JP2002356374A - Free cutting ceramic and its manufacturing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a low thermal expansive free cutting ceramic having excellent machineability and high strength by firing in atmospheric pressure. SOLUTION: Silicon nitride powder containing silicon oxide of 0.5 to 10 mass%, the mean grain diameter of which is <=5 μm, and boron nitride powder containing boron oxide of 2 to 15 mass%, the grain diameter of which is <=0.5 μm are mixed at a ratio of 40 to 85 mass% silicon nitride part to 15 to 60 mass% boron nitride part, then, 15 to 31 mass% sintering aide based on the sum of silicon nitride, boron nitride and sintering aid is mixed thereto, then, the obtained mixed powder is press formed, and fired in an inert gas of atmospheric pressure. The free cutting ceramic has >=200 MPa bending stress, <=4×10<-6> / deg.C thermal expansion coefficient at 25 to 300 deg.C, cutting speed of 18 m/min using carbide tool of K-10 and abrasion width of major flank of cutting tool of <=0.2 mm in the turning test for 5 min. under the condition that feeding speed is 0.03 mm/rev. and cutting is 0.1 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a free-cutting ceramic which has both good machinability and high strength and is made of a ceramic sintered body having low thermal expansion. Ceramics of the present invention, semiconductor manufacturing equipment members and semiconductor inspection equipment members,
It is also suitable for circuit boards and the like.

[0002]

2. Description of the Related Art Ceramic materials are excellent in mechanical characteristics and high-temperature characteristics, and therefore can be applied to semiconductor manufacturing equipment, semiconductor inspection equipment, and insulating structural members for circuit boards. However, since ceramics undergo large shrinkage during sintering, grinding is required to obtain a desired shape and dimensions with high accuracy, and at that time, the difficulty in processing the ceramics becomes a problem.

In order to improve the workability of ceramics, there is known a material called free-cutting ceramics in which another ceramic having a cleavage property, such as mica or boron nitride, is dispersed in a ceramic or glass matrix. However, in order to ensure workability that enables high-precision micromachining, it is necessary to achieve both high strength and good machinability. There are few that have workability. In addition, most of the conventional ceramics having excellent workability are manufactured by a method using pressure sintering, which is expensive and can produce only a simple shape. A free-cutting ceramic that can be fired at normal pressure, in which mica is dispersed in a glass matrix, is also known, but it has a large thermal expansion property, and there is a problem in that the working dimensional accuracy may be degraded due to changes in the operating temperature environment. Was.

[0004] As a ceramic having good workability, a mixture of a silicon nitride powder and a boron nitride powder, as described in Japanese Patent Publication No. 5-85504, is used.
There is a ceramic obtained by sintering a powder composition containing up to 10% by weight of a sintering aid (alumina and yttria). However, the ceramics disclosed in this publication do not have sufficient strength required for fine processing when fired at normal pressure,
Since the surface roughness was large due to the coarse raw material having an average particle diameter of 10 μm, fine processing on the order of several tens of microns using a carbide tool was impossible.

As a method for producing a composite material of silicon nitride and boron nitride by normal-pressure sintering, a raw material powder is prepared without adding a sintering aid, as described in Japanese Patent Application Laid-Open No. 1-131062. There are ceramics fired. However, since the ceramic material obtained by such a method has no sintering aid, the sintering is insufficient, and the strength is insufficient. Was.

[0006]

With the recent increase in the degree of integration of semiconductors, microfabrication such as micron-level holes and slits has been increasingly required for ceramics used in manufacturing equipment, inspection equipment, and circuit boards. It is required that the method can be performed with high accuracy. Since conventional materials do not have ceramics that have both high strength and machinability that can withstand them, it is desirable to provide such ceramics and a method for producing them by normal-pressure sintering that can produce complex shapes at low cost. Was rare.

The present invention can be manufactured by normal-pressure sintering, which can produce complex shapes at low cost, and has high machinability that can be easily machined with a carbide tool and high cracking or chipping during machining such as drilling. It is an object of the present invention to provide a free-cutting ceramic having both strength and low thermal expansion, which is less likely to be out of order even when the operating temperature environment fluctuates, and a method of manufacturing the same.

[0008]

Means for Solving the Problems The present inventors have developed a low thermal expansion ceramic which contains silicon nitride and boron nitride as main components and has a sintering additive, and has excellent workability at normal pressure firing. Investigations were repeated to produce ceramics. As a result, oxides inevitably present on the surfaces of the raw material silicon nitride powder and boron nitride powder, that is, silicon oxide and boron oxide, respectively, react with the sintering aid and burn with these oxides. A grain boundary glass phase composed of a reaction product with a binder (this is referred to as an auxiliary component in the present invention with respect to the main component) is formed, and the main component is bound by the grain boundary glass phase of the sub component. We noticed that sintering occurs. Here, the grain boundary glass phase includes any of crystalline, amorphous, and intermediate states thereof. When the amount of oxide on the powder surface is increased to some extent and a relatively large amount of sintering aid is added, a high-strength ceramic can be obtained even at normal pressure firing, and this ceramic has a poor machinability. Also found to be excellent.

This is considered as follows. Oxide present on the powder surface as the main ingredient (main ingredient)
(Boron oxide and silicon oxide) form an oxide layer covering the entire surface of the powder. By causing this oxide layer to participate in the sintering reaction as a reactive component, a grain boundary glass phase serving as a binder for the powder is generated so as to cover the entire surface of the powder and to be uniformly distributed throughout the sintered body. . In addition, the presence of oxides and sintering aids, which are the reaction components of the sintering reaction, in a sufficient amount, respectively, allows for normal pressure firing,
The main component nitride can be firmly and densely bonded in the grain boundary glass phase, resulting in a high-strength ceramic body.
Further, since the grain boundary glass phase is uniformly distributed, high strength is maintained and machinability is also improved, and particularly, the surface roughness of the processed surface is reduced.

The present invention provides a ceramic comprising a main component consisting of silicon nitride and boron nitride, and a subcomponent which is a reaction product of silicon oxide, boron oxide and a sintering aid, The main component is composed of 40 to 85% by mass of silicon nitride and 15 to 60% by mass of boron nitride, and the amount of the sintering aid is 15 to 31% by mass with respect to the total amount of the sintering aid and the main component. A free-cutting ceramic having a bending strength of 200 MPa or more and a coefficient of thermal expansion at 25 to 300 ° C. of 4 × 10 ⁻⁶ / ° C. or less.

[0011] The free-cutting ceramic of the present invention is made of carbide-K
Grinding speed using 10 kinds of tools 18 m / min, feed rate 0.03 mm /
rev, the tool flank wear width is less than 0.2 mm in a 5-minute turning test under the condition of 0.1 mm depth of cut, and the surface roughness of the work material is R
It exhibits excellent machinability of max 5 μm or less, and has high strength as described above, so that it is excellent in workability and can perform micromachining such as micron level holes and slits with high precision.

According to the present invention, there is also provided a silicon nitride powder having a silicon oxide content of 0.5 to 10% by mass, including a powder having a silicon oxide layer on the surface, and a powder having a boron oxide layer on the surface. A step of mixing a boron nitride powder having a boron oxide content of 2 to 15% by mass with a sintering aid, and a step of press-molding the obtained mixed powder into a predetermined shape. Baking the molded body in an inert atmosphere, wherein the ratio of the silicon nitride powder and the boron nitride powder in the mixing step is such that silicon nitride is added to the total amount of silicon nitride and boron nitride in the powder.
40 to 85 mass%, boron nitride is 15 to 60 mass%, and the amount of the sintering aid is 10 to 31 mass% based on the total amount of the silicon nitride and boron nitride and the sintering aid. A method for producing a free-cutting ceramic is also provided.

In a preferred embodiment of the method, the average particle diameter of the silicon nitride powder is 5 μm or less, and the average particle diameter of the boron nitride powder is 0.5 μm or less. Further, the firing step is preferably performed by normal pressure firing.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the ceramic of the present invention and a method for producing the same will be described more specifically.

The ceramic of the present invention is produced by firing each powder of the main raw materials, boron nitride and silicon nitride, together with a sintering aid under normal pressure. The raw material boron nitride powder is preferably hexagonal (h-BN).

Since the powders of boron nitride and silicon nitride are both oxidizable elements because boron and silicon are easily oxidizable elements, their surfaces are inevitably oxidized. With layers. The oxide layer on the powder surface participates in the sintering reaction during sintering as described above, and forms a glassy grain boundary phase composed of a reaction product of boron oxide, silicon oxide, and a sintering aid. Then, the ceramic of the present invention is obtained by sintering the nitride of the main component by the grain boundary glass phase as the subcomponent.

As described above, in order to positively utilize the oxide layer on the surface of the nitride powder as the main raw material as a sintering component, in the present invention, the amount of the oxide layer of these raw material powders, Is preferably within a specific range.

Specifically, among the raw material powders used in the present invention, the boron nitride powder has a boron oxide content of 2 to 15% by mass, preferably 5 to 12% by mass.
When the content of silicon oxide is 0.5 to 10% by mass, preferably 1 to
5% by mass. If the content of the oxide in the raw material powder is too small, sintering becomes insufficient at normal pressure firing, densification of the sintered body becomes insufficient, and a ceramic having low strength is obtained. When the content of the oxide in the raw material powder is too large, the grain boundary glass layer of the sintered body becomes too large, and the strength is also lowered.

The average particle size of the raw material powder is preferably 0.5 μm or less, more preferably 0.1 μm or less for boron nitride powder, and preferably 5 μm or less, more preferably 1 μm or less for silicon nitride powder. If a raw material powder having an average particle size that is too large is used, the fine structure of the sintered body becomes coarse and the strength is reduced, and the surface roughness after processing is increased, resulting in inconvenience in fine processing.

As the powders of boron nitride and silicon nitride, commercially available powders may be used as long as the oxide content and the average particle size are in the above ranges. Further, for the purpose of increasing the surface oxide layer, a powder obtained by heat-treating a fine boron nitride powder or a silicon nitride powder in an oxidizing atmosphere can be used. This heat treatment can be performed, for example, by heating the powder to a temperature of 800 to 1000 ° C. in the air. The oxide content of the powder can be analyzed by, for example, an oxygen nitrogen analyzer. If there is a purity indication for commercially available boron nitride and silicon nitride powders,
Most of the impurities can be considered as oxides.

Generally, the oxide content of each of the powders of boron nitride and silicon nitride depends on the surface area of the powder. Therefore, as the average particle size of the powder becomes smaller, the oxide content of the powder tends to increase. Therefore, especially when the average particle size of the powder is relatively large, the oxide content of the powder may be insufficient in a commercially available product.If necessary, heat-treat the powder in an oxidizing atmosphere to oxidize the powder. The substance content is adjusted as described above.

A silicon nitride powder and a boron nitride powder as main raw materials having the above-mentioned oxide content and average particle size are mixed with silicon nitride and boron nitride, excluding the oxide, in a total amount of 100.
As mass%, silicon nitride 40 to 85 mass% and boron nitride 15
Mix at a ratio of up to 60% by mass. This percentage is
Preferably, it is 50 to 70% by mass of silicon nitride and 30 to 50% by mass of boron nitride. If the proportion of boron nitride is too small, the machinability decreases and machining with a carbide tool becomes impossible, and if it is too large, cracks or chips occur during micromachining due to insufficient strength.

The compounding amount of the sintering aid is the total amount of silicon nitride in the silicon nitride powder and boron nitride in the boron nitride powder (that is, silicon nitride + boron nitride excluding oxides in the powder). And the sintering aid is 15% by mass based on the sum of the sintering aid and the sum of the sintering aids (sum of silicon nitride + boron nitride + sintering aids).
To be in the range of 31% by mass. The proportion of the sintering aid is preferably from 15 to 25% by weight. Amount of sintering aid is 15
When the amount is less than the mass%, when sintering under normal pressure, sintering of silicon nitride in particular becomes insufficient, and the strength of the sintered body decreases.
If the compounding amount of the sintering aid is too large, the grain boundary glass layer having low strength increases, which causes a decrease in the strength of the sintered body, and a single layer of unreacted auxiliary agent precipitates, and the machinability also deteriorates. I do.

The amount of the sintering aid of 15% by mass or more based on the above standard is larger than the amount used in the prior art. In the case of pressure firing, such a large amount of the sintering aid is not used because it has an adverse effect on the strength of the sintered body. However, in normal-pressure firing, a high-strength sintered body can be obtained by blending a sintering aid in an amount of 15% by mass or more. Among silicon nitride / boron nitride ceramics, those having such a large amount of a sintering aid and having high strength have not been known so far. However, as described later, when the firing step is performed by pressure firing, the ratio of the sintering aid is 10
The sintering can be sufficiently performed with less sintering aid.

As described above, since the oxide in the powder of the main raw material is a sintering reaction component, in the present invention, based on the total amount of silicon nitride and boron nitride excluding this oxide, Determine the amount of the sintering aid.

Since the firing is performed in an inert atmosphere,
No substantial oxidation of silicon nitride or boron nitride occurs during firing. Therefore, after firing, a ceramic containing the sintering aid in the above amount based on the total amount of the main component (silicon nitride + boron nitride) and the sintering aid is obtained.

The sintering aid can be selected from those conventionally used for sintering silicon nitride or boron nitride. Preferred sintering aids are one or more selected from aluminum oxide (alumina), magnesium oxide (magnesia), yttrium oxide (yttria), oxides of lanthanoid metals, and composite oxides such as spinel. And more preferably a mixture of alumina and yttria, or a mixture obtained by further adding magnesia thereto.

In the sintering of a composite material of silicon nitride and boron nitride as in the present invention, boron oxide on the surface of boron nitride powder, silicon oxide on the surface of silicon nitride powder, and an added sintering aid Reacts to generate a liquid phase and sintering is performed. By setting the content of the oxide of each powder and preferably the average particle size, and the amount of the sintering aid as described above,
The distribution and amount of the components involved in the sintering reaction are optimized, and a sintered body having high strength and excellent machinability is obtained by normal pressure firing.

After mixing the two kinds of raw material powder and the sintering aid in the above ratio to prepare a mixed powder, the mixed powder is subjected to pressure molding, and the obtained molded body is placed in an inert atmosphere. To produce the ceramic of the present invention. The operation itself of each of the mixing, molding, and firing steps may be performed according to any appropriate method. Next, an example of the method will be described, but the method is not limited to the illustrated method.

Although the mixing step can be performed by dry mixing, it is desirable to include a small amount of a binder (usually an organic resin) in order to facilitate molding in the next molding step. Wet mixing is advantageous. A binder is added to the powder slurry obtained by wet mixing and then dried by a spray drying method to obtain a mixed powder containing a small amount of binder. The liquid medium for wet grinding is preferably an organic solvent, for example, alcohols. Various resins can be used as the binder. The amount of the binder added may be as small as 1 to 5% by mass based on the total amount of the powder including the sintering aid.

The mixed powder is compacted by, for example, CIP (cold isostatic pressing). The obtained molded body is fired under an inert atmosphere. The firing temperature is generally 1700-19
It is in the range of 50 ° C, preferably in the range of 1700-1800 ° C. If the firing temperature is too low, densification does not occur. If the firing temperature is too high, decomposition of silicon nitride and volatilization of the sintering aid and boron oxide and silicon oxide occur, which adversely affects sintering. When a binder is used, low-temperature heating for removing the binder may be performed before firing. This low-temperature heating may be performed in the air if the temperature is such that oxidation of the raw material powder can be avoided.

The firing is preferably carried out at normal pressure. In the present invention, as described above, by optimizing the amount of the oxide of the raw material powder and the amount of the sintering aid, a sintered body having sufficiently high strength and excellent machinability even at normal pressure firing can be obtained. This makes it possible to manufacture ceramics having a complicated shape at low cost.

However, firing is HIP (hot isostatic pressing)
It is also possible to carry out by sintering under pressure such as hot pressing or hot pressing, whereby a sintered body with further improved bending strength can be obtained. For example, filling the above powder into a graphite mold,
It is also possible to bake while applying pressure while hot. in this case,
Appropriate pressure is in the range of 20-50 Mpa. In this case, as described above, the ratio of the sintering aid is 10 to
It can be reduced to 31% by mass as compared with the case of normal pressure firing. The preferred ratio of the sintering aid in the case of pressure firing is 10 to 15% by mass based on the above-mentioned standard.

In both normal pressure firing and pressure firing, a high-strength and good machinability sintered body that can be fine-processed is obtained, and a fine drilling or slitting process is performed using a carbide tool. In this case, processing without cracking or chipping can be performed with high accuracy, and excessive wear and breakage of the tool can be prevented.

[0035]

EXAMPLES In the following examples and comparative examples,% is% by mass unless otherwise specified. (Examples 1 and 2) Average particle size 0.05 μm, boron oxide content 8
% Hexagonal boron nitride (h-BN) powder, average particle size 0.2 μm,
2.3% silicon oxide (Si ₃ N ₄ ) powder with silicon oxide content
The components were mixed at a ratio such that the weight ratio of Si ₃ N ₄ : BN shown in the main component composition in Table 1 was obtained. To this powder mixture was added 5% alumina and 16% yttria in a ratio based on the total amount of silicon nitride + boron nitride in the powder and the sintering aid,
A slurry was prepared by performing wet ball mill mixing using ethyl alcohol as a liquid medium. To the obtained slurry, an acrylic resin was added as a binder in an amount of 3% based on the total amount of the powder and dissolved, and then the slurry was dried and granulated by a spray drying method to obtain a mixed powder.

This mixed powder was filled in a 120 mm square mold, and pressed under cold isostatic pressure at 1500 kgf / cm ² to obtain a formed body. The obtained molded body is heated to 600 ° C. in the atmosphere to remove the binder, and then calcined at 1750 ° C. in a nitrogen atmosphere for 4 hours under normal pressure to obtain a ceramic sintered body having a thickness of about 15 mm. Was.

The following test was performed on this sintered body. These test results are also shown in Table 1. Cut out a test piece of 30 × 40 × 360 mm size from the bending strength sintered body,
The breaking strength was measured by a three-point bending test, and the bending strength was determined.

[0038] Using the machinability carbide -K10 or tools, grinding rate 18 m / min, feed rate 0.03 mm / rev, performs turning test under the conditions of cut 0.1 mm, workpiece surface after 5 minutes The roughness and the flank wear width of the tool (indicating the degree of tool wear) were measured.

Thermal expansion coefficient The thermal expansion coefficient of the sintered body was measured at room temperature (25
° C) to 300 ° C.

The workability workability was evaluated in both the drilling and slitting. In the drilling process, a 50μm diameter carbide drill (material S) was cut out from a test piece obtained by cutting a sintered body into a thin plate with a thickness of 300μm.
Using KH9), through-holes of 30 rows vertically and 20 rows horizontally (a total of 600 pieces) were drilled with a wall thickness of 10 μm. The diameter of the hole is 60 μm,
The depth was 300 μm.

The accuracy of the hole diameter and the hole pitch of the obtained through holes was measured. If the accuracy was within ± 4 μm and there was no crack or chipping, ○ indicates that the drilling was possible but the accuracy was insufficient. The case where cracking or chipping occurred was evaluated as Δ, and the case where drilling was impossible due to breakage of the drill was evaluated as ×.

In the slit processing, a test piece obtained by cutting a sintered body to a thickness of 500 μm is slit (width = 40 μm, wall thickness) using a grinding wheel (resin bond diamond wheel # 200, thickness 40 μm, outer diameter 50 mm). = 15μm, depth = 30
0 μm).

Slit processing is possible, but if the accuracy is insufficient, (pitch accuracy exceeds ± 4 μm), or if cracking and chipping occur, Was possible, and a case where cracking or chipping did not occur was evaluated as ○.

Example 3 Silicon nitride powder was prepared by adding an average particle size of 1.0
A sintered body was prepared and tested in the same manner as in Example 1 except that the thickness was changed to that of μm and the silicon oxide content was 4.7%.

(Examples 4 and 5) In Example 4, the amount of the sintering aid was changed to 5% alumina and 11% yttria in a ratio based on the total amount described in Example 1. In Example 5, a sintered body was prepared and tested in the same manner as in Example 1 except that the alumina was changed to 6% and the yttria was changed to 20%.

(Comparative Examples 1 and 2) The mixing ratios of the main raw materials (powder of silicon nitride and boron nitride) were determined by excluding oxides.
Except that the amount was changed as shown in Table 1 and that the amount of the sintering aid in Comparative Example 2 was changed to 10% alumina and 21% yttria in a ratio based on the total amount described in Example 1, A sintered body was prepared and tested in the same manner as in Example 1.

(Comparative Example 3) A boron nitride powder having an average particle size of 1.0
μm, a boron oxide content of 1.0%, and a sintered body was prepared in the same manner as in Example 1 except that the compounding amount of the sintering aid was changed in the same manner as in Comparative Example 2. Carried out.

(Comparative Examples 4 and 5) The amount of the sintering aid was changed to 11% alumina and 25% yttria in Comparative Example 4 in a ratio based on the total amount described in Example 1. In Example 5, a sintered body was prepared and tested in the same manner as in Example 1, except that alumina was changed to 2% and yttria was changed to 7%.

[0049]

[Table 1]

As can be seen from Table 1, despite the firing step performed at normal pressure, the ceramic sintered body obtained in the example according to the present invention has excellent machinability and bending strength. It was high enough. Therefore, in both the slit processing and the drilling processing, high-precision fine processing could be performed without causing cracks or chipping. It was also confirmed that the material had low thermal expansion with little dimensional accuracy error at high temperatures.

On the other hand, as shown in the comparative example, the mixing ratio of the main components boron nitride and silicon nitride, the oxide content thereof,
Or, if the compounding amount of the sintering agent is out of the range of the present invention, either the bending strength or machinability deteriorates, chipping or cracking occurs during drilling, tool breakage occurs, or chipping occurs during slit processing. And cracks occurred, causing inconvenience in fine processing.

FIG. 1 is based on Example 1 (that is, the silicon nitride: boron nitride mass ratio = 68: 32, the oxide content of powder and the average particle diameter are the same as in Example 1). FIG. 2 shows the relationship between the bending strength of the sintered body and the amount of the sintering additive added when only the amount of the binder was changed. FIG. 2 shows the thermal expansion coefficient and the sintering aid of the sintered body in this case. The relationship with the compounding amount of the agent is shown. Table 2 shows the relationship between the machinability of the sintered body and the amount of the sintering aid in this case. Of the blending amounts of the sintering aids in Table 2, the example of 11% is 4% of alumina and 7% of yttria, and the others are the same as those of the above-mentioned Examples or Comparative Examples.

[0053]

[Table 2]

FIG. 1 shows that the flexural strength was determined when the amount of the sintering aid was 20%.
%, It is understood that good bending strength cannot be obtained particularly when the amount of the sintering aid is too small. As can be seen from FIG. 2, the coefficient of thermal expansion tends to increase as the amount of the sintering aid increases. From Table 2, it can be seen that regarding the machinability, when the amount of the sintering aid is too large, both the wear width of the tool and the machined surface roughness of the machinable material are deteriorated. Figures 1 and 2 and Table 2
In summary, when the amount of the sintering aid is in the range of 15 to 25%, both the strength and machinability of the sintered body are particularly good.

[0055]

According to the present invention, a ceramic material which is fired under normal pressure has both high strength and excellent machinability enabling fine processing and a small thermal expansion coefficient at 25 to 300 ° C. It is possible to provide conductive ceramics.

The free-cutting ceramic of the present invention is applied to semiconductor manufacturing equipment members, semiconductor inspection equipment jigs, circuit boards, etc., in which it is necessary to accurately form a deep slit or through hole having a small wall thickness and a small width or diameter. it can. Since this ceramic has a small coefficient of thermal expansion, it is difficult for the ceramic to be misaligned due to a temperature change in the use environment, and the reliability when using a machined component is enhanced.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of a sintering aid added and the three-point bending strength of a sintered body.

FIG. 2 is a graph showing the relationship between the amount of a sintering aid added and the coefficient of thermal expansion of a sintered body at 25 to 300 ° C.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuki Yoshitomi 1 Nishinocho, Higashimukaijima, Amagasaki City, Hyogo Sumikin Ceramics Co., Ltd.Kansai Plant (72) Inventor Kuniaki Nakagawa 1142 Urushijimacho, Matsuto City, Ishikawa Pref. 4G001 BA02 BA03 BA04 BA09 BA32 BA35 BB03 BB09 BB32 BB35 BC13 BC23 BC54 BC56 BD05 BD11 BD14 BD38

Claims (4)

[Claims] 1. A ceramic comprising a main component composed of silicon nitride and boron nitride and a subcomponent that is a reaction product of silicon oxide, boron oxide and a sintering aid, wherein the main component is nitrided. 40 to 85% by mass of silicon and 15 to 60% of boron nitride
%, The amount of the sintering aid is 15 to 31% by weight based on the total amount of the sintering aid and the main component, and the bending strength is 20%.
0 MPa or more, coefficient of thermal expansion at 25-300 ° C is 4 × 10 ^-6 / ° C
A free-cutting ceramic characterized by the following. 2. A method for producing a free-cutting ceramic, comprising: a silicon nitride powder having a silicon oxide content of 0.5 to 10% by mass, including a powder having a silicon oxide layer on the surface; A boron oxide content of 2 including powder having an oxide layer;
Mixing boron nitride powder of up to 15% by mass with a sintering aid, pressing the obtained mixed powder into a predetermined shape, and sintering the obtained molded body in an inert atmosphere. Wherein the proportion of the silicon nitride powder and the boron nitride powder in the mixing step is such that silicon nitride is 40 to 85% by mass and boron nitride is 15 to 85% by mass based on the total amount of silicon nitride and boron nitride in the powder. 60% by mass, and the amount of the sintering aid is 10 to 31% by mass based on the total amount of the silicon nitride and boron nitride and the sintering aid. 3. The method according to claim 2, wherein the silicon nitride powder has an average particle size of 5 μm or less, and the boron nitride powder has an average particle size of 0.5 μm or less. 4. The method according to claim 2, wherein the calcination is performed by normal pressure calcination.