JPH07330436A - Silicon nitride heat resistant member and its production - Google Patents

Abstract

PURPOSE:To obtain a heat resistant member reduced in the generation of void on a firing skin and excellent in high temp. property with respect to the heat resistant member, which requires dimensional accuracy, by firing after heating a compact containing silicon powder and a compound of group IIIa element in periodic table to give a specific firing skin. CONSTITUTION:The heat resistant member is composed of a silicon nitride sintered compact obtained by firing after heating the compact containing at least silicon powder and the compound of the group IIIa element in a nitrogen containing atmosphere and has the firing skin, on which the max. void diameter is <=30mum. The heat resistant member is applicable for various members requiring high dimensional accuracy with heat resistance as well as for a structural material for heat engine such as a complicated shaped ceramic gas turbine parts or ceramic turborotor, which are difficult to polish a surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has excellent strength characteristics from room temperature to high temperature and excellent creep resistance, and is particularly useful for automobile parts such as pistons, cylinders, valves, cam rollers, rocker arms, piston rings and piston pins. , Turbine rotor, turbine blade, nozzle, combustor, scroll, nozzle support, seal ring,
TECHNICAL FIELD The present invention relates to a silicon nitride heat-resistant member that is suitably used for gas turbine engine parts such as a spring ring, a diffuser, and a duct, and is particularly required to have dimensional accuracy and strength on the burnt surface, and a manufacturing method thereof. Is.

[0002]

2. Description of the Related Art Conventionally, silicon nitride sintered bodies have
Due to its excellent thermal shock resistance and oxidation resistance, it is being applied to engineering ceramics, especially for heat engines such as turbo rotors. This silicon nitride sintered material is generally used for Y ₂ O ₃ , Al ₂ O _{3 and} silicon nitride.
Alternatively, by adding a sintering aid such as MgO, high density and high strength characteristics are obtained. Further improvement in strength and oxidation resistance at high temperatures is demanded for such silicon nitride sintered bodies when the operating conditions thereof further increase. In order to meet such demands, various improvements have been attempted so far, such as examination of sintering aids and improvement of firing conditions.

Among them, from the viewpoint that oxides such as Al ₂ O ₃ and MgO, which have been conventionally used as a sintering aid, deteriorate the high temperature characteristics, a cycle of Y ₂ O ₃ or the like is added to silicon nitride. A simple ternary system (Si ₃ N ₄ —SiO ₂ —RE) to which a Group 3a element (RE) and silicon oxide are added
₂ O ₃ ) in a sintered body, the melting point of the grain boundary is increased by precipitating a crystal phase such as a YAM phase made of Si-RE-O-N or an apatite phase in the grain boundary of the sintered body. It has been proposed to stabilize. For example, in JP-A-63-100067, Y, Er, Tm, Y
It has been proposed to precipitate a crystal phase having an apatite structure at a grain boundary of a sintered body containing two or more rare earth elements of b and Lu.

Further, as described above, in a system using only silicon nitride powder as a silicon nitride source and using a Group 3a element oxide of the periodic table such as Y ₂ O ₃ and silicon oxide as a sintering aid, a liquid is used. When phase-sintering progresses, firing shrinkage occurs, so when manufacturing complex shaped products that require high dimensional accuracy after firing, it is difficult to control the dimensions to be set as the shrinkage is large, or the polishing process There is a problem that it becomes complicated. Therefore, conventionally, a method has been proposed in which silicon powder is added as a starting material, the silicon is subjected to a nitriding treatment in a nitrogen atmosphere before firing to increase the density of the compact, and then the compact is fired.

[0005]

However, when the conventional step of nitriding using silicon powder is included, it is necessary to set the firing temperature of the nitride to be high. When such high temperature firing is performed, large voids on the burnt surface of the sintered body are likely to be generated due to decomposition of the grain boundary phase components as shown in the SEM photograph of FIG. 1, and the strength of the burnt surface is significantly reduced. Was there. Therefore, when a heat-resistant member having a complicated shape and whose surface cannot be polished is manufactured by a method including a silicon nitriding step, it is possible to avoid the surface roughness of the sintered body due to the occurrence of voids as described above. However, the characteristics of the sintered body were deteriorated.

[0006] Further, although conventionally proposed sintered bodies containing various rare earth elements have a certain level of characteristics with respect to high-temperature strength, they are endowed with oxidation resistance at high temperatures and particularly high load. The creep property in the state was low, which was a major factor that hindered its practical use. For example, JP-A-6
As described in JP-A No. 3-100067, when a complex oxide is formed with two or more kinds of rare earth elements, the eutectic point decreases,
The creep resistance at high temperature was also low.

Therefore, the present invention requires dimensional accuracy,
Moreover, it is an object of the present invention to provide a heat-resistant member having excellent high-temperature characteristics with reduced generation of voids in the heat-resistant member in which it is difficult to polish the surface of the sintered body.

[0008]

DISCLOSURE OF THE INVENTION The inventors of the present invention have found that when a nitride obtained by nitriding silicon contained in a compact is fired at a high temperature, generation of voids causes release of gas during decomposition of grain boundary phase components. It was found that it was due to this, and as a result of investigation based on this, it was found that it is important to raise the melting point of the grain boundary of the sintered body. Therefore, as a result of a specific study on increasing the melting point of the grain boundary, it was found that Lu is contained in the oxide of Group 3a element of the periodic table, which is added as a sintering aid, to control the grain boundary of the sintered body. Found that a sintered body with small voids can be obtained, and excellent high-temperature strength, high-temperature oxidation resistance, and creep resistance can be exhibited even in a sintered body having a burnt surface. It is a thing.

That is, in the silicon nitride heat-resistant member of the present invention, a molded body containing at least silicon powder and a compound of Group 3a element of the periodic table is heat-treated in an atmosphere containing nitrogen to nitride the silicon, and then fired. A heat-resistant member comprising a silicon nitride sintered body obtained by the above, wherein the heat-resistant member has a burnt surface, and the maximum void diameter on the burnt surface is 30 μm or less. More specifically, the Group 3a element compound of the Periodic Table contains a Lu (lutetium) compound, and a crystal phase composed of the Group 3a element of the Periodic Table, silicon and oxygen is present at the grain boundary on the surface of the sintered body. It is characterized by doing.

Furthermore, as a method for producing the above heat-resistant member, 1 to 7 mol% of an oxide of a Group 3a element of the periodic table containing at least Lu (lutetium) and 1 to 15 of silicon oxide are used.
In a nitrogen-containing atmosphere at 800 to 1500 ° C., a molded body composed of mol%, the balance being silicon, or silicon and silicon nitride, and 50% or more of the oxide of Group 3a element of the periodic table being an oxide of Lu is formed. After the heat treatment to nitride the silicon, the silicon is further fired in a non-oxidizing atmosphere containing nitrogen and SiO gas, and at least the grain boundaries on the surface of the sintered body have a periodic table third.
It is characterized in that a crystal phase composed of a group a element, silicon and oxygen is deposited.

The present invention will be described in detail below. The heat resistant member in the present invention is made of a silicon nitride sintered material,
In particular, according to the present invention, since it is applied to a member that requires dimensional accuracy, it is manufactured by a method that reduces shrinkage during firing. As a method of reducing such firing shrinkage, silicon powder is added to the starting material together with a sintering aid, and this is nitrided to form silicon nitride, thereby causing volume expansion and increasing the density of the compact before firing. There is a way to increase.

As described above, the heat-resistant member of the present invention heat-treats a compact containing at least silicon powder and a compound of Group 3a of the periodic table in an atmosphere containing nitrogen to nitride silicon,
It is made of a silicon nitride sintered body obtained by firing.

In the manufacturing process including such a silicon nitriding step, the silicon nitride portion of the silicon nitride in the green body before firing becomes coarse grains, so that it is compared with the case of firing silicon nitride powder. Therefore, it is necessary to perform firing at a high temperature, and as a result, voids are inevitably generated due to the release of gas when the grain boundary phase components are decomposed as shown in FIG.

On the other hand, the heat-resistant member of the present invention has a so-called burnt surface on which the surface is not polished after firing, but the maximum void diameter on the burnt surface is 30 μm or less, particularly 10 μm. The main features are as follows. Voids inevitably exist on the burnt surface of this sintered body, but according to the present invention, the strength of the burnt surface can be greatly improved by reducing the maximum diameter of the void. Therefore, if the maximum void diameter is larger than 30 μm, it becomes a fracture source and deteriorates the mechanical characteristics of the member.

Further, according to the heat-resistant member of the present invention, it is desirable that a Lu compound is contained in the group 3a element compound of the periodic table contained as a sintering aid in the sintered body. This is Lu
In order to reduce the void diameter by suppressing the decomposition of the grain boundary component by increasing the melting point of the grain boundary as compared with elements of Group 3a of the periodic table other than Lu. This is because it becomes difficult to control the maximum void diameter on the burnt surface to 30 μm or less when the compound is made of only the Group 3a element compound.

Further, the silicon nitride-based sintered body constituting the heat-resistant member has an average particle size of 1 to 30 μm made of silicon nitride crystals.
According to the present invention, the main crystal grains of No. 3 and the grain boundary phase existing between the grains are included. The presence of crystals of oxygen is desirable. Periodic table 3a
A crystal composed of a group element (hereinafter collectively referred to as “RE” in the chemical formula), silicon and oxygen is RE ₂
A disilicate phase represented by Si ₂ O ₇ or RE ₂ SiO
There is a monosilicate phase represented by ₅ . Since the above crystal phase containing Lu has a high melting point, it does not decompose and volatilize even during the sintering process, and the generation of voids can be reduced. Such a crystal phase is 1 from the surface of the sintered body.
It is desirable that it exists in a region of 0 μm or more.

As the crystal phase of the grain boundary of the sintered body, the crystal phase in the vicinity of the surface is limited as described above. Silicon oxynitride phase, YAM phase, apatite phase,
It may be composed of crystals such as wollastonite phase.

Next, as a concrete method for producing the heat-resistant member of the present invention, silicon or silicon and silicon nitride as a main component is used as a starting material, and the periodic table is used as an additive component. It contains a Group 3a element oxide and silicon oxide. The silicon oxide herein, and the oxygen partial remaining in the final sintered body as an impurity oxygen contained like unavoidably silicon nitride and silicon powder in addition to those added as silicon oxide powder SiO ₂ converted Things are also included.

The specific composition of the starting material is Lu ₂ O.
1 to 7 mol% of a Group 3a element oxide of the periodic table containing ₃ ,
Especially 3 to 5 mol%, 1 to 15 mol% of silicon oxide, especially 6
.About.12 mol%, the balance being silicon powder, or silicon powder and silicon nitride powder. This is because if the amount of the Group 3a element oxide of the periodic table is less than 1 mol%, the sinterability is deteriorated, and a dense sintered body cannot be obtained. If it exceeds 7 mol%, the voids on the burnt surface are large. This is because the burnt surface strength deteriorates. Further, when the amount of silicon oxide is less than 1 mol%, a compound which deteriorates high temperature oxidation resistance such as melilite which is a compound of silicon nitride and an oxide of a Group 3a element of the periodic table is easily generated at the grain boundary, which is preferable. This is because, if it exceeds 15 mol%, the volume of the grain boundary phase increases and the high temperature characteristics deteriorate.

[0020] According to the present invention, the periodic table group 3a element oxide is the best that there is no periodic table group 3a element oxide other than Lu ₂ O ₃ consists only Lu ₂ O ₃ but There may be some mixing. In that case, Lu ₂ O ₃
The content of the group 3a element oxide of the periodic table other than is 50 mol% or less, particularly 30 mol% or less, and more preferably 10 mol% or less with respect to the total amount of the group 3a element oxide of the periodic table. In addition, as oxides of Group 3a elements of the periodic table other than Lu, Y, Yb, Er, Dy, Ho, Tb, Tm and S are used.
Examples thereof include oxides such as c.

Further, according to the present invention, in order to precipitate crystals of the Group 3a element of the periodic table containing Lu, silicon and oxygen at the grain boundaries on the surface of the sintered body after firing, at least before firing. The ratio (SiO ₂ / RE ₂ O ₃ ) of silicon oxide (SiO ₂ ) to the oxide (RE ₂ O ₃ ) of the Group 3a element of the periodic table on the surface of the molded body is 1.8 or more, particularly 2.0 or more. It is desirable to control so that This is a major factor that determines the composition of grain boundaries, and this ratio is 1.8.
This is because if it is smaller than this, precipitation of crystals of the Group 3a element of the periodic table containing Lu, silicon and oxygen cannot be expected, which is a factor that significantly deteriorates the oxidation resistance of the burnt surface.

In addition, in the starting material, as a additive component, Lu ₂ O ₃ , or a compound consisting of Lu ₂ O ₃ and one or more oxides of Group 3a elements of the periodic table other than Lu ₂ O ₃ and silicon oxide, Or silicon nitride and Lu ₂ O ₃ , or L
It is also possible to use a compound powder made of silicon oxide and one or more oxides of Group 3a element of the periodic table other than u ₂ O ₃ and Lu ₂ O ₃ .

Further, the silicon powder used is preferably fine particles having an average particle size of 10 μm or less, particularly 3 μm or less, in order to facilitate nitriding. Silicon nitride powder is added to improve the sinterability, but at the same time, the amount of deformation of firing increases, so the total amount of silicon nitride powder added is 7%.
It is preferably 5 mol% or less. In that case, the powder used may be either α type or β type,
The particle size is preferably 0.4 to 1.2 μm. In addition,
The silicon nitride powder can be used by any manufacturing method such as a direct nitriding method and an imide decomposition method.

Lu ₂ O ₃ used as an oxide of a Group 3a element of the periodic table preferably has a purity of 90% or more, particularly 95% or more, and an average particle size of about 0.1 to 10 μm.

The silicon oxide powder preferably has a high purity of 99% or more and an average particle size of 0.2 to 5 μm. For example, vapor phase silica is preferably used.

According to the present invention, TiN, TiC, TaC, TaN,
Metals such as VC, NbC, WC, WSi ₂ , Mo ₂ C, etc., of the periodic tables 4a, 5a, 6a and their carbides, nitrides,
Silicides, WO ₃ , and SiC, which are present as dispersed particles or whiskers in the sintered body of the present invention, have a small effect of deteriorating the characteristics. Of course, it is also possible to improve the characteristics. However, the presence of metal oxides such as Al ₂ O ₃ , MgO, and CaO in the system hinders the crystallization of the grain boundary phase and deteriorates the high-temperature strength and high-temperature oxidation resistance, so these oxides are not combined. It is desirable to control the amount to 1% by weight or less, particularly 0.5% by weight or less.

Next, the powder blended according to the above is thoroughly mixed by a rotary mill, a barrel mill, a vibration mill, etc., and the mixed powder is subjected to a known molding method such as press molding, cast molding, extrusion molding, injection molding. , Sludge molding,
Mold into a desired shape by cold isostatic pressing or the like.

Next, this compact is heat-treated at a temperature of 800 to 1500 ° C. in an atmosphere containing nitrogen to nitride silicon contained in the compact to generate silicon nitride. There is no dimensional change upon conversion into silicon nitride, and the weight increases, so that the density of the molded body improves. It is desirable to control such that the ratio of the theoretical density of the molded body after the nitriding treatment is 60% or more. In order to completely nitrid the silicon contained in this nitriding treatment, it is desirable to raise the temperature in multiple steps within the above temperature range while gradually nitriding, and when the nitriding treatment at a constant temperature cannot completely nitrid the silicon. There is. Further, the nitriding can be promoted by treating the atmosphere with a nitrogen pressure atmosphere of 1 to 50 atm.

Next, the high-density molded body obtained as described above is subjected to a known firing method, for example, a hot pressing method, a normal pressure firing method, a nitrogen gas pressure firing method, or a heat treatment after these firing. Hydrostatic pressure treatment (HIP treatment) to theoretical density ratio 95
% To obtain a dense sintered body. If the firing temperature at this time is too high, the surface of the sintered body is decomposed to generate voids having a large grain size, or the silicon nitride crystal grains grow to lower the strength. 195
It is preferably 0 ° C.

Further, in order to effectively suppress the generation of voids due to the decomposition and volatilization of the components on the surface of the sintered body during the firing, it is preferable to generate SiO gas in the firing atmosphere and perform firing.

This SiO gas has the effect of suppressing the decomposition of Si ₃ N ₄ due to the reaction between Si ₃ N ₄ and SiO ₂ ,
This can suppress the generation of voids. This SiO gas is, for example, SiO ₂ powder in the firing furnace together with the compact,
It can be easily generated by arranging a mixed powder of Si and SiO ₂ , a mixed powder of Si ₃ N ₄ and SiO _2, and the like.

Further, as described above, the grain boundary phase of the finally obtained sintered body precipitates crystals of the Group 3a element of the periodic table containing Lu, silicon and oxygen as described above, so that the cooling process in the firing step is performed. Alternatively, it is desirable to temporarily hold the material in the cooling step, or to perform the heat treatment after the completion of the firing step. Specifically, the cooling from the firing temperature is gradually cooled down to 200 ° C./hr or less, or the temperature lowering process from the firing temperature or after completion of the firing 1
The heat treatment may be performed in a nitrogen atmosphere at 000 to 1700 ° C.

[0033]

When manufacturing a member requiring dimensional accuracy, a method is known in which a compact containing at least silicon powder and a sintering aid is nitrided to increase the green density of the compact before firing and then firing. However, according to the manufacturing method including such a nitriding step, since the silicon nitride formed by nitriding exists as coarse particles, the sinterability of the entire system is deteriorated. As one of the methods for improving the sinterability, there is a method of adding a sintering aid such as Al ₂ O ₃ or MgO to generate a liquid phase having a low melting point and firing the mixture. Deteriorates the high temperature characteristics, and therefore, it is necessary to raise the calcination temperature and densify it in order to improve the high temperature characteristics.

On the burned surface of the sintered body produced by such high temperature firing, voids which are considered to be caused by the decomposition of grain boundary components of the sintered body are inevitably generated. If the surface decomposed layer having such voids is removed by polishing or the like, the characteristics are not affected, but if the member has a complicated shape, the surface cannot be polished, so that the high temperature characteristics are significantly deteriorated. It will be.

According to the present invention, a Lu compound is used as a sintering aid as a sintered body which constitutes a heat-resistant member having a dimensional accuracy including a silicon nitriding step and having a burnt surface, and after nitriding. By firing the firing atmosphere in an atmosphere containing nitrogen gas and SiO gas, further, a Lu such as a disilicate phase or a monosilicate phase is added to the grain boundary of the sintered body.
By precipitating a crystal composed of an element of Group 3a of the periodic table containing silicon, silicon and oxygen, it is possible to increase the melting point of the grain boundary component of the sintered body, and by including SiO gas in the firing atmosphere. As a result, it is possible to suppress the generation of gas due to the decomposition of the grain boundary components even when it is fired at a high temperature, and as a result, it is possible to obtain a heat-resistant member having a good burnt surface with small voids on the burnt surface.

The reason why the decomposition of the grain boundary component is suppressed and the generation of voids can be suppressed is L used as a sintering aid.
Since u has the smallest ionic radius among the lanthanoid-based elements and has the largest binding force with other elements, it is a glass or crystal phase with other grain boundary components such as Si ₃ N ₄ or SiO ₂ and has a high grain boundary. It is considered that the melting point was achieved.

According to the heat resistant member of the present invention,
Since Lu used as a sintering aid forms a stable compound even at high temperatures, the high temperature strength, oxidation resistance and creep resistance of the sintered body can be improved.

[0038]

[Example] Silicon powder was used as a raw material powder (average particle size was 3 μm).
m, oxygen amount 1.1% by weight, metal impurity amount 0.05% by weight) and silicon nitride powder (BET specific surface area 8 m ² / g, α
Rate 98%, oxygen content 1.2% by weight, Al, Mg, Ca, F
Lu ₂ O ₃ powder with a metal impurity amount such as e of 0.03% by weight) and a purity of 96% (Yb ₂ O ₃ and Er ₂ O ₃ as impurities).
)), A powder having a purity of 99% or more other than Lu ₂ O _{3 and} having a composition shown in Table 1 using an oxide powder of a Group 3a element of the periodic table, and prepared in isopropyl alcohol,
After mixing for 96 hours using Si ₃ N ₄ balls, after adding a binder, cold isostatic pressing at a pressure of 1 ton / cm ² (C
IP). After degreasing the obtained molded product at 300 ° C. for 2 hours, 1200 ° C.-2 hours-nitrogen 10 atm, 1300 ° C.
-2 hours-nitrogen 6 atm, 1400 [deg.] C.-2 hours-nitrogen 2 atm. At this time, it was confirmed from the weight increase rate that the added silicon was all nitrided in all the samples. Then, the obtained nitride is put in a silicon carbide sagger and heated at 1750 to 1950 ° C. under a nitrogen pressure of 10 atm for 5 times.
Burned for hours. At that time, in order to generate SiO gas, an appropriate amount of a mixed powder compact of Si and SiO ₂ was simultaneously charged. After the firing, hot isostatic treatment was performed at 1700 ° C.-2000 atmospheres for 1 hour, and further heat treatment was performed at 1400 ° C. for 24 hours in nitrogen to crystallize the grain boundaries.

The dimensions of the obtained sintered body were measured,
The shrinkage ratio (%) (= dimension before firing-dimension after firing / dimension before firing) was measured. Further, the surface portion of the sintered body was subjected to X-ray diffraction measurement to identify the grain boundary crystal phase. As the void diameter of the burned surface of the sintered body, the maximum void diameter observed per 1 mm ² from the surface SEM observation was measured, and this was measured at 5 positions on any surface, and the average thereof was calculated.

JIS for measuring the strength of the burnt surface of the sintered body
For the test piece shape defined by R1601 and having only the pulling surface as the burnt surface, the room temperature and 1500 ° C
Regarding the point bending strength, a test piece according to JIS R1601 was cut out from the inside of the sintered body and the whole surface was polished.
Four-point bending strength at 500 ° C. was measured.

The creep resistance is 150
The time until breakage was measured at 0 ° C. under a 4-point bending load of 350 MPa up to 100 hours. Regarding the oxidation resistance, the unpolished test piece was exposed to 1500 ° C. air for 100 hours, and the weight change per unit surface area was calculated from the weight increase amount and the surface area of the sample. The results are shown in Table 2.

[0042]

[Table 1]

[0043]

[Table 2]

As is clear from Tables 1 and 2, the sintered body having a maximum void diameter of 30 μm or less on the burnt surface of the sintered body is 30
Compared with samples Nos. 1 to 3, 13 and 16 exceeding μm,
It was excellent in baked surface strength. Regarding the relationship between this void and the type of sintering aid, samples No. 1 to ₃ to which other oxides of Group 3a group 3a of the periodic table containing no Lu ₂ O ₃ were added alone, and the amount of Lu was small. In No. 13, the maximum void diameter exceeds 30 μm and the characteristics of the burnt surface are low, whereas the use of Lu reduces the occurrence of voids and improves the mechanical strength of the burnt surface. 1
It can be seen that the 500 ° C. strength is also improved. Also, when the total amount of Group 3a element oxides in the periodic table exceeds 7 mol% (Sample No. 16), large voids are easily generated and the burnt surface strength is low.

Further, in the sample of the present invention, comparing the crystal phase of the grain boundary between Sample No. 14 and No. 10 to 12, the apatite phase is compared with the case where the apatite phase exists in the grain boundary (No. 14). It can be seen that the one without (No. 10 to 12) has excellent oxidation resistance at high temperature. Furthermore, in sample No. 7 containing no silicon powder as a raw material, the dimensional change is 20%.
Therefore, it was not suitable for members that required large dimensional accuracy.

[0046]

As described in detail above, according to the present invention,
In a heat resistant member that requires dimensional accuracy, strength deterioration is small from room temperature to high temperature, especially 1500 ° C. on the burnt surface, and creep resistance at high temperature can be improved. As a result, various heat resistance is required, including complicated materials such as ceramic gas turbine parts with complicated shapes whose surface is difficult to polish, ceramic turbo rotors, and other structural materials, as well as complicated shapes and high dimensional accuracy. It can be applied to a member.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing a surface texture in which voids are generated on a burnt surface of a silicon nitride sintered body.

Claims (3)

[Claims] 1. A silicon nitride sintered body obtained by subjecting a molded body containing at least silicon powder and a compound of Group 3a element of the periodic table to heat treatment in an atmosphere containing nitrogen to nitride the silicon and then firing the silicon. A heat-resistant member comprising the heat-resistant member having a burnt surface, and the maximum void diameter on the burnt surface is 30 μm or less. 2. The compound of Group 3a element of the periodic table is Lu
The heat-resistant member according to claim 1, which contains a (lutetium) compound and has a crystal phase composed of an element of Group 3a of the periodic table, silicon, and oxygen at a grain boundary on the surface of the sintered body. 3. 1 to 7 mol% of an oxide of a Group 3a element of the periodic table containing at least Lu (lutetium) and 1 of silicon oxide.
800 to 150% by mol, the balance being silicon powder, or silicon powder and silicon nitride powder, and 50% or more of the oxide of Group 3a element of the periodic table being Lu oxide.
After nitriding the silicon by heat treatment in a nitrogen-containing atmosphere at ˜1500 ° C., firing is further performed in a non-oxidizing atmosphere containing nitrogen and SiO gas, and at least a grain boundary on the surface of the sintered body has a periodic table 3a. A method for manufacturing a silicon nitride heat-resistant member, which comprises depositing a crystal phase comprising a group element, silicon and oxygen.