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24COMBINED METHOD OF PRODUCING AN ALLOY OF IMMISCIBLE ELEMENTS Cu70Fe30 WITH SUBMICRON STRUCTURAL COMPONENTS
V. V. Sanin*", M. R. Filonov", Yu. A. Anikin", E. V. Kosticina", V. I. Yukhvidfi, and D. M. IkornikovA
aNational University of Science and Technology MISiS, Moscow, 119049 Russia bMerzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Moscow, 142432 Russia *e-mail: [email protected]
DOI: 10.24411/9999-0014A-2019-10146
Limited-solubility (LS) alloys have long been impossible to produce in a liquid or solid state by conventional metallurgical methods. The main technological difficulties metallurgists encounter when making such alloys are the significant difference in the unit mass and melting points, as well as a strong tendency to delamination in liquid or solid state in a wide range of temperatures and concentrations.
Copper-iron alloys can be classified as LS alloys [1, 2]. Their phase composition is quite simple, as it contains pure components. This makes such alloys interesting [1]. An optimal production technology can produce a final product that combines the properties of the pure components in a proportion suitable for this or that application. For instance, in Cu-Fe alloys, diamagnetic copper shows high electrical and thermal conductivity, while ferromagnetic iron is stronger than copper. A specifically tailored alloy structure will produce either a highly conductive product like copper with the strength of iron; or a hard-magnetic material with the ductility of copper alloys [1].
In this paper, reaching the necessary operating properties of Cu-Fe alloys is associated with a specific dispersion, in which the iron (Fe) components must be uniformly distributed throughout the entire copper (Cu) matrix while being ellipsoid in shape and 70 to 200 nm in size.
Previously published papers [3] compare the morphological and mechanical properties of the produced Cu70Fe30 alloy. An alloy produced conventionally by VI melting had a dispersed structure; however, the distribution of Fe particles in the Cu matrix was uneven. On the other hand, similarly composed SHS alloys were characterized by a uniform distribution of the structural components while matching the pre-configured particle size; however, the presence of gases (O2 = 0.046; N2 = 0.0021 wt %) affected the quality of the machined products.
To attain the goals, the research team has successfully tested a new combined method that consists of multiple steps:
(I) to produce cast-charge materials (CCM) of Cu70Fe30 by SHS;
(II) to optimize the CCM remaking parameters;
(III) to carry out single-step VIM for producing a long rod;
(IV) to carry out machining and heat treatment, which includes drawing.
The studied alloy was Cu70Fe30. We performed a series of experiments to produce a Cu70Fe30 alloy by SHS metallurgy, then optimized the synthesis conditions and studied how overloading would affect the process parameters.
Chemically, the synthesis could be represented as follows:
Cu2O + Fe2O3 + Al ^ [Cu-Fe] + AhO3 + Q
where the component weights are selected based on the calculated mass balance of the specified
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mixture components, as well as on the actual composition analysis.
Cu70Fe30 alloy were synthesized under various experimental configurations. Figure 1a shows how overloading affected the main macrokinetic parameters of the synthesis process. Figure 1b illustrates the overall view of alloys prepared under different overloads. At low overloads of < 15 g, the shape of alloys is different. The incomplete separation of phases in such specimens made it difficult to identify the metal phase (the target product) from the oxide phase (aluminum oxide); as a result, the ingots were inconsistently top-coated with corundum. Unlike the specimens synthesized at < 30g, the ingots produced under 50g looked solid and did not have explicit macrostructural defects.
(30g) (50g)
(a) (b)
Fig. 1. (a) Dependence of overload (n = a/g) on burning rate (U), scatter of the mixture (^1), and complete yield of the metal phase into the ingot (^1); (b) overall view of the samples obtained at various values of overload.
Figure 2 shows that the alloy has a dispersed structure with a uniform distribution of drop-shaped iron (Fe) particles in the copper (Cu) matrix (direct "emulsion"). In [3], the microstructural analysis was presented in detail. It is shown that the Cu7oFe3o SHS alloy is represented by a multimodal hierarchical structure with three levels. Level 1 (Figs. 2b, 2c) is where drop-shaped iron particles (direct emulsion), sized 10 to 30 p,m on average, are evenly distributed in the copper matrix throughout the specimen. Level 2 (Fig. 3c) releases copper (reverse emulsion) inside the drop-shaped iron particles; the particle size ranges from 200 to 400 nm. Level 3 generates nanoscale iron formations in the copper matrix with a size of 20 to 30 nm. (Fig. 3d). Note that the latter are also observed in the copper particles that are produced at Level 2 (Fig. 3e).
(a) (b) (c)
Fig. 2. Microstructure of alloy Cu7oFe3o obtained by the method of SHS metallurgy: (a, b) transverse and (b) longitudinal section.
(d) (e)
Fig. 3. (a) SEM and (b-e) TEM images of structure of the SHS-alloy of Cu70Fe30.
This could be due to the specifics of SHS metallurgy. SHS mixture burns at ~ 2500°C. This melting temperature (unattainable in vacuum furnaces) improves the mutual solubility of Cu and Fe. At the crystallization stage, as the melt cools down, and the solubility limit drops; copper is released as dispersed nanoscale particles.
The next step was to use SHS ingots with uniform alloy component distribution for a singlestage remelting of the Cu70Fe30 alloy so as to remove gases, then cast it into long rods. However, it was important to retain the original SHS alloy structure or at least to closely reproduce the earlier evenly distributed fine-grained structure (Fig. 4).
Fig. 4. (a) Overall view of a lengthy rod made of Cu70Fe30 alloy obtained from a remelted SHS alloy; (b) element distribution map.
This required optimizing the melting parameters on the basis of the alloy structural parameters sensitive to VIM. To optimize the temperature and time settings of VIM, it seemed necessary to analyze the alloy structure and near-solidus and near-liquidus temperatures. To that end, the research team used a high-temperature unit for research into the viscosity of metallic melts (HTV) [3, 4].
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At the final stage, the researchers studied the production of lengthy products from the obtained long rods. The rod was single-drawn to produce longitudinal structurally ordered components. The initial cast rod was drawn through a spinneret along a rectilinear trajectory from 6 mm to 1.7 mm with s = 92%. Figure 5 shows the overall view and microstructure.
(a) 'lb).........."(cf
Fig. 5. (a) Overall view and (b, c) microstructure of the wire specimens: (b) longitudinal and (c) transverse section.
Analysis of the microstructural data collected from a cut along the rod axis, see Figure 5, shows that such structurally ordered materials could well be used for further studies into their magnetism. Iron structural components consist of a multitude of nanoscale iron and copper particles, which forms the early identified multimodal structure that was obtained in the workpiece SHS and retained in remelting, machining, and thermal treatment.
1. X. Yang, C. Jiang, J. Zou, X. Wang, Preparation and characterization of CuFe alloy ribbons, J. Rare Met. Mater. Eng., 2015, vol. 44, iss. 12, pp. 2949-2953
2. T. Mittlera, T. Gresha, M. Feistlea, M Krinningera, U. Hofmannb, J. Riedleb, R Gollea, W. Volk, Fabrication and processing of metallurgically bonded copper bimetal sheets, J. Mater. Proc. Tech., 2019, vol. 263, pp. 33-41.
3. V.V. Sanin, M.R. Filonov, V.I. Yukhvid, Y.A. Anikin, Structural investigation of 70Cu/30Fe based cast alloy obtained by combined use of centrifugal casting-SHS process and forging, J. MATEC Web Conf, 2017, vol. 129, pp. 1-4.
4. M.R. Filonov, Yu.A. Anikin, Yu.B. Levi, Fundamentals for production of amorphous and nanocrystalline alloys by melt spinning technique, Moscow: Izd. MISiS, 2006, 327 p.
