RU2402507C2 - Ceramic material and preparation method thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of ceramic articles working at high temperatures in aggressive and abrasive media, as well as under impact-dynamic conditions. The ceramic material contains the following in wt %: MgO - 0.7-1.4, Y₂O₃- 4.1-8.2, Al₂O₃ - 5.2-10.4, α-SiC - the rest. The oxides are in a strict eutectic ratio in accordance with the ternary diagram of Al₂O₃-Y₂O₃-MgO on the garnet-spinel section, which defines the melting point of the oxide phase which is equal to 1770°C±5°C. The method of preparing ceramic material involves preparation of a homogeneous mixture from micropowder of α-silicon carbide, magnesium, yttrium and aluminium oxides with addition of α binder, moulding a workpiece, drying and sintering at 1840-1880°C, preferably at 1860°C and maintaining said temperature for 60±5 minutes.

EFFECT: preparation of material with high hardness, strength and low porosity with low power consumption and possibility of widening the range of articles made.

3 cl, 1 tbl

Description

The invention relates to the field of production of products from composite ceramic materials operating at high temperatures in aggressive and abrasive environments, as well as in conditions of shock-dynamic impact, for example, as armored products.

The increase in the operational properties of the material is due to its physico-mechanical parameters - low porosity and high density, strength and hardness.

The development of structural ceramics based on silicon carbide is fraught with a number of difficulties in the physicochemical plan - covalent chemical bonds in the α-SiC lattice allow self-diffusion events to develop at T> 0.9 T, i.e. at temperatures> 2300 ° С, when even at normal pressure (in an argon medium) noticeable evaporation (dissociation) of SiC is observed.

Consequently, sintering acts ensuring the compaction of the porous preform should be carried out at T <2300 ° C. In this regard, three possible ways of activating the mass transfer processes necessary to obtain dense ceramics have been outlined.

The first way is to get the so-called activated SiC powders characterized by high dispersion (13-15 m ² / g with d _SiC ≈0.1-0.2 μm) and impurities capable of creating a defect structure and increasing diffusion activity when dissolved in a SiC lattice. So, a number of foreign companies (San Gobain) produce powders doped with B (or B ₄ C), which are characterized by the specified dispersion and allow to obtain dense ceramics by sintering at 2180 ° C. A significant drawback of such ceramics is that, as a result of the active occurrence of secondary recrystallization, grains 200-600 μm in size appear in the ceramics, which are stress concentrators and provide low crack resistance of the material (K _i <3MPa · m ^1/2 ). The second promising way is associated with the development of composite ceramics based on SiC; modifying the structure and giving a new set of properties, the introduced components must be thermodynamically compatible with SiC before T sintering. First of all, the systems SiC-Me ^d B ₂ , SiC-Me ^d C, SiC-Me ^d Si ₂ should be noted. All of these systems are eutectic, which opens up prospects for creating a large group of composite ceramics based on SiC for various purposes. However, the sintering temperature of such ceramics is also in the range of 2150-2200 ° C, which is comparable with T _eut in this system; nevertheless, the screening role of the diboride phase provides (at 30% by volume) a significant decrease in the d of the SiC grain (4–10 μm) and the associated increase in the strength and crack resistance of ceramics. It should be noted that recently, in the work on sintered silicon carbide, a technique such as the use of oxide activators of the sintering process has been successfully implemented. The apparent "paradoxicality" of this pathway (SiC with oxides is fundamentally thermodynamically incompatible) is explained by the fact that such complex oxides are found that, due to additional chemical bonds between the cations, increase their thermodynamic stability in contact with SiC (MgO · Al ₂ O ₃ spinel, garnet 3Y ₂ O ₃ · 5Al ₂ O ₃ ) compared with pure (individual) oxides. An important role is played by the fact that the surface of SiC particles is coated with an oxide film, which promotes both the wetting of the particles by the melt of the compounds formed at the intermediate stages of sintering (spinel, garnet) when individual oxides are introduced into the stoichiometry of each of these complex oxides. In this case, the sintering temperature and the production of high-strength ceramics do not exceed 1900 ° C.

The prior art in the development of composite ceramic materials based on silicon carbide is characterized by the following closest analogues.

Known sintered ceramic material and the method of its manufacture according to Japan patent No. 4367563, CB 35/10; СВВ 35/565, publ. 12/18/1992, the Material contains as the basis of silicon carbide (SiC) with the addition of aluminum oxides (Al ₂ O ₃ ) and yttrium (Y ₂ O ₃ ). The material is characterized by rather low strength, and the use of hot pressing in its manufacture requires high energy consumption, is inefficient and limits the production of products in terms of size, volume and geometric parameters.

Another close material to the claimed is sintered material based on silicon carbide according to Japanese patent No. 4104944, С04В 35/10, С04В 35/10, publ. 04/07/1992, the Material is obtained by sintering in vacuum and inert atmosphere at temperatures of 1500-1800 ° C using a mixture of fine powders of aluminum oxide (3-20 vol.%) And zirconium dioxide (1-30 vol.%) As sintering activators stabilized with yttrium oxides (2-4 vol.%) and magnesium (0.2-2 vol.%). Low sintering temperature does not allow to obtain a material with high density and strength, because at temperatures above 1800 ° C, the active interaction of zirconium dioxide with silicon carbide begins.

Close to the claimed is US patent No. 5656218, CB 35/565, publ. 08/12/1997, on a sintered ceramic material based on SiC, obtained without applying pressure in the sintering process. The composition of the material includes oxides Al ₂ O ₃ (3.0-15 wt.%) And Y ₂ O ₃ (2.0-10 wt.%). Sintering is carried out in two stages: at 1800-1950 ° C and 1950-2200 ° C. The material under consideration is characterized by not very high values of density and strength, and the disadvantages of manufacturing technology include two-stage heating and a high sintering temperature (2200 ° C), which requires special technological equipment, the use of a gas medium (СО), which ultimately leads to increased energy costs per unit of material produced.

The closest analogue is US patent No. US 5756409, CL. СВВ 35/565, publ. 05/26/1998, on sintered abrasive grain of silicon carbide using oxide sintering additives of aluminum oxide, yttrium oxide, mixtures, including magnesium oxide, obtained by pressing, granulating and sintering at a temperature of 1700-2200 ° C in a gas protective environment.

The disadvantages of this method, as well as in US patent No. 5656218, include the impossibility of obtaining high-strength materials without the use of protective gases (type CO) at temperatures above 1900 ° C. Obtained by this patent, high characteristics of hardness and crack resistance are properties of a single grain (abrasive) and cannot be transferred to structural products.

The claimed technical solution includes two inventions related to the material and the method of its manufacture, interconnected by a single inventive concept.

The objective of the invention is to create a material with high density, strength and hardness with low porosity of the material, as well as its manufacturing technology, which allows to reduce energy consumption, to exclude the use of specific gases such as CO and to expand the range of products by dimensions and geometric parameters.

The problem is solved due to the fact that the ceramic material includes the following ingredients: MgO (0.7-1.4 wt.%), Y ₂ O ₃ (4.1-8.2 wt.%), Al ₂ O ₃ ( 5.2-10.4 wt.%) And α - SiC - the rest, and the method of manufacturing the material involves the preparation of a homogeneous mixture of powders MgO, Y ₂ O ₃ , Al ₂ O ₃ and α - SiC with the addition of a binder, molding the workpiece, drying and sintering in an inert gas atmosphere at a temperature of 1840-1880 ° C, mainly at 1860 ° C, with exposure at the indicated temperature for 60 ± 5 min. The difference of the claimed material from the prototype is the presence of magnesium oxide in a given quantitative composition and the ratio of yttrium and magnesium oxides to aluminum, corresponding to the eutectic composition of the triple eutectic along the garnet / spinel section: 7% - MgO; 41% - Y ₂ O ₃ , 52% - Al ₂ O ₃ , characterized by a melting point of 1770 ° C. The difference between the method consists in one-stage sintering at lower temperature and time values in comparison with the prototype.

The process of liquid-phase sintering and compaction of the material proceeds at temperatures below the active interaction of the components of the composition (≤1990 ° C). Moreover, argon can be used as a protective atmosphere during the sintering of the composition.

The optimum sintering temperature of the composition is 1860 ± 20 ° C. A decrease in sintering temperature to 1800 ° C increases the viscosity of the melt of oxide eutectic, while the wettability of silicon carbide by the melt deteriorates, which leads to increased porosity and a decrease in the strength properties of the material. An increase in sintering temperature to 1900 ° C also leads to a decrease in strength characteristics due to the partial interaction of silicon carbide with oxide sinter activators and the formation of surface porosity in the material.

The optimum content of oxide sintering activators is 10-20%. A decrease in the content of activators in the compositions of less than 10% leads to an increase in the porosity of the material, a decrease in its density and strength characteristics due to the fact that the amount of the liquid phase is insufficient to fill the pores in the volume of the material during the heat treatment. Increasing the concentration of oxide sintering activators above 20% reduces such an important ceramic parameter as hardness (≤17.8 GPa), which negatively affects the operational characteristics of the products.

The method of obtaining products from ceramic material consists in the following process steps:

- in the mixer (paddle, mixer, ball mill) are placed the initial components - micropowder α-silicon carbide with a dispersion of 0.6 ÷ 1.0 μm in an amount of 80-90% and with a purity of at least 99%, oxide micropowders Al ₂ O ₃ , Y ₂ O ₃ and MgO with a dispersion of 0.5 ÷ 3 μm and a purity of 99.9% in an amount of 10 to 20% and a strict ratio between them: Al ₂ O ₃ 52%, Y ₂ O ₃ 41%, MgO 7% . A 5% solution of plasticizers - polyethylene glycol, polyvinylpyrrolidone (PVP) in the amount of 1.5-2.0% in terms of dry weight, 0.2% of oleic acid is added. Distilled water is added to the mixer at a ratio of 1: 1 by volume to the powders. Mixing of the mixtures is carried out for 2 ÷ 4 hours to obtain a homogeneous (homogeneous) mixture (slip);

- a homogeneous mixture is subjected to a drying and granulation process at a temperature of 80-120 ° C to obtain spherical / granules with a size of 140 ÷ 170 microns. From plasticized granules of the press powder, the product blanks are formed on a hydraulic press in steel molds with a pressing force of 80 ÷ 100 MPa;

- molded product blanks are dried in air at a temperature of 80-120 ° C for 6 ÷ 8 hours and sintered in vacuum at a temperature of 1860 ± 20 ° C and isothermal exposure 30 ÷ 240 min.

The sequence of technological operations for the manufacture of ceramic parts and blanks is shown in the drawing.

Example 1. To a micropowder of α-SiC in an amount of 92% add 8% of a mixture of micropowders of oxides Al ₂ About ₃ , Y ₂ O ₃ and MgO in a ratio of 52%: 41%: 7%, add a plasticizer solution and distilled water. The mixture of components is mixed for 2-4 hours in a mixer until a homogeneous slurry is obtained. The slurry is pumped into the granulator, where it is sprayed with nozzles at temperatures of 80-120 ° C and dried in a suspended layer to obtain granules with a size of 140-170 microns and a residual moisture content of 1.2-1.7%. From the obtained granules, blanks of ceramic samples with a size of 6 × 6 × 55 mm are formed by semi-dry pressing on a hydraulic press with a pressing force of 80 ÷ 100 MPa. Samples are dried at a temperature of 80 to 120 ° C for 6 hours, then sintered in vacuum to a temperature of 900 ° C (P = 0.13 Pa) and an argon atmosphere at a temperature of 1860 ± 20 ° C (P = 10 ^-1 MPa ) for 60 minutes. On sintered samples, porosity, density, bending strength, fracture toughness coefficient, and hardness are determined.

Examples 2-5 are similar to example 1, except for the content of the oxide phase - 10, 15, 20 and 25 wt.%, Respectively.

In total, three batches of samples were made (examples 1-5, 6-10, 11-15), which were sintered at temperatures of 1860 ° C, 1900 ° C, and 1800 ° C, respectively, after which the density, bending strength, crack resistance, and hardness were determined by standard methods. The test results are shown in the table. To compare the obtained physical and mechanical parameters of the new material with similar parameters (except hardness) of the prototype, examples 7-12 are taken from the table of US patent No. 5656218.

The results show that the optimum sintering temperature is 1860 ° C, at which the maximum bending strength of the material is reached - 660 ± 20 MPa. The coefficient of crack resistance is 5.6 MPa · m ^1/2 , hardness N _v = 20 GPa. Raising the sintering temperature of the material to 1900 ° C leads to a partial interaction of the components and the evaporation of oxide phases from the surface of the samples, which affects the mechanical characteristics and density. The crack resistance coefficient and hardness on the samples of examples 6, 7, 9, 10 were not measured. A decrease in the sintering temperature of the material to 1800 ° C also leads to a decrease in the characteristics of the material due to the high viscosity of the melt of the oxide phase, which leads to a decrease in the wettability of the carbide phase by it. The crack resistance coefficient and hardness on the samples in examples 11-13 were not measured. Thus, the sintered material at a temperature of 1860 ° C has higher strength characteristics compared to the analogue and prototype.

Table The claimed material No. of measures Contained. oxides, wt.% Temperature sintering, ° С Exposure min Raft
% Durable when bending, MPa Coeff. crack resistance, K _1C , MPa · m ^1/2 Hard., H _v . GPa I stage II stage I stud II stud one 8 1860 - 60 - 95.0 380 3,7 24 2 10 1860 - 60 - 98.8 580 5.3 23 3 fifteen 1860 - 60 - 99.1 600 5.5 22 four twenty 1860 - 60 - - 99.1 660 5,6 twenty 5 25 1860 - 60 - 98.0 600 5.5 eighteen 6 8 1900 - 60 - 91.0 270 - - 7 10 1900 - 60 - 92.3 320 - - 8 fifteen 1900 - 60 - 93.1 335 3,5 21.8 9 twenty 1900 - 60 - 88.2 270 - - 10 25 1900 - 60 - 84.0 210 - - eleven 8 1800 - 60 - 89.1 230 - - 12 10 1800 - 60 - 89.2 250 - - 13 fifteen 1800 - 60 - 90.1 260 - - fourteen twenty 1800 - 60 - 92.1 310 3.0 19.5 fifteen 25 1800 - 60 - 91.8 300 3.0 17.8 Analogue (US Pat. No. 5,656,218) 7 10 1900 2000 120 thirty 99.1 423 5.02 - 8 10 1900 2000 120 thirty 98.4 491 - - 9 10 1900 2000 120 thirty 98.9 538 5.04 - 10 10 1900 2000 120 thirty 99.1 600 5.35 - eleven 10 1900 2000 120 thirty 99.1 532 5.31 - 12 10 1900 2000 120 thirty 98.6 573 - - Prototype (US Pat. No. 5,756,409) 13 10 1900 - 120 - - - 6.0 26

Claims (3)

1. Ceramic material, including α-silicon carbide and aluminum oxides, yttrium, characterized in that it additionally contains magnesium oxide in the following ratio of ingredients, wt.%:
magnesium oxide 0.7-1.4
yttrium oxide 4.1-8.2
alumina 5.2-10.4
α-silicon carbide rest 2. The ceramic material according to claim 1, characterized in that the oxide phases in it are in a strictly eutectic ratio in accordance with the state diagram of the ternary system Al ₂ O ₃ -Y ₂ O ₃ -MgO by section garnet-spinel, wt.%:
MgO 7
Y ₂ O ₃ 41
Al ₂ About ₃ 52, which determines the melting temperature of this eutectic mixture in the value of 1770 ± 5 ° C. 3. A method of manufacturing a ceramic material, including the preparation of a homogeneous charge from fine powders of silicon carbide, magnesium, yttrium and aluminum oxides in a eutectic ratio corresponding to the state diagram of the ternary system Al ₂ O ₃ -Y ₂ O ₃ -MgO along the garnet-spinel section , with the addition of a binder, molding the preform, drying and sintering in an inert gas atmosphere, characterized in that the sintering is carried out at a temperature of 1840-1880 ° C, mainly at 1860 ° C, with exposure at the specified temperature for 60 ± 5 minutes

Images