JPH01119563A - Production of silicon nitride-based sintered compact - Google Patents

Abstract

PURPOSE:To obtain the title Si3N4-based sintered compact having high strength at normal temps. and the strength not significantly decreased at high temp. by sintering the compact of Si powder or the mixed powder consisting essentially of Si at high temp. in gaseous N2 or in a gaseous mixture of gaseous N2 and a gas having low reactivity to Si. CONSTITUTION:Si powder or the mixed powder containing by adding a reinforcing material such as ceramics and whisker, a nitridation promoter, a sintering aid, etc., to Si powder is compacted into specified size by hot pressing, metallic mold pressing, etc. The compact is heated at 1,000-1,500 deg.C in gaseous N2 or in the gaseous mixture of gaseous N2 and an inert gas such as Ar and Ne having low reactivity to Si to nitride Si into Si3N4. By this method, an Si3N4 sintered compact widely used for automobiles, mechanical devices, chemical devices, etc., and appropriate for the part material requiring high-temp. strength is obtained.

Description

[Detailed description of the invention] [Purpose of the invention]

(Field of Industrial Application) This invention is a fine ceramic material that can be used as a material for various structural parts used in a wide range of fields such as automobile machinery, chemical equipment, and aerospace equipment, and has particularly excellent high-temperature strength. The present invention relates to a method for producing a silicon nitride sintered body suitable for obtaining. (Prior art) Sintered bodies mainly composed of silicon nitride are chemically stable at room and high temperatures and have high mechanical strength, so they are used in sliding parts such as bearings and engine parts such as turbocharger rotors. It is a suitable material as However, since it is difficult to sinter silicon nitride alone, MgO is usually added to the silicon nitride powder. A method is used in which sintering is performed by adding a sintering aid such as AfL2o3 or Y2O3. On the other hand, there is a reaction sintering method in which a silicon nitride sintered body is obtained by heating a molded body of silicon powder in a nitrogen atmosphere, and a molded body formed by adding an oxide sintering aid to silicon powder is used. A two-stage sintering method is known in which nitriding is performed in a nitrogen atmosphere and then sintering is performed at a higher temperature for densification. Japanese Patent Publication No. 54-1591
6, Japanese Patent Application Laid-Open No. 60-137873, etc.). (Problems to be Solved by the Invention) However, in the above-mentioned conventional sintering method using silicon nitride as a starting material, sintering is thought to occur through liquid phase sintering, which is mediated by the liquid phase generated during sintering. This liquid phase remains in the sintered body as a glass phase after sintering. On the other hand, high-temperature properties such as creep resistance, high-temperature strength, and oxidation resistance of a sintered body are greatly influenced by the glass phase remaining in the sintered body. In particular, the presence of a large amount of glass phase with a low softening temperature is undesirable because it significantly deteriorates the high-temperature mechanical properties of the silicon nitride sintered body. In addition, although the latter reaction sintering method and two-stage sintering method described above improve high-temperature strength, the mechanical strength at room temperature is not sufficient and the nitriding process requires a long time. In addition, there have been problems in that it is difficult to completely nitridize thick-walled products. In this case, the reason why the nitriding process requires a long time is that the nitriding reaction of silicon is an exothermic reaction, so if nitriding is carried out in a short time, the temperature of the product will rise rapidly due to the exothermic reaction, and the melting point of silicon (approximately 1450 This is because the sample melts when the temperature exceeds 30°F (°C). Furthermore, the reason why it is difficult to completely nitridate thick-walled products is that as the nitriding reaction progresses, the density of the sample increases and the open pores become smaller, making it difficult for gas to move. (Purpose of the Invention) The present invention has been made by focusing on the above-mentioned conventional problems, and it is possible to produce a high-performance silicon nitride sintered body that has high strength at room temperature and little decrease in strength at high temperatures. The object of the present invention is to provide a method of manufacturing a silicon nitride sintered body that is possible.

[Structure of the invention]

(Means for Solving the Problems) In the method for producing a silicon nitride sintered body according to the present invention, silicon powder or a mixture containing silicon powder as a main component is molded, and then nitrogen gas or nitrogen gas is added. 1000-1500 in a mixed gas atmosphere with a gas that is less reactive to silicon
It is characterized by being processed at a temperature of °C. The raw material used in the method for producing a silicon nitride sintered body according to the present invention is silicon powder, or has silicon powder as its main component, and contains ceramics, whiskers, etc.
C reinforcing materials such as whiskers. It is a mixture of a nitridation promoter such as an Fe compound, a reaction control agent such as silicon nitride powder, or an oxide sintering aid such as yttrium oxide, samarium oxide, neodymium oxide, etc. In addition, when molding this raw material, hot press,
Various molding methods are used, such as rubber pressing, mold pressing, and injection molding. Next, the molded body obtained by the above molding is mixed with nitrogen gas (including a nitriding atmosphere forming gas such as ammonia gas) or a gas with low reactivity (including non-reactivity) with nitrogen gas and silicon. 1000-1 under mixed gas atmosphere
Heat treatment is performed at a temperature in the range of 500° C., and silicon is nitrided by this heat treatment to obtain a silicon nitride sintered body. In this case, the atmospheric pressure may be 1 atm or higher than 1 atm. In the method for producing a silicon nitride sintered body according to the first embodiment of the present invention, silicon powder or a mixture containing silicon powder as a main component and whisker added thereto in an amount of preferably 5 to 50% by weight is prepared, preferably in a vacuum or 100 under inert atmosphere
After hot-pressing at a temperature in the range of 0 to 1400°C and a pressure of 50 Kgf/cm2 or more, the molded product obtained by this molding has a low reactivity with nitrogen gas or with nitrogen gas and silicon (including cases where there is no reactivity). ) 1000 to 1500 in a mixed gas atmosphere with a gas such as an inert gas
The heat treatment should be carried out at a temperature in the range of °C. As described above, in the first embodiment of the present invention, silicon powder is used as a starting material, whiskers are added thereto as necessary, and
More preferably, silicon powder or a mixture of silicon powder and whiskers is heated under vacuum or an inert atmosphere to 1000 to 14
By hot pressing and molding at a temperature in the range of 00° C. and a pressure of 50 Kgf/cm 2 or more, a silicon molded body with a high bulk density can be obtained. The bulk density of the compact obtained by this hot pressing is about 70 to 80% of the theoretical density, and the bulk density of the green compact of silicon powder (60% or less), which is the usual method for producing reaction-sintered silicon nitride. taller than. Subsequently, this molded body is heat-treated at a temperature in the range of 1500°C to 1500°C in an atmosphere of nitrogen gas or a mixed gas of nitrogen gas and a gas having low reactivity toward silicon, such as an inert gas, to nitride silicon. The bulk density of the silicon nitride thus obtained is about 70 to 80% of the theoretical density, which is higher than the bulk density of ordinary reaction-sintered silicon nitride. . A high-strength sintered body can be obtained. The silicon powder that is the raw material for this silicon nitride sintered body is 100%
Submicron powder is good, and if necessary, F
A nitridation accelerator such as e-compound and a reaction control agent such as silicon nitride coarse powder can be added. Although whiskers are not particularly limited, in order to obtain a high-strength sintered body, ceramic whiskers, such as ceramic whiskers with a diameter of 10 microns or less and an aspect ratio of 1.
It is better to use 0 or more SiC whiskers, and
It is particularly preferable that the amount of whiskers added is 5 to 50% by weight; that is, if it is less than 5% by weight, the effect of whisker addition is small, and if it exceeds 50% by weight, sintering becomes difficult. Firing in this first embodiment is performed in two stages: a hot pressing process and a nitriding process. Among these, the hot pressing process is performed under vacuum or inert atmosphere.
It is preferable to carry out the process at a temperature in the range of ~1400℃ and a pressure of 50Kgf/Cm2 or more, and the degree of vacuum is preferably 1O-2Torr or less to prevent oxidation of silicon. It is an atmosphere that does not react with silicon at a temperature within a range, and examples include Ar and He. Further, the nitriding step is performed at a temperature in the range of 1000 to 1500°C, preferably in the range of 1200 to 1450°C, in an atmosphere of nitrogen gas or a mixed gas of nitrogen gas and a gas having low reactivity with silicon, such as an inert gas. The atmosphere in this case can be 1 atm of nitrogen gas, but it can also be carried out in ammonia gas.
Hydrogen gas or inert gas may be added as necessary.
The gas pressure at this time is usually 1 atm, but it may be carried out in a high pressure gas exceeding 1 atm. Furthermore, although it is desirable that the hot press step and the nitriding step be performed using different furnaces, they may be performed in the same furnace (hot press furnace). In the method for producing a silicon nitride sintered body according to the second embodiment of the present invention, a mixture of silicon powder or a mixed powder of silicon powder and ceramics, etc., and an oxide auxiliary agent as necessary is molded. The obtained molded body is treated with nitrogen gas or with low reactivity to nitrogen gas and silicon (including cases where it is not present).
1000 in a mixed gas atmosphere with a gas such as an inert gas
After heat treatment at a temperature in the range of ~1500°C and nitriding the silicon powder, the silicon powder was heated at 160 °C in a nitrogen gas atmosphere of 1 atm or more.
Firing is performed at a temperature in the range of 0 to 2200°C. In this case, the partial pressure of the inert gas in the mixed gas is at least twice the partial pressure of nitrogen gas, and the total pressure of the mixed gas is 2 atm or more. It is particularly desirable that the In the method for producing a silicon nitride sintered body in the second embodiment, silicon powder is used as a starting material, ceramics are added thereto as necessary, and the silicon powder or a mixture of silicon powder and ceramics is formed. . When nitriding the silicon in this compact, it is preferable to use a mixed gas of nitrogen gas and inert gas as the atmospheric gas.
That is, when a mixed gas of nitrogen gas and an inert gas is used, the cooling effect of convection caused by the inert gas works more effectively than in nitriding using nitrogen gas alone, so that it is possible to suppress the temperature rise of the compact. Therefore, even if the nitriding treatment is performed in a short time, the molded body does not melt, and a silicon nitride sintered body can be obtained. In addition, by increasing the total pressure of the mixed gas, the movement of gas in the open pores becomes easier, making it possible to manufacture thick-walled parts. In this manufacturing method, the raw material powder is silicon powder, and it is preferable to add ceramics and oxide auxiliary agents to this as necessary.This silicon powder is preferably a powder of 100 microns or less, and as a ceramic, , silicon nitride powder,
Whiskers etc. can be added. Furthermore, if necessary, a nitriding promoter such as an Fe compound can be added. The method for molding these mixtures is not particularly limited, but any conventional ceramic molding method, such as mold press molding, rubber press molding, or injection molding, can be selected depending on the shape of the intended product. A particularly desirable atmospheric gas employed in this second embodiment is a mixed gas of nitrogen gas and, for example, an inert gas that is less reactive with silicon. This inert gas is a gas that does not react with silicon, and examples include argon and helium. The ratio of nitrogen gas and inert gas in the mixed gas is not particularly limited, but it is particularly desirable that the partial pressure of the inert gas in the mixed gas is at least twice the partial pressure of nitrogen gas. This is because if the partial pressure of the inert gas is less than twice, the cooling effect of this inert gas is small. Further, the total pressure of the mixed gas may be 1 atm, but if the pressure is set to a high pressure of 2 atm or more, the nitriding rate will be improved, and furthermore, the nitriding process will be possible in a short time. Note that when the total pressure is increased, heat generation due to the nitriding reaction increases, so it is desirable to increase the proportion of inert gas added. Furthermore, as the oxide aid, one or two of the sintering aids normally used for sintering silicon nitride, such as aluminum oxide, magnesium oxide, yttrium oxide, lanthanum oxide, cerium oxide, samarium oxide, neodymium oxide, etc. A mixture of the above can be used. It is more desirable that the firing in this case be performed in two stages: a nitriding step and a sintering step. The former nitriding step is the same as the case without adding the above-mentioned auxiliary agent. In addition, the latter sintering process is performed at a temperature of 1600 to 2200 in nitrogen gas at 1 atm or more.
It is best to carry out the process at a temperature in the range of °C. In other words, below 1 atm, silicon nitride decomposes violently and a dense sintered body cannot be obtained. The gas pressure required to suppress this decomposition is determined by the firing temperature. High temperatures require high pressure. Further, if the firing temperature is lower than 1,600°C, a sufficient amount of liquid phase will not be generated, and therefore no densification will occur.On the other hand, if the firing temperature is higher than 2,200°C, grain growth will become intense and the strength will decrease. This sintering process is continued until a dense sintered body is obtained. In addition, if the sintering property is poor, such as when the amount of added auxiliary agent is small or when a high melting point auxiliary agent is used, it is better to carry out the firing process by the following two steps. First, the nitrided compact is 1
In the range of 1,600°C to 2,200°C in a nitrogen atmosphere of at least 500 atm. Process at a temperature of The processing time is preferably 10 minutes or more.
In this step, the oxide-based auxiliary agent generates a liquid phase, and sintering progresses by a liquid phase sintering mechanism. At this time, the atmosphere is set to 1 atm or more and less than 500 atm in a nitrogen atmosphere because if it is less than 1 atm, silicon nitride will decompose and will not become dense, and if it is over 500 atm, high pressure nitrogen gas will be trapped in the sintered body. This is because the density is only increased to about 90% of the theoretical density. This process yields a sintered body with a theoretical density of 90% or more.
Next, the sintered body thus treated is further treated at a temperature in the range of 1600° C. or more and 2200° C. or less under a nitrogen gas pressure of 500 atmospheres or more. In this step, the remaining closed pores disappear by a mechanism similar to that of normal HIP processing, and a dense sintered body is obtained. In these two steps, the processing temperature is 160℃.
The reason why the temperature is set from 0°C to 2200°C is that below 1600°C, the amount of liquid phase is small, so densification does not proceed, and above 2200°C, grain growth occurs and the strength at room temperature and high temperature decreases. These treatment steps are preferably carried out in one treatment by controlling the temperature and pressure, but may be carried out in two steps. (Determination) and production■" 90% by weight St grain powder converted to Si3N, 10% by weight SiC whiskers (diameter 0.5~1.0" m + aspect ratio 20~50) and ethanol. A mixed powder was obtained by mixing with a wet ball mill.At this time,
The amount of Si powder converted to Si3N4 is 3S i+2N2=S i3 N4 (
The weight was calculated and added based on the weight change caused by the reaction in 1). Put this mixed powder into a graphite mold with an inner diameter of 50 mm,
While applying a pressure of 200Kgf/cm', 10=To
1200℃ at a heating rate of 500℃ per hour in a vacuum of rr
Hot pressing was performed by heating to . Next, this compact is heated and nitrided in a nitrogen atmosphere according to the nitriding schedule shown in FIG.
．． A sintered body of 40 g/cm3 was obtained. The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and heated to room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average bending strength of the five pieces was 450Mpa and 1200Mpa at room temperature.
A sintered body with a high strength of 500 MPa at ℃ was obtained. Example 2 90% by weight Si powder converted to Si3N4 and 10% by weight SiC whiskers (diameter 0.5 to 1.0J" m + aspect ratio 20 to 50) were mixed in a wet ball mill to which ethanol was added. 200Kg of the mixed powder obtained by
After molding with a pressure of f/cm2, 2000Kgf/
Rubber press molded with cm2 (7) pressure to 6X6X50
Next, this molded body was heated and nitrided in a nitrogen atmosphere according to the nitriding treatment schedule shown in Fig. 1 to give a density of 2.05 g/C.
A sintered body of m3 was obtained. The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm with a diamond wheel at room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average bending strength of the five trees was 305 MPa and 1200 MPa at room temperature.
It was 300 MPa at ℃. Example 3 95% by weight Si powder and 5% by weight in terms of Si3N4
A mixed powder was obtained by mixing SiC whiskers (diameter 0.5 to 1.04 m, aspect ratio 20 to 50) using a wet ball mill with the addition of ethanol.Next, this mixed powder was placed in a graphite mold with an inner diameter of 50 mm. , 200Kgf/cm
In a vacuum of 10-'Torr while applying a pressure of 2,
Hot pressing was performed by heating the compact to 1200°C at a rate of temperature increase of 500°C per hour.Next, this compact was heated and nitrided in a nitrogen atmosphere according to the nitriding treatment schedule shown in Figure 1 to improve its density. 2.38g/cm
A sintered body of ' was obtained. The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and heated to room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average bending strength of the five pieces was 480 MPa and 1200 MPa at room temperature.
A sintered body with a high strength of 470 MPa at ℃ was obtained. Example 4 85% by weight Si powder in terms of Si4N4 and 15% by weight SiC whiskers (diameter 0.5-1.0 lm, aspect ratio 20-50) were mixed in a wet ball mill to which ethanol was added. Next, this mixed powder was put into a graphite mold with an inner diameter of 50 mm and heated at 200 Kgf/c.
Hot pressing was performed by heating to 1250°C at a temperature increase rate of 500°C per hour in a vacuum of 10-4 Torr while applying a pressure of 2 m2.Next, this molded body was subjected to the nitriding treatment schedule shown in Fig. 1. Density 2.50g/cm by heating and nitriding in nitrogen atmosphere
A sintered body of ' was obtained. The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and heated to room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average bending strength of the five trees was 550 MPa and 1200 MPa at room temperature.
A high-strength sintered body with a thermal resistance of 20 MPa was obtained. Seal 1 85% by weight Si powder and 15% by weight SiC whisker (diameter 0.5-1.OJ' m +7 in terms of Si3N4)
Spectral ratio 20-50) was mixed with ethanol using a wet ball mill to obtain a mixed powder.
This mixed powder was placed in a graphite mold with an inner diameter of 50 mm, and
Hot pressing was performed by heating to 1300°C at a rate of 500°C per hour in an argon atmosphere while applying a pressure of 0 kgf/cm2.Then, this molded body was heated according to the nitriding schedule shown in Figure 2. By heating and nitriding in a nitrogen atmosphere, the density is 2.40g/
A sintered body of cm' was obtained. The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and heated to room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average bending strength of the five pieces was 580 MPa and 1200 MPa at room temperature.
A high-strength sintered body with a temperature of 00 MPa was obtained. Mixing 70% by weight of Si powder in terms of Si3N4 and 30% by weight of SiC whiskers (diameter 0.5 to 1.0 m, aspect ratio 20 to 50) using a wet ball mill with the addition of ethanol. Then, this mixed powder was put into a graphite mold with an inner diameter of 50 mm and heated at 400 kgf/c.
5 per hour in an argon atmosphere while applying a pressure of m2.
Hot pressing was performed by heating to 1350°C at a temperature increase rate of 00°C.Then, this molded body was heated and nitrided in a nitrogen atmosphere according to the nitriding treatment schedule shown in Figure 2 to give a density of 2.45g. /cm3 of the sintered body was obtained. The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and then heated at room temperature and 1200°.
C, a three-point bending test with a span of 30 mm was conducted. As a result, the average bending strength of the five trees was 550 MPa and 120 MPa at room temperature.
A sintered body with a high strength of 530 MPa at 0° C. was obtained. 1. 40% by weight Si powder in terms of Si3N4 and 60% by weight SiC whiskers (diameter 0.5-1.01Lm + aspect ratio 20-50) were mixed in a wet ball mill to which ethanol was added. The mixed powder obtained was then put into a graphite mold with an inner diameter of 50 mm and heated to 200 Kgf.
Hot pressing was performed by heating up to 1200°C at a temperature increase rate of 500°C per hour in a vacuum of 1O-4 Torr while applying a pressure of /cm2. Next, this molded body was subjected to the nitriding treatment shown in Fig. 1. Density 2.00g7 by heating and nitriding under nitrogen atmosphere according to schedule
cm3c7) A sintered body was obtained. The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and heated to room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average bending strength of the five pieces was 150 MPa and 1200 MPa at room temperature.
It was 180 MPa at ℃. 85% by weight of 51 powder (calculated as actual mN Si3N4) and 15% by weight of SiC whiskers (diameter 0.5 to 1.0 m, aspect ratio 20 to 50) were mixed in a wet ball mill to which ethanol was added. Next, this mixed powder was put into a graphite mold with an inner diameter of 50 mm and heated at 200 Kgf/c.
Hot pressing was carried out by heating up to 900°C at a temperature increase rate of 500°C per hour in a vacuum of 10 Torr while applying a pressure of 10 m''.Then, this molded body was subjected to the nitriding treatment schedule shown in Figure 1. By heating and nitriding in a nitrogen atmosphere, a sintered body with a density of 2.15 g/cm3 was obtained.The sintered body thus obtained was ground into a shape of 3 x 4 x 40 mm with a diamond wheel, and then heated at room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average bending strength of the five pieces was 330 MPa and 1200 MPa at room temperature.
It was 310 MPa at ℃. 11 times silicon powder with an average particle size of 1101L was heated to 200Kgf/cm2
After molding with a pressure of By heating and nitriding in a mixed gas atmosphere with a nitrogen gas partial pressure of 5 atm and an argon gas partial pressure of 95 atm, the nitriding rate was 93% and the density was 2.42 g.
/cm3 of the sintered body was obtained. The nitriding rate was calculated from the weight change between the weight of the test piece before nitriding and the weight of the test piece after nitriding. The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and heated to room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. The average bending strength of 5 pieces of wood is 320 MPa at room temperature and 350 MPa at 1200°C.
A sintered body whose strength did not decrease at MPa and high temperatures was obtained. A Silicon powder with an average particle size of 10 lm was molded in a mold at a pressure of 200 Kgf/cm2, and then rubber press molded at a pressure of 2000 Kgf/cm2 to form a molded body in the shape of 6 x 6 x 50 mm6. Next, when this compact was fired in nitrogen gas at 100 atmospheres according to the nitriding schedule shown in FIG. 3, a portion of the sintered compact was covered with traces of melted silicon. Further, the nitriding rate was 83%. The density of this sintered body is 2
．． The bending strengths at 30 g/cm', room temperature and 1200°C were 210 MPa and 200 MPa, respectively. 40% by weight of dog 11LL silicon powder, 40% by weight of silicon nitride powder with an average particle size of 1 gm, and 10% by weight of silicon carbide whiskers with an average diameter of 1 gm and a length of 20 lumens were mixed in a wet ball mill with the addition of ethanol. Then, this mixed powder was rubber press molded at a pressure of 2000 Kgf/cm2 to form a molded body having a shape of 30 x 30 x 50 mm. Subsequently, this molded body was subjected to a nitrogen gas partial pressure of 10 atm according to the nitriding treatment schedule shown in FIG. It was heated and nitrided in a mixed gas atmosphere with a helium gas partial pressure of 490 atm to obtain a sintered body with a nitridation rate of 95% and a density of 2.53 g/Cm'. Further, no trace of melted silicon was observed in the sintered body. The sintered body obtained here was cut and ground into a shape of 3 x 4 x 40 mm with a diamond wheel, and
A three-point bending test with a span of 30 mm was conducted at 0°C. As a result, the average bending strength of the five trees was 380 MPa at room temperature, 12
A sintered body whose strength did not decrease at a high temperature of 360 MPa at 00° C. was obtained. Mix 40% by weight of silicon powder, 40% by weight of silicon nitride powder with an average particle size of 1 μm, and 10% by weight of silicon carbide whiskers with an average diameter of 1 μm and a length of 20 m using a wet ball mill with the addition of ethanol. A mixed powder was obtained. Next, this mixed powder was rubber press molded at a pressure of 2000 Kgf/cm 2 to form a molded body having a shape of 30×30×50 mm. Subsequently, this compact was fired in nitrogen gas at 500 atmospheres according to the nitriding schedule shown in FIG. 4, and traces of melted silicon were found in a part of the sintered compact. Further, the nitriding rate was 75%. Furthermore, the density of this sintered body is 2.30g/Cm3. The bending strength at room temperature and 1200”0 is 180MPa and 165MPa respectively
It was a. 51 powder of 96% by weight in terms of Si3N4, 2% by weight of yttrium oxide and 2% by weight of samarium oxide (composition in the sintered body of the final product) was processed in a wet ball mill to which ethanol was added. Next, this mixed powder was molded in a mold at a pressure of 200 Kgf/cm2, and then rubber press molded at a pressure of 2000 Kgf/cm2 to form a molded body of 6 x 6 x 50 mm. Next, this molded body was heated and nitrided in a mixed gas atmosphere with a nitrogen gas partial pressure of 2 atm and an argon gas partial pressure of 998 atm according to the nitriding treatment schedule shown in FIG.
A sintered body with a nitridation rate of 98% and a density of 2.60 g/cm3 was obtained. Further, the sintered body showed no trace of melted silicon.Then, the sintered body was fired under a nitrogen gas pressure of 20 atmospheres according to the firing schedule shown in Figure 6, and the density was 3.30 g/
It was sufficiently densified to cm3. The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and heated to room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. The average bending strength of the five pieces is 760MPa at room temperature and 62o at 1200℃.
MPa, and the obtained sintered body had high strength at room temperature and high temperature. Sato1@@14 49% by weight Si powder in terms of Si3Na, 49% by weight silicon nitride powder, 1% by weight yttrium oxide, and 1% by weight neodymium oxide (composition in the sintered body of the final product) ) were mixed in a wet ball mill to which ethanol was added to obtain a mixed powder.6 Then, this mixed powder was
After molding with a pressure of 0Kgf/cm2, 2000K
Press molded with a pressure of gf/Cm2 to 6X
A molded body having a shape of 8 x 50 mm was molded. Subsequently, this molded body was subjected to a nitrogen gas partial pressure of 200 atm and an argon gas partial pressure of 800 atm according to the nitriding treatment schedule shown in FIG.
Nitriding is performed by heating in a mixed gas atmosphere at atmospheric pressure, and the nitriding rate is 96.
%, and a density of 2.55 g/cm5 was obtained. The sintered body showed no trace of melted silicon.Next, when it was fired under nitrogen gas pressure according to the firing schedule shown in Figure 7, it was sufficiently densified with a density of 3.20 g/cm3. . The sintered body obtained here was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and heated to room temperature and 1200°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average bending strength of the five trees was 730 MPa and 1200 MPa at room temperature.
℃ tear 00 MPa, and the obtained sintered body had high strength at room temperature and high temperature.

【Effect of the invention】

As explained above, in the method for manufacturing a silicon nitride sintered body according to the present invention, after molding silicon powder or a mixture containing silicon powder as a main component, Since the treatment is carried out at a temperature of 1000 to 1500°C in a mixed gas atmosphere with a gas with a small To obtain a fine ceramic material that can be used as a material for various structural parts used in a wide range of fields such as automobile machinery, chemical equipment, and aerospace equipment, and is especially suitable for applications that require high-temperature strength. This has the great effect of making it possible.

[Brief explanation of the drawing]

Figures 1, 2, 3, 4 and 5 are graphs showing the nitriding schedule adopted in the embodiment of this invention, and Figures 6 and 7 are graphs employed in the embodiment of this invention. 3 is a graph showing a firing treatment schedule. Patent applicant Yutaka Oshio, Patent attorney representing Nissan Motor Co., Ltd. Figure 1 Time (hr) Figure 2 Time (hr) Temperature (0C) Transient L (0C) Temperature/L ('C)

Claims (1)

[Claims] (1) After molding silicon powder or a mixture mainly composed of silicon powder, it is heated to
A method for producing a silicon nitride sintered body, characterized in that the process is carried out at a temperature of 0 to 1500°C.