KR101062442B1 - Low Temperature Sintered Silicon Carbide with Excellent High Temperature Properties and Manufacturing Method Thereof - Google Patents

Abstract

The present invention relates to low temperature sintered silicon carbide having excellent high temperature properties and a method of manufacturing the same. More specifically, an Al-BC-based mixture or compound was used as a sintering aid for sintering silicon carbide to obtain a dense sintered body, which is, for example, at least one selected from Al or Al ₄ C ₃ , B or B At least one selected from ₄ C and C, respectively, stoichiometrically mixed and used as it is as a sintering aid, or after the mixture is calcined in a reducing atmosphere to produce a compound and then used as a sintering aid Provided is a low temperature sintered silicon carbide having excellent high temperature properties and a method of manufacturing the same. At this time, the sintering aid prepared by calcining the compound preferably uses Al ₈ B ₄ C ₇ , Al ₃ BC ₃ or a mixture of these two compounds.

By using such a sintering aid, it is possible to obtain a densified sintered body by sintering at a temperature 150 ° C. or more lower than 2000 ° C., which is a sintering temperature of a conventional silicon carbide, and hardly generating secondary phases, and sintering at a conventional sintering temperature. The same physical properties as those of the silicon carbide sintered body can be obtained, so that the economics associated with the process can be improved, and various applications related to the silicon carbide sintered body can be obtained.

 Silicon Carbide, Sintered Body, Sintering Aid, Al8B4C7, Al3BC3, Al-B-C, Densification, Physical Properties, Process Economy, Low Temperature Sintering, High Temperature Properties

Description

Low temperature sintered silicon carbide having excellent high temperature properties and its manufacturing method {Low temperature sintered SiC having enhanced high temperature properties and the manufacturing method of the same}

The present invention relates to low temperature sintered silicon carbide having excellent high temperature properties and a method of manufacturing the same. More specifically, an Al-BC-based mixture or compound was used as a sintering aid for sintering silicon carbide to obtain a dense sintered body, which is, for example, at least one selected from Al or Al ₄ C ₃ , B or B At least one selected from ₄ C and C, respectively, stoichiometrically mixed and used as it is as a sintering aid, or after the mixture is calcined in a reducing atmosphere to produce a compound and then used as a sintering aid Provided is a low temperature sintered silicon carbide having excellent high temperature properties and a method of manufacturing the same. At this time, the sintering aid prepared by calcining the compound preferably uses Al ₈ B ₄ C ₇ , Al ₃ BC ₃ or a mixture of these two compounds.

By using such a sintering aid, it is possible to obtain a densified sintered body by sintering at a temperature 150 ° C. or more lower than 2000 ° C., which is a sintering temperature of a conventional silicon carbide, and hardly generating secondary phases, and sintering at a conventional sintering temperature. The same physical properties as those of the silicon carbide sintered body can be obtained, so that the economics associated with the process can be improved, and various applications related to the silicon carbide sintered body can be obtained.

Silicon carbide is a reinforcing material with high tensile modulus. If alumina (Al ₂ O ₃ ) is representative of oxide ceramics, silicon carbide can be said to be representative of non-oxide ceramics. Silicon carbide is particularly useful because it has excellent physical properties such as mechanical properties such as abrasion resistance, high temperature strength, creep resistance, thermal properties, oxidation resistance, and chemical resistance that represents corrosion resistance. Is widely used in 'mechanical seal', 'bearing', 'various nozzles', 'hot cutting tools', 'fireproof plates', 'abrasive materials', 'steel reducing materials', 'lightning arrester'.

However, the manufacturing cost of the silicon carbide sintered compact is not easy or easy, so the manufacturing cost is very high, and thus there is a limit that cannot be used more actively. Therefore, the manufacturing cost reduction is a big problem in manufacturing the silicon carbide sintered compact.

In particular, in Korea, silicon carbide is not produced at all, and high purity powders such as abrasives, refractory materials, and electricity products depend on imports of about 2,500 tons per month. It is of great economic value.

In the production of such silicon carbide sintered body, a sintering aid is essentially used. Such sintering aids include yttria-alumina-based, metal / iron / aluminum mixtures, beryllium compounds, and boron compounds.

However, even in the case of using such a sintering aid, in producing a silicon carbide sintered body having excellent physical properties at about 1600 ° C, it can be produced for a long time in a very high temperature environment of 2000 ° C or higher to produce a silicon carbide sintered body having a practical meaning. .

In particular, as a method of producing a silicon carbide sintered body having excellent high temperature strength by the liquid phase sintering method, high results have been reported (Kim et. al . Acta Mater., 2007), the sintered body was prepared by sintering at 2000 ℃ for 6 hours, using Sc ₂ O ₃ -Ru ₂ O ₃ -AlN as a social aid, the tensile strength at room temperature at 644MPa, 1600 ℃ Tensile strength of was measured at 600MPa.

Silicon carbide ceramics produced by liquid sintering at lower temperatures showed a sharp decrease in strength in many cases below 1500 ° C. For example, sintering at 1950 ° C was achieved with Al ₂ O ₃ -Y ₂ O ₃ -based sintering aids. However, there was a problem that strong plastic deformation was observed with the decrease in strength when measuring the bending strength at 1400 ° C. (AL Ortiz et al. , J. Europ. Ceram. Soc., 24, 3245-3249 (2004)). In addition, silicon carbide sintered using B ₄ C and C as sintering aids maintained strength higher than room temperature up to 1500 ° C, but there was a problem that a high sintering temperature of 2150 ° C was required for densification (G. Magnani et al. ., J. Europ. Ceram. Soc ., 21, 633-638 (2001)).

That is, the silicon carbide sintered body exhibiting excellent high temperature properties with low strength drop to 1500 ° C. still has a problem of having a very high sintering temperature and requiring a long sintering holding time. This high temperature, long time sintering requires a very large amount of energy, which leads to an increase in the manufacturing cost of the silicon carbide sintered body, therefore, a sintering aid that can control the sintering temperature and holding time while maintaining the properties of silicon carbide The development of and the development of densified silicon carbide sintered at low temperature is urgently needed.

The present invention has been made to solve the above-mentioned problems of the prior art, the present invention is theoretical density in spite of maintaining the sintering at a temperature lower than 150 ℃ for a short time compared to the sintering conditions of the conventional high temperature silicon carbide ceramics 1500 ℃ or higher It is an object of the present invention to provide a densified sintered compact which is close to, and to provide a silicon carbide sintered compact that does not fall in terms of physical properties at a high temperature of about 1500 ° C. or more as compared with the conventional high temperature silicon carbide sintered compact.

In addition, the present invention can reduce the manufacturing temperature of the silicon carbide sintered body by reducing the sintering temperature and at the same time can produce a densified sintered body despite the sintering by shortening the holding time than the conventional holding time of 6 hours or more. It is another object of the present invention to provide a sintering aid for the production of silicon carbide sintered compact, which can contribute to the process economy.

The present invention, in order to achieve the above object, at least any one selected from Al or Al ₄ C ₃ , at least any one selected from B or B ₄ C, and stoichiometrically mixed by mixing the sintering aid Manufacturing step; Mixing the sintering aid with silicon carbide; And sintering the mixture of the sintering aid and silicon carbide at a sintering temperature in the range of 1750 to 1900 ° C., thereby providing a low temperature sintered silicon carbide having excellent high temperature properties.

In addition, the present invention, in order to achieve the above object, at least one selected from Al or Al ₄ C ₃ , at least any one selected from B or B ₄ C, and the stoichiometric weighing step of mixing ; Heat-treating the mixture in a reducing atmosphere to produce a sintering aid compound; Mixing the sintering aid compound with silicon carbide; And sintering the mixture of the sintering aid compound and silicon carbide at a sintering temperature in a range of 1750 to 1900 ° C .;

The sintering step is preferably maintained at 3 minutes to 1 hour 30 minutes at the sintering temperature.

At least one selected from Al or Al ₄ C ₃ , at least one selected from B or B ₄ C, and the compound consisting of C are preferably Al ₈ B ₄ C ₇ or Al ₃ BC ₃ .

The sintering aid is preferably 0.5 to 1.5% by weight based on the total weight of the silicon carbide and the sintering aid mixture when the silicon carbide sintered body is manufactured.

In addition, the present invention provides a low-temperature sintered silicon carbide prepared by the above method, in order to achieve the object as described above, having excellent high temperature properties used as a high temperature material at a temperature of 1500 ℃ or more.

According to the present invention as described above, despite the sintering at a temperature lower than about 150 ℃ than the conventional silicon carbide sintering temperature, the effect that can produce a densified sintered body of the same level as the silicon carbide sintered at the temperature higher than that Have

Moreover, according to this invention, it has the effect of manufacturing the silicon carbide sintered compact which is inferior in a physical property, especially high temperature property compared with the conventional silicon carbide sintered compact.

In addition, according to the present invention, it is possible to reduce the load put into the overall process can reduce the manufacturing cost of the silicon carbide sintered body, and thus has the effect of improving the economics of the manufacturing process.

The present invention relates to a low-temperature sintered silicon carbide and a method for manufacturing the same, which have excellent high-temperature properties despite reducing the sintering temperature of the silicon carbide sintered body as much as possible within the practical range and shortening the sintering holding time.

In this case, in the present invention, in order to implement the above sintering conditions, a sintering aid was developed and used in particular, which is at least one selected from Al or Al ₄ C ₃ , at least one selected from B or B ₄ C, and C. It is a compound prepared by calcining a mixture consisting of or a mixture such as in a reducing atmosphere.

At this time, the above mixture and the compound may be mixed and used.

Especially in the case of compounds such as sintering aids, the starting materials are prepared by mixing the stoichiometrically and mixing the mixture, and heat-treating the mixture in an inert or reducing atmosphere.

At this time, the heat treatment conditions in the case of preparing the compound is preferably adjusted so that the maximum temperature is in the temperature range of 1300 ~ 1900 ℃, it is preferable to maintain for 30 minutes to 4 hours at the maximum temperature.

The sintering aid prepared as described above was confirmed to be an Al-B-C-based compound through X-ray analysis that a single phase compound was produced according to the stoichiometric ratio (not shown).

The heat treatment at the above temperature range and time range is because the different heat treatment temperatures are different in preparing compounds having various stoichiometric ratios. Can be prepared. Therefore, the present invention has the critical meaning in the above temperature range and time range.

The sintering aid compound prepared as above is preferably made of Al ₈ B ₄ C ₇ or Al ₃ BC ₃ . Among them, the degree of densification according to the sintering aid content of the silicon carbide sintered body manufactured by sintering by using Al ₃ BC ₃ as a sintering aid and maintained at 1850 ° C. within 1 hour and 30 minutes is shown in FIG. 1.

As shown, the degree of densification of the silicon carbide sintered body in the heat treatment period was somewhat different depending on the content of the sintering aid, but it was confirmed that the silicon carbide sintered body was densified within 1 hour and 30 minutes at 1850 ° C. The densification was completed after 3 hours at 1800 ° C and 1 hour at 1900 ° C.

In the present invention, since the sintering temperature is not higher than the conventional temperature, the sintering temperature range as described above is very appropriate because of its excellent densification and physical properties.

In addition, even in the case of the sintering holding time for a long time beyond the above upper limit may cause excessive growth of the particles is not preferable, so the upper limit as above has a critical significance. Of course, when sintering at a temperature shorter than the lower limit does not proceed well.

In short, the sintering aid according to the present invention was found to be densified even at a temperature lower than the sintering temperature of the conventional silicon carbide sintered body and a short holding time, even though the content was used in a very small amount of 0.75% by weight.

In the present invention, the sintered body of silicon carbide was prepared using the above sintering aid and the physical properties thereof were evaluated.

In Table 1, two kinds of samples were obtained by manufacturing a silicon carbide sintered body while varying the amount of the sintering aid, and one of them was reheated at 1300 ° C., and the physical properties thereof were measured at room temperature and compared.

Longitude (GPa) Young's modulus (GPa) Toughness (MPa · m ^1/2 ) Temperature (℃) 25 1300 25 1300 25 1300 2.5ABC 20.5 ± 0.6 20.8 ± 0.8 379 395 4.9 ± 0.1 5.0 ± 0.4 7.5ABC 23.0 ± 0.7 21.5 ± 1.3 389 393 5.6 ± 0.3 5.2 ± 0.4 10ABC 18.6 ± 0.8 - 377 - 6.1 ± 0.8

Here, ABC is an abbreviation of Al ₃ BC ₃ in the Al-BC-based sintering aid compound, numbers 2.5, 7.5, 10 in front of ABC are shown by the weight of the amount of the sintering aid, respectively.

As shown in Table 1 above, even when reheating the silicon carbide sintered body manufactured according to the present invention, deterioration hardly occurs in terms of hardness, Young's modulus, and toughness, and thus still retains excellent physical properties. This is because silicon carbide has a very good high temperature property, and a relatively small amount of Al ₃ BC ₃ , whose thermal stability is not superior to silicon carbide, is added.

In order to support this, in FIG. 2, 2.5ABC and 7.5ABC were selected from the two kinds of samples to observe the microstructure thereof, and crack propagation behavior before and after heat treatment at 1300 ° C. was shown using an electron micrograph. As shown, it can be seen that the fracture path proceeds evenly through the grain interface and the particles of the silicon carbide sintered compact, and thus it is assumed that deterioration due to the microstructure change of the silicon carbide sintered compact does not occur even after the reheat treatment. It was.

Here, (a) is the microstructure and crack propagation behavior of the silicon carbide sintered body sintered using 2.5% by weight of the sintering aid to the total weight of the mixture of silicon carbide and the sintering aid, (b) the entire mixture of silicon carbide and the sintering aid The microstructure and crack propagation behavior of the silicon carbide sintered body sintered using 2.5 wt% sintering aid after 1300 ° C reheating treatment, (c) 7.5 wt% sintering aid based on the total weight of the mixture of silicon carbide and sintering aid The microstructure and crack propagation behavior of the sintered silicon carbide sintered body using (d), (d) is 1300 ℃ reheat treatment of the sintered silicon carbide sintered using 7.5% by weight of the sintering aid to the total weight of the mixture of silicon carbide and sintering aid The later microstructure and crack propagation behavior are shown, respectively.

Meanwhile, in FIGS. 3 to 5, the content of the sintering aid according to the present invention is fixed, and a graph showing the stress-strain tendency is measured by changing the measurement temperature.

As shown in FIG. 3 and FIG. 4, it is apparent that the higher the measurement temperature, the smaller the stress is, the more easily deformed and the general stress tends to be lowered. However, when the graphs are compared, the content of the sintering aid is 7.5. In FIG. 3, which is% by weight, the slope of the stress-strain curve is the same and the strength is maintained up to 1300 ° C., but at 1500 ° C., the slope of the curve is greatly lowered and the strength is also decreased, resulting in a high temperature property. And it was found. Particularly, at 1600 ℃, the slope of the curve is further reduced and strength is greatly decreased as compared with 1500 ℃. In addition, the stress-strain curve is significantly out of linear relationship due to the significant deformation of the specimen during bending strength measurement.

As illustrated in FIG. 4, when the amount of the sintering aid was reduced to 2.5 wt%, it was found that the decrease in the slope of the stress-strain curve at 1500 ° C. was significantly smaller than that of the 7.5 wt% sintering aid. It was found that the high temperature properties of the sintered silicon carbide increased as the amount of addition decreased. However, in this case also, when the measurement at 1600 ℃, the slope of the curve decreases, the strength decreases and the plastic deformation behavior can be seen clearly.

However, as illustrated in FIG. 5, when the amount of the sintering aid was reduced to 1.25 wt%, it was found that the fracture stress at the high temperature of the silicon carbide sintered body was increased to improve the high temperature properties. That is, when 1.25% by weight, the slope of the stress-strain curve similar to room temperature was shown up to 1500 ° C. At 1600 ° C, the slope of the curve was observed, but at 1600 ° C, unlike the specimens containing more than 2.5% by weight of sintering aid The strength was maintained in large part in comparison with the room temperature strength and showed brittle fracture without showing plastic deformation behavior up to the point of failure. From these results, it can be seen that when the amount of the sintering aid is 1.25% by weight, the silicon carbide sintered body having similar physical properties to those at room temperature can be manufactured even at a very high temperature of 1600 ° C.

Especially in the case of silicon carbide sintered body manufactured with the amount of sintering aid to 0.75% by weight, it is still possible to densify at low temperature of 1850 ° C, but even at 1600 ° C, the slope of the stress-strain curve is almost the same as the value at room temperature. The strength value was also very high as 413MPa. This is because the Al-B-C sintering aid is a very efficient sintering aid in the production of silicon carbide sintered body, it is possible to densify silicon carbide at low temperature and short time compared to the case of using other sintering aids even with the use of a very small amount.

As the amount of sintering aid is reduced, the excellent high temperature properties of silicon carbide are expressed because the amount of Al ₃ BC _{3 which} is more unstable than silicon carbide is significantly reduced and the original high temperature properties of silicon carbide are expressed. .

Table 2 shows the four-point bending strength of the silicon carbide sintered body under vacuum and various temperature environments.

25 ℃ 1300 ℃ 1400 ℃ 1500 ℃ 1600 ℃ 0.75ABC 725 ± 155 - - - 413 ± 79 1.25ABC 584 ± 22 - 426 ± 11 446 ± 59 371 ± 82 2.5ABC 638 ± 48 552 ± 32 418 ± 86 467 ± 119 241 7.5ABC 564 ± 40 690 ± 23 390 ± 14 439 ± 85 226 7.5 ABC (Ar) 361 ± 27 209 10ABC 545 ± 88 - - 434 ± 124 -

As shown in the above table, the smaller the amount of sintering aid, the higher the bending strength value was. In particular, the strength of the silicon carbide sintered body made of 0.75 wt% sintering aid was about 413, especially at the strength of 1600 ° C. It was found to be very high as MPa.

FIG. 6 is a graph showing differential thermal weight analysis up to 1400 ° C. in air according to the sintering aid content of the silicon carbide sintered body prepared by adding the sintering aid of the present invention.

As shown, it was determined that the lower the content of the sintering aid, the higher the onset temperature of mass increase by oxidation. That is, the smaller the content of the sintering aid is estimated to be less deterioration of the sintered body due to oxidation, it can be seen that generally agrees with the trend shown in Table 2 above.

From these results, in order to satisfy both low temperature sintering and excellent high temperature strength of silicon carbide, the content of Al-BC-based sintering aid is preferably 0.5 to 1.5% by weight based on the total weight of the silicon carbide and sintering aid mixture. In the case of using the sintering aid in such a content, the silicon carbide sintered compact and excellent in physical properties can be produced despite the sintering of silicon carbide in the temperature range of 1750 ~ 1900 ℃.

As described above, the mechanical properties according to the content of the sintering aid was found to be better when the amount of the sintering aid is smaller, but when the content of the sintering aid is less than the above range value, the sintering retention time is long and the particles may grow excessively. And, there is a problem that the sintering temperature is increased, and when the content of the sintering aid is higher than the above range value, the silicon carbide sintered body is deteriorated at a high temperature, the content of the above sintering aid has a critical significance in that range.

Although the present invention has been described in more detail with reference to the embodiments, the present invention is not necessarily limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

1 is a measurement of the degree of densification according to the sintering aid content of the silicon carbide sintered body manufactured by sintering by using Al ₃ BC ₃ according to an embodiment of the present invention as a sintering aid and maintained at 1850 ° C. for 1 hour 30 minutes It is a graph.

FIG. 2 is an electron micrograph of 2.5ABC and 7.5ABC selected from among the sintering aids according to one embodiment of the present invention to observe the microstructure and observe the progress of cracking.

Figure 3 is a stress-strain measurement graph according to the temperature change of the silicon carbide sintered body manufactured using a 7.5 wt% sintering aid according to an embodiment of the present invention.

Figure 4 is a stress-strain measurement graph according to the temperature change of the silicon carbide sintered body manufactured by using a sintering aid of 2.5% by weight according to an embodiment of the present invention.

5 is a stress-strain measurement graph according to temperature change of a silicon carbide sintered body manufactured using 1.25% by weight and 0.75% by weight of a sintering aid according to an embodiment of the present invention.

Figure 6 is a graph showing the differential carbide weight analysis of the silicon carbide sintered body prepared by the addition of the sintering aid according to an embodiment of the present invention to varying sintering aid content to 1400 ℃ in the air.

Claims (6)

Preparing a sintering aid by stoichiometric mixing of Al ₄ C ₃ , B ₄ C and C; Mixing the sintering aid with silicon carbide; And Sintering the mixture of the sintering aid and silicon carbide at a sintering temperature of 1750 ~ 1900 ℃ range; configured to include, The sintering aid is a method for producing low temperature sintered silicon carbide having excellent high-temperature properties, characterized in that 0.5 to 1.5% by weight relative to the mixed weight of silicon carbide and the sintering aid. Stoichiometrically mixing and mixing Al ₄ C ₃ , B ₄ C and C; Heat-treating the mixture in a reducing atmosphere to produce a sintering aid compound; Mixing the sintering aid compound with silicon carbide; And sintering the mixture of the sintering aid compound and silicon carbide at a sintering temperature in the range of 1750 to 1900 ° C .; The sintering aid is a method for producing low temperature sintered silicon carbide having excellent high-temperature properties, characterized in that 0.5 to 1.5% by weight relative to the mixed weight of silicon carbide and the sintering aid. The method according to claim 1 or 2, The sintering step, Process for producing low temperature sintered silicon carbide having excellent high temperature properties, characterized in that for 3 minutes to 1 hour 30 minutes at the sintering temperature. The method of claim 2, The compound consisting of Al ₄ C ₃ , B ₄ C and C is Al ₈ B ₄ C ₇ or Al ₃ BC _{3 The} method for producing low temperature sintered silicon carbide having excellent high temperature properties. delete Prepared by the method of claim 1, Low temperature sintered silicon carbide having excellent high temperature properties, characterized in that it is used as a high temperature material at a temperature of 1500 ℃ or more.

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