CC BY
23GENERATION OF SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS ON THE SURFACE OF SINTERED TITANIUM SPONGE POROUS SAMPLES IN A THIN LAYER BY ELECTRIC IMPULSE
R. P. Golodok*, V. V. Savich, S. V. Poberezhny, O. O. Kuznechik, and E. G. Grigoriev
aO.V. Roman Powder Metallurgy Institute, Minsk, 220005 Belarus 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-2019-10047
It is shown that an electric impulse generates self-propagating high-temperature synthesis on the surface of molded porous permeable materials by electro-impulse sintering of titanium sponge powders. It is localized in the surface layer (from 100 pm for titanium sponge powders with a particle size of 0.63-1.00 mm, up to 400 pm for powders with a particle size of 1.00-3.2 mm). The results of structure and strength properties of the produced samples showed that they are porous, permeable, forming a two-phase system: thin surface oxide-nitride (ceramic) layer-titanium (metal) base.
Introduction
Porous permeable materials of a two-phase thin surface ceramic layer-metal base system produced from titanium powders are promising for the manufacture of filter elements or catalytic systems used in fuel systems of heat engines, technological cycles of chemical industry enterprises, and in power industry [1, 2]. The development and improvement of technologies for producing such materials is a currently important task for powder metallurgy. Practical experience in the research of electro-impulse sintering of titanium sponge powders can be used in order to solve this task [3]. Air generation on the surface of sintered porous permeable materials of self-propagating high-temperature synthesis and the study of the structure and physicomechanical properties of such materials was the objective of this work. Experimental
Titanium sponge powders were used as initial material for producing experimental samples. Their fractional (particle size distribution) and chemical composition are presented in Table 1.
Magnetic-impulse welding equipment Impuls BM was used for sintering of experimental samples. It ensured the conversion of a high-voltage discharge (1.5-2.0 kV) of a capacitor (1200-1500 pF) into an impulse current [2] flowing through titanium sponge powder in a dielectric matrix, and being compressed by electrodes-punches. The modes of electro-impulse effect were chosen in such a way that the used electrodes-punches and dielectric matrix ensured the preparation of experimental samples from initial powders in the form of porous thin-walled (1.5-2.0 mm) rings 25-26 mm in height and 18-20 mm in outer diameter.
Table 1. Chemical composition of titanium sponge powders TU 1715-449-05785388-99
Fraction, Mass Chemical composition, %
Grade fraction, Titanium Mass fraction of impurities
mm minimum Iron Nitrogen Chlorine
TPP-2 -3.2+1.0 80 Base 1.8 0.3 0.3
TPP-5 -1.0+0.63 70 0.5 0.15 0.15
An electric impulse created by the thyristor contactor KT-07 of the resistance spot welding machine MT2201 was used to generate self-propagating high-temperature synthesis on the surface of the molded experimental samples. The resistance welding regulator RKS-801 allowed changing parameters of the electro-impulse effects that were selected in such a way as to provide electrodes-punches with necessary for the generation of self-propagating high-temperature synthesis electrothermal contact with the end faces of the experimental samples.
The surface and structure of the initial powder, as well as the surface structure of the sintered experimental samples were investigated using a Mira scanning electron microscope (Tescan, Czech Republic) and a MeF-3 optical microscope (Reichert-Jung Optische Werke, Austria). The phase composition of the chemical elements of these surfaces was investigated using an INCA Energy 350 X-ray micro analyzer (Oxford Instruments Analytical, United Kingdom).
The permeable properties of experimental samples were investigated on test facility for porous permeable materials [4, 5], and the strength properties were investigated using a Instron 1196 universal test machine (USA). Results and discussion
SEM images of particles of titanium sponge powders are shown in Fig. 1.
(a) (b)
Fig. 1. Particles of the initial titanium sponge powder: (a) TPP-2; (b) TPP-5.
After electro-impulse sintering of titanium sponge powders, experimental samples were produced (Fig. 2a), which were in the form of rings (Fig. 2b) and had a gray metallic color and a porous surface.
(a) (b)
Fig. 2. (a) Experimental samples and (b) state of their surfaces after electro-impulse sintering of titanium sponge powders.
During the electro-impulse effect, the color of the surface changed on the sintered experimental samples from gray to dark gray and then from crimson to bright orange. After the end of the electro-impulse effect on the experimental samples, the appearance of two burning
fronts, having bright yellow and turning white in the contact zones of their end surfaces with electrodes-punches. These fronts moved towards each other from end surface to end surface through the sample.
After the cessation of burning, the experimental samples retained their original shape and their surfaces had a predominantly white-orange color (Fig. 3). The color change indicated the formation of a new substance phase on the surface of the coating.
(a) (b)
Fig. 3. (a) Experimental sample and (b) state of its surface after the generation of self-propagating high-temperature synthesis.
A new phase formed after the end of self-propagating high-temperature synthesis in the surface layer and its interface with the primary one (the lower part of Fig. 4c) are clearly visible in Fig. 4b and in the upper part of Fig. 4c. The results of the study using micro X-ray spectral analysis of surface layers to a depth of 1.8 mm of experimental samples (Fig. 5) have showed that the layer of the new phase can reach a thickness of 100 pm for samples from powder TPP-5 and up to 400 pm for powder TPP-2 consisting of such chemical elements as titanium, oxygen and nitrogen. Thus, a thin layer of new formed phase after self-propagating high-temperature synthesis can be considered as oxide-nitride ceramics.
SEMI.1AG.S00« Digital Mkiotcopy Imaging H »»C StMMAO MO. D.fl«- M.c-o»cop, Im.png H
(a) (b) (c)
Fig. 4. The appearance of the surface of the original sample (a) and the new phase formed in the surface layer (b) and its interface (c) with the primary one (shown by arrow).
Fig. 5. Aliasing of the micro X-ray spectral analysis of the studied surfaces: brown and yellow colors correspond to the initial state of the surface, and the red line corresponds to the final state.
The results of the study of permeability and strength properties of experimental samples are presented in Table 2.
Table 2 - Permeability and strength properties of the studied materials_
Type of titanium p°re size, ^m Coefficient of Porositv 0/ Compressive
sponge powder Dmax Daverage permeability K1013, m2 y 0 strength, MPa
After electro-impulse sintering TPP-2 317-318 219-220 720-722 53-56 100-103
TPP-5 174-175 128-130 369-371 45-47 118-120
After self-propagating high-temperature synthesis
TPP-2 309-312 213-215 680-684 48-50 112-115
TPP-5 165-168 115-117 330-334 41-43 126-130
Research results in Table 2 showed that the used modes of electro-impulse sintering of titanium sponge powders had provided porous permeable materials, which can be used [4, 5] due to their characteristics for the manufacture of promising filter elements of pneumatic and hydraulic drive systems. The use of an electric impulse to generate self-propagating high-temperature synthesis on the surface of sintered samples leads to a decrease in their permeability properties by 14-16% while simultaneously increasing the strength properties by the same amount. The microstructure of materials presented in Figs. 3-5 is a two-phase system, where a thin outer surface layer is represented as nitride oxide ceramics, and the internal volume, including interparticle contacts, remains metallic titanium. As follows from the analysis of references [1, 2], such materials can be used to manufacture elements of filtering or catalytic systems used in fuel systems of heat engines, in technological cycles of chemical industry enterprises, and in power industry.
Conclusions
1. The use of electro-impulse sintering of titanium sponge powders and an electric impulse to generate self-propagating high-temperature synthesis on the surface makes it possible to produce porous permeable composite materials of a two-phase system, where a thin (up to 400 |im) surface layer is represented as nitride oxide ceramics, and the metal base is sponge titanium. The strength and permeability properties of these materials depend not only on the modes of electric impulse effect, but also on the fractional composition of the initial powders.
2. Using electro-impulse sintering of titanium sponge powders with particle sizes of 1.0-3.2 mm and self-propagating high-temperature synthesis in a thin layer of a porous sample, the following properties are achieved: average pore size is 219-220 p,m, coefficient of permeability is (680-684) K1013 m2, porosity is 48-50%, and compressive strength is 112-115 MPa.
3. Using electro-impulse sintering of titanium sponge powders with particle sizes of
0.63-1.0 mm and self-propagating high-temperature synthesis in a thin layer of a porous sample, the following properties are achieved: average pore size is 128-130 |im, coefficient of permeability is (330-334) K1013 m2, porosity is 41-43%, and compressive strength is 126-130 MPa.
4. According to permeability and strength properties, these materials are promising for the production of filter elements or catalytic systems used in the fuel systems of heat engines, in the technological cycles of chemical industry enterprises, and in power industry.
1. V.V. Savich, A.M. Andreev, O.O. Kuznechik, R.P. Golodok, The state and prospects for the development of hydrogen energy and the role of catalyst support materials and getter
materials used in it, New materials and technologies: powder metallurgy, composite materials, protective coatings, welding: materials of the 12th International Scientific and Technical Conference, Minsk: Navukovaya Dumka, 2016. pp. 289-293.
2. A.M. Taraykovich, G.A. Sheko, O.O. Kuznechik, R.P. Golodok, V.E. Romanenkov, T.E. Eutukhova, Production of a promising catalyst support for high-temperature catalytic reforming from titanium sponge powders by electro-impulse sintering and plasma-chemical synthesis, Powder Metall.: Inter-Republican Interdepartmental Collection of Scientific Papers, 2016, no. 39, pp. 77-81.
3. R.P. Golodok, V.V. Savich, A.M. Taraykovich, S.V. Coast, OO Grasshopper, A.O. Konakov, T.N. Vorobyov, Production of permeable materials from titanium sponge with their subsequent surface modification for use in catalytic processes under highly-concentrated flows of electro-impulse energy in air, Powder Metall.: Inter-Republican Interdepartmental Collection of Scientific Papers, 2017, no. 40, pp. 118-124.
4. V.M. Kaptsevich, New filtering materials and prospects for their use, Minsk: Belarusian State Agrarian Technical University, 2008, p. 232.
5. L.P. Pilinevich, Porous powder materials with an anisotropic structure for filtering liquids and gases, Minsk: Tonpiq, 2005, p. 252.
