004.     

Hydrogen-induced phase transformations in alloys based on Sm Co<Subscript>5</Subscript> under pressures of up to 650 kPA

The interaction of alloys based on SmCo₅ with hydrogen is studied by the methods of differential thermal and X-ray phase diffraction analyses under initial pressures of hydrogen of 200, 300, 400, 500, and 650 kPa at temperatures of up to 1223°K. The hydride of the alloy is formed up to a temperature of 343°K. Within the temperature ranges 388–408°K and 488–523°K, hydrogen is released from the hydrides of phases of the alloy. Within the temperature range 823–863°K, the alloy partially disproportionates into Sm H_x and Co. At 1008–1053°K, SmH_x undergoes partial decomposition and the SmCo₅ and Sm₂Co₁₇ phases are detected. The Co, SmCo₅, and Sm₂Co₁₇ phases exist at temperatures above 1168–1188°K. The compositions of the phases depend on the duration of interaction of the alloy with hydrogen. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 1, pp. 94–98, January–February, 2007.     

Features of the HDDR process in R–Fe–B ferromagnetic alloys (R is a mixture of Nd, Pr, Ce, La, Dy and others)

Features of the conventional hydrogenation, disproportionation, desorption, recombination (HDDR) and solid-HDDR processes in some R–Fe–B (R is a mixture of Nd, Pr, Ce, La, Dy) ferromagnetic alloys were studied in the temperature range 20–990 °C and pressure range from 1×10⁻³ Pa to 0.1 MPa. This was carried out by means of differential thermal analysis (DTA), X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) methods. The hydride of the initial phase is formed by heating to 115 °C. The disproportionation of the alloys occurs in the temperature range from 320 to 800 °C. Φ-phase constitutes the base of the initial alloys. Among the disproportionation products, R-hydride, -Fe and two borides (Fe₂B and R_1.1Fe₄B₄) were revealed. The initial phase in all the alloys is recovered after heating in vacuum to a temperature of 990 °C. Full hydrogen desorption occurs in two temperature ranges with the peaks at 200–320 and 630–715 °C.     

Structure of an alloy based on SmCo5 after disproportionation-recombination

By using the X-ray phase diffraction, metallographic, and micro-X-ray spectral analyses, we study the procedure of solid hydrogenation, disproportionation, desorption, and recombination in KS37 alloy formed by the SmCo₅ and SmCo₃ phases for ≈ 4 MPa at 1158°K. The alloy disproportionates in hydrogen into a mixture of samarium hydride and cobalt with grain sizes ≤ 1 μm. The process of recombination ends by the restoration of the original phases accompanied by the formation of a fine-grained structure of the SmCo₃ phase. As a result, the amount of this phase decreases. The procedure of holding of the alloy for 55 min in the course of recombination leads to the formation of a structure with elongated grains. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 65–68, September–October, 2006.     

Influence of Titanium on Hydrogen-Induced Transformations in the Laves Phases Based on Zirconium

By the methods of differential thermal, and X-ray phase analyses, we study the influence of hydrogen (hydrogenation, disproportionation, desorption, and recombination) on the phase transformations in Zr_{1 − x} Ti_xCr₂ (x = 0.1 and 0.2) alloys under a pressure of hydrogen of 5 MPa at temperatures varying from the room temperature to 1238°K. For 3–5 MPa and 1163–1223°K, we observe the decomposition of the Laves phase with C14-type structure accompanied by the formation of Zr_{1 − x} Ti_xCr₂H_y and ZrH_x hydrides and Cr. Under a pressure of 5 MPa, on holding at 1223°K for more than 4 h, the compounds completely disproportionate into zirconium and titanium hydrides and chromium. On holding in a vacuum at 1193– 1238°K, the compounds recombine into the phases with C14- or C15-type structure or their mixture.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 6, pp. 67–72, November–December, 2004.     

Disproportionation in Hydrogen and Recombination of the Laves Phases of Zirconium with Chromium

By the methods of differential thermal, X-ray phase diffraction, and metallographic analyses, we study the processes of conventional and solid HDDR (hydrogenation-disproportionation-desorption-recombination) in ZrCr₂ compound with C14- and C15-type structures under initial pressures of hydrogen of 3 and 5 MPa at temperatures of up to 1243°K. The ZrCr₂ compound with C15-type structure disproportionates at 1048 and 1093°K for P _H2 = 5 and 3 MPa into ZrH _x and Cr and recombines in a vacuum. The temperature of disproportionation of the Laves phase with C15-type structure is lower than for the C14 phase by 120°K. As the pressure of hydrogen increases, the temperature of disproportionation decreases. The application of HDDR to the reconstruction of the C14-type structure of the Laves phase in ZrCr₂ into the C15-type structure makes it possible to decrease the temperature of treatment and its duration as compared with the case of annealing in vacuum. The procedure of HDDR forms a nanostructure in ZrCr₂. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 3, pp. 101–108, May–June, 2005.