JPS6213310B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a high-density and high-strength silicon nitride sintered body. In recent years, there has been active development of equipment that operates at high temperatures, such as high-temperature gas turbines, diesel engines, and MHD power generation, with the aim of improving thermal efficiency, saving fuel, reducing pollution, and reducing weight. However,
The development of these devices is focused on the development of high-temperature structural materials, and the formation of these materials is attracting attention, but conventional heat-resistant metals do not necessarily have sufficient mechanical strength at such high temperatures. In addition, from the perspective of saving heat-resistant metal materials, which are scarce in resources, ceramics made from Si, Al, C, N, etc., which are relatively abundant on earth, are being developed as high-temperature structural materials. Further, the importance of the development of such high-temperature structural materials for use as tools as high-hardness members and as corrosion-resistant materials is similarly recognized, and great interest is being focused. In particular, among these high-temperature ceramic constituent materials, silicon nitride (Si ₃ N ₄ ) is attracting attention as one of the most promising materials that has sufficient strength at high temperatures, is chemically stable, and is resistant to thermal shock. There is. This Si ₃ N ₄ has excellent physical properties as mentioned above, but this is because Si ₃ N ₄ is composed of silicon (Si) and nitrogen (N).
This is because it is a compound consisting of a strong covalent bond with. On the other hand, this means that it is extremely difficult to manufacture products with high density and high strength, and most of the research in this field has focused on how high density and high strength Si ₃ N ₄ At present, most of the time is spent on manufacturing molded bodies. Conventionally, as a method for manufacturing such high-strength Si ₃ N ₄ sintered bodies, recently, hot isostatic pressing (hereinafter referred to as HIP) method is used to press inert gas at high temperature and pressure to shape Si ₃ N ₄ powder into a predetermined shape. A method has been proposed for increasing the density by acting on a compacted compact or a presintered compact obtained by presintering the same. However, when the present inventors conducted an experiment on the correlation between the relative density and strength of the Si ₃ N ₄ sintered body obtained in this way, it was found that the relative density and strength of the Si ₃ N ₄ sintered body were It was found that there is not necessarily a correlation between the two. Therefore, the present inventors further investigated and conducted experiments focusing on the β-type Si ₃ N ₄ of the pre-sintered body. As a result, the β-type Si ₃ N ₄ content of the pre-sintered body and the sintered body It was found that there is a correlation with strength. The present invention has been made based on this knowledge, and provides _a method for producing a high-density and high-strength Si ₃ N ₄ sintered body. A pre-sintered body with a relative density of 80% or more and a β-type Si ₃ N ₄ content of 20 to 80% is produced by adding and mixing a sintering aid to N ₄ powder, molding it into a predetermined shape, and sintering it. Then, the pre-sintered body was heated to 1600°C.
under a high-temperature, high-pressure gas atmosphere of 500 atmospheres or more.
By performing the HIP treatment, most of the residual α-type silicon nitride is turned into β, and a high-density Si ₃ N ₄ sintered body with a relative density of 95% or more is obtained. The present invention will be explained in more detail below. First, the raw materials for the Si ₃ N ₄ powder used in the method of the present invention are those obtained by the nitriding method of metal Si, as well as SiCl ₄ and SiO ₂ reduced powders, gas phase reaction methods, and thermal decomposition methods.
Those manufactured from Si(NH) ₂ are used, but from the viewpoint of the bending strength of the resulting Si ₃ N ₄ sintered material, those manufactured by a gas phase reaction method and a thermal decomposition method are preferable. Note that the ratio of the amorphous, α-type, and β-type of the Si ₃ N ₄ powder is such that the content of β-type Si ₃ N ₄ in the preliminary sintered body obtained by preliminary sintering can be 20 to 80%, as described later. Needless to say, it can be anything. Sintering aids added to the Si ₃ N ₄ powder include oxides or nitrides of Y, Al, Mg, Ti, etc.
ZrO ₂ , BeO, La ₂ O ₃ , CeO ₂ , etc. or a mixture thereof, and the amount of these sintering aids added is 30% by weight or less, preferably 5 to 15% by weight based on the Si ₃ N ₄ powder. Weight%. Si ₃ N ₄ containing sintering aid
The powder is molded into a predetermined shape by an injection molding method, a pressure molding method, a die press molding method, a hydrostatic molding method, or the like. The molded body formed into the predetermined shape is then pre-sintered to obtain a pre-sintered body having a relative density of 80% or more and a β-type Si ₃ N ₄ content of 20 to 80%. Preliminary sintering can be performed by a hot press sintering method, a method of sintering near atmospheric pressure or under a high pressure N ₂ gas atmosphere, but it is preferable to sinter in a non-oxidizing atmosphere such as N ₂ gas. In this case, the sintering temperature varies depending on the type and amount of the sintering aid added and the sintering time, but is suitably 1400 to 1800°C. Figure 1 is an example showing the relationship between the sintering temperature and _the α-type Si ₃ N ₄ content of _the pre-sintered body.
Sintering temperature when 1% by weight, 3% by weight, and 5% _by weight of MgO were added to 6% by weight of Y ₂ O ₃ and 2% by weight of Al ₂ O 3 and sintered for 200 minutes at different sintering temperatures. This figure shows the relationship between α-type Si ₃ N ₄ content of the pre-sintered body and α-type Si 3 N 4 content. As is clear from Figure 1, the α-type Si ₃ N ₄ content of the pre-sintered body varies depending on the amount of sintering aid added, but when the sintering temperature is in the range of 1500 to 1600°C, α-type Si ₃ N ₄ The content is approximately 80% to 20%, therefore the β of the pre-sintered body
In order to obtain a mold Si ₃ N ₄ content of 20 to 80%, the sintering temperature is preferably in the low temperature range of 1500 to 1600°C. On the other hand, the sintering time varies depending on the type and amount of the sintering aid added and the sintering time, but is suitably 50 to 200 minutes. Figure 2 is an example showing the relationship between the sintering time and _the α-type Si ₃ N ₄ content _{of the pre} -sintered body. ₂ O ₃ to 2% by weight
Sintering time and α-type Si 3 N 4 of pre-sintered body when sintering was carried out by adding 1% by weight, 3% by weight, and ₅ % by weight of MgO, respectively, and changing the sintering time at a sintering temperature of ₁₆₀₀ °C. It shows the relationship with the content rate. As is clear from Figure 2, the α-type Si ₃ N ₄ content of the pre-sintered body varies depending on the amount of sintering aid added, but the sintering time is 50 to 200.
In the range of minutes, the α-type Si ₃ N ₄ content of the pre-sintered body is
approximately 80-20%, and therefore the β type of the pre-sintered body
The sintering time is 50% for _Si3N4 content of 20-80% _.
It turns out that setting the time to ~200 minutes is appropriate. What is important in this preliminary sintering is that the bending strength of the preliminary sintered body obtained by the preliminary sintering is increased by the HIP treatment described later, and the β-type Si ₃ N ₄ of the preliminary sintered body is It is necessary that the content is 20-80%. The reason for this is not clear, but if the content of β-type Si ₃ N ₄ in the preliminary sintering exceeds 80%, the fracture surface after the bending test of the Si ₃ N ₄ sintered body obtained by HIP treatment is Observation shows that the content of β-type Si ₃ N ₄ is 80
% or less, that is, the α-type Si ₃ N ₄ content is 20% or more, which is considered to prevent the β-type crystals generated or grown by the HIP treatment from becoming coarser. The pre-sintered body obtained as described above is then
Relative density 95% or more after HIP treatment, β-type Si ₃ N ₄
The content is preferably a high-density sintered body of 95% or more. In this case, the relative density of the pre-sintered body is 80% or more, but if the relative density of the pre-sintered body is low within this range, the pores in the sintered body are open pores that communicate with the surface. If the HIP process is performed as it is, only the closed pores will disappear and the open pores will remain, so the pre-sintered body with a low relative density should be made of oxides or nitrides such as Si or Al. It is preferable to cover the sintered body, perform a sealing process, and then subject it to HIP treatment, but according to the research of the present inventors, when the relative density of the preliminary sintered body is 92% or more, air bubbles in the sintered body are
Most of them have open pores that do not open on the surface, so there is no need to seal them, so you can use HIP as is.
Can be subjected to processing. Of course, the relative density is 92%
Even with the above pre-sintered bodies, coating treatment may be performed for other purposes such as preventing the decomposition reaction of Si ₃ N ₄ when using Ar gas as the pressure medium gas.
It goes without saying that HIP processing is possible. HIP processing is performed in an inert gas atmosphere such as Ar gas or N ₂ gas, but it is recommended to perform it in an N ₂ gas atmosphere because it can prevent the decomposition reaction of Si ₃ N ₄ and increase the density. preferable. HIP temperature is 1600℃ or higher, preferably
The temperature is preferably 1700 to 2000°C, which is higher than the pre-sintering temperature. This HIP temperature must naturally be below the decomposition temperature of Si ₃ N ₄ , and this decomposition temperature also increases the HIP pressure, but it must be at least 100°C lower than the decomposition temperature at the pressure during the HIP process. It is preferable to carry out the following. Next, it is best to perform HIP at a pressure of 500 atm or higher. If the HIP pressure is lower than 500 atm, the HIP process will take a long time and the amount of Si ₃ N ₄ decomposed will increase in proportion to the time, resulting in a decrease in the weight of the sintered body. In addition to inviting
High density itself becomes difficult to achieve. Therefore, it is desirable that the HIP pressure be at least 500 atmospheres, preferably 700 atmospheres or more. On the other hand, the higher the HIP pressure, the more likely it is to suppress the decomposition reaction of Si ₃ N ₄ and achieve higher density. This increases the size of the device, making it impractical. Therefore, practically 2500
It is desirable to HIP at pressures up to atmospheric pressure. Moreover, it is preferable that the HIP treatment time is in the range of 5 minutes to 5 hours. The Si ₃ N ₄ sintered body subjected to the HIP treatment as described above becomes a high-density sintered body with a relative density of 95% or more. As described above, in the method of the present invention, the content of β-type Si ₃ N ₄ in the pre-sintered body is set at 20 to 80% and the HIP treatment is performed. In addition, most of the Si ₃ N ₄ sintered body obtained by HIP treatment is β-type Si ₃ N ₄
, and its structure is minute.
A high-density Si ₃ N ₄ sintered body with improved bending strength can be produced. In addition, HIP processing allows for easy densification and high-temperature processing, so it is possible to convert α-type Si ₃ N 4 to β-type Si 3 N ₄ .
The time required for transition to type Si ₃ N ₄ can be shortened, and costs can be reduced by shortening processing time. Furthermore, since the method of the present invention involves molding a mixture of Si ₃ N ₄ powder and a sintering aid into a pre-sintered body, it is easy to mold even complex shapes, and moreover, it can be easily molded by HIP treatment. Since it is possible to increase the density and improve the strength, the method of the present invention has _the advantage that it is possible to easily produce a high-density and high-strength Si ₃ N ₄ sintered body of any complex _shape . This method is extremely effective as an industrial manufacturing method for sintered bodies. The method of the present invention will be explained in more detail below with reference to Examples. Example 1 As a raw material powder, commercially available Si ₃ N ₄ powder (α type content 90%, β type content 10%) produced by nitriding metal Si was used.
%, average particle size 1 μm), and 6% by weight _{of Y2O3} , 2% by weight of MgO3, and ₂ % by weight of _Al2O3 as sintering aids.
were added and mixed, and after cold forming at a pressure of 1 ton/ ^cm2 , each was sintered at different sintering temperatures in a _N2 stream under atmospheric pressure.
Sintering was performed for 200 minutes to produce preliminary sintered bodies having the characteristics shown in Sample Nos. 1 to 7 of Table 1. Next, these preliminary sintered bodies were prepared as Samples Nos. 1 to 7 in Table 2 without sealing.
HIP processing was performed under the HIP processing conditions shown in Table 2, and the characteristics of the obtained sintered material were investigated.
The results shown are obtained. Sample No. in Tables 1 and 2.
Samples 1 to 4, 6 and 7 are examples of the present invention, and Sample No. 5 is a comparative example.

【table】

[Table] As is clear from the results in the table above, sample No. of the comparative example.
Samples Nos. 1 to 4, 6, and 7 of the present invention examples except No. 5 have β-type content in the pre-sintered body in the range of 25 to 76%, and in all of them, the relative density is improved by HIP treatment,
Moreover, it can be seen that the bending strength is significantly improved. On the other hand, in sample No. 5 in which the β-type content of the preliminary sintered body exceeds 80%, although the relative density is improved by the HIP treatment, the bending strength is rather decreased. In addition, sample No. ₂ uses N2 gas as the pressure medium gas.
Comparing Sample No. 1 and Sample No. 3, which used Ar gas, and looking at the influence of the type of pressure medium gas during HIP treatment, it was found that Ar
In the case of gas, no improvement in relative density was observed after HIP treatment, but bending strength was improved;
In the case of N ₂ gas, both the relative density and the bending strength are improved by HIP treatment, and it is clear that it is preferable to use N ₂ gas as the pressure medium gas. Example 2 Using the same Si ₃ N ₄ powder as in Example 1, the samples in Table 1 were prepared.
As shown in Nos. 8 to 12, the type and amount of sintering aid added were changed, and Nos. 8, 9, and 12 were molded and presintered in the same manner as in Example 1, and Nos. 10 and 11 were 1600℃ and 1700
Preliminary sintering was carried out by hot pressing at 250 kg/cm ² for 30 minutes at a temperature of 0.degree. Next, these preliminary sintered bodies were subjected to HIP treatment in the same manner as in Example 1 under the HIP treatment conditions shown in Sample Nos. 8 to 12 of Table 2, and the characteristics of the obtained sintered bodies were investigated. The results shown in Sample Nos. 8 to 12 in Table 2 were obtained. In Tables 1 and 2, sample No.
Sample Nos. 9 and 10 are examples of the present invention, and Samples Nos. 8, 11, and 12 are comparative examples. From the results in the table above, samples No. 9 and 10, which are examples of the present invention,
It can be seen that even though the sintering aid was different from that in Example 1, the relative density was improved by the HIP treatment in all cases as in Example 1, and the bending strength was greatly improved. In contrast, the β-type content of the pre-sintered body was 81
%, 90% or 100% high samples No. 8, 11 and
Although the relative density of No. 12 increases with HIP treatment, there is almost no improvement in bending strength, and even if the β-type content of the pre-sintered body is 100%, the It can be seen that the strength is not improved. Example 3 Produced by gas phase method as raw material Si ₃ N ₄ powder
Si ₃ N ₄ powder (amorphous part 60%, α type content 57
%, β type content 3%, average particle size 1 μm),
The same sintering aid as in Example 1 was mixed, molding and preliminary sintering were performed in the same manner as in Example 1, and Sample No. 1 in Table 1 was obtained.
Preliminary sintered bodies with the characteristics shown in 13 and 14 were prepared. Next, these preliminary sinterings were performed in the same manner as in Example 1, and HIP processing was performed under the HIP processing conditions shown in Table 2 Sample Nos. 13 and 14, and the characteristics of the obtained sintered bodies were investigated.
The results shown in Sample Nos. 13 and 14 in Table 2 were obtained. 1st
In Table 2, Sample No. 13 shows the present invention, and Sample No. 14 shows the comparative example. From the results in the table above, sample No. 13, whose pre-sintered body has a β-type content of 35%, has a β-type content of 83%.
The bending strength is greatly improved compared to sample No. 14, which is the same, and even if Si ₃ N ₄ powder produced by the vapor phase method is used, the effect of improving the bending strength of the sintered body by the method of the present invention is large. I understand that. Also, from the table above, when Si ₃ N ₄ powder produced by the vapor phase method is used as the starting material, the resistance by HIP treatment is lower than when Si ₃ N ₄ powder produced by the nitriding method is used as the starting material (Example 1). It is clear that the effect of improving the bending strength is significantly large. Example 4 Using the same Si ₃ N ₄ powder as in Example 1, the samples in Table 1 were prepared.
Example 1 by adding and mixing the sintering aids shown in Nos. 15 and 16.
Molding and preliminary sintering were performed in the same manner as in Table 1, No.
Preliminary sintered bodies with the characteristics shown in 15 and 16 were prepared.
These preliminary sintered bodies were immersed in an organic solvent slurry of mixed powder of 80% by weight of Si ₃ N ₄ , 10% by weight of SiO ₂ , and 10% by weight of Al ₂ O ₃ to coat the surface.
The openings were sealed by drying and firing. Next, in the same manner as in Example 1, HIP treatment was performed under the HIP treatment conditions shown in Table 2 Samples No. 15 and 16, and the properties of the obtained sintered bodies were investigated. The results shown in 16 were obtained. In Tables 1 and 2, sample No.
Sample No. 15 shows an example of the present invention, and Sample No. 16 shows a comparative example. From the table above, the sample has a pre-sintered body with a β-type content of 66%.
No. 15 has a greater increase in bending strength due to HIP treatment than sample No. 16, which has a β-type content of 95%.
It can be seen that the method of the present invention has a large effect of improving the bending strength of the sintered body even when the HIP treatment is performed with a sealing treatment performed during the HIP treatment. Combining the results of Examples 1, 2, 3, and 4 above,
According to the method of the present invention, the effect of improving relative density and bending strength is large, and high density and high strength Si ₃ N ₄
It is clear that sintering can be produced.

[Brief explanation of the drawing]

Figure 1 is a graph showing an example of the relationship between sintering temperature and α-type content in the pre-sintered body, and Figure 2 is a graph showing an example of the relationship between sintering time and α-type content in the pre-sintered body. It is a graph.

Claims (1)

[Claims] 1. A sintering aid is added to and mixed with silicon nitride powder, which is molded into a predetermined shape and then sintered to achieve a relative density of 80%.
As described above, a pre-sintered body with a β-type silicon nitride content of 20 to 80% is produced, and then the pre-sintered body is subjected to hot isostatic pressing in a high-temperature, high-pressure gas atmosphere of 1600°C or higher and 500 atm or higher. A method for producing a high-density silicon nitride sintered body, characterized in that most of the residual α-type silicon nitride is turned into β by this process, and a high-density silicon nitride sintered body with a relative density of 95% or more is obtained. 2. The method for producing a high-density silicon nitride sintered body according to claim 1, wherein the silicon nitride powder is produced by a gas phase reaction method or a thermal decomposition method. 3 Y ₂ O ₃ , Al ₂ O ₃ , MgO as sintering aids,
The high-density silicon nitride sintered material according to claim 1 or 2, which contains at least 30% by weight of one or more of ZrO ₂ , TiO ₂ , BeO, La ₂ O ₃ , CeO ₂ , TiN, and AlN. Method for producing solids. 4 Sintering temperature is 1500~1600℃, sintering time is 50~
A method for manufacturing a high-density silicon nitride sintered body according to any one of claims 1 to 3, wherein the manufacturing time is 200 minutes. 5 The relative density of the preliminary sintered body is 92% or more,
5. A method for producing a high-density silicon nitride sintered body according to any one of claims 1 to 4, wherein the preliminary sintered body is subjected to hot isostatic pressing treatment without performing a sealing treatment. 6. The method for producing a high-density silicon nitride sintered body according to any one of claims 1 to 5, wherein the hot isostatic pressing temperature of the preliminary sintered body is equal to or higher than the sintering temperature. 7. The method for producing a high-density silicon nitride sintered body according to any one of claims 1 to 5, wherein the hot isostatic pressing treatment is performed in an _N2 gas atmosphere. 8. The method for producing a high-density silicon nitride sintered body according to any one of claims 1 to 7, wherein the β-type silicon nitride content after hot isostatic pressing is 95% or more.