JPS61281070A - Silicon carbide base sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a silicon carbide sintered body that has excellent strength and toughness characteristics and is highly corrosion resistant. -Relates to a method for producing a silicon carbide sintered body suitable for contact members that require excellent corrosion resistance even under harsh conditions, such as throat buttons. The present invention also relates to a silicon carbide sintered body having a novel microstructure.

(Prior art) Silicon carbide sintered bodies have various excellent properties such as oxidation resistance, corrosion resistance, heat resistance, thermal shock resistance, and high temperature strength, so they are used as high-temperature gas turbine parts, automobile engine parts, corrosion-resistant parts, and wear-resistant parts. It is a suitable material for parts etc. However, since silicon carbide sintered bodies are difficult to sinter, various sintering aids are added to obtain dense sintered bodies. Examples of this sintering aid include boron (B)-carbon (C)-based additives, but they require relatively high temperature firing to obtain a dense sintered body, and they also require crystallization of the sintered body. The structure is generally equiaxed grains with very few grain boundary phases. Therefore, due to this, the toughness of the sintered body is low, and further improvement in corrosion resistance at high temperatures cannot be expected. For example, the material σ1 of a skid button that comes into contact with iron or the like at high temperatures does not have sufficiently satisfactory corrosion resistance.

That is, as is conventionally known, by using a silicon carbide sintered body for the skid button, a cooling source for the skid button is not required, the occurrence of skid marks is reduced, and the thermal efficiency in the heating furnace is improved. became. However, in the above-mentioned skid button application, when the red-hot slab comes into contact with the silicon carbide sintered body, the silica component in the silicon carbide reacts with iron to form a molten material, which causes corrosion of the sintered body. progresses.

On the other hand, the use of aluminum-based additives such as alumina (Al□0.) facilitates densification, but as the sintered body has a large volume, densification becomes uneven between the inside and outside of the sintered body. It is known to occur.

In other words, in order to use aluminum-based additives, it is necessary to add 3% by weight or more of aluminum, and because there are many grain boundary components and the amount of decomposition is large, uniform densification cannot be achieved inside and outside the sintered body. and excellent corrosion resistance has not been obtained.

(Means for Solving the Problems) An object of the present invention is to provide a silicon carbide sintered body that is uniformly densified throughout the inside and outside of the sintered body and has excellent strength and toughness properties, and a method for producing the same. That is.

Another object of the present invention is to provide a silicon carbide sintered body that has high corrosion resistance, especially when it comes into contact with iron at high temperatures, and a method for producing the same. The present invention provides a silicon carbide sintered body as a material suitable for a member that comes into contact with iron at the bottom.

According to the present invention, 3.5 to 1 in terms of aluminum element
0% by weight aluminum component, 0.2 in terms of chromium element
A silicon carbide sintered body containing 5% by weight of a chromium component and a residual amount of silicon carbide, wherein the crystal grain boundaries containing the aluminum component and chromium component contain chromium as determined by analysis using an X-ray microanalyzer. A silicon carbide sintered body is proposed, which contains aluminum and silicon as main components and is characterized by the presence of particles that exhibit high brightness under a metallurgical microscope.

Further, according to the present invention, at least one selected from aluminum alone and compounds has a value of 3.
After mixing starting materials containing 0.2 to 5 weight % of at least one element selected from 5I3 to 10 weight percent, chromium alone and compounds, and the balance consisting of silicon carbide, this mixed powder is added. Provided is a method for producing a silicon carbide sintered body characterized by pressure molding and sintering or pressure sintering.

In the silicon carbide sintered body according to the present invention, a chromium component and an aluminum component are present at the grain boundaries of silicon carbide, and it is remarkable that the chromium component is present at the grain boundaries as lumps or particles of a certain grain size. It is a characteristic. That is, the present invention allows the chromium component present in the above-mentioned form at the grain boundaries of the silicon carbide sintered body to interact with the iron in contact with the silicon carbide sintered body and the silica contained in the silicon carbide at high temperatures. Based on the new knowledge that the corrosion of the sintered body is significantly suppressed by suppressing the reaction with silicon oxide (which actually exists as silicon oxide on the surface), thereby effectively eliminating the deterioration in the properties of the sintered body. It is something.

In the silicon carbide sintered body of the present invention, silicon carbide has a substantially spherical shape and an average grain size within the range of 0.5 to 2 μm, and a maximum grain size of 20 μm or less, depending on the size of the sintered body. In particular, it exists as particles with an α-type crystal structure of 5 μm or less. In other words, in this sintered body, coarse grain growth occurs during sintering, the grain size is almost uniform, and the grain shape is almost spherical with equiaxed crystals, with the maximum dimension of one grain / The ratio of the minimum dimensions is 2 or less.

A thing exists.

That is, the silicon carbide sintered body of the present invention has grains with significantly higher brightness than silicon carbide crystal particles when observed with a metallurgical microscope when compared to a silicon carbide sintered body that does not contain a chromium component. Diameter 0.5 to 20μm, especially 0.5
The fact that particles of 5 μm to 5 μm are present becomes clear. Analysis results using an X-ray microanalyzer revealed that the particles mainly contained chromium, and also contained aluminum and silicon.

In the present invention, the reason why the chromium-containing particles present at the grain boundaries effectively act to prevent corrosion of the sintered body itself even when the sintered body and iron come into contact at high temperatures remains to be elucidated. Although this has not yet been achieved, the present inventor has found that silicon carbide crystal particles are protected by grain boundary compounds or compositions, and that when a chromium component is mixed into iron oxide or silicon oxide, the melting point increases, and this causes a melting reaction. It is presumed that this is due to the fact that the generation of is controlled.

In the silicon carbide sintered body of the present invention, silicon carbide preferably accounts for 97 to 85% by weight, particularly 90 to 95% by weight. However, in the sintered body of the present invention, it is thought that in addition to silicon carbide, silicon compounds of chromium and aluminum may also be included to some extent in the occupation ratio of silicon carbide. In addition, it is important from the viewpoint of corrosion resistance that the chromium component is present in an amount of 0.2 to 5% by weight, especially 0.4 to 3.5% by weight in terms of chromium element, while the aluminum component is present in an amount of 0.2 to 5% by weight in terms of aluminum element.
．． It is preferably present in an amount of 5 to 10% by weight, especially 3 to 6% by weight.

A method for producing a silicon carbide sintered body according to the present invention will be described below.

The silicon carbide used as the raw material powder may be either α-phase or β-phase, but α-phase is preferable because it is inexpensive and can be produced in large quantities. Further, the average particle diameter is desirably 1.0 μm or less, preferably 0.5 μm or less.

Aluminum alone or compound (first component) includes aluminum metal, oxide, carbide, nitride, sulfide, etc. For example, alumina powder, alumina sol, alumina gel,
Aluminum carbide (AltCs), aluminum nitride (
Other examples include aluminum sulfate, aluminum nitrate (AI (N(h) 3), and aluminum carbonate (Ah(COi)i). These aluminum components promote the sintering of silicon carbide. However, it itself forms grain boundaries of crystal grains.In the present invention,
Among these, it is particularly desirable to use alumina and aluminum nitride. That is, since alumina has a high melting point and melts at a temperature close to or lower than the sintering temperature of silicon carbide, a homogeneous and dense sintered body can be obtained. In addition, aluminum nitride has a higher melting point than alumina, and unlike oxides, it has less tendency to release oxygen and create voids during sintering, making it a sintered body with the best heat resistance and density. Best suited for manufacturing purposes.

Chromium alone or compound (second component) includes chromium metal,
There are oxides, carbides, etc., and chromates, chromium halides, etc. can also be considered. However, in the present invention, it is most desirable to use chromium carbide. That is, when chromium oxide is used, oxygen is separated and released during sintering, silicide of chromium is likely to be formed, voids are likely to occur in the sintered body, and mechanical strength is likely to decrease. The chromium carbide having a composition of Cr5Ct having a high melting point is most advantageously used, but chromium carbide having a composition other than this may also include Cr, C3, and Crz:+C6.

In the raw material powder described above, it is preferable to use the first component in an amount of 3.5 to 10% by weight, especially 3 to 6% by weight in terms of aluminum element; if the amount is less than the above range, the sinterability will be unsatisfactory and a sufficiently dense body will not be formed. If the amount is not obtained or exceeds the above range,
The strength at high temperatures decreases, and the corrosion resistance also tends to decrease. Further, the object of the present invention can be advantageously achieved by using the second component in an amount of 0.2 to 5% by weight, particularly 0.4 to 3% by weight, calculated as chromium element.

According to the present invention, the amounts of the first component and the second component as described above are set within predetermined ranges, and each component can be used alone or in combination. Further, if the starting material is a solution, it will promote densification of the sintered body, but if it is a powder, it is desirable to reduce the particle size. The average particle size does not require a particularly strict range setting, but is preferably 1.011rn or less.

Although the silicon carbide sintered body according to the present invention contains the first component and the second component as essential components, this sintered body does not exclude the inclusion of components other than the above-mentioned components.

For example, when a grinding medium such as a ball is used when mixing and grinding additive components, the components constituting this grinding medium will inevitably be contained in the mixed and pulverized product. As long as the mixed component does not react with or have an adverse effect on silicon carbide, the first component, and the second component during sintering, the mixing of such a component is of course allowed.

Components that are allowed to be mixed into the silicon carbide sintered body of the present invention include zirconia (ZrOz), tungsten carbide (WC), silicon nitride (SiJ4), and the like. Further, the first component and the second component may be contained in the mixed pulverized material by incorporating an additive component such as alumina into the balls or by using alumina balls.

In the manufacturing method of the present invention, the raw materials obtained as described above are wet-mixed, a molding binder and the like are added, and after drying and granulation, it is molded into a desired shape by a pressing method or the like.

Next, this compact is sintered in a non-oxidizing atmosphere such as an argon atmosphere or a nitrogen-containing atmosphere.

Alternatively, pressure sintering (hot press, etc.) may be used to perform molding and sintering at the same time.

According to the present invention, the firing temperature may be set in the range of 1850 to 2050'C, especially 1900 to 1950'C (temperature range of 1750 to 20509C in hot press); if it is less than 18509C, sintering will be insufficient and uniform. It was experimentally confirmed that if the temperature exceeds 2050'C, decomposition becomes intense during firing, abnormal grain growth occurs, and the properties of the obtained sintered body deteriorate significantly. . Further, the firing time may be about 0.5 to 10 hours.

(Example) Next, examples of the present invention will be described.

The first component (
average particle size: 0.6 μm) and the second component (average particle size: 0.8 μm)
μIm) was added to achieve a composition ratio as shown in Table 1.

This blended powder was wet mixed in a rotary mill, and an appropriate amount of an organic binder was added as a solution to this mixed slurry, followed by spray dry granulation. Then 120 x 120 x 10m
Samples 1 to 20 were obtained by molding the sample into a flat plate having a diameter of m and after removing the binder, it was fired in an inert atmosphere at the firing temperature shown in Table 1.

The sintered body thus obtained was 4 x 3 x 35 mm (
After cutting into a shape for anti-folding according to JIS standard,
- R-1601 4-point bending test method at room temperature and 13
The bending strength at 0.00" C was measured. Toughness properties were measured as fracture toughness from the length of cracks generated from the edge of the indentation under a constant load on each sample using a Pinkers indenter. Corrosion resistance tests were performed using a 100 x lOOX 5 mm flat plate. 12506C.
10S for 24 hours in an oxidizing atmosphere of 1% water vapor 20Vo
The steel slab was raised and lowered repeatedly at a ratio of ec/cycle, and then the amount of erosion caused by the steel slab was measured. The degree of erosion was evaluated according to the following five grades: 1, 2, 3, and 4.5.

C. Front car 1° Due to the production of iron-silica molten reactants, the upper surface of the sample sintered body eroded by more than 3 mm, some corners were eroded and became rounded, and the lower surface was also eroded by the molten reactants.

2. The erosion on the top surface reaches the order of 2 mm, and some corners of the top surface become rounded. The reaction melt also flows onto the alumina plate that serves as a support.

3. The entire upper surface of the sample sintered body is eroded, and the reaction melt flows down to the side. Erosion t within 1mm.

4. Several eroded parts (points) with a diameter of 1 mm or less occur. No erosion is observed in other parts.

5. No corrosion due to reaction with iron or iron oxide is observed in the sample sintered body.

As is clear from Table 1, in the samples Nos. 014.6 to 9.12 to 17 of the present invention, the strength was 30 kg/mm.
``From the above, it was found that the toughness was 5 MN/m2 or more and that it exhibited excellent corrosion resistance.In addition, for each sample, the specific gravity and hardness of the cut pieces from the center and outer periphery of the sintered body were measured. However, almost no difference was observed, and it was a uniform dense body.

However, in sample NO5, the sintering temperature was low, resulting in poor sintering, and in sample NOI, 2.10.11, the blending ratio of the aluminum component was within the range of the present invention, and in sample No. 3, 18, 19, 20, the blending ratio of the chromium component was within the range of the present invention. Excellent properties in terms of strength, toughness, or corrosion resistance could not be obtained because of the deviation from the standard.

According to sample No. 021.22, it is clear that the excellent properties of the present invention cannot be obtained if the additive components according to the present invention are missing or other sintering aids are used.

〔Effect of the invention〕

As described above, the silicon carbide sintered body obtained by the manufacturing method of the present invention has excellent strength and toughness characteristics by uniformly densifying the inside and outside of the sintered body. Furthermore, it exhibits high corrosion resistance and can provide contact parts that require excellent corrosion resistance even under harsh conditions, such as skid buttons that contact iron materials at high temperatures.

Claims (2)

[Claims] (1) A silicon carbide sintered body containing an aluminum component of 3.5 to 10% by weight in terms of aluminum element, a chromium component of 0.2 to 5% by weight in terms of chromium element, and a residual amount of silicon carbide. Therefore, analysis using an X-ray microanalyzer revealed that particles containing chromium as a main component, aluminum and silicon, and showing high brightness under a metallurgical microscope were present in the grain boundaries containing the aluminum and chromium components. Features: Silicon carbide sintered body. (2) 3.5 to 10% by weight of at least one selected from the simple substance and compounds of aluminum in terms of aluminum element, and 0.2 to 5% by weight of at least one selected from the simple substance and compounds of chromium in terms of chromium element. 1. A method for producing a silicon carbide sintered body, which comprises mixing starting materials containing silicon carbide with the remainder being silicon carbide, and then pressure molding and sintering or pressure sintering the mixed powder.