JP2851717B2 - Sliding member - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding member having high strength and excellent sliding characteristics and suitable for a mechanical seal, a bearing and the like.

[0002]

2. Description of the Related Art Non-oxide ceramics represented by silicon carbide and silicon nitride have attracted attention as materials having excellent hardness, strength, toughness, chemical stability and the like as compared with other ceramics and metals. Mechanical seal parts,
It is used as bearing parts and valve members for chemicals.

However, since silicon nitride and silicon carbide alone cannot provide sufficient sliding characteristics, Al ₂ O 3 is used as a sintering aid for silicon nitride powder or silicon carbide powder.
By adding a solid lubricant such as graphite or BN at the same time as adding the element oxide of group ₃ or the element of group 3a of the periodic table, or carbon and B ₄ C, and baking this in a vacuum or in an inert atmosphere, By uniformly dispersing the solid lubricant in an aggregate made of silicon nitride or silicon carbide,
Attempts have been made to improve the sliding properties of the surface of the sintered body.

[0004]

In order to enhance the sliding characteristics, it is desirable that the amount of the solid lubricant in the surface layer of the sintered body is large. And the strength of the ceramic itself as a so-called aggregate is reduced, so that the sliding member is liable to be cracked or chipped. Therefore, the amount of the solid lubricant added was naturally limited.

[0005] In addition, it is necessary to uniformly disperse the solid lubricant itself in the manufacturing method, and in some cases, the solid lubricant inside the sintered body acts as a destruction source of the sintered body, resulting in a problem that the strength is reduced. Moreover, a sintered body in which a solid lubricant is dispersed using silicon nitride as a matrix has poor chemical resistance due to the presence of a metal oxide added as a sintering aid at the grain boundaries of the silicon nitride crystal, and its use range is limited. There is also the problem of being limited.

[0006]

Means for Solving the Problems The inventors of the present invention have studied the above problems, and as a result, have formed a sintered body mainly composed of silicon carbide and silicon nitride and dispersedly contained as a solid lubricant. A large amount of carbon is present in the surface layer from the inside of the sintered body, and by further impregnating such a system with lubricating oil, the friction coefficient in the surface layer is reduced without reducing the strength of the sintered body itself. It has been found that slidability can be improved, and thereby, various kinds of sliding members can exhibit stable and highly reliable characteristics.

According to the present invention, the sliding characteristics of the ceramic sintered body are characteristics that are governed by the structure and structure of the surface layer portion of the sintered body, and the inside of the sintered body acts as a so-called support member for sliding. From the idea of doing so, the amount of carbon as a solid lubricant added to greatly improve the sliding characteristics is reduced from the surface layer to the inside of the sintered body as shown in FIG. And

[0008] The aggregate made of the sintered body of the present invention is made of a composite of silicon carbide and silicon nitride, has high strength per se, and has sliding characteristics as compared with other ceramics. It has excellent properties. In addition, carbon as a solid lubricant is preferably present at a volume ratio of about 5 to 30% in the surface layer portion of the sintered body, and if less than 5%, desired sliding characteristics can be obtained. On the other hand, if it exceeds 30%, the strength in the surface layer decreases, so that the sliding surface is likely to be damaged. On the other hand, the interior of the sintered body may not substantially contain carbon from the viewpoint that it does not contribute to the sliding characteristics, and may be made of silicon carbide or silicon nitride as an aggregate component.

However, if the composition or the structure changes suddenly from the surface layer portion of the sintered body to the inside, stress is likely to be generated due to a difference in characteristics at the boundary portion, and cracks or chips may occur. As shown in FIG. 1, it is preferable that the amount of the solid lubricant gradually decreases toward the inside.

Further, according to the present invention, it is a great feature that the sintered body having the above structure is impregnated with lubricating oil. In order to impregnate the lubricating oil, the sintered body needs to have an appropriate open pore, specifically, 0.1 to 5%
It is desirable to have an open porosity of Examples of the lubricating oil to be impregnated include paraffin oil, silicone oil, naphthene oil, and fluorine oil. In addition,
The oil content in the sintered body is desirably 0.01 to 1% by weight.

The method of obtaining the sliding member of the present invention will be described. In the conventional method of mixing and firing carbon powder with an aggregate component such as silicon carbide or silicon nitride, a uniform structure is obtained. No structure having a different carbon content is formed between the surface layer portion and the inside thereof.

Therefore, according to the present invention, silicon carbide powder is first prepared as a raw material powder. As the silicon carbide powder to be used, any of α-SiC and β-SiC, or a mixture thereof can be used. The average particle size of the silicon carbide powder is suitably from 0.1 to 2 μm. Further as additives for the silicon carbide powder, phenol resin, coal tar pitch capable of producing carbon from carbon powder or thermal decomposition, such as carbon black and graphite, and organic materials such as sucrose, B ₄ C-like The boron-containing compound can be added at a ratio of 10% by weight or less.

After sufficiently adding and mixing the above-mentioned silicon carbide powder and the above-mentioned additives in some cases, a binder or the like is added to the above-mentioned powder, and a known molding method, for example, press molding, extrusion molding, casting molding, cold isostatic pressing is performed. It is formed into a desired shape by molding or the like. If desired, the molded body can be calcined at 200 to 800 ° C. to generate carbon from a carbon-forming compound such as a phenol resin.

Next, the molded body obtained as described above is fired. According to the present invention, this firing is carried out by the following equation (1).

As shown by 3SiC + 2N ₂ → Si ₃ N ₄ + 3C, firing is performed in an atmosphere in which silicon nitride and carbon can be generated by a reaction between silicon carbide and nitrogen. Specifically, nitrogen gas is contained as an essential component in the atmosphere at a temperature of 1000 ° C. or higher, especially 1500 ° C. or higher, and the nitrogen gas is fired under a pressure of 500 atm or more, particularly 1000 atm or more, so that The reaction can proceed.

According to this firing, high densification is achieved in both the inside and the surface layer, and the above-mentioned reaction particularly occurs actively in the surface layer of the sintered body, so that carbon is more present in the surface layer of the sintered body than in the inside. A specific sintered body that increases is formed.

Although the mechanism of the sintering is not clear, the reaction of silicon carbide particles into silicon nitride proceeds from the surface of the silicon carbide particles in a nitrogen atmosphere under high temperature and high pressure, resulting in a volume expansion and, to a certain degree, a high density. When the formation progresses and a dense layer is once formed on the surface portion, the entry of nitrogen gas into the sintered body is suppressed, and as a result, the surface layer portion and the inside become a dense body with a porosity of 10% or less. It is considered that a different structure is formed almost continuously between the surface layer and the inside.

Therefore, according to the above-described firing, the amount of carbon generated in the surface layer portion can be increased by controlling the firing temperature, the firing time, and the like, and the generation of carbon in the sintered body can be suppressed. Desirably, the surface portion of the sintered body is allowed to completely react and is composed of silicon nitride and carbon. In this case, a structure in which silicon nitride is used as an aggregate and carbon is uniformly dispersed at a ratio of about 26% by volume is formed in the surface layer.

Another feature of the sintered body is that the ratio of the amounts of silicon carbide and silicon nitride, which are aggregates, changes from the surface layer portion to the inside, and the ratio is silicon carbide / (silicon nitride + silicon carbide). ) Increases from the surface layer portion to the inside. According to such a configuration, the surface layer has silicon nitride-like characteristics, that is, characteristics excellent in thermal shock resistance and toughness. According to a normal silicon nitride-based sintered body, the metal oxide used as a sintering aid exists as a grain boundary phase between silicon nitride crystal grains. Another major feature is that the metal oxide does not substantially exist between the silicon crystal particles, so that the chemical resistance can be improved and the application range as a sliding member can be expanded.

The surface portion having a carbon content of at least 20% by volume desirably has a thickness of 10 to 2000 μm. If the thickness is less than 10 μm, the long-term stability of the sliding characteristics is lacking. The strength of the portion is reduced, and chipping or the like is likely to occur.

On the other hand, the interior of the sintered body is preferably composed mainly of silicon carbide or silicon carbide and silicon nitride, and the composition ratio of silicon carbide / (silicon carbide + silicon nitride) is 0.2 or more. Desirably.

Next, the sintered body obtained by the above method is impregnated with a lubricating oil. As a method of impregnation, immersion in a lubricating oil bath to impregnate the sintered body,
The lubricating oil is heated to about 80 to 120 ° C. and left in a vacuum with the oil clay lowered to defoam the sintered body. Thereafter, the lubricating oil is taken out of the lubricating oil bath, so that the lubricating oil is in the open pores in the sintered body. Impregnated.

[0022]

According to the present invention, a large amount of carbon, which is a solid lubricant in the surface layer portion, is present only in the surface layer portion of the sintered body and impregnated with the lubricating oil. Since the liquid lubricant oozes out on the sliding surface and can be used in combination with liquid lubrication, it can have both solid lubricating action and liquid lubricating action, and can reduce the friction coefficient in the surface layer portion. Also, the presence of a large amount of carbon only in the surface layer portion does not reduce the strength of the sintered body as a whole, and the strength of the inside is high even if a relatively large amount of carbon is present in the surface layer portion. As a result, stable sliding characteristics can be exhibited. Moreover,
Since the structural change from the surface layer portion to the inside is formed almost continuously, the stress generated due to the difference in the characteristics in the sintered body can be reduced.

In addition, since a large amount of carbon can be present in the surface layer, the thermal conductivity of the sintered body itself can be increased, and the heat generated during sliding can be efficiently radiated. it can. Furthermore, the electric resistance of the entire sintered body can be reduced by allowing an appropriate amount of carbon to be present in the inside, whereby electric discharge machining can be performed.

Further, by forming the surface layer aggregate mainly composed of silicon nitride as the aggregate, the thermal shock resistance of the surface layer portion of the sliding member can be enhanced.

[0025]

EXAMPLES As shown in Table 1, various additives were added to and mixed with β-SiC powder (average particle size 0.4 μm, oxygen content 0.1% by weight) as a binder for molding. An appropriate amount of a resol type phenol resin 20% solution was added, and an appropriate amount of acetone was further added as a solvent. After kneading and drying, the mixture was passed through a sieve to obtain granules for molding. The granules are pressed with a molding press at a molding pressure of 2000 kg / cm ² and an outer diameter of 20 m.
m, a disk-shaped molded body having a thickness of 10 mm was prepared. Next, the molded body is calcined in an inert atmosphere (in a stream of N ₂ ) at 600 ° C.
The composition of the calcined body was analyzed by carbonizing the phenol resin. Then, the calcined body was fired under the conditions shown in Table 1 to obtain a sample N
o, 1 to 8 were obtained.

The specific gravity and open porosity of the obtained sintered body were measured by the Archimedes method. Further, the bending strength was measured based on JISR1601. Furthermore, after cutting and pulverizing from the surface layer part and the inside of the sintered body from the sintered body, LE
Total carbon and total nitrogen were measured by the CO method, nitrogen was calculated as silicon nitride, the remaining silicon was calculated assuming that it was present as silicon carbide, and the remaining carbon was calculated as free carbon. The constituent phases of the sintered body were analyzed by X-ray analysis. In addition, in the sample to which B ₄ C was added as an additive, B ₄ C was also nitrided and became BN.
It was not detected by line diffraction measurement.

Each of the obtained sintered bodies is polished into a disk shape of φ50 × t10, the surface is lapped, washed and dried, and then immersed in a general-purpose lubricating oil bath using a paraffin type extremely low pour point base oil. And in a vacuum (20 mmtorr) vessel for 110
Heated at 0 ° C. for 1 hour. The oil content of the sample was determined from the change in weight before and after the impregnation.

Next, the sliding characteristics were evaluated by a ball-on-disk method in which a SUJII steel ball was brought into contact with the sample disk as a fixing pin and the sample disk was rotated. The contact load and the frictional force were measured to calculate the friction coefficient.

[0029]

[Table 1]

[0030]

[Table 2]

According to Tables 1 and 2, the sliding member (sample No. 4) made of a conventional SiC sintered body has a friction coefficient of 0.1.
In contrast to the value of about 6, the sliding members of the present invention all exhibited excellent characteristics with a friction coefficient of about 0.1. Further, as a comparison, excellent sliding characteristics were shown as compared with a sample not impregnated with a lubricating oil.

As described in detail above, according to the present invention, silicon carbide and silicon nitride are used as aggregates, and more carbon is present in the surface layer of the sintered body than in the interior and impregnated with lubricating oil. Thereby, excellent sliding characteristics can be obtained while maintaining the high strength of the entire sintered body. In addition, the thermal conductivity and electrical conductivity of the sintered body itself can be increased by allowing a large amount of carbon as a solid lubricant to be present in the surface layer, thereby efficiently radiating heat generated during sliding. And electrical discharge machining can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in carbon amount with respect to a depth from a surface layer in a sliding member of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C10M 103/02 F16J 15/20 F16C 33/24 B23Q 1/26 Z F16J 15/20 C04B 35/56 101H // B23Q 1/26 35/58 102L C10N 30:00 40:02 50:08 (58) Fields investigated (Int. Cl. ⁶ , DB name) C10M 111/00 C10M 101/02 C10M 103/00 C10M 103/02 F16C 33/24 C10N 40:02 C10N 50:08 C04B 35/565 C04B 35/584 F16J 15/20 B23Q 1/26

Claims (3)

(57) [Claims] 1. A sliding member comprising a sintered body mainly composed of silicon carbide and silicon nitride and containing carbon as a solid lubricant in a dispersed manner, wherein said carbon is present in a surface layer more than in an interior thereof. A sliding member, wherein the sliding member has an open porosity of 0.1 to 5%, and the open pores are impregnated with a lubricating oil. 2. The sliding member according to claim 1, wherein the amount of carbon in the surface layer portion of the sintered body is 5 to 30% by volume. 3. The sliding member according to claim 1, wherein the inside of the sintered body is mainly composed of silicon carbide, and the surface layer portion contains at least silicon nitride and carbon.