JPS61163174A - Silicon carbide sliding member - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sliding member, and in particular, the present invention relates to a sliding member made of a silicon carbide material mainly composed of a porous silicon carbide sintered body having excellent sliding properties in a wet state. Related to material sliding members.

[Conventional technology]

Silicon carbide sintered bodies generally have extremely excellent chemical and physical properties, so they are used in various products that are used under harsh conditions, such as in gas turbine parts and high-temperature heat exchangers. It is known as a suitable material for applications, and is particularly useful as sliding members such as rotating and sliding parts such as bearings and seams of mechanical devices.

Conventionally, attempts to apply silicon carbide as sliding members have been made, for example, in Japanese Patent Application Laid-open No. 143412/1983, which describes the use of silicon carbide as a main component in sliding members used in rotating and sliding parts of mechanical devices. A dry sliding member characterized in that it is composed of a sintered body of
- Publication No. 100421 [In a mechanical device, one of the rotating member and the fixed member, which are sliding members of the rotating part and the fixed part, is a sintered body mainly composed of silicon nitride, and the other is made of a sintered body mainly composed of silicon carbide. The invention relates to a ceramic sliding device J characterized in that each ceramic sliding device J is made of a sintered body.

However, although it is stated in the above-mentioned JP-A-54-143412 and JP-A-55-100421 that silicon carbide sintered bodies are suitable as dry sliding members, these sliding members are There was no mention that the material had excellent sliding properties, especially in a wet state.

By the way, the present inventors have discovered that compared to the previously known sliding members made of silicon carbide sintered bodies, the coefficient of friction is significantly lower and the efficiency of dissipating frictional heat is better, especially when used in wet conditions. , with the aim of providing a sliding member with extremely excellent durability, and previously published in Japanese Patent Application No. 59-248770 ``A sliding member in which at least a portion of the sliding surface is made of a silicon carbide sintered body. , a silicon carbide sliding member characterized in that at least 50% by weight of the silicon carbide sintered body is made of β-type silicon carbide."

[Problem that the invention seeks to solve]

However, the sliding member proposed in the above-mentioned Japanese Patent Application No. 59-248770 has a structure in which plate-shaped crystals with relatively uniform grain size, that is, crystals with a large aspect ratio intersect with each other, and the gaps are filled with finer grain size. It is made of a dense silicon carbide sintered body with a microstructure filled with crystal grains having However, there was a drawback in that the sliding surface was significantly worn away by abrasion powder produced by detachment of crystal particles of the silicon carbide sintered body.

[Failure to solve the problem]

An object of the present invention is to provide a sliding member that can be used at a particularly high PV value and has excellent wear resistance compared to conventional sliding members made of silicon carbide sintered bodies. In a sliding member in which at least a part of the sliding surface is made of a silicon carbide sintered body, the silicon carbide sintered body has an average aspect ratio of 3 to 50 and a long axis direction. The above object is achieved by a silicon carbide sliding member characterized by being a porous body having a three-dimensional network structure mainly composed of silicon carbide plate crystals with an average length of 0.5 to 1000 μm. be able to.

Next, the present invention will be explained in detail.

The silicon carbide sintered body constituting the sliding member of the present invention is mainly composed of silicon carbide plate crystals having an average aspect ratio of 3 to 50 and an average length in the major axis direction of 0.5 to 1000 μm. It is necessary that the porous body has a three-dimensional network structure.

The reason why the silicon carbide sintered body constituting the sliding member is required to be a porous body is that the wear powder released from the silicon carbide sintered body during sliding is generally removed between the sliding member and the slidable body. Although it acts as an abrasive by intervening between the sliding surfaces of the moving member and causes significant wear on each sliding surface, as in the present invention, a porous material is used as the silicon carbide sintered body constituting the sliding member. By using a silicon carbide sintered body, even if the wear powder is detached from the silicon carbide sintered body during sliding, the wear powder is quickly retained in the nearby pores. This is because there is almost no abrasive action caused by detached abrasion powder, making it extremely excellent as a sliding material.

The reason why it is necessary that the average aspect ratio of the porous body constituting the sliding member is 3 to 50 is that by setting the average aspect ratio to 3 or more, the pores constituted by the silicon carbide plate crystals become crystalline. This is because a relatively large porous body can be formed compared to the volume occupied by the porous body.On the other hand, if the average aspect ratio is larger than 50, there are few joints between crystals, so the strength of the porous body is low. This is because it cannot withstand use as a sliding member. In addition, it is more suitable that the said average aspect ratio is 5-30.

Further, the average length of the plate-like crystals in the long axis direction is 0.5 to 1
000 μm. The reason for this is that when the average length in the major axis direction is as small as 0.5 μm, the pores formed by the plate-shaped crystals are small, and in some cases, some of the pores may become independent pores. This is because the powder retention effect is small and the wear resistance is poor.

On the other hand, if the length is 1000 μm or more, stress tends to concentrate at the joints of the plate-like crystals, and the strength of the porous body itself is low. The average length of the plate crystals in the major axis direction is preferably 1 to 1.
A thickness of 800 μm is more suitable.

Note that the length of silicon carbide plate crystals in the present invention refers to the maximum length (X) of each individual plate crystal observed in any cross section of the sintered body; The ratio (R) is expressed as the ratio of the maximum thickness (Y) of the plate crystal to the crystal length (X), ie, R=X.

Further, the average cross-sectional area of the open pores of the network structure is 0.01
It is preferable that it is 250,000μ. The reason for this is that when the average cross-sectional area of open pores is 0.01μ or more, the effect of retaining wear particles is small and the wear resistance is poor.On the other hand, when the average cross-sectional area of open pores is larger than 250,000μ, It is more preferable that the strength of the porous body itself is low, and that the average cross-sectional area of the open pores of the network structure is 0.25 to 90,000 μm.

and 3 to 50 parts by weight of 100 parts by weight of crystals in the porous body.
Preferably, the platelet crystals having an aspect ratio of 20% by weight account for at least 20 parts by weight. Incidentally, the content of the plate crystals can be determined by analyzing a structural photograph of the crystals. Here, the entire porous material is 20 parts by weight or more of 3 to 50 parts by weight.
The reason why it is preferable that the plate crystals be occupied by plate crystals having an aspect ratio of This is because the retention effect is small.

In particular, it is advantageous for the plate crystals to account for at least 40 parts by weight of 100 parts by weight of the crystals in the porous body.

The open porosity of the porous cured silicon sintered body is 10 to 60 volumetric units based on the total volume of the sintered body. It is preferable. The reason for this is that when the open porosity is as small as 10 volume, the effect of retaining wear particles is small; on the other hand, when the open porosity is as large as 60 volume, the effect of retaining wear particles is large.
This is because the strength of the porous body is low and it is difficult to use it as a sliding member, and it is particularly advantageous that the porous body has a volume ratio of 20 to 50.

When the sliding member of the present invention has a large end face load and a high sliding speed, for example, when it is used under wet conditions where the end face load is 5"J"/ea or more and the sliding speed is 1000"Aec or more, Demonstrates extremely excellent sliding properties.

The sliding member of the present invention is particularly suitable for use under wet conditions, and the wet condition refers to the condition in which the sliding member A condition in which liquid is present in at least a portion of the liquid.

The liquid that satisfies the wet conditions is advantageously a substance that can form a monomolecular layer of the liquid on at least a portion of the sliding surface between the sliding member and the slidable member during sliding. Can be used for water, oil, water, etc.
methanol, ethanol, propatool, butanol,
Isobutyl alcohol tanol, impentyl alcohol, phenol, creso μ. Ammonia Nato 1
One or more species can be advantageously used. Note that slurry-like liquids in which various finely powdered solid substances are mixed in the liquid and liquids in which various chemical substances are mixed can also be used.

In the sliding member of the present invention, it is sufficient that at least the sliding surface is made of a silicon carbide sintered body that satisfies the various properties described above, and the other parts other than the sliding surface are made of silicon carbide. Materials other than sintered bodies or various composite bodies can be used, and it is particularly advantageous to use those with high thermal conductivity.

Next, a method for manufacturing a porous body constituting the sliding member of the present invention will be explained.

According to the first method, (a) silicon carbide powder having an average particle size of 10 μm or less and containing at least 60% by weight of β-type, 2H-type and amorphous silicon carbide is used as a desired silicon carbide powder. (b) The molded product obtained in step (a) is placed in a heat-resistant container to block outside air from entering, and (b) 1900~
The process of firing within a temperature range of 2300°C results in a three-dimensional network structure mainly composed of silicon carbide plate crystals with an average length in the long sleeve direction of 10 to 1000 μm and an average aspect ratio of 3 to 50. A porous silicon carbide sintered body can be obtained in which the average cross-sectional area of the open pores of the structure is within the range of 400 to 250,000 microns.

According to the first method, the starting material is advantageously a silicon carbide containing at least 60% by weight of beta, 2H and amorphous silicon carbide cysts. The reason for this is that β-type crystals, 2HW crystals, and amorphous silicon carbide crystals are low-temperature stable crystals that are synthesized at relatively low temperatures.
Not only does it easily undergo a phase transition to high-temperature stable α-type crystals such as R-type crystals, but also has excellent crystal growth properties, especially β-type reverted silicon with a content of 60% by weight or more. This is because the porous body targeted by the present invention can be produced by using a starting material consisting of. Among these, it is preferable to use a starting material containing at least 70% by weight of β type, 2H type and amorphous silicon carbide.

It is advantageous that the starting material is a fine powder with an average particle size of 10 μm or less. Powder with an average particle size as small as 10μ has a relatively large number of contact points between particles, and is highly thermally active at the sintering temperature of silicon carbide, resulting in less movement of atoms between silicon carbide particles. Because they are extremely large, bonding between silicon carbide particles is extremely likely to occur. Therefore, the growth rate of plate crystals is extremely high. In particular, it is preferable that the average particle size of the starting material is 5 μm or less, which gives favorable results for the growth of plate crystals.

Then, the silicon carbide composite formed into a desired shape from the starting materials is placed in a heat-resistant container made of graphite, silicon carbide, etc., and heated from 1,900 to
It is necessary to fire within the temperature range of 2300°C.

The reason why the material is charged in a heat-resistant container and fired while blocking the intrusion of outside air is that it allows adjacent silicon carbide crystals to fuse together and promotes the growth of plate-shaped crystals. . The reason why it is possible to fuse adjacent silicon carbide crystals together and promote the growth of plate-shaped crystals by charging them in a heat-resistant container and firing them while blocking the intrusion of outside air as described above is that silicon carbide This is thought to be because it can promote the movement of silicon carbide molecules between particles by evaporation-recondensation and/or surface diffusion.

In contrast, when conventional pressureless sintering, atmospheric pressure sintering, or sintering under reduced pressure was tried, not only was it difficult to grow plate-shaped crystals, but the joints of silicon carbide particles were The sintered body had a constricted neck shape, and the strength of the sintered body decreased. The heat-resistant container is made of graphite, silicon carbide, or tungsten carbide.

It is more preferable to use a heat-resistant container made of at least one material selected from molybdenum and molybdenum carbide.

Also, tI! According to method j2, (a) silicon carbide having an average particle size of 10 μm or less, this powder is silicon carbide powder consisting of α-type, β-type and/or amorphous silicon carbide and inevitable impurities; For 100 parts by weight of this powder, aluminum, aluminum diboride, aluminum carbide,
Aluminum nitride, a) V miniram, boron, boron carbide, boron nitride, boron oxide, calcium oxide, μsium carbide, chromium, chromium boride, chromium nitride, chromium oxide, iron, iron carbide, iron oxide.

One or more selected from lanthanum boride, lanthanum oxide, lithium oxide, silicon, silicon nitride, titanium, titanium oxide, titanium dioxide, titanium trioxide, and yttrium oxide in a uniform amount of 10 parts by weight or less Mixing step ('b) Step 1 of molding the mixture obtained in step (a) above; and (C) Charge the molded product obtained in step (b) into a heat-resistant container. 1700 ~ while blocking the intrusion of outside air
The process of firing within a temperature range of 2300°C produces a three-dimensional network structure mainly composed of silicon carbide plate crystals with an average length in the major axis direction of 0.5 to 200 μm and an average aspect ratio of 3 to 50. It is possible to obtain a porous silicon carbide sintered body having an average cross-sectional area of open pores in the network structure within a range of 0.01 to 10,000 μm.

According to a second method, the starting material has an average particle size of 10μ
Advantageously, it is a fine powder of less than m. Average particle size is 1
Powders smaller than 0 μm have a relatively large number of contact points between particles, and at the sintering temperature of silicon carbide, the thermal activity is large and the movement of atoms between silicon carbide particles is extremely large. Mutual bonding is extremely likely to occur. Therefore, the growth rate of plate crystals is extremely high. especially,
It is preferable that the average particle size of the starting material is 5 μm or less, which gives more favorable results for the growth of plate crystals.

According to the second method, apminium, aluminum diboride, aluminum carbide, aluminum nitride.

aluminum oxide, boron, boron carbide, boron nitride,
Boron oxide, calcium oxide, carbide.

Chromium, chromium boride, chromium nitride, chromium oxide.

Iron, iron carbide, iron trioxide, lanthanum boride, lanthanum oxide, lithium oxide, silicon, silicon nitride, titanium.

One or more selected from titanium oxide, titanium dioxide, titanium trioxide, and yttrium oxide are added. The substance has the function of significantly increasing the rate of crystal growth of silicon carbide, and on the other hand, the substance produces vapor of the substance and/or vapor of decomposition products at a firing temperature of 1700 to 2300°C of the silicon carbide molded body. However, it diffuses to every corner of the silicon carbide molded body, and a large number of plate-like crystal nuclei are formed, and the plate-like crystals develop in each part.9 As a result, the size of the plate-like crystals formed increases. This is because the particles are restricted and form a fine three-dimensional network structure. Among the above compounds, boron, boron carbide,
Boron nitride, aluminum oxide, aluminum nitride, iron, aluminum carbide, aluminum diboride, aluminum can be used advantageously.

On the other hand, it is advantageous that the amount of the substance added is 10 parts by weight or less per 100 parts by weight of the starting material mainly composed of silicon carbide. The reason is that even if more than 10 parts by weight is added, the vapor partial pressure of the compound and/or its decomposition product hardly changes within the firing temperature range of the silicon carbide molded body. On the contrary, since the amount of the substance remaining in the molded body increases, the original properties of silicon carbide are lost.

Further, the amount of the compound suitable for growth of plate crystals added is preferably 5 parts by weight or less per 100 parts by weight of the silicon carbide starting material.

Further, the silicon carbide used as the starting material may be any of α-type silicon carbide, β-type silicon carbide, and/or amorphous silicon carbide.

According to the second method, a carbon source can be added that leaves free carbon during firing. As such a carbon source, any carbon source that exists in the carbon state at the start of sintering can be used, such as phenol resin, lignin sulfonate, polyvinyl alcohol, cornstarch, and silicone.
, coal tar pitch, alginates, or pyrolytic carbons such as carbon black, acetylene black, etc. can be advantageously used.

When free carbon exists simultaneously with the above substances, it suppresses crystal growth and forms fine silicon carbide plate crystals, which is effective in obtaining a porous body having fine pores.

Further, it is advantageous that the free carbon content is 5 parts by weight or less based on 100 parts by weight of the starting material.

The reason for this is that even if more than 5 parts by weight is added, the effect remains, but on the contrary, a large amount remains in the porous body, and the oxidation resistance of the porous body is reduced. It is most effective that the amount is 3 parts by weight or less.

According to the second method, the heat-resistant container includes graphite, expanded silicon, aluminum nitride, zirconium oxide, tungsten carbide, titanium carbide, magnesium oxide, molybdenum carbide, molybdenum, and tantalum carbide. A container made of any one selected from tantalum, zirconium carbide, and graphite-silicon carbide composite can be used.

These containers do not melt within the firing temperature range and can maintain their shape, and also prevent the vapors of the additives and/or decomposition products from leaking out of the system. It has the effect of suppressing the additives and spreading the effects of the additives to every corner of the silicon carbide molded body. Among them, primary silicon graphite, graphite-silicon carbide composite, tungsten carbide, aluminum nitride, titanium carbide, molybdenum,
Molybdenum carbide can be used effectively.

When producing the porous body of the present invention, the formed body is placed in a heat-resistant container that can block outside air and fired, thereby reducing the volatilization rate of silicon carbide to 5% by weight during firing. It is advantageous that:

In addition, in order to obtain a porous body having open pores with a relatively large average cross-sectional area, it is necessary to increase the temperature during firing at a relatively slow rate, set the maximum temperature relatively high, and/or It is preferable to increase the holding time at the temperature. Under these conditions, individual silicon carbide plate crystals can be grown to a large size, and as a result, a porous body having a large pore cross-sectional area can be obtained.

On the other hand, in order to obtain a porous body having open pores with a relatively small average cross-sectional area, the heating rate during firing should be relatively fast, the maximum temperature should be relatively small, and/or the holding time at the maximum temperature should be It is preferable to make it short. This is because, under these conditions, individual plate-shaped crystals of silicon carbide are not allowed to grow much.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

Example 1 The silicon carbide fine powder used as a starting material consisted of 94.6% by weight of β-type crystals and the remainder substantially of 2H-type crystals,
0.39 wt% free carbon, 0.17 wt% oxygen, 0
．． It mainly contained 0.03% by weight of iron, 0.03% by weight of aluminum, and had an average particle size of 0.28 μm.

15 parts by weight of polyvinyl alcohol/L and 300 parts by weight of water were blended with 100 parts by weight of the silicon carbide fine powder, mixed for 5 hours in a Ball MiP, and then dried.

An appropriate amount of this dry mixture was taken, granulated, pre-molded using a metal mold at a pressure of 50 momme, and then molded using an isostatic press at a pressure of 1.3 p. The density of this product was 2.0 and the dry weight of PI31 was 217'.

The formed body was placed in a graphite crucible that can be shut off from outside air, and fired in an argon gas atmosphere at 1 atm using a Tammann type firing furnace. The graphite crucible used had an internal volume of 504 cm.

For firing, the temperature was raised to 2200°C at 2.5°C, and the maximum temperature was 2.
It was held at 200″C for 6 hours.

The weight of the obtained sintered body was 19.67', and its crystal structure, when observed with a scanning electron microscope, was composed of many plate-like crystals with an average aspect ratio of 8 and an average length in the long sleeve direction of 150 μm. The content of plate-shaped crystals having a three-dimensional structure intricately intertwined in the directions and having an aspect ratio of 3 to 50 was 98% of the total weight of the porous body. Further, the pores of this porous body were non-linear open pores, and the open porosity was 38 times the total volume.

Next, the sintered body was molded into a ring shape with an inner diameter of 20mm, an outer diameter of 25.6mm, and a thickness of 15mm, and was soaked in water maintained at about 30°C to contain silicon carbide with a density of 8.12%. The sliding characteristics of the pressurized sintered body were evaluated using the ring-on-ring method in which the body was slid at a sliding speed of 1000-tin, with an end face load of 180'F. When measured, the friction coefficient was extremely stable at 0.005 to 0.01, and the friction coefficient was 12 times.
2) was confirmed. Further, as can be seen from the scanning electron micrograph (75x magnification) in FIG. 1, the sliding surface of this sintered body after the measurement of the sliding characteristics showed no particles falling off or chipping. Note that the amount of wear is the amount of weight loss during measurement of sliding characteristics for 90 minutes.

Comparative Example 1 Same as Example 1, but with particle size 15, which is commercially available as a sintering aid.
A dry mixture was prepared by mixing 1 part by weight of No. 00 boron carbide with carbon black powder having a specific surface area of 120. An appropriate amount of this dry mixture was collected, granulated, and then preformed using a metal mold at a pressure of 0.15t/:i, and then using a hydrostatic press machine at a pressure of 1.8t/:i. Molded with. The density of the formed body obtained by the above molding was 59% (
It was 1,90 heli.

The formed body was placed in a Tammann type sintering furnace and fired in an argon gas flow at 1 atm.

For firing, the temperature was raised to 1650°C at 5V minutes, held at 1650°C for 40 minutes, and then further raised at 5°C until the maximum temperature was 2.
The temperature was maintained at 000°C for 30 minutes. The argon gas flow rate was adjusted appropriately so that the partial pressure of CO gas during sintering was 5 KPa or less from room temperature to 1650°C, 0.5 KPa or less when held at 1650°C, and 5 KPa or less in the high temperature range above 1650°C. .

The obtained sintered body had a density of 3.14 J/l9, an average grain size of 5.2μ, an average aspect ratio of 2.7, and a content of plate crystals. 67 was in charge of weight.

When the sliding properties of this sintered body were measured in the same manner as in Example 1, the coefficient of friction was 0.01 to 0.03, and the amount of wear was 43, compared to the porous body of Example 1. It was observed that the sliding properties were inferior.

In addition, the sliding surface after measuring the sliding characteristics of this sintered body is reference No. 1.
As can be seen from the scanning electron micrograph (75x magnification) in the figure, significant roughness was observed.

Example 2 Porous silicon carbide sintered bodies as shown in Table 1 were produced in the same manner as in Example 1, but by varying the heating rate, maximum firing temperature, and holding time at the maximum firing temperature. The sliding properties of these sintered bodies were measured in the same manner as in Example 1 and are shown in Table 1.

As can be seen from the results shown in Table 1, all of the sintered bodies of this example had a low coefficient of friction, were stable, had a small amount of wear, and had excellent sliding properties.

Example 3 The fine silicon carbide powder used as a raw material for hydrogenation contained 94.6% by weight of β-type crystals and the remainder was substantially 2H-type crystals.9.
0.399 wt% free carbon, 0.177 wt% oxygen, 0
．． It mainly contained 0.088% by weight iron and 0.033% by weight aluminum, and had an average particle size of 0.28 μm.

To 100 parts by weight of the silicon carbide fine powder, 0.8 parts by weight of amorphous boron, 1 part by weight of polyethylene glycol/I/1 as a molding binder, and 4 parts by weight of polyacrylic ester.
parts by weight, and 100 parts by weight of benzene were mixed in a ball mill. An appropriate amount of this dry mixture was taken, granulated, and then pre-molded using a metal mold at a pressure of 50 momme, and then molded using a hydrostatic press at a pressure of 1.31 kg. . The density of this generated form is 1.
9 gou, dry weight was 21/2.

Graphite i1/ capable of shielding the formed body from outside air
The material was charged into a receptacle and fired in an argon gas atmosphere at 1 atm using a Tammann type firing furnace. The graphite crucible used had an internal volume of 504 cm.

The famous firing is heated up to 2200℃ in 5℃ increments, and the optimum temperature is 220℃.
It was held at 0°C for 4 hours.

The crystal structure of the obtained sintered body has an average aspect ratio of 6, as shown in the scanning electron micrograph (75x magnification) in Figure 2.
It has a three-dimensional tree structure in which plate-like crystals with an average length in the major axis direction of about 100 μm are intricately intertwined in multiple directions.
The content of plate crystals having an aspect ratio of 0 was 96% of the total weight of the porous body. Further, the pores of this porous body were non-linear open pores, and the open porosity was 24% of the total volume.

The sliding characteristics of this sintered body were measured in the same manner as in Example 1, and the friction coefficient was 0.003 to 0.005.
The amount of wear was 2.77', and it was recognized that it had extremely excellent sliding characteristics.

〔Effect of the invention〕

As described above, the silicon carbide sliding member of the present invention has extremely excellent sliding properties, and can be applied to mechanical components with significant friction phenomena such as bearings of mechanical devices. Furthermore, the durability and reliability of the device can be significantly improved.

[Brief explanation of drawings]

Claims (1)

[Scope of Claims] 1. In a sliding member in which at least a portion of the sliding surface is made of a silicon carbide sintered body, the silicon carbide sintered body has an average aspect ratio of 3 to 50 and a long length. A silicon carbide sliding member characterized in that it is a porous body having a three-dimensional network structure mainly composed of silicon carbide plate crystals having an average length in the axial direction of 0.5 to 1000 μm. 2. 3 to 5 parts by weight of 100 parts by weight of the silicon carbide sintered body
2. A sliding member according to claim 1, wherein the platelet crystals having an aspect ratio of 0 are at least 20 parts by weight. 3. The silicon carbide sintered body has an average cross-sectional area of 0.01~
The sliding member according to claim 1 or 2, having open pores of 250,000 μm^2. 4. The silicon carbide sintered body has an open porosity of 10 to 60% by volume based on the total volume of the sintered body, claim 1.
The sliding member according to any one of items 1 to 3. 5. The sliding member according to any one of claims 1 to 4, wherein the sliding member is particularly suitable for use under wet conditions where the end face load is 5 kgf/cm^2 or more and the sliding speed is 1000 mm/sec or more. sliding member. 6. Any one of claims 1 to 5, wherein the sliding member is particularly suitable for use under wet conditions where at least a liquid is present between the sliding surfaces of the sliding member and the slidable member. The sliding member described in Crab.