JPH01100064A - Production of silicon nitride sintered compact - Google Patents

Abstract

PURPOSE:To obtain the titled sintered compact having excellent strength at high temperature, by molding a mixture of Si powder with an oxide consisting of Nd2O3 and/or Sm2O3 and Y2O3 and having a specific composition or precursor thereof and heat-treating the resultant moldings in N2. CONSTITUTION:A mixture of Si powder and Si3N4 powder, as necessary used by converting to Si powder with an oxide consisting of Nd2O3 and/or Sm2O3 and Y2O3 and expressed by the formula (Y2O3)x(M2O3)1-x [M is Nd and/or Sm; 0 or 1<=x=0.9 (mol. ratio)] or a precursor (e.g. carbonate salt) capable of providing the oxide having the above-mentioned ratio by heat treatment is molded and subjected to nitriding reaction under N2 atmosphere at 1,000-1,500 deg.C and then sintered under N2 atmosphere of >=1atm. to provide the titled sintered compact.

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 engines such as turbocharger rotors. This material is suitable for use as a member. However, since it is difficult to sinter silicon nitride alone, MgO, A1203. A method is used in which sintering is performed by adding a sintering aid such as Y2O3. In addition, in order to reduce the amount of glass phase remaining in the sintered body, a method of creating it by hot pressing and a method of firing a mixture of Si powder and Y2O3 after nitriding are known (silicon nitride sintering). The method for producing the solid body is described in Japanese Patent Application Laid-open No. 54-15
No. 916, JP-A-49-63710, JP-A-60-1
There are many examples disclosed in No. 37873 and others. ). (Problems to be Solved by the Invention) However, in the conventional firing method using silicon nitride as a starting material mentioned above, sintering is thought to be liquid phase sintering mediated by the liquid phase generated during firing. , 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. Further, although the method using hot pressing can produce a dense sintered body with excellent sinterability, it has the problem that it can only be applied to products with simple shapes. Furthermore, in the above-mentioned method of firing after nitriding, although an improvement in high temperature strength was observed, the mechanical strength at room temperature was not sufficient. This is Y, which is a high melting point sintering aid.
This is because sinterability was not sufficient because 2O3 was added alone. (Purpose of the Invention) This invention has been made by focusing on the above-mentioned conventional problems, and has developed a method for producing a silicon nitride sintered body that has particularly excellent strength at room temperature and less decrease in strength at high temperatures. , which aims to solve the above-mentioned conventional problems.

[Structure of the invention]

(Means for Solving the Problems) The method for producing a silicon nitride sintered body according to the present invention includes at least silicon powder selected from among silicon powder and silicon nitride powder, and one selected from Nd203, Sm203, or The following formula is composed of a combination of two types and Y2O3: % Formula % (1) (However, 1M is one or two types selected from Nd and Sm, and 0.1≦X≦0. A molded body obtained by molding a mixture of an oxide with a ratio of 9 (molar ratio) and/or a compound that becomes an oxide with the above ratio after heat treatment in a nitrogen atmosphere -T! The above-mentioned conventional problems have been solved by going through a manufacturing process in which heat treatment is performed at a temperature in the range of 1000 to 1500 °C, and then heat treated at a temperature in the range of 1600 to 2200 °C in a nitrogen atmosphere of 1 atm or more. be. In the method for producing a silicon nitride sintered body according to the present invention, at least silicon powder of silicon powder and silicon nitride powder;
The starting material is an oxide auxiliary agent. Then, a molded body obtained by molding a mixed powder of silicon powder, silicon nitride powder used by replacing silicon powder with silicon powder as necessary, and an oxide auxiliary agent by an appropriate method is heated to 1000° C. under a nitrogen atmosphere. By heat treatment at a temperature in the range from 1500° C. to 1500° C., the silicon is nitrided to form a mixture of silicon nitride and oxide coagent. The bulk density of this mixture is about 70% of the theoretical density, and the bulk density of the compacted powder of silicon nitride powder and oxide (60%
(below) higher than 160, which is why the second processing step
The amount of shrinkage during the firing process from 0°C to 2200°C is small; 1) It is possible to fire at a lower temperature than conventional methods. Y2O3 used as a sintering aid in this invention has a high melting point, so when used as a single component, a sufficient amount of low Since a viscous liquid phase is not generated, the sinterability is poor, and conventionally it has been often used when pressure is applied from outside, such as in a hot press. Therefore, in this invention. By using an oxide containing Y2O3 and one or two of Nd203 and Sm203,
The melting point of the oxide is lowered until a liquid phase sufficient for sintering is obtained at a sintering temperature of 1600° C. or higher and 2200° C. or lower. Moreover, this liquid phase is different from conventional MgO, A
Sentence 2 Since the melting point is higher than that of the liquid phase when o3-Y2O3 is used as an auxiliary agent, it is thought that even if it remains in the sintered body after sintering, the strength will not deteriorate at high temperatures. . In this invention, the raw material powder is silicon powder. Silicon nitride powder, which is used as a partial substitute for the silicon powder as necessary, and Y2O3, Nd203, and Sm
A mixed powder consisting of an oxide powder which is a combination of one or two selected from 203 is used. Even if some of the silicon powder is replaced with silicon nitride powder, it is desirable that the silicon powder be at least 3% by weight, more preferably at least 30% by weight. This is to ensure that the effect of increasing density is sufficiently obtained. In addition, Y2O3, which is a sintering aid, and N
It is more preferable that d2O3 and/or Sm2O3 be in the form of fine powders; You can. When using Y2O3 and Nd2O3 as sintering aids, (
Y O) (Nd O) (Said 23X
231-X (see formula (1)), sintering is possible in the range of 0.1≦X≦0.9 (molar ratio). Also, when using Y2O3 and Sm2O3, (Y2O3) x (Sm O)
(See equation (1) above). Sintering is possible within the range of 2 3 1-X 0.1≦X≦0.9 (molar ratio). At this time,! If x is <0.1, the strength of the sintered body will decrease, which is undesirable. If x>0.9, a sufficient amount of liquid phase will not be generated during firing at 1600°C or higher, and densification will not occur, which is undesirable. The optimal range of the amount of the sintering aid varies depending on the type and composition, but by setting the content in the final sintered body to 3 to 20% by weight, the density and strength are further improved. However, if the auxiliary agent is added in an amount greater than that required for densification, the strength at high temperatures will be reduced. The method for molding these mixtures is not particularly limited, but for example, any conventional ceramic molding method such as mold press molding, rubber press molding, injection molding, etc. can be selected according to the shape of the desired product. can. The heat treatment employed in the method for producing a silicon nitride sintered body according to the present invention is performed in two stages: a nitriding step and a sintering step. Of these. The nitriding process is performed at 1000°C to 1500°C in a nitrogen atmosphere.
The nitrogen atmosphere can be carried out at a temperature in the range of 1,200°C to 1,450°C, preferably in the range of 1 atm of nitrogen-containing gas, but it may also be carried out in ammonia gas. Included in the definition of atmosphere. Furthermore, the definition of nitrogen atmosphere in this invention also includes an atmosphere to which hydrogen gas and inert gas are added as necessary. The gas pressure in this nitrogen atmosphere is usually 1 atm, but it may also be carried out in a high pressure gas exceeding 1 atm. Nitriding is promoted in a high pressure nitrogen atmosphere, so it is effective for nitriding thick-walled parts. It is. Next, the sintering process is performed at 160° C. in a nitrogen atmosphere of 1 atm or more.
It is carried out at temperatures ranging from 0°C to 2200°C. At this time, if the pressure of the nitrogen atmosphere is lower than 1 atm, silicon nitride decomposes violently and a dense sintered body cannot be obtained. In this case, the gas pressure required to suppress the decomposition of silicon nitride depends on the firing temperature. The higher the temperature, the higher the pressure required. In addition, if the firing temperature is lower than 1600°C, a sufficient amount of liquid phase will not be generated and no densification will occur, and if the firing temperature exceeds 2200°C, grain growth will become intense and the strength will decrease.
The temperature is 0°C or higher and 2200°C or lower. This sintering process is continued until a dense sintered body is obtained. If the sintering properties are poor, such as when the amount of the additive auxiliary agent mentioned above is small or when a high-melting auxiliary agent is used, the firing process should be performed in the following two ways.
It is better to do it by process. First, the nitrided molded body is treated in a nitrogen atmosphere of 1 atm or more and less than 500 atm at a temperature in the range of 1600°C to 2200°C. This 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 reason why the atmosphere is set to 1 atm or more and less than 500 atm in a nitrogen atmosphere is 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. In this process, a sintered body with a theoretical density of 90% or more is obtained.The sintered body thus treated is further heated at a temperature in the range of 1600°C to 2200°C in a nitrogen atmosphere of 500 atm or more. Process. 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. The reason why the treatment temperature is set from 1600°C to 2200°C in these two steps is because the amount of liquid phase is small below 1600°C.
Densification does not progress and grain growth occurs at temperatures exceeding 2200°C.
This is because 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. (Example) Examples of the present invention are shown below together with comparative examples. The results of Examples 1 to 7 and Comparative Examples 1.2 are shown in Table 1, and The results are summarized in Table 2. 90% by weight Si powder and 5% by weight in terms of Si3N4
of yttrium oxide and 5% by weight of neodymium oxide (N
d203 / (Y203 +Nd203)”0.4
0 molar ratio) in a wet ball mill to which ethanol was added to obtain a mixed powder. At this time, Si3N,
The amount of Si powder converted to is 3S i +2N2 =S i3 N4...(
It was calculated and added based on the assumption that the weight would change due to the reaction in 2). This mixed powder was molded into a mold at a pressure of 20 MPa, and then rubber press molded at a pressure of 200 MPa to form a 6x6
A molded article having a shape of 50 mm was molded. This molded body was heated and nitrided in a nitrogen atmosphere according to the nitriding treatment schedule shown in Fig. 1.Then, it was heated at a temperature of 1850°C for 1 hour under a nitrogen gas pressure of 10 atm, and the density was 3.45 g/
A sintered body of cm' was obtained. The sintered body obtained here was 3 x 4 x 40 mm
The shape was ground using a diamond wheel, and a three-point bending test with a span of 30 mm was performed at room temperature and 1350°C. As a result, the average value of the five trees was 800 MPa at room temperature, 1
A sintered body with a high strength of 550 MPa at 350° C. was obtained. 90% by weight of 31 powder and 5% by weight in terms of Si3N4
Yttrium oxide and 5% by weight of aluminum oxide were mixed in a wet ball mill to which ethanol was added to obtain a mixed powder. This mixed powder was heated to 20 MPa
After molding with a force of 200 MPa, rubber press molding was performed at a pressure of 200 MPa to form a molded product with a size of 6 x 6 x 50 mm. This molded body was heated and nitrided in a nitrogen atmosphere according to the nitriding schedule shown in Fig. 1.
It was heated at a temperature of 1850° C. for 1 hour under a nitrogen gas pressure of 10 atm to obtain a sintered body having a density of 3.18 g/cm 3 . 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 1350°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average value of the five pieces was 900 MPa at room temperature and 1 at 1350°C.
20 MPa, and although this sintered body had high strength at room temperature, the strength significantly decreased at high temperatures. Salt Glaze 90% by weight of Si powder and 10% by weight of yttrium oxide in terms of Si3N4 were mixed in a wet ball mill to which ethanol was added to obtain a mixed powder. After molding this mixed powder with a mold at a pressure of 20 MPa,
Rubber press molding was carried out under a pressure of Pa to form a molded article having a shape of 6 x 6 x 50 mm. This compact was nitrided by heating in a nitrogen atmosphere according to the nitriding schedule shown in Figure 1.Then, when it was heated at a temperature of 1850°C for 1 hour under a nitrogen gas pressure of 10 atm, the density was 2.80 g/cm.
3, it wasn't dense enough. 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 1350°C.
A three-point bending test with a span of 30 mm was conducted. The average value of the five pieces is 320 MPa at room temperature and 250 MPa at 1350°C.
The strength of the sintered body was low at room temperature and high temperature.衷m2j Si powder having the composition shown in Table 1 and a sintering aid were mixed in a wet ball mill to which ethanol was added to obtain a mixed powder. This mixed powder was molded with a mold at a pressure of 20 MPa, and then rubber press molded at a pressure of 200 MPa to form a 6X
A molded article having a shape of 6×50 mm was molded. This compact was nitrided by heating in a nitrogen atmosphere according to the nitriding schedule shown in FIG. 1 or 2. Firing was performed under the same conditions shown in Table 1. The density of the sintered body thus obtained is also shown in Table 1. 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 1350°C.
A three-point bending test with a span of 30 mm was conducted. The average values of the room temperature strength and high temperature strength of the five pieces are also shown in Table 1.
As shown in Table 1, the obtained sintered body had high strength at room temperature and high temperature. 94% by weight Si powder and 3% by weight calculated as Si3N4
of yttrium oxide and 3% by weight of samarium oxide (
Sm20s/(Y203+Sm2O3)=0.39
molar ratio) were mixed in a wet ball mill to which ethanol was added to obtain a mixed powder. 20MP of this mixed powder
After molding with a pressure of 1.a, rubber press molding was performed at a pressure of 200 MPa to form a molded product with a size of 6 x 6 x 50 mm. This molded body was heated and nitrided in a nitrogen atmosphere according to the nitriding schedule shown in Fig. 2.Then, when it was fired under the conditions shown in Fig. 3, the density was 3.46.
It was fully densified with g/cm3. 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 1350°C.
A three-point bending test with a span of 30 mm was conducted. As a result, the average value of the five pieces was 850 MPa at room temperature and 6
20 MPa, and the obtained sintered body had high strength at room temperature and high temperature. Harm] 94% by weight of Si powder and 3% by weight in terms of u1ヱ5i3Na
of yttrium oxide and 3% by weight of neodymium oxide (N
dz O+s/(Y203+Nd203)=0.
40 molar ratio) using a wet ball mill to which ethanol was added to obtain a mixed powder. 20% of this mixed powder
After molding with a mold at a pressure of MPa, rubber press molding was performed at a pressure of 200 MPa to form a molded article having a shape of 8 x 6 x 50 mm. When this compact was heated in a nitrogen atmosphere and subjected to nitriding and sintering according to the schedule shown in FIG. 4, the compact was sufficiently densified with a density of 3.48 g/Cm3. Here, the obtained sintered body was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and
A three-point bending test with a span of 30 mm was conducted at . The average value of 5 trees is 900MPa at room temperature and 650MPa at 1350℃
a, and the obtained sintered body had high strength at room temperature and high temperature. A mixed powder was obtained by mixing Si3N4 with 47.5% by weight of Si powder, 2.5% by weight of yttrium oxide, and 2.5% by weight of neodymium oxide using a wet ball mill with the addition of ethanol. Ta. After molding this mixed powder with a mold at a pressure of 20 MPa, 2
Rubber press molded at a pressure of 00MPa to 6X6X5
A molded article having a shape of 0 mm was molded. This compact was nitrided by heating in a nitrogen atmosphere according to the nitriding treatment schedule shown in Figure 1.
Heated at a temperature of 50℃ for 1 hour, density 3.25g/cm
A sintered body of No. 3 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 1350°C.
A three-point bending test with a span of 30'mm was conducted. The average value of 5 pieces is 850MPa at room temperature and 680MPa at 1350℃
A high-strength sintered body was obtained. A mixed powder was obtained by mixing 2.5% by weight of yttrium oxide and 2.5% by weight of neodymium oxide with 3Nm of salted Yu-Si using a wet ball mill to which ethanol was added. After molding this mixed powder with a mold at a pressure of 20 MPa, 200 M
Rubber press molding was carried out under a pressure of Pa to form a molded article having a shape of 6 x 6 x 50 mm. This compact was nitrided by heating in a nitrogen atmosphere according to the nitriding schedule shown in Figure 1.Then, when it was heated at a temperature of 1850°C for 1 hour under a nitrogen gas pressure of 10 atm, the density was 2.75 g/Cm.
3, and it was not sufficiently densified. Here, the obtained sintered body was ground into a shape of 3 x 4 x 40 mm using a diamond wheel, and
A three-point bending test with a span of 30 mm was conducted at . The average value of 5 pieces is 320MPa at room temperature and 200MPa at 1350℃
a, and both room temperature and high temperature strength were low. 45% by weight of Si powder and 10% by weight of yttrium oxide were mixed in Si3N4 using a wet ball mill to which ethanol was added to obtain a mixed powder. 20% of this mixed powder
After molding with a pressure of MPa, rubber press molding was performed with a pressure of 200 MPa to form a molded body with a shape of 6 x 6 x 50 mm. This molded body was subjected to a nitriding treatment schedule shown in Fig. 1 in an - elemental atmosphere. The material was then heated at a temperature of 1850° C. for 1 hour under a nitrogen gas pressure of 10 atm, but the density was 2.80 g/am', which was not sufficient to densify the material. 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 1350°C.
A three-point dlf test with a span of 30 mm was conducted. The average value of 5 pieces is 320MPa at room temperature and 250MPa at 1350℃
a, and the strength of the sintered body was low at room temperature and high temperature. Salt bed ■l 45% by weight of Si powder, 5% by weight of yttrium oxide and 5% by weight of aluminum oxide are added to Si3N4,
A mixed powder was obtained by mixing in a wet ball mill to which ethanol was added. This mixed powder was molded in a mold at a pressure of 20 MPa, and then rubber press molded at a pressure of 200 MPa to form a molded body having a shape of 6 x 6 x 50 mm. This compact was nitrided by heating in a nitrogen atmosphere according to the nitriding schedule shown in Figure 1.Then, it was heated at a temperature of 1850°C for 1 hour under a nitrogen gas pressure of 10 atm.
A sintered body with an E degree of 3.18 g/cm3 was obtained. The sintered body obtained here was ground with a diamond wheel in the shape of 3 x 4 x 40 mm, and was heated to room temperature and 1350°C.
A three-point bending test was conducted with a span of 30 mm. The average value of 5 pieces is 900MPa at room temperature and 120M at 1350℃
Pa, and this sintered body has high strength at room temperature,
The strength decreased significantly at high temperatures. Silicon nitride powder, Si powder, and sintering aid having the compositions shown in Table 2 were mixed in a wet ball mill to which ethanol was added to obtain a mixed powder. This mixed powder was heated to 20 MPa.
After molding with a mold at a pressure of a, rubber press molding was performed at a pressure of 200 MPa to form a molded product having a shape of 6 x 6 x 50 mm. This compact was heated and nitrided in a nitrogen atmosphere according to the nitriding schedule shown in FIGS. 1 and 2. Then, it was fired under the same conditions shown in Table 2 and FIG. 3. The density of the obtained sintered body is also shown in Table 2. 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 1350°C.
A three-point bending test with a span of 30 mm was conducted. The average values of the five pieces of room temperature strength and high temperature strength are also shown in Table 2.
The obtained sintered body had high strength at room temperature and high temperature.

【Effect of the invention】

As explained above, according to the method for manufacturing a silicon nitride sintered body according to the present invention, at least silicon powder out of silicon powder and silicon nitride powder. It consists of a combination of one or two selected from Nd203 and Sm203 and Y2O3, and the following formula: % formula %) (However, 1M is one or two selected from Nd and Sm. A molded body obtained by molding a mixture of an oxide with a ratio of 0.1≦X≦0.9 (molar ratio) and/or a compound that becomes an oxide with the above ratio after heat treatment. was heat-treated at a temperature in the range of 1000 to 1500°C under a nitrogen atmosphere, and then heated at a temperature of 16
Because it is heat-treated at a temperature in the range of 00 to 2,200°C, it is required to have excellent strength especially at room temperature, and to have significantly less strength loss at high temperatures, and to have excellent strength not only at room temperature but also at high temperature. This brings about the very excellent effect that it is possible to provide a silicon nitride sintered body suitable as a material for various structural parts.

[Brief explanation of the drawing]

Figures 1 and 2 are graphs showing nitriding schedules adopted in Examples and Comparative Examples of the present invention, Figure 3 is a graph showing firing conditions adopted in Examples of the invention, and Figure 4 is a graph showing the firing conditions of the invention. 3 is a graph showing nitriding and firing conditions employed in Examples. Patent Applicant Nissan Motor Co., Ltd. Representative Patent Attorney Ryo Koshio Toyoon (0C) Pressure (atmospheric pressure) iIL ("c) Nz force" large pressure (fi pressure)

Claims (1)

[Claims] (1) At least silicon powder among silicon powder and silicon nitride powder, and 1 selected from Nd_2O_3 and Sm_2O_3
It consists of a species or a combination of two species and Y_2O_3 and has the following formula: (Y_2O_3)_x(M_2O_3)_1_-_x(
However, M is one or two selected from Nd and Sm, and represents 0.1≦x≦0.9 (molar ratio). ) and/or a compound that becomes an oxide in the above ratio after heat treatment, a molded body obtained by molding the mixture is heat-treated at a temperature in the range of 1000 to 1500°C in a nitrogen atmosphere, and then 160 in a nitrogen atmosphere of 1 atm or more
A method for producing a silicon nitride sintered body, the method comprising heat treating at a temperature in the range of 0 to 2200°C.