RU2414991C1 - Method of producing ceramic articles with nanostructure - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to powder metallurgy, particularly, to production of ceramic articles with nanostructure by self-propagating high-temperature synthesis (SHS), and extrusion. Articles thus produced may be used as cutting tools, targets for composite coat application, electrodes for electric spark alloying, etc. Exothermic mix containing powders of TiO₂, C, B, Al, Zr, with particle size of 1-100 mcm is used to form the billet. Produced billet is heated to 100-150°C, reaction of combustion in SHS conditions is initiated at 0.01-0.5 MPa, and combustion products are extruded. Note here that ratio of components for production of target products is as follows in wt %: TiB₂ - 22-25; TiC - 20-30; 35-44.5 - (Al₂O₃-ZrO₂) eut.; (ZrO₂)β making the rest.

EFFECT: ceramic articles that feature high wear-, heat- and corrosion resistance, micro hardness and low porosity.

1 dwg, 1 tbl

Description

The invention relates to the field of powder metallurgy, in particular for the production of ceramic products with a nanoscale structure by the method of combining self-propagating high-temperature synthesis (SHS) and extrusion.

Traditional methods for producing technical ceramics are known, which consist in hot pressing fine powders and holding them at high temperatures for a long time. The disadvantages of these technical solutions are a large number of technological operations, many of which are complex, energy intensive and time consuming, and the resulting ceramics has a micron structure and has low mechanical properties. (Balkevich VL Technical ceramics: Textbook for technical colleges. - 2nd ed., Revised and additional - M .: Stroyizdat, 1984. - 256 p.)

Improving the mechanical properties of ceramics is possible by obtaining nanoscale structural components.

A known method for the synthesis of non-metallic SHS nitrides, from which powders with a submicron structure are obtained by chemical dispersion (Borovinskaya I.P., Ignatyeva T.I., Vershnikov V.I., Miloserdova OM, Semenova V.N. - and nanosized powders of titanium carbide and tungsten carbide. Powder metallurgy. - 2008. - No. 9/10. - S.3-12).

There is a method in which the production of submicron powders of titanium diboride and nanometric powders of nickel aluminide occurs by fulfilling special conditions: dilution of a charge with a low-melting diluent and long-term machining (Merzhanov A.G. Combustion processes and synthesis of materials. / Ed. V.T. , A.V. Khachoyan, Chernogolovka: ISMAN, 1998.512 s.).

There is a known method in which initial ultrafine refractory powders are used to obtain a nanocrystalline structure (Pogozhev Yu.S., Levashov EA, Kudryashov A.E., Ulyanova TM, Dedov N.V., Matyukha V.A. On the effect of nanocrystalline powders of refractory compounds on the combustion process, structure formation, phase composition and properties of a SHC alloy based on TiC-TiAL. University proceedings. Non-ferrous metallurgy, 2006, No. 5, pp. 23-31).

Common disadvantages of the above technical solutions is the use of the initial ultrafine powders, or subsequent chemical or mechanical processing to obtain a submicron structure. In this case, powders are obtained that are used in further technological processes to obtain finished products.

A known method of manufacturing an in-situ composite oxide of aluminum- (Ti, Zr) borides (RU 2283207, 09/10/2006). To obtain an in-situ composite alumina- (Ti, Zr) borides, a mixture is prepared containing boron oxide, aluminum, titanium, zirconium, titanium and zirconium oxides. Then granulation of the mixture is carried out to obtain granules with a diameter of 10-80 mm and a height of 15-20 mm. Initiate a reaction (SHS) to obtain a composite. Simultaneously with SHS, the composite is compacted under a load of 40-200 atmospheres. The disadvantages of this technical solution is the use of high pressures in the compaction process, while the resulting composite has large particle sizes of 0.5-5 microns.

Closest to the technical nature of the claimed invention is a method of manufacturing long products from powder materials, which includes preparing an exothermic mixture of powders of at least one metal and one non-metal from the series carbon, boron, silicon, initiating the combustion reaction, compaction before extrusion during the combustion process products with a pressure of 0.01-0.5 MPa, extrusion of combustion products at a pressure of 20-100 MPa (RU 2013186, 05/30/1994). When implementing the prototype method, the objects of SHS extrusion are synthetic solid instrumental materials (STIM) containing a wear-resistant component (carbides, borides) and a binder metal or alloy (Stolin AM, Merzhanov A.G., Radugin A.V. Technological basis for SHS extrusion // IFZh. - 1992. - T. - 63. - No. 5, p. 525-537). The plasticity of such materials is due precisely to the presence of a metal bond, which at sufficiently high temperatures plays the role of a lubricant that facilitates the sliding of particles of a solid base. The disadvantages of this technical solution is to obtain a micron structure (5-200 μm) of synthesized materials with relatively low mechanical properties.

The technical result of the proposed method is to obtain ceramic products with a nanoscale structure with improved mechanical characteristics and minimal porosity.

The technical result is achieved by the fact that the method of producing ceramic products with a nanoscale structure, including the preparation of an exothermic mixture of powders of the starting components, molding of the workpiece from the mixture, initiating the combustion reaction in the SHS mode, compaction before extrusion during combustion of products with a pressure of 0.01-0.5 MPa , extrusion of combustion products, according to the invention as starting components used TiO _2, C, B, Al, Zr in the form of powders having a particle size of 1-100 microns in a ratio, which is taken to obtain the title mater ala composition, wt%: 22-25 TiV _2;. 20-30 TiC; 35-44.5 (Al ₂ O ₃ -ZrO ₂ ) eut .; the rest (ZrO ₂ ) β, while before starting the combustion reaction, the workpiece is heated to 100-150 ° C.

The essence of the proposed method is as follows. The powders of titanium dioxide, aluminum (ASD-4), amorphous boron, zirconium and carbon black are mixed in a certain ratio so that the final synthesized ceramic contains titanium carbide, titanium diboride, eutectic from aluminum oxide and zirconium oxide and tetragonal modification of zirconium oxide in the following ratio components, wt.%:

TiB ₂ 22-25 Tic 20-30 (Al ₂ O ₃ —ZrO ₂ ) eut. 35-44.5 (ZrO ₂ ) β rest

The resulting mixture of powders is molded into a preform with a diameter of 30 mm, a height of 27 mm and a relative density of 0.45-0.55. The resulting preform is heated in an oven to 100-150 ° C. Preheating allows you to increase the temperature and burning rate of the molded material, which leads to the possibility of extruding this composition. Without heating or weak heating of the initial billet (less than 100 ° C), the synthesized material is not extruded and clogs the matrix, which brings it out of operation. When heated to more than 150 ° C, ignition of the initial preform occurs. The heated billet is placed in the mold, a tungsten spiral initiates a combustion wave in the SHS mode. After a certain delay time, the synthesized material is extruded through the forming matrix. The result is ceramic products with a nanoscale structure with various cross-sectional shapes (square, circle, oval, spiral) up to 350 mm long.

The formation of a nanoscale structure during SHS extrusion occurs in stages. At the first stage, titanium oxide is reduced by aluminum and zirconium to form Ti and the liquid phase Al ₂ O ₃ and ZrO ₂ . At the second stage, titanium interacts with soot and amorphous boron with the formation of refractory grains TiC and TiB ₂ . During cooling, zirconia undergoes a martensitic tetragonal-monoclinic transformation, which occurs in the temperature range 1443-1693K and is accompanied by an increase in volume by 3-7%. During extrusion, axial and radial stresses undergo volumetric deformation of the synthesized material, which provides a high degree of deformation and, as a result, the formation of a dense ceramic material and nanoscale structural elements. The high cooling rates of the extruded material contribute to an even greater reduction in particle size.

According to the results of X-ray phase and electron microscopy analyzes, it was found that ceramics with a nanoscale structure was obtained, which has a uniform phase distribution, low porosity (not more than 5%) and high microhardness (up to 2100 kg / mm ² ), which is at the level of special grades hard alloys and cutting ceramics.

The drawing shows the microstructure of the obtained ceramics. The light phase is zirconium oxide ZrO ₂ , the dark phase is Al ₂ O ₃ . They form a eutectic consisting of elongated flagella with a thickness of up to 100 nm and a length of 2-3 μm (ZrO ₂ ) and a ceramic matrix Al ₂ O ₃ , which is uniformly distributed throughout the volume of the material. The eutectic Al ₂ O ₃ —ZrO ₂ is surrounded by TiC and TiB ₂ grains less than 2–3 μm in size, and individual flaky ZrO ₂ grains with sizes less than 5 μm are also found.

The composition and properties of the obtained ceramics in comparison with the known are presented in the table.

Thus, the proposed combination of features of the invention allows to obtain products that can be used as a cutting tool, targets for applying composite coatings, electrodes for spark alloying and other purposes, when it is necessary to provide increased wear, heat and corrosion resistance with high microhardness and low porosity.

Claims (1)

A method of producing ceramic products with a nanoscale structure, including preparing an exothermic mixture of powders of the starting components, molding a preform from a mixture, initiating a combustion reaction in the SHS mode, densifying products during combustion of 0.01-0.5 MPa and extruding combustion products, characterized in that as the starting components use TiO ₂ , C, B, Al, Zr in the form of powders with particle sizes of 1-100 μm in the ratio taken to obtain the target material composition, wt.%:
TiB ₂ 22-25 Tic 20-30 (Al ₂ O ₃ —ZrO ₂ ) eut. 35-44.5 (ZrO ₂ ) β rest
in this case, before initiating the combustion reaction, the preform is heated to 100-150 ° C.

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