JPH08319165A - Silicon nitride sintered material and its production - Google Patents

Abstract

PURPOSE: To produce a silicon nitride sintered material having superior high- temperature strength and fracture toughness when compared with a conventional product by depositing crystals in a grain boundary phase. CONSTITUTION: This is a silicon nitride sintered material composed of <=20wt.% of a grain boundary phase of and a particulate phase of Si3 N4 and/or sialon in the remaining main phase. The ratio of quantity of β-Si3 N4 and/or β'-sialon based on the main phase is 0.5-1.0. The grain boundary phase contains Re2 A7 O17 (Re is an element of the group 3A and A is an element of the group 4A) as a crystal component. The objective sintered material is produced by adding thereto AO2 , Re2 O3 , etc., sintering the mixture and subsequently treating this mixture at 1050-1600 deg.C for nucleation and crystal growth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride-based sintered body suitable as a cutting tool, a wear resistant tool, a machine structural component, etc., which is required to have high strength and high toughness at high temperatures, and a method for producing the same.

[0002]

2. Description of the Related Art Silicon nitride sintered bodies are expected as materials for cutting tools, wear resistant tools, machine structural parts, wear resistant parts and the like which are required to have high heat resistance and high strength.

Since silicon nitride is difficult to sinter by itself,
Conventionally, sintering aid components such as Y ₂ O ₃ and Al ₂ O ₃ are added,
A dense substance is obtained by mass transfer due to the formation of the liquid phase. However, if only ordinary liquid phase sintering is used,
_Since the liquid phase forming components other than ₃ N ₄ mainly become a glass phase to form a grain boundary phase, the glass phase is softened at a high temperature of 1200 ° C. or higher and the strength is remarkably lowered.

For example, according to Japanese Patent Publication No. 56-28865, Si ₃ N ₄ .Y ₂ O ₃ crystal phase is precipitated at the grain boundary during sintering, but the bending strength at 1300 ° C. is 75 to 93 k.
It is as small as g / mm ² . Also, JP-A-60-
No. 186,469 discloses ReAlO ₃ and Re ₃ Al ₅ O _12.
(Here, Re is a rare earth element) is added and sintered, but its bending strength is about 70 kg / mm ² even at room temperature. In JP-A-4-130062, Y ₂ O ₃ such as YAG is used. -By adding Al ₂ O ₃ based sintering agent, 100 at room temperature
Sintered bodies exceeding kg / mm ² have been obtained, but 1200 ° C
However, the strength is about 80 kg / mm ² .

As described above, since the grain boundary phase is the glass phase, the strength of the Si ₃ N ₄ sintered body, especially the high temperature strength is remarkably lowered. Therefore, various attempts have been made to improve the high temperature strength by crystallization of the glass phase. Has been done. For example, Japanese Patent Publication No.
In Japanese Patent No. 45724, a small amount of Ti is used as a crystallization accelerator.
After adding O ₂ and sintering using SiO ₂ and Al ₂ O ₃ as sintering aids, heat treatment is performed at 700 to 1400 ° C. to precipitate crystals such as cordierite and cristobalite at 1200 ° C. With a bending strength of 60 kg / mm ² .

Further, Japanese Patent Application Laid-Open No. 3-122055 discloses that
After adding Al ₂ O ₃ and Y ₂ O ₃ , 900 to 97 during cooling.
According to a heat treatment program of holding at 0 ° C. and further raising the temperature to 1200 to 1300 ° C., Si ₃ N ₄ · Y ₂ O ₃ or Si ₂ N
A method of precipitating fine crystals of ₂ O is disclosed, but the bending strength of the obtained sintered body is 67 kg / mm at 1200 ° C.
It remains around ² .

In Japanese Laid-Open Patent Publication No. 3-199165, Re ₂ O ₃ (where Re is a rare earth element) in which Si ₂ N ₂ O crystals are precipitated by controlling the cooling rate after sintering is disclosed.
Although it is described that a SiO ₂ type grain boundary phase is formed,
Its bending strength is 83 to 99 kg / mm ² , 140 at room temperature.
It is 51 to 63 kg / mm ² at 0 ° C. JP-A-4-23
In Japanese Patent No. 1379, a Si ₂ N ₂ O crystal is formed in a grain boundary phase by a heat treatment at 1200 ° C. after sintering, and 100 k at room temperature.
g / mm ₂ approximately and 1400 ° C. to obtain a 63kg / mm ² about the Si ₃ N ₄ sintered body strength are described.

In Japanese Patent Laid-Open No. 5-294731, there is 15
Re ₂ O ₃ (where Re
Is a rare earth element) and a ZrSiO ₄ composite crystal phase is formed, and a strength of 50 kg / mm ² or more at 1400 ° C.,
Sintered body of 5 or more toughness value K _IC is described to be obtained. Japanese Patent Application Laid-Open No. 5-330919 discloses 850.
After nucleation at 1050 ° C and crystal growth at 1100 to 1500 ° C, Al-Yb-Si-O-N-based or Al-Er-Si-O-N-based microcrystals are formed in the grain boundary phase. 130
It is described that a sintered body having a bending strength of about 60 kg / mm ² at 0 ° C. is obtained.

Further, in Japanese Patent Laid-Open No. 5-58740,
MgO or TiO ₂ is added as a nucleating agent, and Y ₂ O ₃ and Al ₂ are added.
After sintering with O ₃ as a sintering aid, the sintered body is 850 to 1
Y ₂ Si ₂ O ₇ , Al ₅ Y ₃ O ₁₂ , A by nucleation at 050 ° C. and crystal growth at 1200 to 1300 ° C.
l ₆ Y ₂ O such as _{Si 2 O 13 3 -Al 2 O} 3 to precipitate -SiO ₂ based oxide crystal phase, to obtain Si ₃ N ₄ sintered body at room temperature at 50 kg / mm ² approximately flexural strength Is listed.

There is also a case where a group 4A element compound is added to a silicon nitride-based sintered body to improve the strength. For example, in Japanese Patent Laid-Open No. 63-60162, 1 to 20% by weight of ZrO _{2 in} which HfO ₂ is dissolved is added and sintered to obtain a bending strength at room temperature of 90 kg / mm ² and a fracture toughness. It is introduced that a silicon nitride based sintered body having a value of 18.5 MN / m ^3/2 can be obtained.

Japanese Patent Publication No. 5-59074 discloses that Si ₃
Sialon sintering in which a glass phase containing Y and Y ₂ Hf ₂ O ₇ microcrystals are precipitated at the grain boundaries of the sintered body by mixing N ₄ powder, Sialon powder and HfO ₂ powder, shaping and sintering. The body is disclosed, and the bending strength at 1400 ° C. is 99 kg / mm ² , and the fracture toughness value is 8.3 MN / m ^3/2 . According to Japanese Patent Laid-Open No. 4-240162, Si ₃ N ₄ powder added with 8% by weight or less of rare earth oxide, 10% by weight of Al ₂ O ₃ powder and 8% by weight or less of Hf compound powder is sintered at room temperature. A sintered body having a bending strength of 110 kg / mm ² is obtained.

Japanese Unexamined Patent Publication (Kokai) No. 5-294732 discloses a silicon nitride-based sintered body containing Y ₂ Hf ₂ O ₇ and Y ₅ N (SiO ₄ ) ₃ phases in grain boundaries, and bending at 1400 ° C. Strength is 870
The strength characteristics (No. 25 in Table 2) having a fracture toughness value of 8.1 MN / m ^3/2 at MPa and room temperature are obtained. This sintered body is Y ₂
It is manufactured by adding O ₃ powder, HfO ₂ powder and SiO ₂ powder to Si ₃ N ₄ powder, performing hot press sintering, and then performing heat treatment at 1600 ° C. in nitrogen.

Japanese Unexamined Patent Publication No. 5-306172 discloses Y ₂
By hot press sintering with addition of O ₃ powder and HfO ₂ powder, a silicon nitride-based sintered body having Y ₂ Hf ₂ O ₇ crystals precipitated at grain boundaries was obtained, and its bending strength at 1400 ° C. was 664.
MPa, fracture toughness value 7.96MN / m ^3/2 (Table 1 (2)
Sample D) of the above.

Japanese Unexamined Patent Publication No. 6-157143 discloses Hf.
A cutting tool composed of a silicon nitride-based sintered body obtained by sintering a powder containing Si _3, N ₄ added with O ₂ , Y ₂ O ₃ , rare earth oxide, SiO ₂ , and ZrO ₂ is described. 6-2
Japanese Patent Publication No. 98567 discloses a silicon nitride-based sintered body which is sintered by performing HIP after pressureless sintering and precipitating Dy ₂ Hf ₂ O ₇ and Y ₂ Hf ₂ O ₇ crystals in a grain boundary phase. ing.

As a silicon nitride-based sintered body in which Y ₂ Hf ₂ O ₇ is precipitated at the grain boundary, one containing SiC in addition is disclosed in Japanese Patent Laid-Open No. 6-58242.
No. 305836, Si, Hf, Zr at grain boundaries.
Japanese Unexamined Patent Publication No. 6-329470 discloses a crystal deposited from a composite compound of one or more of the above and a rare earth element.

As described above, it has been attempted to improve the high temperature strength and toughness by combining the type and amount of the sintering aid and the crystallization treatment conditions. Particularly, compound crystals containing a Group 4A element such as HfO ₂ Although the high temperature strength has been further improved by precipitating slag at the grain boundaries, the demand for strength and toughness becomes more stringent in the field of high-efficiency cutting tools, which has been especially required in recent years, because higher speed machining is performed. ing. Therefore, at a temperature of 1300 ° C or higher, 1
Although there is a great need for a Si ₃ N ₄ system sintered body which can stably obtain a bending strength of about 00 kg / mm ² or more, no one satisfying this condition has been reported yet.

[0017]

SUMMARY OF THE INVENTION In view of such conventional circumstances, the present invention is a silicon nitride-based sintered body which precipitates crystals in a grain boundary phase and is superior in strength and fracture toughness at a higher temperature than before,
And a method for producing the same.

[0018]

In order to achieve the above object, the silicon nitride-based sintered body provided by the present invention has a grain boundary phase of 20% by weight or less and the balance of silicon nitride and / or sialon. A silicon nitride-based sintered body comprising a main phase of crystal particles of silicon nitride; wherein the main phase is β-Si ₃ N ₄ and / or
Or a particle phase consisting of β'-sialon, and the amount ratio of the particle phase of β-Si ₃ N ₄ and / or β'-sialon to the main phase is in the range of 0.5 to 1.0; The grain boundary phase is characterized by containing Re ₂ A ₇ O ₁₇ (wherein Re means a 3A group element and A means a 4A group element; the same applies hereinafter) as a crystal component.

Further, in the grain boundary phase of the silicon nitride-based sintered body of the present invention, in addition to the first crystal component composed of Re ₂ A ₇ O ₁₇ , the second crystal component is ReSiNO ₂ , Re ₃ Al
_At least one of ₅ O ₁₂ , ReAlO _3, and Si ₃ N ₄ .Y ₂ O ₃ may be contained. The ratio of the crystal components in the grain boundary phase to the particle phase of β-Si ₃ N ₄ and / or β'-sialon in the main phase is preferably in the range of 0.3 to 4.0.

In the present invention, β-S for the main phase
The amount ratio of the particle phase of i ₃ N ₄ and / or β′-sialon is the main ratio with respect to the sum of the peak intensities of the X-ray diffraction lines of all the crystal particles of Si ₃ N ₄ and sialon constituting the main phase. It is the ratio of the sum of the peak intensities of the crystal particles of β-Si ₃ N ₄ and β'-sialon in the phase.

In the present invention, the amount ratio of β-Si ₃ N ₄ and / or β'-sialon in the main phase of the crystal component in the grain boundary phase to the particle phase is shown in JCPDS33-1160 card. This means the ratio of the sum of the peak intensities of the X-ray diffraction lines of all the crystal components in the grain boundary phase to the peak intensity of the X-ray diffraction lines of (200) or β′-sialon corresponding thereto.

The method for producing a silicon nitride-based sintered body provided by the present invention comprises: 80 to 98% by weight of silicon nitride-based powder;
₂ (where A means group 4A element) 1st consisting of powder
Component and Re ₂ O ₃ (where Re means a Group 3A element,
The same shall apply hereinafter) and AlN, ReN, SiO ₂ , Al ₂ O ₃ , M _x
O _y (where M _x O _y is an oxide, M is Li, Na, Ca,
Powder of a single compound in combination with at least one of Mg or a group 3A element), or powder of a compound compound in which the single compound is combined, or Si ₃
2 to 20% by weight of a sintering aid system powder, which is composed of a second component selected from at least one of the mixed powders to which the N ₄ · Y ₂ O ₃ powder is added, is mixed; After sintering the compact formed by molding the raw material powder in a nitrogen pressure atmosphere; for the nucleation and crystal growth of the obtained sintered body in a temperature range of 1050 ° C to 1600 ° C in a non-oxidizing atmosphere. Is characterized by performing the heat treatment of.

[0023]

The silicon nitride-based sintered body of the present invention has the grain boundary phase of 20% by weight or less and the remaining main phase of Si ₃ N _{4 as described above.}
And / or sialon crystal particles. It is more preferable that the grain boundary phase is 2 to 20% by weight and the main phase is 80 to 98% by weight. If the main phase is less than 80% by weight, that is, if the grain boundary phase exceeds 20% by weight, a sintered body having sufficient strength may not be obtained even if the grain boundary phase contains a crystal component, and If the boundary phase is less than 2% by weight, that is, the main phase exceeds 98% by weight, it may be difficult to densify by sintering, which is not preferable.

The main phase composed of Si ₃ N ₄ and / or sialon contains the β-Si ₃ N ₄ and / or β′-sialon particle phase, and the combination thereof is summarized in Table 1.
Here, α′-sialon is M _x (Si, Al) ₁₂ (O, N)
₁₆ (where 0 <x ≦ 2) and β′-sialon are represented by the formula Si _6-z Al _z N _8-z (where 0 <x ≦ 4.2). However, in the above chemical formula, M
Is Na, Li, Mg, Ca, or one or two of Group 3A elements
Means more than species.

[0025]

[Table 1] (Note) ○ indicates the existing phase.

Regarding the above main phases, α phase and β shown in Table 1
Β in a crystal grain consisting of a combination of α phase and α'phase β'phase
Ratio to the total crystal grains of -Si ₃ N ₄ and / or β'- sialon, i.e. by the peak intensity of X-ray diffraction lines as defined above and (β + β ') / ( α + β + α' + β ') ratio of 0.
It must be 5 to 1. When the amount ratio of β-Si ₃ N ₄ and / or β'-sialon is less than 0.5, equiaxed α-
Si ₃ N ₄ or α′-sialon increases, and β-Si ₃
A network structure of N ₄ and / or β′-sialon is not sufficiently formed, and therefore a sintered body having high toughness cannot be obtained.

When the α'-sialon is exposed to a high temperature, a part of the α'-sialon is transformed into a β'-sialon, which causes Y or Al incorporated in the crystal to be precipitated at the grain boundaries. The characteristics deteriorate. Therefore, the main phase Si
_In the combination of ₃ N ₄ and sialon, α-Si ₃ N ₄ and β'-
Most preferred is a combination of sialon. The main phase is all β
It may be —Si ₃ N ₄ or β′-sialon, in which case the above amount ratio is 1.

The β-Si ₃ N ₄ particles or β'-sialon particles preferably have an average major axis diameter of 0.4 to 10 μm and an aspect ratio of 1.4 to 10. That is,
When β-Si ₃ N ₄ particles or β'-sialon particles, which are the main phase, become too fine or have a shape close to an equiaxed crystal,
The number of joints in the network structure of β-Si ₃ N ₄ or β'-sialon increases, and the impact resistance and toughness are less improved than those in the above range. This is because it becomes more difficult to obtain a dense sintered body as compared with the one inside, and as a result, the improvement in strength and toughness becomes smaller.

On the other hand, the grain boundary phase is Re as the first crystal component.
₂ A ₇ O ₁₇ must be contained, and ReS as the second crystal component.
iNO ₂ (ReN · SiO ₂ ), Re ₃ Al ₅ O ₁₂ (3Re ₂
O ₃ · 5Al ₂ O ₃ ), ReAlO ₃ (Re ₂ O ₃ · Al ₂ O ₃ )
And often contains at least one of Si ₃ N ₄ .Y ₂ O ₃ . The first crystal component is preferably one in which Re is Y or A is Hf, and the second crystal component is also one in which Re is Y.
It is preferable that the composition is

As a quantitative index of each crystal component in the grain boundary phase, the amount ratio of the crystal component in the grain boundary phase to the β-Si ₃ N ₄ phase and / or the β'-sialon phase in the main phase, that is, Grain boundary crystal by the X-ray diffraction line main peak intensity defined above /
The ratio of (β + β ′) is preferably in the range of 0.3 to 4.0, and more preferably in the range of 0.5 to 2.0. If the amount ratio of the grain boundary crystal components is less than 0.3, the fine crystals of the above combination are not generated in the grain boundary phase or the amount thereof is small, so that the strength, toughness, and wear resistance at high temperatures are deteriorated. . On the contrary, if the amount ratio of the grain boundary crystal component exceeds 4.0, the amount of Si ₃ N ₄ or sialon in the sintered body is relatively decreased,
It becomes impossible to obtain sufficient strength.

The silicon nitride-based sintered body of the present invention having the above-mentioned crystal component in the grain boundary phase has a bending strength of 1200 M at room temperature.
Flexural strength 90 at Pa or higher and 1300 ° C to 1400 ° C
A strength characteristic of 0 MPa or more is stably obtained, and a fracture toughness value K _IC is 5 MPa ^3/2 or more, which has both high strength and excellent toughness.

The silicon nitride-based sintered body of the present invention is characterized by a combination of a starting material silicon nitride-based powder and a specific sintering aid-based powder mixed therewith, and a heat treatment step after sintering. It can be manufactured. First, α-Si ₃ N ₄ powder is used as the starting material silicon nitride-based powder, but β-Si ₃ N ₄ powder can be added if necessary.

A sintering aid type powder is added to the silicon nitride type powder, and the sintering aid type powder is AO ₂ as the first component.
It consists of powder and a second component, the second component being Re ₂ O ₃ and Al.
A mixed powder of a single compound with at least one of N, ReN, SiO ₂ , Al ₂ O ₃ and M _x O _y , or a composite compound powder having a composition in which these single compounds are combined, or these powders It is composed of a mixed powder to which Si ₃ N ₄ .Y ₂ O ₃ powder is added. Of the above-mentioned sintering aids, the second component also acts as a sialon-forming agent, and a part or all of them form a solid solution in the Si ₃ N ₄ particles to form sialon. Here, Re represents a 3A group element, and specifically, in addition to Y, La, Sc, C
e, Pr, Nd, Pm, Sm, Eu, Gd, Dy, E
It also includes lanthanides such as r and Yb. A is a Group 4A element and represents Ti, Zr, and Hf.

Regarding the form of the second component of the sintering aid type powder, Re ₂ O ₃ , AlN,
Although it may be added in the form of a single compound such as ReN, SiO ₂ , Al ₂ O ₃ and M _x O _y, it may be added in the form of a composite compound of any composition in which at least two of these single compounds are combined. It is more preferable to add. By adding in the form of such a composite compound, the sintering progresses more homogeneously than in the conventional case where a single compound is added as it is to form a composite compound by sintering, and it is possible to densify at a lower temperature. Because. As a result, the crystal grains of the main phase become finer,
It is possible to obtain a sintered body excellent in strength, toughness, and wear resistance.

For example, FIG. 1 is an example showing the difference between the addition form of the sintering aid type powder added together with the HfO ₂ powder and the effect thereof when the main phase is Si ₃ N ₄ . Compared with the case where Al ₂ O ₃ and 3 mol Y ₂ O ₃ are respectively added as a single compound, 5 mol Al ₂ O ₃ and 3 mol Y ₂ are added.
It can be understood that the addition of O ₃ as the composite compound Y ₃ Al ₅ O ₁₂ lowers the sintering temperature by about 100 ° C. and densifies at low temperature. This point is Sialon or Sialon and S
It is also applicable when i ₃ N ₄ is the main phase. Further, at least one kind of powder of the single compound may be added to the composite compound powder for use.

The mixing ratio of the silicon nitride powder and the sintering aid powder is 80 to 98% by weight of the silicon nitride powder and 2 to 20% by weight of the sintering aid powder. 2 powders of sintering aid system
If it exceeds 0% by weight, the amount of silicon nitride powder becomes too small, so that only a brittle sintered body can be obtained, and the strength sharply decreases at high temperatures. This is because if the amount of the sintering aid type powder is less than 2% by weight, the amount of the sintering aid is too small and the sintering does not proceed sufficiently. As described above, since the sintering aid also contains a component that forms a solid solution with Si ₃ N ₄ to form sialon, the grain structure of the sintered body is 20% by weight of the grain boundary phase. It cannot be exceeded.

The above-mentioned silicon nitride powder and sintering aid powder are mixed as usual, and the mixed powder is molded by various molding methods. This molded body is made into a silicon nitride-based sintered body by sintering in a nitrogen pressure atmosphere. In the method of the present invention, the obtained sintered body is further subjected to heat treatment for nucleation and crystal growth. As a result, the grain boundary phase finally satisfies the above-mentioned crystal component and its quantitative index. By further densifying the sintered body in a high-pressure nitrogen atmosphere of 50 to 1000 atm, a more dense and high-strength sintered body can be obtained.

The heat treatment temperature of the silicon nitride sintered body is 10
Within the temperature range of 50 ° C or higher and 1600 ° C or lower. Within this temperature range, the formation of nuclei to be the crystal component of the grain boundary phase and the crystal growth of the nuclei are realized. The heat treatment atmosphere is set to a non-oxidizing atmosphere in order to prevent the surface of the sintered body from being oxidized and from being deteriorated in strength.

The heat treatment temperature is 1050 ° C. to 1600 ° C.
When the temperature is lower than 1050 ° C, crystal nuclei are not formed in the grain boundary phase, and when the temperature exceeds 1600 ° C, the crystal component of the intended composition cannot be obtained in the grain boundary phase, or the main phase This is because the ingredients may sublime. When there is a eutectic point corresponding to the combined composition of the single compounds added up to 1600 ° C., the heat treatment temperature is up to the eutectic point temperature. The eutectic point corresponding to the combined composition of single compounds corresponds to the composition of 5 mols Al ₂ O ₃ and 3 mols Y ₂ O _{3 when} the composite compound is Y ₃ Al ₅ O ₁₂ , for example,
Its eutectic point is 1760 ° C.

As a preferred mode of the heat treatment step, 1
After nucleation at 050 to 1350 ° C. for 0.5 to 12 hours, the temperature can be continuously raised to perform crystal growth within a temperature range of 1300 to 1600 ° C. (or the eutectic point). In this case, it goes without saying that the crystal growth temperature must be higher than the crystal nucleus formation temperature. By performing the two-step process as described above, it becomes possible to crystallize more of the grain boundary phase, which was the glass phase at the time of sintering, as compared with the one-step process.
The toughness and wear resistance are further improved. That is, the bending strength at room temperature is 1220 MPa or more, the bending strength at 1300 ° C. is 950 MPa or more, and the fracture toughness K _IC is 5.5 MPa ^3/2.
The above can be stably obtained.

In the above nucleation step, nucleation is not performed under nucleation conditions of less than 1050 ° C. or less than 0.5 hours, and at the nucleation temperature of more than 1350 ° C., the necessary combination of crystal components and its quantitative index are shown. Can't meet. Further, the nuclei formed do not increase even if the nucleation time exceeds 12 hours, so that it is preferably within 12 hours.

In the subsequent crystal growth step,
If the crystal growth temperature is lower than 1300 ° C., the crystal nuclei do not grow sufficiently, and if it exceeds 1600 ° C. or exceeds the eutectic point corresponding to the combined composition of single compounds, the crystal of the target composition in the grain boundary phase is obtained. This is because the components may not be obtained or the main phase component may sublime. Crystal growth time is 0.5-2
4 hours is preferred. This is because if the time is less than 0.5 hours, the desired characteristics cannot be obtained because the crystallization does not proceed, and if the time exceeds 24 hours, the crystallization does not proceed any more and the surface of the sintered body becomes rough.

A heat treatment process for nucleation and crystal growth, preferably a heat treatment process consisting of the above two steps,
The crystallization of the grain boundary phase is further promoted by engraving the program of the time of one cycle within the upper limit of the above time and the temperature within the above range and repeating the cycle two or more times continuously. High temperature strength, toughness, and wear resistance are further improved. That is, by the above repeated heat treatment, the bending strength at room temperature is 1300 MPa or more, the bending strength at 1300 ° C. is 1100 MPa or more, and the fracture toughness K _IC is 6.
A value of 0 MPa ^3/2 or more can be stably obtained.

The heat treatment process may be carried out by incorporating it into the cooling process of the sintering process for obtaining the sintered body. Alternatively, it may be performed after the sintering step is cut off and the sintered body obtained by sintering is subjected to machining or coating treatment. In particular, when heat treatment is performed after machining, the secondary effect that the scratches and defects on the surface during machining are restored by the healing effect is obtained. Furthermore, before performing the crystal nucleation step, the temperature is raised to a temperature at which a liquid phase occurs in the grain boundary phase and held in advance, then cooled to the crystal nucleation temperature, and the crystal nucleation step and the crystal growth step are performed. Is also good.

[0045]

Example 1 90% by weight of α-Si ₃ N ₄ powder having an average particle size of 0.7 μm,
Composite compound Y ₃ Al having an average particle size of 0.8 μm as a sintering aid
8% by weight of ₅ O ₁₂ powder and 2% by weight of HfO ₂ powder were mixed. The Y ₃ Al ₅ O ₁₂ powder is obtained by previously mixing the Y ₂ O ₃ powder and the Al ₂ O ₃ powder and firing the mixture at 1150 to 1650 ° C.

To 100 parts by weight of this mixed powder, 3 parts by weight of polyethyleneamine as a dispersant and 120 parts by weight of ethanol as a solvent were added, and the mixture was uniformly mixed with an alumina ball, dried and then dried at 5 t / cm ² . A hydrostatic press was used to form a disk having a diameter of 70 mm and a thickness of 8 mm.
The obtained molded body was heated to 600 ° C. in vacuum and held for 1 hour to degrease.

For comparison, the above composite compound Y ₃ Al ₅ O
Instead of the ₁₂ powders, a single compound was combined, ie 5% by weight of Al ₂ O ₃ powder having an average particle size of 0.6 μm and 3% by weight of Y ₂ O ₃ powder having an average particle size of 1.0 μm. A molded body was produced by the same method as described above.

Each of the above-mentioned compacts was subjected to 1700 ° C., 1750 ° C., 1800 ° C., 1850 ° C. in a nitrogen pressure atmosphere of 8 atm.
C. and 1900.degree. C. for 4 hours to obtain a sintered body. The result of measuring the density of each obtained sintered body is shown in FIG. As is clear from FIG. 1, it is better to add these single compounds in the form of a composite compound than to use a single compound in combination as a sintering aid, and to improve the sinterability at a lower temperature. It can be seen that various sintered bodies can be obtained.

Next, using the above-mentioned composite compound as a sintering aid, a plurality of compacts produced in the same manner as above were sintered at 1800 ° C. for 4 hours, and each of the resulting sintered compacts was subjected to a bending test piece shape. Then, heat treatment was performed in a nitrogen atmosphere of 1.5 atm (Sample 13 is in the air) according to the crystallization treatment pattern of the nucleation treatment and the crystal growth treatment shown in FIG. At this time, the temperature a of the nucleation treatment and the holding time b, and the temperature c of the crystal growth treatment
And the retention time d are shown in Table 2 below. The rate of temperature increase was 10 ° C./min and the cooling was air cooling.

[0050]

[Table 2] (Note) Samples marked with * in the table are comparative examples. Sample 4 is an example of the present invention in which one-step heat treatment is performed, and sample 14 is a comparative example without heat treatment. Further, sample 13 is a comparative example in which the heat treatment was performed in the atmosphere.

For each sintered body after the above heat treatment, the crystal component contained in the grain boundary phase was determined by the X-ray diffraction method, and
The amount ratio of β-Si ₃ N ₄ and / or β'-sialon in the main phase of the grain boundary phase crystal component to the particle phase (hereinafter referred to as grain boundary crystal amount ratio) was determined, and the results are shown in Table 3. It was still,
The amount ratio of β-Si ₃ N ₄ and / or β′-sialon in the main phase Si ₃ N ₄ and sialon crystal particles (hereinafter referred to as β, β ′ amount ratio) is 1 in each sample. Met.

[0052]

[Table 3] (Note) Samples marked with * in the table are comparative examples.

For each sintered body, the relative density, the three-point bending strength at room temperature and 1400 ° C., and the fracture toughness were measured,
Further, the hardness at room temperature and 1400 ° C. was measured, and the results are shown in Table 4 below. Roughness was observed in the sintered bodies of Samples 8 and 12, and in Sample 9, a part of the sintered body sublimated.

[0054]

[Table 4] Bending strength (kg / mm ² ) Fracture toughness (MPa ^3/2 ) Relative density hardness (H _V ) Sample normal temperature 1300 ℃ Normal temperature 1300 ℃ (%) Normal temperature 1300 ℃ 1 122 99 5.5 4.1 99.4 1532 1050 2 126 97 5.7 4.3 99.4 1543 1038 3 125 101 5.5 4.0 99.2 1516 1041 4 120 90 5.0 3.8 99.5 1538 1011 5 * 112 48 4.5 2.5 97.4 1509 911 6 * 118 56 4.7 3.1 99.1 1530 911 7 * 110 53 4.9 2.2 99.2 1521 893 8 * 127 73 5.0 2.5 99.4 1509 953 9 * 58 28 4.7 3.1 90.3 1423 879 10 * 98 31 4.8 2.9 99.4 1530 882 11 * 118 43 4.5 3.0 99.2 1522 903 12 * 126 88 4.8 3.0 99.5 1531 901 13 * 110 39 3.1 2.8 94.8 1479 819 14 * 111 42 4.9 2.4 99.3 1476 891 (Note) The samples marked with * in the table are comparative examples.

From the above results, Y ₂ Hf ₇ O ₁₇ was always precipitated in the grain boundary phase of the sample of the present invention, and further YSiNO ₂ ,
In some cases, crystal components such as Y ₃ Al ₅ O ₁₂ , YAlO ₃ , and Si ₃ N ₄ .Y ₂ O ₃ are precipitated. On the other hand, in the grain boundary phase of the sample of the comparative example, the crystal component of Y ₂ Hf ₇ O ₁₇ was not obtained.
Samples 1 and 4 are equal to the maximum temperature of the heat treatment and the treatment time at that temperature is equal to 12 hours at 1480 ° C., respectively, but it can be seen that Sample 1 provided with the crystal nucleation step is superior in high temperature characteristics. In addition, the sample 4 is the sample 14 which is not heat-treated.
High temperature characteristics are better than Further, it can be seen that the sample of the present invention example is far superior in bending strength and fracture toughness at room temperature and high temperature as compared with the sample of the comparative example.

Example 2 In the same manner as in Example 1, the composite compound Y ₃ Al ₅ O ₁₂ powder and HfO ₂ powder were added to α-Si ₃ N ₄ powder as a sintering aid to manufacture a sintered body. This sintered body is continuously heat-treated (nucleation + crystal growth) under the same conditions as in Sample 2 of Example 1,
This was Sample 15 of this example. Further, a sintered body was manufactured in the same manner, and the sintered body was continuously subjected to heat treatment in which the crystallization treatment of nucleation and crystal growth shown in FIG. 3 was repeated twice, to obtain Sample 16 of this example. After that, both samples 15 and 16 are model S
It processed into the cutting tool shape of NG434.

Further, the sintered body manufactured as in Example 1 as described above was processed into the shape of a cutting tool of model number SNG434, and then heat-treated under the same conditions as in Sample 2 of Example 1 (nucleation +
Crystal growth) was performed to obtain Sample 17 of this example. After processing the sintered body in the same manner, a heat treatment of repeating nucleation and crystal growth treatment shown in FIG. 3 was performed twice to obtain a sample 18 of this example. In addition, as a comparative example, a sample 19 was similarly processed as it was but not subjected to heat treatment.

For each of these samples, the crystal component in the grain boundary phase and the grain boundary crystal amount ratio were determined by the X-ray diffraction method in the same manner as in Example 1. The crystal components of the grain boundary phase in Samples 15 to 18 are the same as those in Sample 2 shown in Table 3 of Example 1 in Y ₂
Hf ₇ O ₁₇ and YSiNO ₂ were included, but in Sample 19, no crystal component was precipitated in the grain boundary phase. Further, in all the samples, the β / β ′ amount ratio was 1.

With respect to the sintered body of each of the above-mentioned samples, at room temperature and 1
Three-point bending strength at 400 ° C., fracture toughness at room temperature, and relative density were determined. In order to evaluate cutting performance, V = 40
FC250 disc brake 1 as a work material under the cutting conditions of 0 m / min, f = 0.1 mm / blade, and d = 1.5 mm.
Wet cutting of 00 pieces was carried out, and the wear amount of each chip was obtained.

Further, using a test piece having a diameter of 8 mm and a length of 25 mm made of each sample manufactured in the same manner as described above, 100
A friction wear test was carried out at 0 ° C. to determine the specific wear amount. The mating material was steel, and the rotation speed was 900 rpm and the load was 300 N. The results are summarized in Table 5 below together with the grain boundary crystal amount ratio.

[0061]

Table 5 Grain boundary crystal strength (kg / mm ²⁾ Fracture toughness density cutting test ratio frictional sample weight ratio ordinary temperature ^{1300 ℃ (MPa 3/2) (%} ) wear amount (mm) 耗量 15 0.99 130 103 6.1 99.3 0.298 7.9 16 0.81 132 108 6.5 99.4 0.222 5.4 17 0.98 131 105 6.3 99.2 0.251 6.9 18 2.83 136 113 6.7 99.3 0.196 4.5 19 * None 121 28 5.4 99.2 0.713 13.0 (Note) Samples marked with * in the table are comparative examples. Is. The unit of the specific wear amount is × 10 ^-9 mm ³ / N · mm.

From the results of the above cutting test, it can be seen that the high temperature characteristics and the cutting performance are better when the material is once processed after sintering and then heat treated than when continuously heat treated as it is after sintering. Further, it has been found that the characteristics are further improved by continuously performing the heat treatment for nucleation and crystal growth twice or more than once.

Also in the friction and wear test, sample 18 processed after sintering and further heat-treated twice successively has the smallest amount of wear, and sample 1 which has not been heat-treated for crystallization.
9 is the most worn. From this result, it was found that the wear resistance is improved by crystallizing the grain boundary phase.

Example 3 Si ₃ N ₄ powder having an average particle size of 0.9 μm was mixed with a sintering aid powder shown in Table 6 below, and kneaded in a ball mill for 48 hours using acetone as a solvent. To 100 parts by weight of the obtained mixed powder, 3 parts by weight of polyethyleneamine as a dispersant and 120 parts by weight of ethanol as a solvent were added, uniformly mixed with alumina balls, dried, and pressed into rectangular parallelepipeds. Each molded body was heated to 600 ° C. in vacuum and kept for 1 hour for degreasing.

[0065]

[Table 6] (Note) Samples marked with * in the table are comparative examples.

For samples 20 to 24 of the present invention, the degreased compacts were sintered at 1800 ° C. for 4 hours in a nitrogen atmosphere at 6 atm, and then 1820 ° C. in a nitrogen atmosphere at 1000 atm. HIP treatment was performed for 2 hours. After that, a heat treatment for crystallizing the grain boundary phase was performed. The heat treatment condition is 12 in a nitrogen atmosphere of 1.5 atm.
After holding at 00 ° C for 2 hours, it was held at 1550 ° C for 5 hours.

On the other hand, among the comparative examples, Samples 25 and 28 were sintered in the same manner as described above, subjected to HIP treatment in the same manner, and then subjected to heat treatment in the same manner as in Sample 25.
No. 8 did not undergo heat treatment. Samples 26 and 27 are
After sintering at 1750 ° C. for 3 hours in the same nitrogen atmosphere as above, HIP treatment was performed under the same conditions as above, but no heat treatment was performed.

For each sintered body manufactured as described above,
In the same manner as in Example 1, the crystal components in the grain boundary phase and the grain boundary crystal amount ratio were determined, and the results are shown in Table 7. In addition, in samples 20, 23, 24, and 25, β'-sialon was formed.

[0069]

[Table 7] (Note) Samples marked with * in the table are comparative examples.

For each of the above-mentioned sintered bodies, room temperature and 14
Three-point bending strength at 00 ° C. and fracture toughness were determined. Further, each sintered body sample was molded into an SNG432 shape,
V = 600 mm / mi using a sintered and processed tool
Under the conditions of n, f = 0.8 mm / rev and d = 2.0 mm,
The abrasion state was investigated after 40 disc-shaped FC250 materials having a diameter of 200 mm were ground. The results are shown in Table 8.

[0071]

[Table 8] (Note) Samples marked with * in the table are comparative examples.

Since Sample 25 did not contain HfO ₂ , a predetermined crystal component did not precipitate in the grain boundary phase due to the heat treatment.
Bending strength and toughness at high temperature are significantly reduced. Sample 2
In Nos. 6 and 27, Y ₂ Hf ₂ O ₇ was present in the grain boundary phase, but the high temperature characteristics were poor. Further, since the sample 28 was not heat-treated, the grain boundary phase was in the glass phase state, and the flexural strength and toughness at high temperatures drastically decreased. It can be seen that Samples 20 to 24 according to the present invention have a higher degree of crystallization of the crystal phase, higher bending strength and toughness at high temperatures, and excellent cutting performance as compared with Comparative Examples. Example 4

Si ₃ N ₄ powder having an average particle size of 1.1 μm, Y ₃ Al ₅ O ₁₂ powder and MgO powder having an average particle size of 0.9 μm, AlN powder having an average particle size of 1.3 μm, and an average particle size of 1. 2 μm H
The fO ₂ powder was mixed in the proportions shown in Table 9 below.

[0074]

[Table 9] (Note) Samples marked with * in the table are comparative examples.

Using these raw material powders, mixing, molding, sintering and HIP treatment were carried out in the same manner as in Example 3 to produce sintered bodies. Further, each sintered body was held at 1100 ° C. for 1 hour in a nitrogen atmosphere of 1.5 atm, and subsequently, heat treatment was performed at 1440 ° C. for 5 hours.

For each sintered body manufactured as described above,
In the same manner as in Example 1, the crystal components in the grain boundary phase and the grain boundary crystal amount ratio were determined, and the results are shown in Table 10. Note that samples 29, 30, and 32 had α'- and β'-sialon formed. Further, the three-point bending strength and the fracture toughness were measured in the same manner as in Example 1, and the results are also shown in Table 10.

[0077]

[Table 10] Grain boundary crystal bending strength (kg / mm ² ) Fracture toughness (MPa ^3/2 ) Sample amount Specific grain boundary phase Crystal component room temperature 1400 ℃ room temperature 1400 ℃ 29 1.31 Y ₂ Hf ₇ O ₁₇ 130 95 5.8 4.6 30 1.06 Y ₂ Hf ₇ O ₁₇ Y ₂ Si ₂ O ₇ 126 93 6.6 4.4 31 0.96 Y ₂ Hf ₇ O ₁₇ 122 94 6.8 4.8 32 * 0.21 Y ₂ Si ₂ O ₇ 115 34 6.5 2.8 (Note) In the table The sample marked with * is a comparative example.

From these results, it is understood that in Samples 29 to 31 of the present invention, Y ₂ Hf ₇ O ₁₇ is present in the grain boundary phase, and the high temperature characteristics are superior to those of the comparative example.

Example 5 91% by weight of Si ₃ N ₄ powder having an average particle size of 1.5 μm and Dy ₃ Al ₅ O ₁₂ powder 4 having an average particle size of 0.9 μm as a sintering aid
% By weight, 1% by weight of MgO powder having an average particle size of 1.3 μm, ₂ % by weight of Al ₂ O ₃ powder, and 2% by weight of HfO ₂ powder having an average particle size of 1.2 μm. As a comparative example (Sample 37) containing no HfO ₂ powder, 93 wt% of the same Si ₃ N ₄ powder,
5 wt% of Dy ₃ Al ₅ O ₁₂ powder, 1 wt% of MgO powder, and ₂ wt% of Al ₂ O ₃ powder were mixed.

After mixing, molding and degreasing each of these raw material powders in the same manner as in Example 3, sintering and HIP treatment were carried out under the conditions shown in Table 11 below. Sintering and HIP are all performed in a nitrogen atmosphere, sintering is 3 atm and HIP is 500
It was carried out under pressure at atmospheric pressure. Furthermore, 1.
After holding at 1160 ° C. for 3 hours in a nitrogen atmosphere of 5 atm, heat treatment was performed at 1450 ° C. for 8 hours.

[0081]

[Table 11] Sample firing conditions HIP condition 33 1650 ℃ × 4H 1520 ℃ × 2H 34 1750 ℃ × 4H 1620 ℃ × 2H 35 1850 ℃ × 4H 1700 ℃ × 2H 36 1850 ℃ × 8H 1810 ℃ × 2H 37 * 1750 ℃ × 4H 1700 ℃ × 2H (Note) * marked sample in the table is a comparative example.

For each sintered body manufactured as described above,
In the same manner as in Example 1, the β, β'amount ratio, the crystal component in the grain boundary phase and the grain boundary crystal amount ratio, and the average major axis diameter of the β-Si ₃ N ₄ particles or the β'-sialon particles were determined. The aspect ratio was determined and the results are shown in Table 12. In addition, three-point bending strength and fracture toughness were measured in the same manner as in Example 1, and the results are shown in Table 13.

[0083]

TABLE 12 beta, beta 'grain boundary crystal average major axis diameter sample weight ratio amount ratio grain boundary phase crystal component ([mu] m) Asuhe ° transfected ratio _{33 0.52 3.1 Dy 2 Hf 7 O} 17 0.9 1.8 34 0.71 2.1 Dy 2 Hf 7 O 17 3.3 6.7 35 0.88 1.3 Dy ₂ Hf ₇ O ₁₇ Dy ₂ SiO ₅ 9.1 9.0 36 1.00 0.9 Dy ₂ Hf ₇ O ₁₇ 9.9 12 37 * 1.00 0.2 Dy ₂ Si ₂ O ₇ 3.3 6.7 (Note) * in the table The sample is a comparative example.

[0084]

[Table 13] (Note) Samples marked with * in the table are comparative examples.

From these results, in Samples 33 to 36 of the present invention, Dy ₂ Hf ₇ O ₁₇ was present as a crystal component in the grain boundary phase, and the crystallinity (grain boundary crystal amount ratio) of the grain boundary phase crystal component was 0. .9-3.
However, in the sample 37 of the comparative example, Dy ₂ Si ₂
O ₇ was present as a crystal component, and its grain boundary crystal amount ratio was only 0.2. Further, in the sample of the present invention, β-Si ₃ N ₄
Or, the aspect ratio of β'-sialon particles is 1.4 to 1
It is in the range of 2. From these, the sample of the present invention has remarkably excellent characteristics as compared with the comparative example, but from the comparison of the samples 35 and 36, the aspect ratio of β-Si ₃ N ₄ or β'-sialon particles is 1.4. It has been found that a range of -10 is more preferable.

Example 6 Si ₃ N ₄ powder having an average particle size of 1.5 μm, average particle size of 0.9 μm
Y ₃ Al ₅ O ₁₂ powder, MgO powder with an average particle size of 1.3 μm, Al ₂ O ₃ powder, AlN powder, Y ₂ O ₃ powder with an average particle size of 1.4 μm, TiO _{2 with} an average particle size of 1.1 μm Powder or Zr
The O ₂ powders were mixed in the proportions shown in Table 14, respectively.

[0087]

[Table 14] Si ₃ N ₄ sintering aid and additive amount (wt%) Sample (wt%) Y ₃ Al ₅ O ₁₂ Al ₂ O ₃ Y ₂ O ₃ MgO AlN TiO ₂ ZrO ₂ 38 83 8 3 2 1 1 2 0 39 88 5 3 2 0 1 1 0 40 95 2 2 0 0 0 1 0 41 83 8 3 2 1 1 0 2 42 * 84 7 4 2 2 1 0 0 43 * 93 4 2 1 0 0 0 0 (Note) Samples marked with * in the table are comparative examples.

These raw material powders were treated in the same manner as in Example 3,
After mixing, molding and degreasing, sintering and HIP treatment were performed. Further, each of the obtained sintered bodies was heat-treated by holding it at 1,060 ° C. for 1 hour in a nitrogen atmosphere of 1.5 atm and then at 1,400 ° C. for 2 hours.

For each sintered body manufactured as described above,
The crystal component in the grain boundary phase and the grain boundary crystal amount ratio were determined in the same manner as in Example 1, and the results are shown in Table 15. In addition, β-Si ₃ N ₄ was formed in the main phases of Samples 40 and 43, and α′- and β′-sialon were formed in the main phases of the other samples. Further, the three-point bending strength and the fracture toughness were measured in the same manner as in Example 1, and the results are also shown in Table 15. Table 1 below
From the result of No. 5, it was confirmed that Y ₂ Ti ₇ O ₁₇ or Y ₂ Zr _{7 was} added to the grain boundary phase.
It can be seen that the high temperature characteristics are excellent when the crystal component of O ₁₇ is deposited.

[0090]

[Table 15] Grain boundary crystal bending strength (kg / mm ² ) Fracture toughness (MPa ^3/2 ) Sample amount Specific grain boundary phase Crystal component room temperature 1400 ℃ room temperature 1400 ℃ 38 0.97 Y ₂ Ti ₇ O ₁₇ 127 100 6.7 4.2 39 0.81 Y ₂ Ti ₇ O ₁₇ 121 93 6.8 4.1 40 0.71 Y ₂ Ti ₇ O ₁₇ Y ₂ Si ₂ O ₇ 123 92 6.4 4.4 41 0.98 Y ₂ Zr ₇ O ₁₇ 125 96 6.6 4.2 42 * 0.58 Y ₂ SiO ₅ 120 26 6.3 3.2 43 * 0.31 Y ₂ Si ₂ O ₇ 120 30 5.1 2.7 (Note) The samples marked with * in the table are comparative examples.

Example 7 Si ₃ N ₄ powder having an average particle size of 0.7 μm, average particle size of 1.6 μm
Y ₃ Al ₅ O ₁₂ powder, AlN powder, average particle size 1.3 μm
MgO powder and HfO ₂ powder having an average particle diameter of 1.2 μm were mixed in the proportions shown in Table 16.

[0092]

[Table 16] (Note) Samples marked with * in the table are comparative examples.

These raw material powders were treated in the same manner as in Example 3,
After mixing, molding and degreasing, sintering and HIP treatment were performed. Further, each of the obtained sintered bodies was heat-treated by holding it at 1100 ° C. for 3 hours in a nitrogen atmosphere of 1.5 atm, and then at 1450 ° C. for 4 hours.

For each sintered body manufactured as described above,
In the same manner as in Example 1, the crystal components in the grain boundary phase and the grain boundary crystal amount ratio were determined, and the results are shown in Table 17. Further, the three-point bending strength and the fracture toughness were measured in the same manner as in Example 1, and the results are also shown in Table 17.

[0095]

[Table 17] Grain boundary crystal Grain boundary phase Bending strength (kg / mm ² ) Fracture toughness (MPa ^3/2 ) Sample amount Specific crystal composition chamber temperature 1400 ° C chamber temperature 1400 ° C 44 1.43 Y ₂ Hf ₇ O ₁₇ 123 99 6.8 4.3 45 0.98 Y ₂ Hf ₇ O ₁₇ 120 96 6.7 4.3 46 1.23 Y ₂ Hf ₇ O ₁₇ 122 97 6.8 4.2 47 * 0.24 Y ₂ Hf ₂ O ₇ 89 32 4.3 2.3 48 * 1.55 Y ₂ Hf ₂ O ₇ 78 26 4.3 2.1 (Note) Samples marked with * in the table are comparative examples.

From the above results, it is understood that when the addition amount of the sintering aid is less than 2% by weight or exceeds 20% by weight, the mechanical properties are deteriorated not only at high temperature but also at room temperature. That is, if the amount of the sintering aid is less than 2% by weight, the sintering is not sufficiently performed, and if it exceeds 20% by weight, the mechanical properties of silicon nitride itself cannot be exhibited.

Example 8 A test piece of a sintered body manufactured in the same manner as the sample 44 of Example 7 was once taken out from the furnace, processed into a characteristic evaluation test piece and a cutting test piece, and then subjected to the following heat treatment. As a comparative example, a sample without heat treatment was also prepared for the same test piece.

That is, as to the sample 49, as shown in FIG. 4, the temperature was once raised from room temperature to 1700 ° C. and kept at that temperature for 1 hour, then cooled to 1100 ° C. and kept at that temperature for 4 hours. The temperature was further raised to 1450 ° C. and the temperature was maintained for 5 hours. As shown in FIG. 5, the sample 50 was heated from room temperature to 1100 ° C. and held at that temperature for 4 hours, then heated to 1450 ° C. and held at that temperature for 5 hours.

With respect to the characteristic evaluation test pieces of each of the obtained samples, the crystal components in the grain boundary phase and the grain boundary crystal amount ratio were determined in the same manner as in Example 1, and the three-point bending strength and the fracture toughness were measured. The results are shown in Table 18. For each cutting test piece (SNG432 shape), V = 800 mm /
Under the conditions of min, f = 0.4 mm / rev, and d = 1.5 mm, the wear state after 50 disc-shaped FC250 materials with a diameter of 200 mm were ground was examined, and Table 18 shows the wear amount.

[0100]

[Table 18] Grain boundary crystal Grain boundary phase Bending strength (kg / mm ² ) Fracture toughness (MPa ^3/2 ) Cutting test sample volume Specific crystal component chamber temperature 1400 ° C chamber temperature 1400 ° C Wear amount (mm) 49 3.11 Y ₂ Hf ₇ O ₁₇ 124 101 6.8 4.2 0.277 50 1.26 Y ₂ Hf ₇ O ₁₇ 122 91 6.8 4.1 0.311 51 * 0 None 122 34 6.8 2.7 0.698 (Note) Samples marked with * in the table are comparative examples.

As in the case of sample 49, it is better to go through the process of once raising the temperature of the grain boundary phase to a liquid state and then growing by forming crystal nuclei during cooling. It can be seen that a large amount is formed and therefore the high temperature characteristics are also excellent.

[0102]

EFFECTS OF THE INVENTION According to the present invention, by precipitating a specific crystal component in the grain boundary phase, a silicon nitride-based calcinated that is more excellent in strength and fracture toughness than before, and particularly excellent in high temperature strength and fracture toughness. A tie can be provided.

Since this silicon nitride-based sintered body is excellent in strength and fracture toughness as well as in hardness and wear resistance at high temperatures, cutting tool materials, wear resistant tool materials, structural materials, etc. Is particularly useful as

[Brief description of drawings]

FIG. 1 is a graph showing the sinterability when two kinds of single compounds and their composite compounds are used as the second component of the sintering aid in the method of the present invention.

2 is a graph showing a heat treatment program for crystallizing a grain boundary phase in Example 1. FIG.

FIG. 3 is a graph showing a heat treatment program for grain boundary phase crystallization in Example 2.

FIG. 4 is a graph showing one heat treatment program used for comparison of grain boundary phase crystallization in Example 8.

5 is a graph showing another heat treatment program used for comparison of grain boundary phase crystallization in Example 8. FIG.

Claims (11)

[Claims] 1. A silicon nitride-based sintered body comprising a grain boundary phase in a weight ratio of 20% or less, the remainder being silicon nitride and / or a main phase of crystal particles of sialon and silicon nitride; wherein the main phase is beta-Si ₃ includes N ₄ and / or particulate phase consisting of β'- sialon, and the relative main phase beta-Si ₃ N ₄ and /
Or the amount ratio of the β'-sialon particle phase is in the range of 0.5 to 1.0; the grain boundary phase is a crystalline component of Re ₂ A ₇ O ₁₇
(However, Re means 3A group element, A means 4A group element)
A silicon nitride-based sintered body comprising: 2. The grain boundary phase is Re as a second crystal component.
SiNO ₂ (however, Re means a Group 3A element, the same applies hereinafter), Re ₃ Al ₅ O ₁₂ , ReAlO ₃ and Si ₃ N ₄ Y ₂
The silicon nitride-based sintered body according to claim 1, comprising at least one kind of O ₃ . 3. β- in the main phase of the crystal component in the grain boundary phase
The silicon nitride-based sintered body according to claim 1 or 2, wherein the ratio of the amount of Si ₃ N ₄ and / or β'-sialon to the particle phase is in the range of 0.3 to 4.0. 4. The Re is Y,
The silicon nitride-based sintered body according to claim 1. 5. The above A is Hf,
The silicon nitride-based sintered body according to claim 1. 6. The average major axis diameter of the β-Si ₃ N ₄ particles or β′-sialon particles is 0.4 to 10 μm, and the aspect ratio is 1.4 to 10. ~
5. The silicon nitride-based sintered body according to any one of 5 above. 7. A silicon nitride powder of 80 to 98% by weight,
AO ₂ (however, A means group 4A element) powder as the first component, Re ₂ O ₃ (however, Re means group 3A element, the same applies hereinafter), AlN, ReN, SiO ₂ , Al
₂ O ₃ , M _x O _y (where M _x O _y is an oxide, M is Li, N
a, Ca, Mg or at least one of Group 3A elements) in combination with a single compound powder, or a composite compound powder in which the single compound is combined, or Si ₃ N ₄ ·. _{2 to} 20% by weight of a sintering aid powder, which is composed of a second component selected from at least one of the Y ₂ O ₃ powders, is mixed; After sintering the formed compact in a nitrogen pressure atmosphere, the obtained sintered body is subjected to 10 in a non-oxidizing atmosphere.
A method for producing a silicon nitride-based sintered body, which comprises performing heat treatment for nucleation and crystal growth within a temperature range of 50 ° C to 1600 ° C. 8. The heat treatment process comprises 1050 to 1350.
The silicon nitride-based sintering according to claim 7, wherein after the nucleation is performed at 0.5 ° C for 0.5 to 12 hours, the temperature is subsequently raised to perform crystal growth within a temperature range of 1300 to 1600 ° C. Body manufacturing method. 9. The method for producing a silicon nitride-based sintered body according to claim 8, wherein the heat treatment step including the nucleation treatment and the crystal growth treatment is continuously repeated a plurality of times. 10. The heat treatment process according to claim 7, wherein the heat treatment process is performed during a cooling process of the sintering process.
9. A method for producing a silicon nitride-based sintered body according to any one of 1. 11. The heat treatment step according to claim 7, wherein the heat treatment step is performed after the sintered body obtained in the sintering step is subjected to machining or coating treatment. A method for manufacturing a silicon nitride-based sintered body.