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20■SHS 2019 Moscow, Russia
STRUCTURE AND PHASE COMPOSITION OF Nb-Si-C-BASED
COMPOSITES PREPARED BY SHS METHOD
R. M. Nikonova*", N. S. Larionova", V. I. Lad'yanov", B. E. Pushkarev",
and A. V. PanteleyevaA
aUdmurt Federal Research Center, Ural Branch, Russian Academy of Sciences,
Izhevsk, 426067 Russia bUdmurt State University, Izhevsk, 426034 Russia *e-mail: [email protected]
DOI: 10.24411/9999-0014A-2019-10109
Modern heat-resistant alloys (HRAs) applied in manufacturing shoulder-blades of gasturbine engines are only able to endure temperatures up to 1100-1150°C, which is 80-85% of their melting temperature [1]. Usually nickel alloys are used as heat-resistant alloys. Additional doping of nickel with high-melting elements results in an increased density of the material and makes the alloys costly. As an alternative Nb-Si-based composite materials [1-5], which have lower density and high melting temperatures in comparison with Ni-HRA, are considered promising. Rotor shoulder-blades from NbSi-based materials will endure the temperature up to 1350°C, which is 200-250oC higher than the temperatures in case of Ni-HRA [1]. It is assumed that high heat resistance of Nb-Si materials can be achieved at the expense of the combined strengthening of Ni-Si-based materials by intermetallides NbxSiy and carbide NbC. With account of high melting temperature (~ 2500oC) and low density (~ 7 g/cm2), Nb5Si3 is the best variant of all the other silicides [1].
Nb-Si-based ceramic materials are mainly produced by hybrid spark plasma sintering of powders, vacuum arc melting, and by precision investment casting [5-7]. A promising technique for preparation of alloys is self-propagating high-temperature synthesis (SHS). It seems highly attractive due to its simplicity, low energy consumption, and high purity of combustion products.
The Nb-Si-C alloy described in this paper was prepared by SHS. The sample was synthesized from the mixture of Nb2O5 + SiC + aluminum-magnesium powder (AMP) in Ar atmosphere (Pa = 80 atm). For better wetting and hence reactivity cryolite was added. To increase exothermicity potassium perchlorate was introduced.
To determine phase composition, a DRON-6 diffractometer with Fe^a radiation and a MISA software package were used. Neophot-21 optical microscope, Philips SEM-515 scanning electron microscope equipped with a Genesis 2000 XMS energy-dispersive X-ray microanalysis system, and FEI Inspect S50 scanning electron microscope were used to study the microstructure of sample. Quantitative chemical analysis to measure the content of Si, Mg, and Al was performed by atomic-emission spectroscopy using a Spectroflame Modula S scanning ICP spectrometer. To measure carbon content, the sample was placed in an Exan carbon analyzer where it was combusted in oxygen flux.
XRD pattern of obtained sample is seen in Fig. 1 to contain two basic phases Nb5Si3 and NbC, and a small amount of NbSi2.
Figure 2 shows the SEM images of fracture and grinding face. It can be seen that the alloy obtained was represented by a dense uniform structure with a grain size of 5-20 ^m (Fig. 2).
Spot analysis of the sample surface confirmed that the composite mainly consisted of intermetallide Nb5Si3, carbide phase NbC, and a small amount of intermetallide NbSi2 (Fig. 3).
Thus, the results obtained evidence the possibility of using SHS to prepare the composite Nb-Si-C strengthened by the combination of intermetallides Nb5Si3, NbSi2, and carbide NbC.
XV International Symposium on Self-Propagating High-Temperature Synthesis
à -JL_l _ s ,1 Ii J.--,,„», ,, .....1,il 1 ...
| NbSi2 III . . il . . 1 1 . i . i .
l 1 1 NbC
...........,......JL 1 Nb5 Si3 Tiilin'.....iiiii'iiiiiiiifinlf Ii'iliil......'I-If.....il'......Illirt l'i
30 40 50 60 70 80 90 100 110 120 29, deg
Fig.1. X-ray diffraction pattern of obtained Nb-Si-C composite.
^rv^Jt-: v
r j^ycs \
v. •• ■ . ■ j
Fig. 2. Destruction surface of the alloy. Scanning electron microscopy.
èw^ÊÊ^mÊÊ M
Content of elements, wt % Estimated
№ C O Mg Al Si Nb Phase
1 4.04 1.62 0 0.66 15.38 78.30 Nb5Si3
2 18.34 2.87 0 0.11 0.80 77.88 NbC
3 14.19 2.26 0.22 3.44 30.3 49.59 NbSi2, NbC
1 2
h ■ M„ LAJ l
3
Fig. 3. General view of the sample surface and energy spectra obtained from different sites. X 2500
ISHS 2019 Moscow, Russia
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