JP2001172085A - Silicon nitride sintered compact, production process therefor, and silicon nitride abrasion-resistant material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride abrasion-resistant material having a long life and high reliability. SOLUTION: The objective sintered silicon nitride has the grain boundary phase and the maximum crystal size in the grain boundary phase is adjusted to <=100 μm in the depth range of 1 mm from the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wear-resistant member made of a silicon nitride sintered body and a method for manufacturing the same.

[0002]

2. Description of the Related Art A silicon nitride sintered body is expected to be used as a material for structural mechanical parts because of its high strength and excellent wear resistance and rigidity. Used for moving balls and rollers.

In sintering the above silicon nitride sintered body,
Since silicon nitride as a raw material of the silicon nitride-based sintered body has no self-sintering property, sintering is performed by adding a sintering aid.
As the sintering aid, rare earth oxides such as Y ₂ O ₃ and oxides such as Al ₂ O ₃ , MgO and CaO are generally used in combination. Then, after mixing these sintering aids with silicon nitride powder and molding, sintering is performed to obtain a silicon nitride-based sintered body. Examples of the sintering method include atmospheric pressure sintering performed under normal pressure and atmospheric pressure sintering with nitrogen or the like, and further, in a sintered body obtained by the normal pressure sintering, HIP (Hot Isostatic Pressing) processing is performed to improve mechanical strength by processing at high temperature and high gas pressure to eliminate residual pores.

[0004] In particular, when used as a bearing material, atmospheric pressure sintering or HIP processing is used because minute defects (pores and the like) inherent in the material cause peeling on the surface due to rolling fatigue. . The sintered body thus obtained is used as a bearing component after precision processing as a product.

[0005] Since the rolling element receives a high tensile stress on the surface or in the vicinity of the surface layer, it is important that no defects exist on the surface or in the vicinity of the surface layer. In particular, it is required that there be no defects (pores, inclusions, abnormalities in tissue, etc.).

Further, in recent years, with the increase in speed of machine tools, which are the main applications of ceramic bearings, and the market development in the aviation and space industries, the need for high-load ceramic bearings in higher temperature environments has been increasing. In addition, the need for ceramic bearings for high-speed HDDs is increasing because of their light weight.

[0007]

However, the bearing material using the silicon nitride-based sintered body obtained as described above has a problem that the mechanical properties are reduced due to the generation of frictional heat. . In particular, when a white pattern was generated in the sintered body when observed with an optical microscope and could not be removed before being processed into a product and remained on the surface of the product, the mechanical characteristics were significantly reduced. This white pattern is due to the lack of grain boundaries, and the pattern remaining on the surface is not a clear defect indication pattern in the fluorescence inspection inspection of the product surface, but develops a weak color.

[0008] Japanese Patent Application Laid-Open No. 6-329472 also describes the following problem with respect to the rolling life required for a bearing material of a silicon nitride sintered body having such a pattern. .

When the depth from the surface exceeds 1 mm,
The size of the grain boundary phase missing part constituting the pattern is 0.3 μm.
m, and causes peeling due to rolling fatigue. Further, the size of the aggregate of the grain boundary phase lacking portions constituting the pattern of the silicon nitride based sintered body is 0.3 μm.
However, if the size of the aggregate at the grain boundary phase-missing portion is 0.5 mm or more, there is a problem in that a bearing that is used at a high operating temperature even if the temperature is not more than 0.5 m causes peeling due to rolling fatigue in a short time.

[0010] In Japanese Patent Application Laid-Open No. 6-329472,
Although the above-mentioned problem is also shown, the defect size is set to 0.
Only the definition of the aggregate of microvoids of 3 μm or less has not been taken as a fundamental measure.

[0011]

Means for Solving the Problems In view of the above problems, the present inventor has made various studies and as a result, has found that a silicon nitride based sintered body in which at least a part of a crystal grain boundary phase is crystallized, It has been found that the above problem can be solved by setting the maximum crystal diameter to 100 μm or less.

As a method of producing such a sintered body, a mixture containing silicon nitride as a main component and a rare earth element oxide powder and an aluminum oxide powder as sintering aids is formed, and then molded in a non-oxide atmosphere. 1600 ℃ ～ 20
After sintering at a temperature of 00 ° C. for densification and rapid cooling, 9
It has been found that heat treatment at a temperature of 00 ° C to 1200 ° C is effective. It is important to improve the thermal conductivity by crystallizing the grain boundaries in order to improve the high-temperature durability due to frictional heat.Furthermore, the crystal size of the grain boundary phase causes The present invention was found to have an effect on the high-temperature durability, thereby leading to the present invention.

It has also been found that the grain boundary phase lacking portion is caused by the maximum crystal diameter of the grain boundary phase. Therefore, by reducing the maximum crystal diameter of the grain boundary phase, the occurrence of the grain boundary phase lacking portion is reduced, and it is found that a dendritic white pattern, which is a collection of the grain boundary phase lacking portion, is less likely to occur. It was.

Here, what is indicated as a grain boundary crystal phase is as follows:
It does not mean the grain boundary crystal phase as a defect existing so as to be surrounded by the silicon nitride crystal phase that has been pointed out conventionally, but means a group of grain boundary phases in which a group of silicon nitride crystal phases are dispersed. Can be observed by polishing and observing with a polarizing microscope. The grain boundary crystal phases thus observed can be distinguished from other parts because the crystals are arranged radially from one point.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

First, the silicon nitride sintered body of the present invention will be described. The silicon nitride of the present invention contains a rare earth element compound in an amount of 1 to 30% by weight in terms of oxide, as well as silicon oxide and aluminum oxide, as a sintering aid. Also,
At least a part of the grain boundary phase formed by the sintering aid is crystallized, and the maximum crystal diameter of the grain boundary phase is 10%.
It is not more than 0 μm.

First, a schematic diagram of a grain boundary crystal phase of a conventional silicon nitride sintered body will be described with reference to FIG. When a conventional silicon nitride sintered body is polished on its surface or fractured surface and its structure is observed with a polarizing microscope, when the angle of polarization is adjusted, as shown in FIG. This is the grain boundary crystal phase 1. Depending on its size, 10-2
It can be observed at a magnification of about 00. When the grain boundary crystal phase 1 is larger than 100 μm, it can be seen that a resinous white pattern as the grain boundary phase lacking layer 2 is generated around the grain boundary crystal phase 1. On the other hand, the grain boundary crystal phase of the silicon nitride sintered body of the present invention has a grain boundary crystal phase 1 having a size of 10 as shown in FIG.
It is characterized by a small size of 0 μm or less, and no resin-like white pattern, which is a grain boundary phase missing portion, is not observed around it.

By observing the grain boundary crystal phases 1 well, the present inventors have found that they are the grain boundary crystal phases 1 which are crystallized radially from a certain starting point. It was found that the structure contained silicon nitride crystals. In addition, since these porcelains are cooled after firing and greatly shrink when the grain boundary crystal phase 1 is formed, a gap is formed between the liquid phase components remaining and the crystallized grain boundary crystal. It was found out that a gap formed around the phase 1 was the grain boundary phase missing part 2.

However, it is important for the silicon nitride sintered body of the present invention that at least a part of the grain boundary phase is crystallized. The reason for this is that although there is a bearing component as an application of the silicon nitride-based sintered body, there is a problem that mechanical properties are deteriorated due to generation of frictional heat during use. It is necessary to efficiently release the friction heat generated there. Since silicon nitride has no self-sintering property, sintering is performed by adding a sintering aid. In general, metals and substances with good crystallinity are excellent in thermal conductivity, but if the grain boundary phase between silicon nitride particles is amorphous, the amorphous portion has low thermal conductivity, so friction is low. Heat is not efficiently dissipated. However, when the grain boundary phase is crystallized, the thermal conductivity is high, frictional heat can be efficiently released, and there is no decrease in mechanical properties when using a silicon nitride sintered body as a bearing component. I found it.

Regarding defects in the grain boundary phase, see JP-A No. 2-14 / 1990.
Japanese Patent No. 1474 discloses that it is necessary that there is no grain boundary precipitation portion of 100 μm or more. However, the grain boundary precipitation portion described in the above patent publication is formed between silicon nitride particles. The grain boundary precipitation portion, which is a defect and is trapped in the present invention, is basically a group of grain boundary phases including a group of silicon nitride particles in which grain boundary crystal phases are arranged radially from a certain point. Are different. There is no description in the patent document indicating that the maximum crystal diameter of the grain boundary phase in which silicon nitride crystals are dispersed is 100 μm or less. Regarding the crystallization of the grain boundary phase, Japanese Patent Application No. 63-44001 discloses that it is necessary to use a silicon nitride material in which 50% or less of the grain boundary phase is crystallized. However, as in the present invention, the maximum crystal diameter in which silicon nitride crystals are dispersed is not described.

Further, according to the present invention, by reducing the maximum crystal diameter of the grain boundary phase, the occurrence of the grain boundary phase lacking portion 2 is reduced, and a dendritic white pattern, which is a collection of the grain boundary phase lacking portion 2, is less likely to occur. can do. That is, the occurrence of the grain boundary phase missing portion is explained as follows.

During sintering, components mainly including the sintering aid which is in a liquid phase undergo thermal contraction with cooling, but when a part or all of the components crystallize, rapid volume contraction (volume) accompanying crystallization occurs. (Several% by shrinkage), a gap is formed between the crystal at the adjacent grain boundary or the amorphous portion in the supercooled state, and a missing part of the grain boundary phase is generated. At this time, the maximum crystal diameter of the grain boundary phase is large, and the smaller the number is, the larger the gap generated due to volume shrinkage accompanying crystallization becomes, and a larger grain boundary phase lacking part is generated. Therefore, in order to suppress the generation of the grain boundary phase lacking portion 2, it is sufficient that there are many crystals at the grain boundaries having a small grain size.

In order to generate a large number of crystals having small grain boundaries having a maximum grain size of 100 μm or less, the grain boundaries are made amorphous by rapidly cooling after firing, and thereafter, at the nucleation temperature of the crystals. It is necessary to crystallize after heat treatment to generate many nuclei. However, if the quenching is not performed after firing, crystals having a large size are generated in the cooling process, and the grain boundary phase missing portions are generated due to the volume shrinkage occurring at that time. Therefore, it is necessary to quench after firing and to make the grain boundary phase amorphous once, so that a large number of small crystal nuclei of 100 μm or less are obtained by heat treatment at 900 ° C. to 1200 ° C. performed after firing. Precipitate,
The crystal phase at the grain boundary does not grow to a size of 100 μm or more.

The maximum crystal diameter of the grain boundary phase at this time will be described.

Usually, when a grain boundary is crystallized, the maximum crystal diameter has been considered to be a size of sub-μm to several mm. The grain boundary phase usually observed by a scanning electron microscope or the like refers to a region between two planes sandwiched between two silicon nitride particles, a triple junction region sandwiched between three silicon nitride particles, and the like. At most, it is observed as large as tens of μm (several tens of μm if there is segregation). However, since the two-plane region and the triple point region of the silicon nitride particles are actually connected three-dimensionally, when crystallized, one crystal extends over a wide three-dimensionally connected region (for example, several mm). There are things.
This is clear from the fact that when the silicon nitride sintered body is sliced and observed with a polarizing microscope or the like, the grain boundary phase may be crystallized with the same orientation over a region of several mm.

When the maximum crystal diameter is several mm, several mm
Is a form in which silicon nitride particles are densely dispersed in a crystal phase (for example, RE ₂ Si ₂ O ₇ crystal or the like). The maximum crystal diameter of the grain boundary phase defined in the present invention is 10 to 100 μm.
When observed with a polarizing microscope, a silicon nitride-based sintered body sliced to a thickness of about m or a thickness at which a grain boundary crystal phase was confirmed, a group of white-shining crystals that grew radially from one point could be confirmed. In this case, the size of this crystal group was determined to be the maximum crystal diameter of the grain boundary phase. When observing with a microscope,
Observation can be made at about 20 to 200 times depending on the size of the grain boundary crystal phase. In the present invention, 5 mm square portions were observed at five locations per sample. This size was measured from a micrograph.

According to the observation in this manner, when the maximum crystal diameter of the grain boundary phase is 100 μm or less, preferably 10 μm or less, the volume shrinkage due to crystallization is small, and the space between the grain boundary crystals or partial crystallization does not occur. The grain boundary missing portions generated in the gaps between the amorphous portions remaining in the crystal grains are reduced. When the maximum crystal diameter of the grain boundary phase is controlled as described above, the size of the dendritic white pattern, which is a set of the grain boundary phase-missing portions, becomes 300 μm or less, preferably 100 μm or less, and more preferably 10 μm or less. It was found that no peeling was caused by the peeling.

Furthermore, ceramic parts, especially wear-resistant parts such as bearings, are subjected to stress in the vicinity of the surface even when the surface is ground or not ground, so that a grain boundary phase missing portion within 1 mm from the surface is formed. The size of a dendritic white pattern, which is a set of grain boundary phase missing portions of 1 μm or less and 1 μm or less, is 30
It is particularly important that the thickness be 0 μm or less.

Further, when a rare earth element oxide is used as a sintering aid, generation of grain boundary phase missing portions is smaller than when magnesium oxide or calcium oxide is used.
Although the reason is not clear, it seems that the properties of the grain boundary phase are different.

Particularly, the rare earth element oxide is important as a sintering aid, and its amount is desirably 1 to 30% by weight. The reason for selecting this range is that if it is less than 1% by weight, the firing temperature must be high in order to densify it, so that the mechanical properties tend to deteriorate, and if it exceeds 30% by weight, This is because the intrinsic properties of silicon nitride, that is, mechanical properties, tend to decrease.

Further, the amount of oxygen contained in the added rare earth element oxide was subtracted from the amount of oxygen obtained by analyzing the silicon nitride-based porcelain, and calculation was performed assuming that the remaining oxygen was SiO ₂ . In some cases, when the weight ratio of SiO ₂ : rare earth element oxide is 1: 0.3 to 1:15, a silicon nitride ceramic sintered body having good wear resistance can be obtained.

If the weight ratio is less than 1: 0.3, the grain boundary phase tends to separate a phase rich in SiO ₂ , and a white pattern (structure with grain boundaries dropped out) tends to be generated. If the ratio is 1:15 or more, the composition deviates significantly from the low-melting point composition due to the reaction of SiO ₂ -rare earth element oxide. This is because they tend to be united.

It is to be noted that SiO ₂ may be added as a sintering aid in addition to the one originally contained in the silicon nitride raw material, and may be added during the manufacturing process due to oxidation of the raw material or decomposition by firing. Such a decrease may occur.

The rare earth elements used in the present invention are preferably Y, Er, Yb, and Lu. Among these elements, it is most preferable to use a heavy rare earth element such as Yb or Er, since a white pattern (a structure in which grain boundaries have fallen off) hardly occurs.

Further, it is desirable to add aluminum oxide as a subcomponent in that the sintering surface and the grain boundary phase are once made amorphous. Maximum grain size of grain boundary phase is 100μm
In order to reduce the temperature to below, it is necessary to rapidly cool the grain boundary phase after firing and to make the grain boundary phase amorphous once. Many crystal nuclei are precipitated, and the crystal phase of the grain boundary phase does not grow to a size of 100 μm or more. The preferred amount of aluminum oxide is selected so that the weight ratio of aluminum oxide to the rare earth element oxide is 1: 0.5 to 1:10, and more preferably 1: 1 to 1: 5.

The reason for this is that when the ratio of aluminum oxide: rare earth element oxide is 1: 0.5 or more, the fracture toughness tends to decrease. Further, when the ratio of aluminum oxide: rare earth element oxide is less than 1:10, the sinterability is poor and the crushing load tends to be low. In addition, the grain boundary phase is less likely to become amorphous, and the grain boundary phase missing portion is more likely to occur.

In the above sintered body, the average particle size is 3 μm.
It is preferable to contain a tungsten silicide of m or less. Originally, a small amount of Fe was contained as an impurity in the silicon nitride raw material, and Fe was unevenly distributed after firing, which might be a source of destruction, resulting in a decrease in strength and crushing when used as a wear-resistant member. The load is reduced and the rolling life is shortened. Since tungsten silicide has the property of dissolving Fe, the uneven distribution of Fe after firing is reduced, and the mechanical properties are improved.

Here, the particle size of these W silicides is 3 μm
The reason for the limitation is that if the tungsten silicide is larger than 3 μm, the dispersion in the grain boundary phase becomes insufficient, and the tungsten silicide itself becomes a fracture source and lowers the strength of the sintered body, and the desired strength is obtained. Because there is no.

In addition, W ₅ Si ₃ or W
In order to generate Si ₂ , one or more types of W silicides, carbides, oxides, and nitrides having an average particle size of 3 μm or less are added in 0.1%.
Add 〜10.0% by weight. These W compounds react with silicon nitride or SiO ₂ during firing and form W ₅ Si of 3 μm or less.
₃ and WSi ₂ are generated.

In the sintered body of the present invention, in addition to the W component, metals having periodicity of groups 4a, 5a and 6a such as Ti, Ta, Mo, Nb, V and Mn, and silicides and carbides thereof. , Oxides, nitrides, and also dispersed particles or whiskers of SiC or the like in the sintered body of the present invention have little effect of deteriorating the properties. Of course, it is also possible to improve the characteristics as a composite material.

Further, among the silicides of W, W_FiveSi_Threeparticle
Is WSi_TwoW is considered to have higher heat resistance than particles._Five
Si_ThreeRolling life is better when particles are included
You. W _FiveSi_ThreeAnd WSi_TwoAnd the ratio (W_FiveSi_Three/ WSi_Two)
Ceramic sintered body composed of 0.1 or more
Is preferred. More preferably, the ratio is 0.3 to
It is desirably 1.5.

Next, a method for producing the silicon nitride sintered body of the present invention will be described.

A predetermined amount of the raw material powder is weighed and mixed by a known mixing method, for example, a rotary mill, a vibration mill, or a barrel mill using IPA, methanol, water or the like as a solvent. In some cases, dry mixing without using a solvent may be used.

[0044] The mixed powder thus obtained is subjected to desired molding means,
For example, an arbitrary shape is formed by a die press, a cold isostatic press, an extrusion molding, an injection molding, a casting molding, or the like.
Depending on the molding method, granulation by spray drying or the like,
Preparations such as preparation of a clay having a certain viscosity together with water and an organic binder are also required, but a normal ceramics molding procedure may be used.

If drying and degreasing are required after molding, heat treatment is performed at a temperature of 50 ° C. to 1400 ° C. in nitrogen, vacuum, or air.

The firing is performed at 1600 ° C. to 2000 ° C. in a nitrogen-containing non-oxide atmosphere. When firing at 1800 ° C. or higher, decomposition of silicon nitride occurs,
Requires a partial pressure of nitrogen of at least one atmosphere. Further, after sintering, sintering is performed by hot isostatic pressing (HIP) or the like to obtain a denser sintered body. If the firing temperature is too high, the main phase, silicon nitride crystal, grows to reduce the strength, so that the firing temperature is desirably 1650 to 1950 ° C.

Further, when the molded body is fired by the glass bath HIP method, a dense sintered body can be produced in a short time at a low temperature, so that it is particularly suitable for ceramic parts requiring high strength and wear-resistant parts.

In order to reduce the maximum crystal diameter of the grain boundary phase to 100 μm or less, it is necessary to make the grain boundary phase amorphous once. The higher the speed, the better. In particular, it is better to cool the temperature range of 1600 to 800 ° C. for 3 hours, preferably 1 hour, and more preferably within 30 minutes.

Further, in order to precipitate the amorphized grain boundary phase as crystals having a small crystal diameter, 900 ° C. to 1200 ° C.
Heat treatment at a temperature of ° C. to generate crystal nuclei. This heat treatment may be a single heat treatment that is completely cooled after firing and then taken out of the furnace and individually performed in another furnace, or may be a continuous heat treatment performed in the same furnace as a firing pattern following cooling. By this firing, silicon nitride becomes β-Si ₃ N ₄ regardless of whether the raw material is α or β.

By this firing, a sintered body containing a β-silicon nitride main crystal phase and a grain boundary phase is finally obtained. In particular, when a rare earth element oxide or aluminum oxide is used as a sintering aid, W _5, which is composed of a grain boundary phase containing a rare earth element, aluminum, oxygen and nitrogen, and has an average particle size of 3 μm or less in the grain boundary. A sintered body containing Si ₃ or W ₅ Si ₃ + WSi ₂ can be obtained. The portion to be crystallized here is a grain boundary portion mainly composed of a ceramic component such as a rare earth oxide, aluminum oxide, and silicon oxide.

Further, WSi ₂ or W ₅ Si ₃ is monodispersed at the grain boundaries and has an effect of relaxing the stress when an external stress is applied, and also has an effect as a sintering aid. As a result, it is possible to have high toughness having a fracture toughness of 5.6 MPa√m or more and an Hv10 hardness of 14.5 or more and high mechanical properties of high hardness. In other words, according to the present invention, there is no white dendritic pattern observed, the silicon nitride sintered body is highly reliable, has a small amount of alteration, has a small grinding allowance, and has high fracture toughness and high hardness. It is possible to obtain.

The above-mentioned silicon nitride sintered body of the present invention is made of various ceramic parts, especially rolling elements, piston pins, roller pins, rocker arm chips, roller bushes,
It can be used for wear-resistant parts such as cam rollers and valves.

[0053]

Embodiment 1 An embodiment will be described below.

First, silicon nitride powder (BET specific surface area 9 m ²
/ G) The sintering aids shown in Table 1 were added to the powder and mixed with IPA in a barrel mill for 40 hours. After mixing, foreign matter was removed from the slurry through a # 500 mesh and dried.
Water and an organic binder were added to this mixed powder, and after mixing for 20 hours, raw material granules were obtained by spray drying. Using the raw material granules, a spherical molded body and a test piece for measuring the strength were prepared by press molding.

Next, this compact was heated in a temperature range of 800 to 1400 ° C. under a reduced pressure of 10 Torr or less, and then heated at 1750 to 1400 ° C.
It was densified at 850 ° C. under a nitrogen atmosphere to a relative specific gravity of 99% or more. In addition, under a pressure of 2000 atm.
The spherical ceramic sintered body of the present invention having a diameter of 3/8 inch is subjected to a HIP treatment at 0 ° C., and a heat treatment in a temperature range of 900 ° C. to 1200 ° C. with a cooling time of 1600 to 800 ° C. for 1 or 6 hours. A test piece for measurement was obtained.

The crushing load of the spherical ceramic is obtained by superposing two balls of the same size and applying a compressive load.
The measurement was performed at a crosshead speed of 5 mm / min using an Instron universal testing machine according to B-1501.

The strength was measured by a four-point bending test according to JIS R1601 on a test piece processed into a shape of 3 × 4 × 35 mm.

The size of the grain boundary phase missing portion was determined by using an optical microscope 100.
After observation at × 2, it was measured by an SEM image. The size of the dendritic white pattern, which is an aggregate of the grain boundary phase-missing portions, was measured from a photograph taken with an optical microscope (× 100).

The maximum crystal diameter of the grain boundary phase is determined by determining the presence or absence of crystals by X-ray diffraction of a powder obtained by pulverizing a sintered body. Further, a spherical ceramic body of the same lot is sliced to 20 μm and subjected to a polarizing microscope. The maximum crystal diameter of the grain boundary phase was confirmed. As for the sample, a 5 mm square portion under each condition was examined at five locations. When the sample is set on the polarizing microscope and the sample is rotated, there is a part that looks white when there is an orientation. At this time, the portion that looks white is a crystal of one grain boundary phase, and the evaluation results are summarized in Table 1.

[0060]

[Table 1]

As is clear from Table 1, the strength of Samples 2 and 3 in which the maximum crystal diameter of the grain boundary phase is larger than 100 μm is inferior.
On the other hand, Samples 1, 4 to 6 in which the crystal size of the grain boundary phase within the scope of the present invention is 100 μm or less were high in strength and excellent in crushing load.

Example 2 A sintered body was produced in the same manner as in Example 1. The crystallization conditions were set to the cooling time and heat treatment temperature shown in Table 2, and each of the obtained sintered bodies was evaluated in the same manner as in Example 1.

The fracture toughness value was in accordance with JIS R1607. Table 2 summarizes the results of these evaluations.

[0064]

[Table 2]

As is clear from Table 2, Sample 7 containing 40% by weight of Yb ₂ O ₃ which is a rare earth element oxide and having a SiO ₂ : rare earth element oxide ratio of 1:20 was insufficiently sintered. Was. Further, 0.5% by weight of the aforementioned Yb ₂ O _3
2 : Sample 3 having a rare earth element oxide ratio of 1: 0.2,
The maximum crystal diameter of the grain boundary phase was 140 μm, and the strength, crushing load, and K1c were low.

On the other hand, the rare earth element oxide is 1 to 30
In weight%, the weight ratio of SiO ₂ : rare earth element oxide is 1:
Samples 1, 2, 4 to 6, and 8 having a grain size of 0.3 to 1:15 had a crystal size of the grain boundary phase of 100 μm or less, and were excellent in mechanical properties.

In Samples 1, 2, and 5 to which the same weight ratio of rare earth oxide was added, Samples 2 and 5 using Er and Yb were particularly excellent in strength.

Example 3 A sintered body was produced in the same manner as in Example 1. The grain boundary phase was crystallized at the cooling time and heat treatment temperature shown in Table 3, and the obtained sintered body was evaluated in the same manner as in Example 1.

The fracture toughness value was in accordance with JIS R1607. Table 3 summarizes the results of these evaluations.

[0070]

[Table 3]

As is clear from Table 3, in Samples 1 to 11, the aluminum oxide: rare earth element oxide ratio was 1: 1.
Samples 1, 3, and 5 with less aluminum oxide than 10 had insufficient sintering, and Sample 11 with an aluminum oxide: rare earth element oxide ratio of more than 1: 0.5 aluminum oxide was inferior in fracture toughness value and crushing load. However, Samples 2, 4, 6 to 10 in which the ratio of aluminum oxide: the rare earth element oxide was 1: 0.5 to 1:10 had excellent sinterability, and the maximum crystal diameter of the grain boundary phase was large. It was 100 μm or less, the grain boundary phase missing part was 1 μm or less, and the dendritic white pattern, which is a set of grain boundary phase missing parts, was 300 μm or less, and had excellent mechanical properties.

[0072]

As described above in detail, according to the present invention, in a silicon nitride sintered body having a grain boundary phase, 1 m
m is within 100 μm.
And the size of the grain boundary phase missing portion between the silicon nitride particles is 1 μm or less, and the size of the dendritic white pattern which is a set of the grain boundary phase missing portions of 1 μm or less is 30 μm or less.
A silicon nitride-based sintered body having high mechanical properties and a long-wearing wear-resistant member with a small grinding allowance can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a grain boundary crystal phase in a silicon nitride based sintered body of the present invention.

FIG. 2 is a schematic view showing a grain boundary crystal phase in a conventional silicon nitride based sintered body.

[Explanation of symbols]

 1: grain boundary crystal phase 2: grain boundary phase missing part

Claims (5)

[Claims] 1. A silicon nitride sintered body in which at least a part of a crystal grain boundary phase is crystallized, wherein a maximum crystal diameter of the grain boundary phase is 100 μm or less. Union. 2. As an additive component, at least 1 in terms of oxide.
-30% by weight of a rare earth element compound, and the weight ratio of silicon oxide: rare earth element oxide in terms of oxide is 1: 0.3-
The silicon nitride based sintered body according to claim 1, wherein the ratio is 1:15. 3. The nitride according to claim 2, wherein an aluminum compound is contained as an additional component, and the weight ratio of aluminum oxide to rare earth element oxide in terms of oxide is 1: 0.5 to 1:10. Silicone sintered body. 4. A silicon nitride-based wear-resistant member comprising the silicon nitride-based sintered body according to claim 1. 5. After forming a powder containing silicon nitride as a main component, the powder is fired at a temperature of 1600 ° C. to 2000 ° C. in a non-oxide atmosphere, and cooled in a temperature range of 1600 ° C. to 800 ° C. within 3 hours. And a subsequent heat treatment at a temperature of 900 ° C. to 1200 ° C.