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17XV International Symposium on Self-Propagating High-Temperature Synthesis
HIGH TEMPERATURE GAS EXTRUSION OF POWDER MIXTURE Ni + Al
F. F. Galiev*", I. V. Saikov", M. I. Alymov", V. D. BerbentsevA, A. V. GulyutinA, V. I. BugakovA, N. V. Sachkova", and S. V. Konovalikhin"
aMerzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Moscow, 142432 Russia
bVereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow, 142190 Russia *e-mail: fanis.galiev@mail.ru
DOI: 10.24411/9999-0014A-2019-10044
The method of high-temperature gas extrusion (HTGE) is one of the methods of metal forming, in which the material is subjected to severe plastic deformation by extrusion under high hydrostatic pressure of an inert gas. This method involves local heating in the deformation zone. HTGE also allows to change the temperature and pressure during extrusion, which in turn allows to adjust the rate of deformation. As noted in [1], this method can be used to process brittle metals, powder and composite materials. Powder materials are treated with high-temperature gas extrusion in 2 ways. The first method includes pre-pressing, sintering, and extrusion. The second is placing the powder into a thin-walled metal tube, the ends of the tube are sealed and extruded together with a powder mixture [1]. This research is devoted to the combination of SHS and HTGE to obtain long-dimensional intermetallic and cermet rods during extrusion of reactive powder mixtures. The second method of extrusion of the powder mixture [1] was used in the experiments. The mixture of Ni-Al with stoichiometric ratio of 68.5:31.5 was taken as the model system. Steel rod 10 mm in a diameter with a drilled blind hole was used as a shell, which was filled with pre-compressed tablets of the powder mixture. The scheme of the installation of high-temperature gas extrusion is shown in Fig. 1.
Fig. 1. The scheme of the installation of high-temperature gas extrusion. 1 high pressure vessel, 2 inlet gas pipeline, 3 sample for extrusion, 4 Ni-Al compacted powder, 5 plug with axial drilling for thermocouple, 6 gas extrusion matrix, 7 heater, 8 thermocouple, 9 pins for temperature measurement.
HTGE was carried out in the following mode: gas pressure 200 MPa, the temperature of the beginning of extrusion 780°C. The diameter of the matrix was 6 mm. Thus, the degree of deformation was 64%.
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The image of the polished sample of the resulting rod is shown in Fig. 2a. The obtained samples were characterized by X-ray phase analysis using a Dron-3M diffractometer (CuXa radiation) with an angle step of 0.02° and an exposure time for 1 s. The microstructure was studied using optical microscope and Zeiss Ultra plus Field Emission scanning electron microscope equipped with an INCA 350 Oxford Instruments X-ray microanalyzer. Quantitative X-ray phase analysis (according to the Rietveld Method) shows that the sample subjected to gas extrusion consists of about 50% NiAl intermetallic, Ni3Al, and Ni2Ab. No spectra of Ni and Al were detected. The microhardness of the sample ranged from 585 to 1150 HV0.1, depending on the indentation zone. The SEM studies showed that the structure of the synthesized sample is heterogeneous and consists of zones with different chemical compositions. According to the Ni-Al phase diagram [2], such zones correspond to various intermetallic compounds (Ni2Ab, NiAl, Ni5Al3, Ni3Al) and Al solid solution in pure Ni. The heterogeneity of the phase composition is associated with incomplete reaction of components. The microstructure of the sample is shown in the Fig.2 b.
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Thus, a high-temperature gas extrusion of reactive powder mixture was carried out on the Ni-Al model system, and long cylindrical rods of Ni-Al intermetallic in a steel shell were obtained.
1. V.D. Berbentcev, M.I. Alymov, S.S. Bedov, Consolidation of nanopowders by gas extrusion, Russ. Nanotech., 2007, vol. 2, nos. 7-8, pp. 116-120.
2. N.P. Lyakishev, State diagrams of double metal systems, M.: Engineering, 1996, vol. 1, 992 p.
