Institute of Metallurgy of Ural Branch of Russian Academy of Sciences, Ekaterinburg, Russia:

L. E. Bodrova, Senior Researcher, e-mail: berseneval@mail.ru
E. A. Pastukhov, Сhief Researcher
L. A. Ovchinnikova, Senior Researcher
E. Yu. Goyda, Researcher

The existing technologies for production of Cu – Cr (W) electrocontact alloys with a finely dispersed nonporous structure are multistage and/or energy-consuming. In this paper, we propose a more economical method of their obtaining, based on the potential for self-dispersion of phases. In the Cr – W system, this feature is conditioned by the presence of a continuous series of decay regions of (W, Cr) (W) + (Cr) solid solutions in a wide concentration range. The alloys of Cu – 10%Cr – 10%W initial composition were obtained by impregnating a noncompacted or compacted mixture of Cr and W powders with copper melt. The formation of solid solutions and their subsequent decomposition was intensified through low-frequency treatment of solid-liquid compositions. The treatment temperature (1300 ^оC) was below 100 deg below the equilibrium line of (W, Cr) solid solution formation, whilst the treatment time was 10 min. The phase composition, lattice parameters of phase, macro- and microstructure and elemental composition of the phase components were studied regarding the obtained alloys. The macrostructure of alloys is characterized by variable phase ratio over the height of the ingot. A two-layer composite structure with an enrichment of the lower layer to ~50vol.% (Cr + W) was formed without prior compaction of powders. The alloy with a content of ~90–95vol.% (Cr + W), surrounded from all sides by α-Cu, was obtained by a copper molten impregnation of compacted powders. The porosity of the alloys was lower than 2%. The analysis of the structural characteristics of the alloys revealed that the formation of (W, Cr) solid solutions and α-Cu and their subsequent disintegration occurred in the process of obtaining alloys. The primary W and Cr in alloys were not detected. Tungsten dimensions of secondary generation in both alloys were 1 μm, which is several times lower than the initial sizes. Compacting of a powder mixture prior to impregnation intensifies diffusion and chemical processes, which leads to a more complete decomposition of solid solutions. Formation of decay structures with fine-grained precipitates of secondary tungsten in Cu – Cr – W alloys can be activated by low-frequency vibrational activity on “Cu-mixture of W and Cr powders” compositions. This method significantly reduces the costs of energy and time when obtaining such alloys.
This work was carried out within the state task of the Institute of Metallurgy of Ural Branch RAS (subject No. 0396-2015-0078) using the equipment of the Center “URAL-M”.

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