JPH046672B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention is a silicon nitride material that is used as a high-temperature structural material, and has excellent joint strength (hereinafter referred to as bending strength) of the joint part for obtaining molded products with complex desired shapes. The present invention relates to a bonded body made of quality materials and a method for bonding the same. Conventional technology In general, this type of joined body has a weak bending strength at high temperatures if it is joined at a relatively low temperature, and on the other hand, a joined body with high bending strength at the joint part using a method that can be expected to have little deterioration in strength at high temperatures. difficult to obtain. Conventional bonding methods using hot presses are not suitable for bonding parts with complex surfaces because a load can only be applied in one direction. In addition, the method using HIP (hot isostatic pressing) requires a glass capsule, and the reaction between the glass of the capsule and the bonding material causes the bending strength of the bonded part to be low, and the work process is long and complicated. . In addition, the method of applying a slurry containing silicon nitride to the bonding surface and sintering it causes less deterioration in bending strength at high temperatures, but due to the high temperature heat treatment, the already processed surface may become rough and sintered. The subsequent bending strength is not sufficient.
Further, a method in which a glass component or an oxide containing silica, alumina, etc., which becomes a glass phase, is applied to the joint surface and sintered can provide a certain degree of bending strength, but the bending strength deteriorates significantly at high temperatures. Furthermore, in the method of mirror-finishing the bonding surfaces and performing heat diffusion bonding, the bending strength of the bonded portion is low. Problems to be solved by the invention In view of the above-mentioned current situation, the inventor has conducted extensive research and found that
The surface of a silicon nitride material having a surface roughness below a certain level is heat-treated to generate an appropriate oxide layer on the surface, and then the surfaces are joined together and heat-treated in nitrogen gas or an inert atmosphere containing nitrogen. It has been found that a bonded body of silicon nitride material having a bonding layer of 20 μm or less and a bending strength of the bonded portion of 250 MN/m ² or more can be obtained by this method. Purpose of the Invention The present invention provides a bonded body made of silicon nitride material that has excellent bending strength (joint strength) of the bonded portion, especially at high temperatures.
Another object of the present invention is to provide a method in which materials can be joined relatively easily even when the joining surfaces have relatively complicated shapes. Means for Solving the Problems The present invention is a bonded body of silicon nitride materials, in which the bonding layer is 20 μm or less, and the bending strength of the bonded portion having the bonding layer is 20 μm or less.
A bonded body of silicon nitride material having a density of 250 MN/m ² or more is provided. In addition, in order to obtain the above bonded body, the surface of the silicon nitride material with a surface roughness of Ra10 or less was
0.5-24 in an oxidizing atmosphere containing oxygen at 900-1500℃
A suitable oxide layer is formed on the surface by heat treatment for a period of time, and the surfaces of the silicon nitride materials are bonded together using this oxide layer as an adhesive medium, and then placed in a nitrogen gas or an inert atmosphere containing nitrogen at a pressure of 1 to 10 atm. 1300〜
A method for joining silicon nitride materials is provided, which involves heat treatment at 1800° C. for 2 to 168 hours. In the bonding method of the present invention, it is necessary that the surface roughness of both silicon nitride materials to be bonded is less than Ra10; if it exceeds Ra10, sufficient bending strength of the bonded portion will not be obtained even if bonding is possible. . In addition, in the present invention, the surfaces of both silicon nitride materials to be joined are heat-treated for 0.5 to 24 hours in an oxidizing atmosphere at 900 to 1500°C to which oxygen is actively supplied, to form a suitable oxide layer on the surfaces. This is very important. By actively supplying oxygen to the oxidizing atmosphere at such a heat treatment temperature and time, it is possible to form a dense oxide layer that is uniform and has an appropriate thickness on the surface of the material. Heat treatment temperature
At temperatures below 900℃, an oxide layer with a sufficient thickness suitable for bonding cannot be produced, and at temperatures above 1500℃, the strength of the silicon nitride material itself deteriorates due to oxidation, and the surface of the material has many pores, resulting in uneven thickness. This results in an oxide layer that does not become dense, making it unsuitable for bonding. In addition, heat treatment
If it is less than 0.5 hours, an oxide layer with sufficient thickness suitable for bonding cannot be generated, and if it exceeds 24 hours, the oxidation reaction progresses and the strength of the material itself deteriorates. Furthermore, in the present invention, the silicon nitride materials are bonded together using the oxide layer formed on the surface of the silicon nitride material in the above step as an adhesive medium, and then placed in a nitrogen gas or an inert atmosphere containing nitrogen at 1 to 10 atm. at 1300~1800
It is necessary to heat treat at ℃ for 2 to 168 hours (7 days). Heat treatment conditions: less than 1300℃,
At temperatures above 1800°C, times of less than 2 hours, more than 168 hours (7 days), and atmospheric pressures of less than 1 atm and more than 10 atm, the oxynitride crystal phase generated in the oxide layer at the joint cannot be sufficiently obtained. First, it is difficult to obtain a joined body with sufficient bending strength at high temperatures. Furthermore, in the bonded body obtained by the bonding method detailed above, the thickness of the bonding layer is 20 μm or less, and the bending strength of the bonded part having this bonding layer is
Certified to be 250MN/m2 or ^more . In other words, when joining by the hot press method, silicon nitride powder is interposed between the joint surfaces, and this is used as an adhesive medium for pressure firing, so the bending strength is 250 MN/
Even if a bonding layer of more than m ² is obtained, the bonding layer will be extremely thick and will not be less than 20 μm. Similarly, in HIP (hot isostatic pressing), silicon nitride powder is interposed between the joint surfaces of both materials in a glass capsule, and this is used as an adhesive medium, so the bending strength is 250 MN/ ^m2 or more. Even if something could be obtained, the bonding layer would be extremely thick and would not be less than 20 μm. The method of applying a silicon nitride slurry to the joint surface and firing, and the method of applying a glass component or oxide containing silica, alumina, etc. that becomes the glass phase to the joint surface and firing are the same as in the case of hot pressing and HIP. 250MN/
Although a bending strength of the bonded portion of m ² or more can be obtained, the thickness of the bonded layer cannot be less than 20 μm. On the other hand, in the method of mirror-finishing the bonding surfaces and heat diffusion bonding, the thickness of the bonding layer is extremely thin, less than 20 μm, but the bending strength of the bonded portion is less than 250 MN/ ^m2 , making it impossible to obtain a bonded body with sufficient strength. . Example 1 A fired body consisting of 92% by weight of silicon nitride (95% by weight of α type) and 4% by weight of alumina and 4% by weight of yttria as sintering aids was prepared in the vertical direction shown in FIG.
A plurality of pairs of members 1 and 2 to be joined were obtained, each of which had dimensions l1, width l2, and thickness d of 20×25×3±0.1 mm, and was formed into a corrugated shape with concavities and convexities having a radius R of 8 mm on the joint surfaces S1 and S2.
The joining surfaces S1 and S2 of the plurality of members to be joined 1 and 2 were polished using a diamond grindstone with a radius R so that they had Ra values shown in the surface roughness (Ra) column of Table 1. After that, as shown in Figure 2, protective materials 3 and 4 (used as necessary to prevent oxidation of other surfaces)
The members to be joined 1 and 2 polished by the method are heated in an oxidizing atmosphere in which oxygen is actively supplied and controlled according to the heat treatment temperature and heat treatment time shown in the oxide layer production joining conditions column of Table 1, and the bonding surfaces S1 and S2 are heated. A moderate oxide layer was formed. Next, as shown in FIG. 3, each pair of members to be joined 1 and 2 are joined using this oxide layer as an adhesive medium, and each pair is heated at 1200°C for 3 hours to form a joined body 5 as shown in FIG. Obtained. Thereafter, the obtained bonded bodies 5 were heat-treated at the gas pressure (nitrogen atmosphere), heat treatment temperature, and heat treatment time shown in the post-bonding heat treatment column of Table 1 to obtain Samples 1 to 27 in Table 1. Each of these samples 1
27, the thickness of the bonding layer was measured using a scaled microscope before the destructive test. In addition, a test piece was cut out according to JISR1601 so that the joint was in the center, and it was heated at room temperature and 1100 mm with a bottom span of 30 mm and a top span of 10 mm.
A four-point bending test was conducted at ℃. The above results are the first
Shown in the table.

【table】

[Table] Samples marked with * are outside the scope of the present invention.
As can be seen from Table 1, Sample 1, in which the surface roughness of the joint surface was Ra10 or less, had extremely low bending strength.
Sample 3 where the heat treatment temperature during bonding was outside the range of 900 to 1500 °C and the heat treatment time was outside the range of 0.5 to 24 hours,
In Nos. 7, 8, and 12, the bonding layer was not thick enough or had defects, resulting in deterioration in bending strength. Regarding the heat treatment conditions after bonding, sample 17 in which the gas pressure exceeds 10 atm in a nitrogen gas atmosphere has a particularly low bending strength of about 248MN/ ^m2 at 1100℃, and the heat treatment temperature and time are 1300 to 1800℃ and 2 to 168℃.
Samples 18, 22, 23, and 27 outside the time range all had particularly deteriorated bending strength at high temperatures of about 230 MN/m ² or less. In contrast, samples 2, 4-6, 9-11, 14-16, 19-21 and
Samples 24 to 26 all have a bending strength of 260 MN/ ^m2 or higher at 1100°C, and sample 15 in particular has a bending strength of 1100 MN/m2 or higher.
The bending strength at ℃ is 341MN/ ^m2 , which is excellent.
In addition, the thickness of the bonding layer in each sample within the scope of the present invention is 20 μm or less, and the bending strength is
It is excellent at ^over 260MN/m2. Example 2 Next, samples 15 and 26 in the above example and a pair of objects to be joined having the same composition and shape as in the above example were subjected to the conventional hot pressing method and HIP (hot isostatic pressing method). ), multiple samples were bonded using an atmosphere firing method in which a slurry of silicon nitride raw material was applied to the joint surfaces, an atmosphere firing method in which a glass component or an oxide to become the glass phase was applied to the joint surfaces, and an atmosphere firing method using mirror treatment. Comparative examples are shown in Table 2.

【table】

[Table] Samples marked with * are representative numbers of multiple samples joined using the conventional joining method.
Samples 28 to 31, which were bonded using the conventional technique, had bending strength at room temperature that of sample 15 of the present invention.
It is about the same level as 26 or slightly lower, but
It is understood that the bending strength at a high temperature of 1100° C. is significantly deteriorated compared to the examples falling within the scope of the present invention, and the bonding layer is thick at 400 μm or more.
Sample 32 has a bonding thickness of about 14 μm, but it is understood that its bending strength at room temperature and 1100° C. is extremely low.

[Brief explanation of drawings]

1 to 4 are process diagrams of a joining method constructed according to the present invention. 1, 2... Member to be joined, 3, 4... Protective material, 5
...Zygote.

Claims (1)

[Claims] 1. A bonded body of silicon nitride materials, in which the bonding layer is 20 μm or less, and the bending strength at high temperatures of the bonded portion having the bonding layer is 20 μm or less.
A bonded body of silicon nitride material, characterized in that it has a density of 250 MN/m ² or more. 2 The surface of a silicon nitride material with a surface roughness of Ra10 or less is heat treated in an oxidizing atmosphere containing oxygen at 900 to 1500°C for 0.5 to 24 hours to form an oxide layer on the surface, and this oxide layer is The surfaces of silicon nitride materials are bonded together as an adhesive medium, and then heated at 1300 m in nitrogen gas or an inert atmosphere containing nitrogen at a pressure of 1 to 10 atm.
A method for joining silicon nitride materials, characterized by heat treatment at ~1800°C for 2 to 168 hours.