JP2016064971A - Silicon nitride sintered body and abrasion resistant member using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride sintered body high in chemical resistance to acid, alkali or the like.SOLUTION: There is provided silicon nitride sintered body having silicon nitride crystal particles 1 and a grain boundary phase 2, where the grain boundary phase 2 contains no rare earth element and has area ratio of the grain boundary phase 2 per unit area of 20 μm×20 μm of 10 to 20% when taking a picture of any cross section of the silicon nitride sintered body. There is particle containing one kind of 4A group element selected from Ti, Zr and Hf in the grain boundary phase 2 and the particle exists as a single body of a compound of oxide, nitride, hydride or carbide of 4A group element, a major axis is preferably 2 μm or less, there is preferably 1 to 5 particles containing the elements per unit area of 20 μm×20 μm, and Si and 2A group element form preferably no solid solution in the particle.SELECTED DRAWING: Figure 1

Description

Embodiments relate to a silicon nitride sintered body and a wear-resistant member using the same.

Ceramic sintered bodies based on silicon nitride have excellent heat resistance and low thermal expansion coefficient, so they have various characteristics such as excellent thermal shock resistance. As structural materials, application to engine parts, machine parts for steel making, etc. has been attempted. Moreover, since it is excellent also in abrasion resistance, the practical use as a rolling member or a cutting tool is also achieved.

In Japanese Patent No. 5362758 (Patent Document 1), a predetermined amount of rare earth oxide, aluminum oxide, titanium oxide or the like as a sintering aid is added to the raw material powder to improve the sinterability, and dense and high-strength nitriding. A silicon sintered body is obtained. On the other hand, since the silicon nitride sintered body as shown in Patent Document 1 contains a rare earth oxide, there is a problem that the corrosion resistance against chemicals such as acid and alkali is insufficient.
In order to improve the corrosion resistance against chemicals, Japanese Patent No. 2829229 has developed a silicon nitride sintered body containing no rare earth oxide. In Patent Document 2, MgO.
Al ₂ O ₃ spinel, SiC, SiO ₂ and TiO ₂ were used. Corrosion resistance to chemicals has been improved by such a combination of sintering aids.

Japanese Patent No. 5362758 Japanese Patent No. 2829229

In recent years, sintered silicon nitride has been used for various wear-resistant members such as engine parts, machine parts, bearing balls, and cutting tools. Since the silicon nitride sintered body is far more durable than metal members such as bearing steel (SUJ2), long-term reliability is obtained in various wear-resistant members. For this reason, maintenance-free for a long time is also realized.
However, conventional silicon nitride sintered bodies have not always been sufficient in terms of long-term reliability of corrosion resistance against chemicals such as acids and alkalis.

The silicon nitride sintered body according to the embodiment is for solving such a problem. When an arbitrary cross section of the silicon nitride sintered body including the silicon nitride crystal particles and the grain boundary phase is photographed, The boundary phase does not contain rare earth elements, and the area ratio of the grain boundary phase per unit area 20 μm × 20 μm is 10 to 20%.
It is characterized by being.

The silicon nitride sintered body according to the embodiment does not contain a rare earth element and controls the area ratio of the grain boundary phase per unit area. This makes it possible to maintain the corrosion resistance against chemicals for a long time while maintaining the durability of the silicon nitride sintered body. Therefore, the wear-resistant member using the silicon nitride sintered body of the embodiment can maintain reliability for a long time even in an environment where there is a chemical such as acid or alkali.

The figure which shows an example of the cross-sectional structure | tissue photograph of the silicon nitride sintered compact concerning embodiment.

In the silicon nitride sintered body according to the embodiment, when an arbitrary cross section of a silicon nitride sintered body having silicon nitride crystal grains and a grain boundary phase is photographed, the grain boundary phase does not contain a rare earth element, and the unit area is 20 μm × 2
The area ratio of the grain boundary phase per 0 μm is 10 to 20%.
The silicon nitride sintered body includes silicon nitride crystal grains as a main phase and a grain boundary phase as a sub phase. The grain boundary phase is mainly formed from a compound obtained by reacting the sintering aids with each other or with the sintering aid and silicon nitride (including impurity oxygen) in the sintering step. The sintering aid is added to control the sinterability, and the grain boundary phase is formed in the gaps (grain boundaries) between the silicon nitride crystal grains. The bonding force between the silicon nitride crystal grains is strengthened by the grain boundary phase.
When the silicon nitride crystal particles and the grain boundary phase are compared, the grain boundary phase is inferior in chemical resistance characteristics to the silicon nitride crystal particles. In particular, it has been found that a grain boundary phase composed of an oxide-derived amorphous phase is significantly inferior to silicon nitride crystal particles in resistance to acids and alkalis. Among the grain boundary phases, the grain boundary phase containing rare earth elements has low resistance to acids and alkalis. For this reason, the silicon nitride sintered body according to the embodiment is characterized in that the grain boundary phase does not contain a rare earth element. In addition, the corrosion resistance to an acid or an alkali shall be called chemical resistance.
Further, the area ratio of the grain boundary phase is set to 10 to 10 in a minute region such as a unit area of 20 μm × 20 μm.
The range is 20%. If the grain boundary phase is less than 10%, the grain boundary phase is too small and the wear resistance of the silicon nitride sintered body is lowered. Moreover, when the area ratio of a grain boundary phase exceeds 20%, there are too many grain boundary phases and chemical-resistant characteristics deteriorate. Therefore, the ratio of the grain boundary phase is 10 to 20%, preferably 10 to 15%. In the silicon nitride sintered body of the present invention, the area ratio of the grain boundary phase is in the range of 10 to 20% in a minute region having a unit area of 20 μm × 20 μm in an arbitrary cross section.

The method for measuring the area ratio of the grain boundary phase is as follows. First, an arbitrary cross section of the silicon nitride sintered body is obtained. This cross section is mirror-finished with a surface roughness Ra of 1 μm or less. In order to clarify the region between the silicon nitride crystal grains and the grain boundary phase, plasma etching is performed on the obtained mirror surface. When the plasma etching process is performed, the etching rate of the silicon nitride crystal grains and the grain boundary phase are different, and either one of them is largely deleted. For example, in plasma etching using CF 4, silicon nitride crystal particles have a higher etching rate (easily etched), so that the silicon nitride crystal particles are concave and the grain boundary phase is convex. The etching process can also be chemical etching using acid and alkali. SEM image of mirror surface after etching process (100
0x or higher magnification). In the SEM photograph, the silicon nitride particles and the grain boundary phase can be distinguished by the difference in contrast. Usually, the grain boundary phase appears white. By performing the etching process, the difference in contrast can be made clearer. By analyzing the image of the SEM photograph, the area ratio of the grain boundary phase per unit area can be measured. For image analysis, it is effective to perform image analysis by color mapping the grain boundary phase portion. FIG. 1 shows an example of an SEM photograph (5000 times). In FIG. 1, 2 is a silicon nitride particle part and 3 is a grain boundary phase part. FIG. 1 shows an example in which the grain boundary phase portion is a convex portion and the silicon nitride particle portion is a concave portion. When the image analysis is performed, the area ratio of the grain boundary phase is 15%. If the unit area does not become 20 μm × 20 μm, the image may be taken a plurality of times and the unit area may be 20 μm × 20 μm in total.

Further, it is preferable that particles containing one kind of group 4A element selected from Ti (titanium), Zr (zirconium), and Hf (hafnium) exist in the grain boundary phase. The particles containing a 4A group element are preferably a single compound of any of oxides, nitrides, hydrides, and carbides of the 4A group element. In the case of Ti, the compound simple substance is at least one of TiO ₂ (titanium oxide), TiN (titanium nitride), TiH ₂ (titanium hydride), and TiC (titanium carbide). Zr
In this case, one or more of ZrO ₂ (zirconium oxide), ZrN (zirconium nitride), ZrH ₂ (zirconium hydride), and ZrC (zirconium carbide) are used. H
In the case of f, one or more of HfO ₂ (hafnium oxide), HfN (hafnium nitride), HfH ₂ (hafnium hydride), and HfC (hafnium carbide) are used. 4 of these
A nitride or carbide of group A element is preferred. In particular, TiN or TiC is preferable.
The particles containing a 4A group element may be added as a single compound as a sintering aid, or may be changed into a single compound during the sintering process.
Moreover, the compound containing the 4A group element alone is a crystal particle. The presence of crystal grains in the grain boundary phase can reduce the proportion of the amorphous phase in the grain boundary phase. In addition, it can be qualitatively analyzed by TEM etc. whether it is a collection particle.
Moreover, it is preferable that the particle | grains containing a 4A group element are not dissolved with Si element and 2A group element. When dissolved with the Si element and the 2A group element, the single compound of the 4A group element becomes a composite compound of the 4A group element and the Si element or the 2A group element. The compound compound has lower chemical resistance than the compound alone. For this reason, the compound simple substance which does not form a complex compound with Si element or 2A group element is preferable. The above-mentioned TiN and TiC are preferable because it is difficult to form a composite compound.
Moreover, it is preferable that the particle | grains containing a 4A group element are 2 micrometers or less in long diameter. When the long diameter exceeds 2 μm, when particles (particles containing a 4A group element) remain at the triple point between the silicon nitride crystal particles,
This is a region where strength characteristics are locally weak, which may adversely affect wear resistance. For this reason, it is preferable that the long diameter of the particle | grains containing a 4A group element is 1.5 micrometers or less. 4A
If the particle containing a group element is too small, the effect of improving the chemical resistance of the grain boundary phase may not be sufficiently obtained. Therefore, it is preferable that the long diameter of the particle | grains containing a 4A group element is 0.5 micrometer or more.
Further, when an arbitrary cross-sectional structure of the silicon nitride sintered body is photographed, the unit area is 20 μm × 20 μm.
It is preferable that 1 to 5 particles containing a group 4A element exist. When the number per unit area is zero, there is a risk that the chemical resistance of the region where the particles containing the group 4A element are not present is lowered. On the other hand, if the number exceeds 5, the densification during sintering is inhibited, and internal defects may be generated to adversely affect the wear resistance and chemical resistance.
Most preferably, the particles containing a group 4A element are all a single compound, a major axis of 2 μm or less, and 1 to 5 particles per unit area of 20 μm × 20 μm.

Further, in order to further improve the chemical resistance of the grain boundary phase, it is desirable to improve the crystallinity of the grain boundary phase. It has been found that a highly crystalline grain boundary phase has higher chemical resistance than a grain boundary phase composed of an amorphous phase. In the silicon nitride sintered body according to the embodiment, when XRD analysis was performed, 41
. It is preferable that the peak of the grain boundary phase is detected in the range of 5 to 42.5 °. The fact that a peak is observed by XRD means that a compound having crystallinity exists in the grain boundary phase. At this time, in the XRD analysis, a polished surface obtained by polishing an arbitrary cross section of the silicon nitride sintered body until the surface roughness Ra was 1 μm or less was used as a measurement surface. Measurement conditions are Cu target (Cu-Kα
), Tube voltage 40 kV, tube current 40 mA, scan speed 2.0 ° / min, slit (
RS) 0.15 mm, scanning range (2θ) 20-70 °.
In addition, the component in which the peak is detected in the range of 41.5 to 42.5 ° may be particles containing the aforementioned 4A group element, or may be a crystalline component other than that.

Further, when the silicon nitride sintered body according to the embodiment was subjected to XRD analysis, 41.5 to 42.5 °.
The maximum peak in the range of I _{41.5-42.5 °} , the maximum peak intensity of _β- silicon nitride is I _{β-S
When i3N4} , it is preferable that _{I41.5-42.5 °} / _{Iβ -Si3N4} = _0.005-0.020 .
The maximum peak of β-silicon nitride crystal particles is detected around 36 °. I _{41.5-42.5 °}
/ I by the presence in the range to be the _β-Si3N4 = _0.005~0.020, can be crystalline grain boundary phase. When the peak ratio is large, the grain boundary phase having a high crystallinity becomes excessive and becomes difficult to sinter. Moreover, when the peak ratio is low, the chemical resistance of the grain boundary phase is not sufficiently improved.

Moreover, the silicon nitride sintered body contains 0.1 to 2.5% by mass of Al and 0.1 to 1.2.
0.1% to 3.8% by mass of any one or more of 5% by mass, Group 4A element, Group 5A element and Group 6A element
It is preferable to contain the mass%. Al, 4A group elements, 5A group elements, and 6A group elements are used as sintering aids for forming grain boundary phases. When reacting in the sintering process to become a grain boundary phase component, the ratio of the grain boundary phase is easily controlled to be within the above range.
The method of adding the Al component is not particularly limited as long as it contains Al,
One or more of AlN, Al ₂ O ₃ , and MgAl ₂ O ₄ spinel are preferable. Al forms a grain boundary phase and has a function of improving sinterability. When the content is lower than 0.1% by mass, the sinterability is poor and a sufficiently dense body cannot be obtained. On the other hand, when the content is more than 2.5% by mass, the grain boundary phase of the amorphous phase becomes excessive and the chemical resistance deteriorates.

In addition, when adding a group 2A element, Be (beryllium), Mg (magnesium), Ca (
It is desirable to select any one of calcium, Sr (strontium), Ba (barium), and Ra (radium), and if possible, any one of Be, Mg, Ca, and Sr.
When adding a Group 2 element component as a sintering aid, it is desirable to add any one of oxide, carbide, and nitride. When these elements coexist with Al, they form not only the effect of promoting sintering but also a crystalline grain boundary phase with high chemical resistance. When the content is less than 0.1% by mass, the improvement of sinterability and chemical resistance is insufficient, and when the content is more than 1.5% by mass, the crystallinity of the grain boundary is lowered, It adversely affects chemical properties.

When adding any of the 4A group element, 5A group element, and 6A group element, the 4A group element is Ti (titanium), Zr (zirconium), Hf (hafnium), and the 5A group element is V (vanadium). ), Nb (niobium), Ta (tantalum), Group 6A elements are Cr (chromium), Mo
It is desirable to select from (molybdenum) and W (tungsten). When adding a 4A group element component, a 5A group element component, or a 6A group element component as a sintering aid, it is desirable to add any one of oxide, carbide, and nitride. When the content is lower than 0.1% by mass, the crystal component in the grain boundary phase is insufficient, and the chemical resistance is deteriorated. If the content is more than 3.8% by mass,
This adversely affects the sinterability, impairs densification of the sintered body, and deteriorates the wear resistance.

The silicon nitride sintered body does not contain a rare earth element. The rare earth elements are Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), N
d (neodymium), Pm (promethium), Sm (samarium), Eu (europium)
Gd (gadlium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium).
When rare earth elements are added in the sintering of silicon nitride, the sinterability is improved and the aspect ratio of the silicon nitride crystal particles is improved. As a result, a sintered body having excellent strength characteristics and wear resistance can be obtained. I can do it. However, the addition of rare earth elements has a problem that the crystallinity of the grain boundary phase is lowered and the chemical resistance is deteriorated. Therefore, in the present invention, the chemical resistance of the grain boundary phase is improved without adding rare earth elements.

The silicon nitride is a silicon nitride crystal having a major axis of 2.0 μm or more per unit area of 20 μm × 20 μm when an arbitrary cross section of a silicon nitride sintered body having silicon nitride crystal grains and a grain boundary phase is photographed. When the particles are observed, silicon nitride particles having an aspect ratio of 2 or more are preferably 90% or more. Note that the ratio of silicon nitride particles having an aspect ratio of 2 or more is obtained as an area ratio. By adopting such a structure, it is possible to provide a silicon nitride sintered body having both strength characteristics and chemical resistance. If the ratio of the aspect ratio of 2 or more is less than 90%, the strength, particularly the fracture toughness value, decreases.
Further, when the average value of the major axis and the minor axis is defined as the particle size, the silicon nitride particles having a particle size of 2.0 μm or less may be 70% or more in area ratio with respect to the total area of the entire silicon nitride particles. desirable.
By using fine particles having a large aspect ratio as a main component, it is possible to improve material strength and wear resistance. When the silicon nitride particles having a particle size of 2.0 μm or less are 70% or less in terms of the area ratio with respect to the total area of the entire silicon nitride particles, the particles are likely to fall out during stress concentration, resulting in high wear resistance. It becomes insufficient.

Next, a manufacturing method will be described. As long as the silicon nitride sintered body according to the embodiment has the above-described configuration, the manufacturing method is not particularly limited.
First, silicon nitride powder is prepared. The silicon nitride powder preferably has an oxygen content of 4% by mass or less, contains α-phase silicon nitride of 85% by mass or more, and has an average particle size of 0.8 μm or less.
A silicon nitride sintered body having excellent wear resistance can be obtained by growing α-Si ₃ N ₄ powder into β-Si ₃ N ₄ crystal particles in the sintering step.
In the silicon nitride sintered body of the present invention, the area ratio of the grain boundary phase is controlled. In order to perform such control, it is effective to control the amount of the sintering aid. In order to control the amount of the sintering aid, it is effective to control the addition amount and to uniformly disperse the silicon nitride powder.
The additive amount of the sintering aid is 0.1 to 2.5% by mass of Al and 0.1 to 1.5% by mass of 2A group element.
It is preferable that at least one of the 4A group element, 5A group element, and 6A group element is 0.1 to 3.8% by mass. The average particle size of the sintering aid powder is preferably 1.8 μm or less.

In order to uniformly disperse the silicon nitride powder and the sintering aid powder, it is effective to perform the mixing process for a long time. A crushing and mixing process using a ball mill or the like is effective, and it is preferably performed for a long time of 50 hours or more. The crushing and mixing time is preferably 80 hours or longer. The crushing and mixing step can prevent secondary particles in which silicon nitride powders, sintering aid powders, silicon nitride powder and sintering aid powder are combined. Uniform dispersion can be achieved by most of the silicon nitride powder and the sintering aid powder becoming primary particles.
In order to control the area ratio of the grain boundary phase, it is effective to allow sufficient sintering even with a small amount of sintering aid. For this purpose, it is effective to oxidize the surface of the silicon nitride powder in advance. By using the silicon nitride powder with an oxide film, the silicon nitride powder can be activated and the reaction with the sintering aid can be promoted. Examples of the oxidation treatment to the silicon nitride powder include heat treatment in the air and water treatment. When oxidation is performed by heat treatment, 600 to 900 ° C in the air
The condition of 4 hours is desirable. When the temperature is 600 ° C. or lower, an oxide film is not sufficiently formed on the surface of the silicon nitride powder, and there is no effect of improving sinterability. Moreover, since sintering of silicon nitride powder proceeds at a temperature of 900 ° C. or higher and a large number of hard aggregated particles are generated, it is difficult to obtain primary particles in the crushing and mixing step. In addition, since the abrasion resistance of a silicon nitride sintered compact will fall if the oxidation process to a silicon nitride powder is performed too much, it is preferable that it is an oxide film of 0.5 micrometer or less as a film thickness.
Next, a binder is added to the raw material mixture obtained by mixing the silicon nitride powder and the sintering aid powder. The mixing of the raw material mixture and the binder is performed using a ball mill or the like while performing pulverization and granulation as necessary. The raw material mixture is formed into a desired shape. The molding process is performed by a die press, a cold isostatic press (CIP), or the like. The molding pressure is preferably 100 MPa or more. The molded body obtained in the molding process is degreased. The degreasing step is preferably performed at a temperature in the range of 300 to 600 ° C. The degreasing step is performed in the air or in a non-oxidizing atmosphere, and the atmosphere is not particularly limited.

Next, the degreased body obtained in the degreasing step is sintered at a temperature in the range of 1600 to 1900 ° C. If the sintering temperature is less than 1600 ° C., the crystal growth of silicon nitride crystal particles may be insufficient. That is, the reaction from α-phase type silicon nitride to β-phase type silicon nitride is insufficient, and a dense sintered body structure may not be obtained. In this case, the reliability as a material of the silicon nitride sintered body is lowered. When the sintering temperature exceeds 1900 ° C., silicon nitride crystal particles grow too much, and the workability may be reduced. The sintering step may be performed by either normal pressure sintering or pressure sintering. The sintering step is preferably performed in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include a nitrogen atmosphere and an argon atmosphere.

After the sintering process, it is preferable to perform a hot isostatic pressing (HIP) treatment of 10 MPa or more in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include a nitrogen atmosphere and an argon atmosphere. The HIP treatment temperature is preferably in the range of 1500-1900 ° C. By performing the HIP process, the pores in the silicon nitride sintered body can be eliminated. HIP
If the treatment pressure is less than 10 MPa, such an effect cannot be sufficiently obtained.

The silicon nitride sintered body thus manufactured is subjected to a polishing process at a necessary location to produce an abrasion resistant member. The polishing process is preferably performed using diamond abrasive grains.

(Example)
(Examples 1-8, Comparative Examples 1-7)
The silicon nitride powder and the sintering aid shown in Table 1 and Table 2 were prepared to prepare raw material powder. The amount of the sintering aid added is a ratio when the total amount of the silicon nitride powder and the sintering aid is 100 wt%. The crushing and mixing step was performed by a ball mill. Further, as shown in Tables 1 and 2, the silicon nitride powder used was a part of which was oxidized.

A resin binder was mixed with the obtained raw material mixture, and a molding step was performed at a molding pressure of 150 MPa. The obtained molded body was subjected to a degreasing process at 500 ° C. 1800 ° C. for the obtained defatted body
The normal pressure sintering for 4 hours and the HIP treatment for 1600 ° C. × 20 MPa × 2 hours were performed. Through this step, silicon nitride sintered bodies according to Examples and Comparative Examples were produced.
For each silicon nitride sintered body, an arbitrary cross section was cut and an enlarged photograph (SEM photograph) having a unit area of 20 μm × 20 μm was taken. Using an enlarged photograph, the area ratio of the grain boundary phase per unit area, the area ratio of silicon nitride crystal particles having a major axis of 2 μm or more, the area ratio of silicon nitride particles having a grain diameter of 2.0 μm or less, and a compound crystal containing a group 4A element The number of was determined. The results are shown in Table 3.

In the silicon nitride sintered bodies according to Examples 1 to 8, the area ratio of the grain boundary phase is 10 to 20%, and the ratio of the silicon nitride crystal particles having a major axis of 2 μm or more having an aspect ratio of 2 or more is 90% or more. The number of crystals of the group element compound was 1 to 3. For each sintered body, substantially no pores were confirmed. As a result of TEM observation, the group 4A element compound crystal of the silicon nitride sintered body according to the example was a single compound.
Regarding Comparative Examples 1 to 7, the area ratio of the grain boundary phase does not necessarily fall within the range of 10 to 20%, and the ratio of particles having an aspect ratio of 2 or more of silicon nitride crystal grains having a major axis of 2 μm or more is not necessarily 90%.
%, And the number of 4A group element compound crystals was not necessarily in the range of 1 to 5. In Comparative Examples 1, 2, 4, and 6, substantially no pores were observed, but in Comparative Examples 3, 5, and 7, pores were observed inside.
Next, XRD analysis was performed on the cross section of each silicon nitride sintered body. The results are shown in Table 4.

When the silicon nitride sintered bodies according to Examples 1 to 8 were subjected to XRD analysis, the peak heights I _41.5 to _42.5 and 36 ° of the grain boundary phase appearing in the range of _41.5 to _42.5 °. The ratio of the peak height _{Iβ -Si3N4} of _β silicon nitride appearing in the vicinity I _{41.5-42.5 °} / I _β-Si3N4 is _0.1 .
It was within the range of 005 to 0.020. In Comparative Examples 1, 3, 4, 6, and 7, it was within the same range, but in Comparative Example 2, the corresponding peak was not detected, and in Comparative Example 5, the peak ratio was 0.02.
The value was greater than zero. In the comparative example, since the Al component is too much, the crystallinity of the grain boundary phase is lost, and the peak is considered to disappear. In Comparative Example 5, it is considered that the peak ratio was increased due to the excessive Ti of the crystal component.
Next, Table 4 shows the results of measuring the relative density, three-point bending strength σf, Vickers hardness Hv, and fracture toughness value K1C of each silicon nitride sintered body. The three-point bending strength is measured according to the standard described in JIS-R-1632, the Vickers hardness and fracture toughness value are measured using the IF method described in JIS-R-1607, and the fracture toughness value is calculated. The Niihara formula was used for. Further, in order to evaluate the evaluation of chemical resistance, each sintered body was immersed in a 30% strength HCl solution, and 1 ° C. at 90 ° C.
After heat treatment for 00 hours, the weight loss and bending strength, Vickers hardness and fracture toughness values after the treatment were measured. The results are also shown in Table 5.

The silicon nitride sintered bodies according to Examples 1 to 8 all have a relative density of 99.5% or more, and are sufficiently densified. The three-point bending strength is also a high value of 990 MPa or more, and the Vickers hardness and the fracture toughness value are also sufficiently high. As a result of carrying out acid immersion on these under predetermined conditions, the weight loss was 0.01% in all cases. The three-point bending strength after immersion is also 90
The value is 0 MPa or more, and the Vickers hardness and toughness value are hardly deteriorated. Thus, the silicon nitride sintered body according to the example showed excellent chemical resistance even after an acid immersion time of 100 hours.
On the other hand, in Comparative Examples 1-7, there are many things with low three-point bending strength before immersion, and many things which densification has not fully advanced. The weight loss after immersion was 0.02 to 0.11%, which was larger than that of the examples, and the three-point bending strength value after immersion did not exceed 900 MPa.
Table 6 shows the results of a wear resistance reliability test performed on these samples before and after immersion. The contents of the test are as follows. The test piece was prepared by producing a disc test piece having a diameter of 60 mm or more and a thickness of 3 mm or more with a corresponding sintered body and polishing with a diamond grindstone until the surface roughness Ra was 0.01 μm. On the surface, a ball of around 10 mm made of SUS420J is pressed with a pressure of 5.5 to 6.5 GPa, and a rotational and dynamic load is applied at a speed of 1.5 m / s or more in a lubricating oil environment. This test can evaluate the wear resistance and reliability of ceramic bearing balls. When peeling does not occur on the surface of the test piece beyond the reference time, it can be said that the reliability as a ceramic bearing ball is sufficient. In Table 6, those that did not peel over the reference time were not peeled off, and those that were peeled off were the reference time 100
It is indicated by the ratio of the peeling time when it is set as%.

In the silicon nitride sintered bodies according to the examples, no peeling occurred over the standard test time regardless of the presence or absence of immersion. On the other hand, in Comparative Examples 1, 2, and 6, peeling did not occur before immersion, but peeling occurred before the reference time after immersion. In Comparative Examples 3, 4, 5, and 7,
Although peeling has occurred before immersion, the time for peeling has become shorter after immersion. In particular, in Comparative Examples 2 and 5 where the weight loss after immersion was large, the reliability before and after immersion was greatly deteriorated.
As shown in Tables 5 and 6, it was found that the silicon nitride sintered bodies according to the examples showed little deterioration in strength characteristics after acid immersion and no deterioration in wear reliability. Thereby, it turned out that the silicon nitride sintered compact concerning a present Example is very excellent in chemical resistance and abrasion resistance.

As mentioned above, although several embodiment of this invention was illustrated, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments are:
The present invention can be implemented in various other forms, and various omissions, replacements, changes, and the like can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and equivalents thereof. Further, the above-described embodiments can be implemented in combination with each other.

DESCRIPTION OF SYMBOLS 1 ... Silicon nitride crystal grain 2 ... Grain boundary phase

Claims (11)

When an arbitrary cross-section of a silicon nitride sintered body having silicon nitride crystal grains and a grain boundary phase is photographed, the grain boundary phase does not contain a rare earth element, and the area ratio of the grain boundary phase per unit area 20 μm × 20 μm is 10 to 10 μm. 2
A silicon nitride sintered body characterized by being 0%. 2. The silicon nitride sintered product according to claim 1, wherein the grain boundary phase includes particles containing one kind of group 4A element selected from Ti, Zr, and Hf, and the major axis of the particles is 2 μm or less. body. The grain boundary phase includes particles containing one kind of Group 4A element selected from Ti, Zr, and Hf, and the Si element and Group 2A element are not dissolved in the particles. The silicon nitride sintered body according to any one of claims 2 to 3. In the grain boundary phase, there is a particle containing one kind of group 4A element selected from Ti, Zr, and Hf, and the particle is a single compound of any of oxide, nitride, hydride, and carbide of group 4A element. The silicon nitride sintered body according to any one of claims 1 to 3, wherein the silicon nitride sintered body is present. When an arbitrary cross section of a silicon nitride sintered body having silicon nitride crystal grains and a grain boundary phase is photographed, particles containing one kind of group 4A element selected from Ti, Zr, and Hf per unit area of 20 μm × 20 μm The silicon nitride sintered body according to any one of claims 1 to 4, wherein 1 to 5 are present. The silicon nitride according to any one of claims 1 to 5, wherein when the silicon nitride sintered body is subjected to XRD analysis, a peak is detected in a range of 41.5 to 42.5 °. Sintered body. When the silicon nitride sintered body was subjected to XRD analysis, the maximum peak in the range of _41.5 to _{42.5 °} was I _41.5 to _{42.5 °} , and the maximum peak intensity of _β- silicon nitride was I _β-Si3N4 . When I
_The silicon nitride sintered body according to any one of claims 1 to 6, wherein _{41.5 to 42.5 °} / _{Iβ -Si3N4} = 0.005 to _0.020 . 0.1 to 2.5% by mass of Al, 0.1 to 1.5% by mass of 2A group element, 0.1A to 1.5% by mass of 4A group element, 5A group element, and 6A group element of 0.1 to 3%. The silicon nitride sintered body according to any one of claims 1 to 7, characterized by containing 8% by mass. When an arbitrary cross section of the silicon nitride sintered body is photographed, the ratio of the aspect ratio of 2 or more is 90% or more for silicon nitride particles having a major axis of 2.0 μm or more per unit area of 20 μm × 20 μm. The silicon nitride sintered body according to any one of claims 1 to 8. When an arbitrary cross section of the silicon nitride sintered body is photographed, when the average of the major axis and the minor axis is defined as the particle diameter per unit area of 20 μm × 20 μm, silicon nitride particles having a particle diameter of 2.0 μm or less are nitrided 10. The silicon nitride sintered body according to claim 1, wherein the silicon nitride sintered body occupies an area ratio of 70% or more with respect to a total area of the entire silicon particles. A wear-resistant member using the silicon nitride sintered body according to any one of claims 1 to 10.

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