Trostianchyn A. The concept of hydrogen treatment to improve the structural-phase state and properties of functional materials based on alloys of rare earth and transition metals

Українська версія

Thesis for the degree of Doctor of Science (DSc)

State registration number


Applicant for


  • 05.02.01 - Матеріалознавство


Specialized Academic Board

Д 35.052.20

Lviv Polytechnic National University


The dissertation is devoted to the complex research of hydrogen-initiated phase transformations in alloys based on rare earth (REM) and transition metals of La-Ni-Co, La-Nd-Ni-Al, Sm-Co and Nd-Fe-B systems. These materials are used in high-tech industries to produce negative electrodes of nickel-metal hydride batteries and high-energy permanent magnets. The common regularities of phase transformations in hydride materials based on LaNi5 compound and in ferromagnetic materials based on SmCo5, Sm2Co17 and Nd2Fe14B compounds have been established. Based on this, the concept of processing functional materials based on REM alloys in a hydrogen environment is proposed, which consists in establishing a regulatory mechanism for purposeful changes in the microstructure, phase composition and technological parameters to ensure the necessary operational properties. The experimental confirmation of the proposed assumption regarding the mechanism of crystallographic texture formation in REM-based alloys resulting from hydrogen treatment by means of hydrogenation, disproportionation, desorption, and recombination (HDDR) was obtained. The presence of residues of the initial phase among the products of its disproportionation is a necessary condition for texture formation. The regularities of changes in the phase composition, microstructure, crystallographic characteristics and properties of the studied materials were established depending on the modes (ordinary or solid HDDR, milling in hydrogen, heat treatment in hydrogen or vacuum, as well as their various combinations) and parameters (hydrogen pressure, rotation frequency of the planetary mill chamber, maximum heating temperature, duration of exposure) of hydrogen treatment. Combined hydrogen treatment, which merges milling in a planetary mill with a frequency of 100 rpm for 40 min with the subsequent application of solid HDDR under a hydrogen pressure of 0.4 MPa, allows obtaining the highest magnetic properties values for KС37 industrial ferromagnetic alloy based on the SmCo5 compound. In particular, the highest value of the coercive force of ~ 41 kE was obtained at a recombination temperature during solid HDDR of 950 °С. The peculiarities of implementing the combined hydrogen treatment method in Nd-Fe-B system alloys have been established. The necessity of using oleic acid during milling as a protective medium is shown to prevent the agglomeration of highly dispersed powder particles. The high reactivity of the powders requires using a modified scheme of hydrogen treatment to prevent their oxidation: heating to a temperature of 600 °C under a hydrogen pressure of 0.25 MPa, followed by its reduction to 0.05...0.07 MPa and continued heating to 760 °C. The experimental results of the research made it possible to develop an understanding of the effect of complex doping of Zr and Fe on the change in the phase composition and microstructure of ferromagnetic alloys based on the Nd2Fe14B compound as a result of hydrogen treatment. An experimental database was created to develop an algorithm for computer prediction of magnetic properties of the Sm-Co system ferromagnetic alloys using machine learning methods. It was established that simple machine learning methods did not provide sufficient forecast accuracy. However, it was possible to implement it using ensemble methods of computational intelligence, which ensured an increase in the accuracy of the forecast of magnetic properties by 12-15%. Furthermore, the developed machine learning algorithms allow choosing the optimal modes of hydrogen processing to obtain the specified functional properties.


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