CC BY
25ÏSHS2019
Moscow, Russia
INTEGRATED PROCESS SHS-REMELTING-PREP FLOW SHEET PRODUCTION OF NiAl-Fe COMPOSITE MICROGRANULES FOR THE
ADDITIVE TECHNOLOGY
V. V. Sanin*", M. R. Filonov", E. A. Levashov", V. I. Yukhvid0, Zh. A. Sentyurinac,
and A. I. Logachevac
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 cJSC Kompozit, Korolev, 141070 Russia.
*e-mail: sanin@misis.ru
DOI: 10.24411/9999-0014A-2019-10148
Granular metallurgy is one of the most effective ways to make products of brittle and hard-to-machine materials. Making products of a complex shape by AT requires a source powder, where microgranules have regular spherical shape and regulated and rather narrow particle-size distribution. One urgent problem of today is the need to develop brand-new technologies for the production of microgranules (powders) and metal-powder compositions in Russia, tailored to address its environmental and energy-saving challenges. The alloyed intermetallic NiAl is a promising basis for lightweight high-temperature structural materials for use in aerospace industries. Earlier papers [1, 2] described the difficulties and problems of making electrodes from complex-alloyed intermetallic (CompoNiAl) alloys by combining SHS and VIM methods.
This paper proposes a brand-new combined sequential method for making composite (CompoNiAl) spherical microgranules. The proposed process consists of the following steps: (1) synthesis of CompoNiAl intermetallic alloy of a regulated chemical composition by the centrifugal SHS method; (2) machining of synthesized SHS materials (CCM) by vacuum induction melting or inert medium melting, then casting in special tube mold tube to make a shell; (3) centrifugally spraying (PREP) of produced steel-shell electrode to make spherical composite microgranules. This method can produce composite intermetallic microgranules consisting of remelted alloy and shell material (Fe, Ni, etc.). The research team originally ran a series of experiments to optimize the synthesis of the multicomponent intermetallic alloy CompoNiAl by SHS metallurgy [1, 3]. The high gravity of the centrifugal unit would scatter the combustion products during such synthesis, intensify the separation of metal phase (the alloy) from oxide phase (corundum), and facilitate the homogenization of the alloy, producing a finer-grained structure. Figure 1 shows experimental ingots produced under various overloads (from 1 to 300 g).
1g 15g 50g 150g 300g
Fig. 1. Overall view of samples obtained under various overloads (g).
XV International Symposium on Self-Propagating High-Temperature Synthesis
Ingots synthesized at 150 to 300 g had no visible inclusions or residual porosity. All the specimen produced at the specified overload looked solid-cased and had two pronounced layers: target alloy and oxide layer (AhO3).
We preliminarily studied the two-phase area of the synthesized SHS alloy and identified its melting point. To that end, we adjusted the attenuation decrement (the logarithm of the preceding-to-previous amplitude ratio) of the HTV machine [3, 4]. This method is suitable for study of phase transitions, construction of various functions, and for analyze of influence of heating parameters and exposures on the coagulation and dissolution of the strengthening phases. The next step was to use vacuum induction melting (VIM) of the SHS-produced CompoNiAl workpieces for casting in steel tubes of various diameters.
Melt and cast of the alloy in the molds of various diameters were carried out (Fig. 2). The optimal option was to use a cylindrical mold with 6 mm thick walls. Raising the mold wall thickness to 6 mm produced defect-free, holistic, layered electrodes from the intermetallic alloy in a steel shell without any chemical impact or "blurring" the inner wall (Fig. 2c). CompoNiAl does not chemically react with the steel tube mold. The alloy is retained due to friction as well as due to the fact that CompoNiAl and steel tube are close in the coefficient of thermal expansion (CTE). The integrity, lack of inner pores and cavities in the produced layered electrode are confirmed by ultrasonic testing (Fig. 3).
(a) (b) (c)
Fig. 2. Experimental samples of pipe-molds with different wall thicknesses: (a) 3 mm, (b) 5 mm, and (c) 6 mm.
(a)
(b)
Fig. 3. Analysis of the UT: (a) 3D visualization of the integrity of the inner part of the layered electrode (alloy CompoNiAl); (b) analysis of the integrity of the shell (steel pipe)
The final stage of the work is the approbation of sputtering of the obtained CompoNiAl + Fe layered electrode, obtaining and studying the final product in the form of spherical composite microgranules.
During the plasma rotating electrode process (PREP), under the action of centrifugal forces, the melt in the film moves from the center to the periphery of the consumable electrode, then accumulates on the edge with a Fe-shell and fuses with it. Thus, the compositions are mixed
■SHS 2019 Moscow, Russia
with the formation of a composite microgranule.
The image of composite microgranules obtained is presented in Fig. 4b. Most microgranules have a spherical shape. There are no satellite particles on the surface of the granules, which is one of the advantages of PREP. Also microcrystals contain no crystallization defects (pores).
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Fig. 4. (a) Fractional composition of composite microgranules; (b) SEM image of microgranules; (c) microgranule component distribution map.
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Particle-size distribution is shown in Fig. 4a. The proposed method was able to produce microgranules of different size. Most of the composite microgranules are within 50 to 150 ^m, which suits the needs of AT products. Figure 4c shows the structural component distribution maps. The basis here is the dendritic NiAl grains distributed across the entire microgranule with an average dendritic-branch size of 2 to 15 ^m. Fe and Co are distributed throughout a microgranule.
1. Yu.S. Pogozhev, V.N. Sanin, D.M. Ikornikov, D.E. Andreev, V.I. Yukhvid, E.A. Levashov, Zh.A. Sentyurina, A.I. Logacheva, A.N. Timofeev, NiAl-based electrodes by combined use of centrifugal SHS and induction remelting, Int. J. Self-Propag. High-Temp. Synth., 2016, vol. 25, no. 3, pp. 186-199.
2. A.A. Zaitsev, Zh.A. Sentyurina, E.A. Levashov, Yu. S. Pogozhev, V.N. Sanin, P.A. Loginov, M.I. Petrzhik, Structure and properties of NiAl-Cr(Co,Hf) alloys prepared by centrifugal SHS casting, J. Mater. Sci. Eng. A, 2017, pp. 463-472.
3. V.V. Sanin, Yu.A. Anikin, V.I. Yukhvid, M.R. Filonov, Structural heredity of alloys produced by centrifugal SHS: influence of remelting temperature, Int. J. Self-Propag. High-Temp. Synth., 2015, vol. 24, no. 4, pp. 210-214.
4. M.R. Filonov, Yu.A. Anikin, Yu.B. Levin, Fundamentals for production of amorphous and nanocrystalline alloys by melt spinning technique, Moscow: Izd. MISiS, 2006, 327 p.
