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30iSHS 2019
Moscow, Russia
CHARACTERISTICS OF THE CAPILLARY SPREADING OF COPPER ON THE POROUS FRAMEWORK OF THE PRODUCTS OF THE SHS
MIXTURE OF Ni-Al
R. M. Gabbasov*", A. M. Shulpekov", and V. D. Kitler"
aTomsk Scientific Center, SB, RAS, Tomsk, 634055 Russia.
*e-mail: [email protected]
DOI: 10.24411/9999-0014A-2019-10043
The use of technological combustion for synthesis of high-temperature cermet materials is hampered by insufficient knowledge of the physicochemical processes in the high-temperature synthesis wave. The effect of capillary metal melt flows on non-isothermal spatial waves of chemical transformation in porous heterogeneous systems has been studied even less. A review of the existing literature shows that the description of heat and mass transfer in a porous medium remains fragmentary for a number of practically important applications [1]. The classical analysis of the kinetics of the impregnation of porous bodies with melts encounters considerable difficulties with intensive heating, changing the particle size of the porous medium and the course of a chemical reaction [2]. Melting the reagents and wetting the more refractory components of the mixture with the melt increases the heat release rate in the heterogeneous reaction and, accordingly, increases the temperature in the zone of chemical transformation. At the same time, the rate of thermocapillary flow and convective heat transfer increase. The mechanism for the implementation of thermocapillary convection - the Marangoni effect in a heterogeneous reaction medium has not been studied enough. The results of the study, on the one hand, are of great fundamental importance for the development of the theory of nonlinear wave processes in heterogeneous systems, and on the other, practical for the development of technologies for the synthesis of metal-ceramic and composite materials. In the above works it was assumed that the impregnation material and the carcass material do not interact with each other and can be considered as independent phases. However, as was shown by the authors on the example of the combustion of Ti-Si-C systems with nickel and copper, the impregnation material interacts with the framework material, which leads to a change in the phase composition of the material [3, 4]. In this paper, as an extreme case, the Ni-Al-Cu system was taken for the study, in which we initially assumed a strong chemical interaction between the components. Due to the proximity of the atomic radii of Ni and Cu in this binary system, a continuous series of solid solutions is formed. Therefore, we assumed that the process of formation of a porous skeleton and its impregnation can proceed simultaneously.
The aim of the work was to study the processes occurring during SHS of Ni-Al system while simultaneously interacting with copper wire, as well as the macro- and microstructure, phase composition of the samples.
For the study, Ni (PNC1-L7) and Al (ASD-4) powders were used. The powders were mixed in a ratio of 68.5 wt % Ni and 31.5 wt % Al (NiAl stoichiometry). The resulting mixture was held for 3 h in a vacuum furnace at a temperature of 200°C. The mixture was pressed into a cylinder with a diameter of 15 mm. The relative density of the samples, depending on the pressing force, was in the range of 0.4-0.6. In a series of experiments, a copper wire 1 mm in diameter was placed along the sample axis. The initiation of the reaction was performed using a tablet of a mixture of 70 wt % Ti with 30 wt % B, which was heated by an electric spiral. The experimental setup is shown in Fig. 1. To record thermograms, thermocouples of the brand WRe 5/20 were connected to an ADC and a personal computer. The speed of propagation of
XV International Symposium on Self-Propagating High-Temperature Synthesis
the combustion wave front was determined using a high-speed Motion ProX-3 video camera. The phase composition of the synthesis products was determined on a portable tabletop X-ray device RIKOR (CoKa radiation) at the Tomsk common use center (SB, RAS). Microstructural studies were performed using an optical microscope (Axiovert 200M, Karl Zeiss). The copper concentration in the samples was determined using local X-ray microanalysis (EDAX).
High video camera
Fig. 1. Experimental setup.
The dependence of relative density on the pressing force consists of three sections with different inclinations relative to the x axis (Fig. 2a). This may indicate the existence of three different macrostructures in the powder mixture. The front propagation velocity monotonously increases with an increase in the relative density of the sample, while the dependence of the maximum temperature has a maximum at a relative density of 0.43 (Fig. 2b).
(a) (b)
Fig. 2. (a) Relative density of samples at different pressing forces, (b) speed (curve 1) and maximum temperature of the combustion wave front (curve 2).
The distribution of copper in the radial direction from the center of the sample was studied by the method of local X-ray microanalysis. The sample in this case was a cylinder made of a pressed mixture of Ni and Al with a diameter of 15 mm and a height of 10-12 mm with copper wire 1 mm in diameter located along its axis. After synthesis, on all samples except one with a density of 0.4, a cylindrical cavity with a diameter of about 1 mm is formed in place of the copper wire. Copper is redistributed in the radial direction, and its concentration decreases from the center to the edge of the sample (Fig. 3a). And the depth of its penetration into the sample increases with an increase in the relative density of the sample (Fig. 3b). Figure 4a shows a thermogram for a sample with pressed copper wire, the thermocouple in this case was located so that the junction was in direct contact with the copper wire. The initial temperature surge is associated with a higher thermal conductivity of copper relative to the thermal conductivity of the original mixture. The temperature minimum following it coincides with the melting point of copper (T = 1080°C). A smooth rise in temperature is probably due to the interaction of the copper melt with the porous NiAl framework. The above assumptions are confirmed by high-
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Moscow, Russia
speed video. According to X-ray powder diffraction data, a solid solution of copper in NiAl is formed in the area of copper spreading, which confirms the interaction of copper and NiAl.
(a) (b)
Fig. 3 (a) The distribution of copper along the radial axis of the sample, (b) the depth of penetration of copper depending on the relative density of the sample: 1 0.4; 2 0.47; 3 0.51; and 4 0.57.
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(a) (b)
Fig. 4. (a) Changes in temperature in the copper wire, (b) XRD patterns of samples with different contents of copper powder in the mixture.
Thus, it was found that with an increase in the relative density in the range of 0.4-0.6, the depth of penetration of copper increases. The capillary spreading of copper over the porous NiAl framework is carried out by melting copper and the interaction of the melt with the forming porous framework with the formation of a solid solution of copper in NiAl.
This work was supported by the Russian Foundation for Basic Research (project no. 19-0300081) and as part of a state assignment for the Tomsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences (project no. 0365-2019-0004).
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4. A.P. Amosov, E.I. Latukhin, A.M. Ryabov, E.R. Umerov, V.A. Novikov, The application of the SHS process for the manufacture of copper-titanium silicon carbide composite (Cu-Ti3SiC2), IOP Conf. Ser., 2018, vol. 1115.
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