Structure of an alloy based on SmCo 5 after disproportionation-recombination
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STRUCTURE OF AN ALLOY BASED ON Sm Co5 AFTER DISPROPORTIONATION–RECOMBINATION I. I. Bulyk and A. M. Trostyanchyn
UDC 546.3-19′ 11
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 Sm Co5 and Sm Co3 phases for P H2 ≈ 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.
The application of the procedure of hydrogenation, disproportionation, desorption, and recombination (HDDR) for the production of highly coercive magnetic powders based on Nd2 Fe14 B and Sm2 Fe17 Nx alloys gives positive results [1, 2]. The specific features of this process and its influence on the magnetic properties of single-phase samarium–cobalt compounds system are studied in [3–5]. Under mild conditions (PH2 ≈ 0.1 MPa), the HDDR procedure in samarium–cobalt alloys is impossible due to their high thermodynamic stability under the conditions of disproportionation. For this reason, either the pressure of hydrogen is increased to 4 MPa or the procedure of milling in hydrogen is applied [3–5]. The conditions and phase composition of the products of HDDR in commercial alloys based on the Sm Co5 (KS37) and Sm2 ( Co, Fe, Cu, Zr )17 (KS25) compounds are investigated in [6, 7]. Thus, in particular, it is shown that the KS37 alloy subjected to ordinary and solid hydrogenation and disproportionation at ∼ 850–858°K disproportionates into samarium hydride and cobalt (in the mode of ordinary hydrogenation and disproportionation, the alloy is heated in hydrogen from the room temperature and decays into powder; in the mode of solid HDDR, hydrogen is delivered into the evacuated chamber containing the alloy and heated to a high temperature; as a result, the alloy remains intact). Since the changes in the microstructure of this alloy in the course of HDDR are not revealed, we present the results of metallographic investigations of the KS37 alloy in the course of solid HDDR for PH2 ≈ 4 MPa. Experimental Procedure We study ingots of commercial alloy melted in the induction furnace. The X-ray phase diffraction analysis is performed by using diffractograms obtained in an HZG-4A diffractometer (FeKα-radiation) and indexed with the help of the PowderCell program. The lattice constants are found by using the Lattic program [8]. The procedure of solid HDDR is studied in the temperature range 293–1158°K in hydrogen with an initial pressure of 4 MPa and in a vacuum of (5–40) ⋅ 10– 3 Pa in the installation described in [9]. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, Lviv. Tran
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