RU2697987C1 - Method of making ceramics based on silicon nitride - titanium nitride composite - Google Patents

Abstract

FIELD: manufacturing technology.

SUBSTANCE: invention relates to a method of producing a ceramic composite from silicon nitride, hardened with titanium nitride, having a combination of physical and mechanical properties, such as high strength and hardness, low coefficient of thermal expansion, wear resistance and electrical conductivity. This type of ceramics is designed for operation in acidic and aggressive media, in conditions of high temperatures and prolonged mechanical action. Proposed method comprises mixing silicon nitride powder with sintering additive and titanium metal produced by plasma chemical method, grinding in medium of isopropanol in planetary mill, drying, addition of 3 wt% aqueous 10 % solution of polyvinylpyrrolidone, cold uniaxial pressing of blanks. Subsequent sintering and nitriding of workpieces is carried out in one step by hot pressing in graphite mold at 1,650 °C with maximum specific pressure of 30 MPa for 60 minutes in nitrogen atmosphere.

EFFECT: method enables to obtain in one stage dense ceramic materials having strength of up to 565 MPa, density higher than 3_14 g/cm³ and conducting electric current.

1 cl, 1 dwg, 1 tbl, 2 ex

Description

The invention relates to a method for producing ceramic composites - a composite of silicon nitride (Si ₃ N ₄ ), hardened by titanium nitride (TiN), having a combination of physical and mechanical properties such as high strength and hardness, low coefficient of thermal expansion and wear resistance. This type of ceramic is designed to work in acidic and aggressive environments, under conditions of high temperatures and prolonged mechanical stress. The invention relates to a method for producing silicon ceramic nitride reinforced with a refractory filler titanium nitride.

A method of manufacturing a composite based on silicon nitride reinforced with titanium nitride, involves mixing the components - a fine powder of silicon nitride, containing as a sintering additive calcium aluminate with a eutectic melting point of 1600 ° C and metal titanium. In the firing process, titanium metal goes through a nitriding step and forms titanium nitride particles, which are a reinforcing agent. The technical attractiveness of the use of metallic titanium is due to the fact that during sintering, metallic titanium undergoes a plastic deformation stage, due to which Ti particles increase the mobility of Si ₃ N ₄ particles and compaction of silicon nitride. Next is the nitriding process with the formation of a reinforcing titanium nitride additive. TiN additive combines a number of important operational characteristics, such as high melting point, excellent chemical resistance, high strength, high elastic modulus and high electrical conductivity. The introduction of titanium nitride reinforces the structure of the material, increasing the microhardness and bending strength, and also allows the ceramic composite to conduct electric current.

The invention relates to a technology for producing ceramic materials, and in particular to the field of obtaining products based on silicon nitride ceramics (Si ₃ N ₄ ) reinforced with titanium nitride (TiN).

Silicon nitride is a promising material with a combination of properties that allow its wide use as electrical insulating and radio engineering products, magnetically permeable ceramics, armor ceramics, cutting tools, as well as sliding and rolling bearings. Composites of the Si ₃ N ₄ -TiN system are of interest for use as thin nanocrystalline films (hardness comparable to that of diamond), materials for cutting tools, electrically conductive materials capable of electropulse processing (http://www.findpatent.ru/patent/ 238 / 2382690.html).

Over the past decade, research has been conducted in Russia on the development of composite materials based on silicon nitride and titanium nitride, in which the above compounds can be both a matrix and a reinforcing filler in the form of nano particles or discrete fibers, whiskers.

A known method of producing ceramics consisting of Si ₃ N ₄ and titanium nitride (TiN). The method consists in mixing and pressing powders of silicon nitride and titanium nitride with aluminum and yttrium oxides. Sintering of samples is carried out at temperatures of 1200-1800 ° C and a pressure of 2.5 GPa for 30 seconds in containers of lithographic stone (VB Shapilo et al. Features of sintering at high pressure of ceramic from silicon nitride. Inorganic materials, 1997, t 33, No. 10, pp. 1269-1272).

A known method for producing a composite of the Si ₃ N ₄ -TiN system (V. S. Urbanovich, R. A. Andrievsky, S. S. Turbinsky, K. I. Yanushkevich. Structure and properties of nanocomposites based on silicon and titanium nitrides, sintered at high pressures Abstracts of the second All-Russian conference on nanomaterials "NANO 2007", March 13-16, 2007, Novosibirsk, p. 249). The initial mixture, consisting of powders of amorphous silicon nitride with a particle size of up to 13 nm and nanocrystalline titanium nitride with a particle size of 80 nm, is mixed and compacted at a pressure of up to 4 GPa at temperatures up to 1800 ° C.

A known method for producing composites described in patent RU No. 2382690 published 02.27.2010 B22F 009/02, B22F 009/16, B22F 001/00, "A method for producing a composite ceramic powder based on silicon nitride and titanium nitride." An exothermic mixture is prepared by mixing ferrosilicon containing 65-95 wt. % Si, ilmenite, containing 60-65 wt. % titanium dioxide, and pre-nitrided ferrosilicon, with a ratio of components in the mixture: ferrosilicon - 40-55 wt. %, ilmenite - 20-40 wt. % and nitrated ferrosilicon - 25-40 wt. % After exothermic synthesis, nitriding of the mixture is carried out for 30-40 minutes, followed by grinding.

A known method of producing nanocomposites TiN-Si ₃ N ₄ (Ostap B. Zgalat-Lozinskyy et. Al. RCS of TiN-Si ₃ N ₄ nanocomposites. In book: Science of sintering: current problems and new trends, 2003, Beograd, Serbian, p. 138-143). The composite composition of 95 wt. % TiN + 5 wt. % Si ₃ N ₄ and 50 wt. % TiN + 50 wt. % Si ₃ N _{4 is} obtained by mixing powders of silicon nitride and titanium with additives of yttrium oxide and alumina, then sintering the compositions in an atmosphere of hydrogen or nitrogen at temperatures of 1500-1700 ° C.

The disadvantages of the above methods for producing a composite of the Si ₃ N ₄ -TiN system are the use of expensive pure powders or pre-synthesized initial components of the charge, the use of activating additives, the inability to control intensive recrystallization during sintering, the inadmissibility of obtaining a functional part with a nanodispersed microstructure and the duration of the process of preparing the charge (mixing starting components in a ball mill for 10 hours).

The closest is the method of producing the composite described in patent RU No. 2544942 published 03/20/2013 С04В 035/596, С04В 035/628, B82Y 030/00, "Method for producing a nanocomposite from ceramic powder", which describes a method for producing a composite material based on nitride silicon and titanium nitride obtained from liquid phase titanium alcoholate. A method of producing a nanocomposite includes mixing ceramic particles of Si ₃ N ₄ in ethanol, followed by adding titanium alcohol phase alcoholate to the resulting suspension and pre-heating the suspension to obtain a powdery mass. Then the organic part is evaporated at 60 ° C for 24 hours and at 120 ° C for 2 hours, in the second stage at 300-600 ° C the formation of anatase and the complete removal of the organic component occurs, then nitriding in ammonia at 800-1200 ° C to the formation of titanium nitride.

The disadvantage of this method is its many stages, the duration of the powder preparation process and the environmental process, since in the process of preparing the powder, a large proportion of the organic component is removed.

The task of the invention is to obtain composite ceramics in one process combining sintering and nitriding.

The technical result to which the claimed invention is directed is to provide the possibility of obtaining a ceramic composite Si ₃ N ₄ -TiN with a homogeneous microstructure in one step by nitriding metal titanium directly during hot pressing, while the material becomes conductive, maintains mechanical strength at pure silicon nitride and increases the microhardness of the composite.

The technical result is achieved by mixing the silicon nitride powder with a sintering additive and metallic titanium in isopropanol medium in a planetary mill, drying the resulting mixture at 120 ° C, adding 3 wt. % aqueous 10% solution of polyvinylpyrrolidone by molding blanks with a specific pressure of 100 MPa at room temperature and sintering in a high purity nitrogen medium in a hot pressing furnace at a temperature of 1650 ° C for 60 minutes at a maximum specific pressure of 30 MPa.

The difference from the prototype is that at the stage of mixing the components, metal titanium obtained by plasma chemical synthesis is used. Sintering is carried out by hot pressing. The use of metallic titanium increases the mobility of the grains of silicon nitride during sintering and reduces the porosity of the product.

Products from the proposed ceramic material are obtained as follows:

As the starting material used commercial silicon nitride (LLC Plazmotherm). Powder of titanium metal obtained by plasma-chemical method at the Institute of Metallurgy and Materials A.A. Baykova (IMET RAS) particle size 25-30 microns (Fig. 1). The powders of silicon nitride and sintering additive of calcium aluminate (T _evk = 1600 ° C), taken in the required quantities, are mixed with titanium metal in a planetary mill for 60 min in isovpropyl alcohol. The resulting mixture was dried until the alcohol was completely removed at 120 ° C. The dried mixture is wiped through a sieve and pressed by double-sided pressing in a metal mold with a pressure of 100 MPa at room temperature. The obtained raw materials are subjected to hot pressing in a graphite mold at 1650 ° C for 60 minutes in a nitrogen environment, the pressing pressure of 30 MPa. Table No. 1 presents the properties of the obtained ceramic materials based on silicon nitride with a sintering additive of calcium aluminate and different contents of titanium nitride. From the data in table No. 1 it can be seen that the flexural strength with an increase in the content of titanium metal in the initial charge decreases from 565 MPa to 365 MPa (respectively for 5 and 30 wt.% Ti), while the composite begins to conduct electric current, only at titanium content ≥20 wt. %

Example 1. Prepare a mixture of the following composition, wt. %: silicon nitride - 90, calcium aluminate - 10; titanium metal - 5 (relative to the total mass of silicon nitride with a sintering additive).

Silicon nitride powder is mixed in a Teflon drum with a sintering additive of calcium aluminate (T _PL = 1600 ° C), based on the total weight of the resulting mixture, titanium metal is introduced into the mixture. Mixing and grinding is carried out in a planetary mill for 60 minutes in isovpropyl alcohol. As grinding bodies, balls of zirconium dioxide with a diameter of 5 mm are used. The resulting mixture was dried at 120 ° C in air until the alcohol was completely removed. The dried mixture is wiped through a 0063 sieve, the necessary amount of charge is weighed, 3 wt. % aqueous 10% solution of polyvinylpyrrolidone and conduct preliminary bilateral pressing in a metal mold at room temperature. The resulting raw material is subjected to hot pressing and nitriding in a graphite mold at 1650 ° C for 60 minutes in a high-purity nitrogen environment. The obtained ceramic composite Si ₃ N ₄ -TiN has a bending strength at room temperature of 580 MPa, a density of 3.02 g / cm ³ , an open porosity of 0.09% and does not conduct electric current.

Example 2. Prepare a mixture of the following composition, wt. %: silicon nitride - 90, calcium aluminate - 10; titanium metal - 30 (relative to the total mass of silicon nitride with a sintering additive).

Silicon nitride powder is mixed in a Teflon drum with a sintering additive of calcium aluminate (T _PL = 1600 ° C), based on the total weight of the resulting mixture, titanium metal is introduced into the mixture. Mixing and grinding is carried out in a planetary mill for 60 min in isovpropyl alcohol. As grinding bodies, balls of zirconium dioxide with a diameter of 5 mm are used. The resulting mixture was dried at 120 ° C in air until the alcohol was completely removed. The dried mixture is wiped through a 0063 sieve, the necessary amount of charge is weighed, 3 wt. % aqueous 10-% solution of polyvinylpyrrolidone and conduct preliminary bilateral pressing in a metal mold at room temperature. The resulting raw material is subjected to hot pressing and nitriding in a graphite mold at 1650 ° C for 60 minutes in a high-purity nitrogen environment. The resulting ceramic composite Si ₃ N ₄ -TiN has a bending strength at room temperature of 365 MPa, a density of 3.41 g / cm ³ , an open porosity of 0.09%, and a specific electrical resistance of 3 Ohm * cm.

Claims (1)

A method of manufacturing ceramics based on a composite of silicon nitride - titanium nitride, comprising mixing silicon nitride powder with a sintering additive and metallic titanium in an isopropanol medium in a planetary mill, drying the resulting mixture at 120 ° C, adding 3 wt. % aqueous 10% solution of polyvinylpyrrolidone, forming blanks at room temperature and sintering in high-purity nitrogen medium, characterized in that metal titanium obtained by the plasma-chemical method is used as the initial reinforcing component, the blanks are formed by cold uniaxial double-sided pressing in a steel mold under pressure 100 MPa, subsequent sintering and nitriding is carried out in one stage by hot pressing in a graphite mold at a temperature of 1650 ° C with maximum at a pressure of 30 MPa for 60 minutes in a nitrogen atmosphere.

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