SIDOROV Evgeny Vladimir State university

Spoluautoři PIKUNOV M.V., DRÁPALA J.

There is a large group of commercial alloys corresponding to definite stoichiometric compositions (intermetallic compounds) which ensure the best physical properties. To such alloys belong for example magnetic SmCo5, Nd2Fe14B, magnetostriction TbFe2 alloys and others. Such alloy compositions are mainly obtained by the melting technique with subsequent solidification of the melt. Crystallization of such alloys is going on as a rule with the formation of solid phases of other compositions in the beginning, and the required intermetallic compounds form by the peritectic transformations in the middle and lower parts of the equilibrium crystallization range. Because of the restricted diffusion in the solid phase (DS≈10-12 m2/s) as compared to the liquid phase (DL≈10-9 m2/s), the solid phase compositions, which were formed at first, at the temperature decrease have no time to change their compositions to new equilibrium ones, accordingly the liquid phase enriches in low melting point components and the crystallization process ends at the lower non-equilibrium solidus temperature. As a result of such process, when the crystallization ends, besides the equilibrium phase the presence of non-equilibrium phases is revealed in the alloy microstructure, some of which are retained even after the homogenizing annealing. Accordingly the desirable physical properties of products are not the highest possible. In the present work crystallization processes of alloys of stoichiometric compositions with peritectic transformations in the Al-Ni, Cu-Sn, Ni-Sn systems were investigated. It was found out that the peritectic transformation is not realized completely in a wide cooling rate range. The transformation process itself takes place in a temperature range, and when the crystallization ends, the solid phase, which was formed at the beginning before the peritectic transformation, is retained, as well as the phases formed below the equilibrium solidus temperature. The investigations made it possible to develop a new technique of the controlled solidification of the melt and to obtain castings with the single phase microstructure corresponding to the required stoichiometric composition.

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