JPH04293998A - Sliding member - Google Patents

Abstract

PURPOSE:To improve the strength, sliding properties, heat conductivity, and electric conductivity of a sliding member based on SiC and/or Si3N4 by forming a surface layer having a higher carbon content than that in the inner part of the member. CONSTITUTION:SiC and/or Si3N4 having an average particle diameter of 0.1 to 2mum is mixed as a base material with 10wt.% or less solid lubricant which is a carbon powder, an organic material generating carbon upon pyrolysis, or a boron compound, thereby obtaining a mixture. To this mixture are added a binder and so forth. The resulting mixture is shaped into a desired form and then fired at 1,000 deg.C or above in a nitrogen gas atmosphere having a pressure of 500atm or more. Thus, a sinter is obtained which has a 10 to 2,000mum- thick surface layer having a carbon content of 5 to 30vol.% that is higher than that of the inner part of the product, and which has an open pore content of 0.1 to 5%. This sinter is immersed in a lubricant bath and heated to 80 to 120 deg.C in a vacuum, thereby to deaerate it and infiltrate the lubricant into the open pores of it.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding member that has high strength and excellent sliding properties and is suitable for mechanical seals, bearings, and the like.

0002

[Prior Art] Non-oxide ceramics such as silicon carbide and silicon nitride have attracted attention as materials that have superior hardness, strength, toughness, and chemical stability compared to other ceramics and metals. Used as mechanical seal parts, bearing parts, and chemical valve parts.

However, silicon nitride and silicon carbide alone cannot provide sufficient sliding properties, so Al2 is used as a sintering aid for silicon nitride powder and silicon carbide powder.
At the same time as adding O3, oxides of Group 3a elements of the periodic table, or carbon and B4C, graphite and BN are added.
By adding a solid lubricant such as and firing it in a vacuum or an inert atmosphere, the solid lubricant is uniformly dispersed in the aggregate made of silicon nitride or silicon carbide, and the surface of the sintered body is improved. Attempts are being made to improve the sliding properties of.

0004

[Problems to be Solved by the Invention] In order to improve the sliding properties, it is desirable to have a large amount of solid lubricant on the surface layer of the sintered body, but if a large amount of solid lubricant is added, the sintered body itself There is a problem in that the densification of ceramics is inhibited, and the strength of the ceramic itself as so-called aggregate becomes low, making it easy for sliding members to crack or chip. For this reason, there was naturally a limit to the amount of solid lubricant added.

[0005] Furthermore, due to the manufacturing method, it is necessary to uniformly disperse the solid lubricant itself, and in some cases, there is a problem that the solid lubricant inside the sintered body becomes a source of destruction of the sintered body, reducing its strength. Moreover, a sintered body made of silicon nitride as a matrix and a solid lubricant dispersed therein has poor chemical resistance due to the presence of metal oxides added as sintering aids at the grain boundaries of the silicon nitride crystals, and its range of use is limited. There is also the problem of being limited.

[0006]

[Means for Solving the Problems] As a result of repeated studies on the above problems, the present inventors have found that in systems using silicon carbide and/or silicon nitride as aggregates, dispersion-containing solid lubricants can be used as solid lubricants. By making a larger amount of carbon exist in the surface layer than in the interior of the sintered body, and by further impregnating this system with lubricating oil, the coefficient of friction in the surface layer can be lowered without reducing the strength of the sintered body itself. The inventors have discovered that it is possible to reduce the amount of friction, improve sliding properties, and thereby exhibit highly reliable and stable characteristics as various sliding members.

The present invention provides that the sliding characteristics of a ceramic sintered body are controlled by the structure and organization of the surface layer of the sintered body, and that the inside of the sintered body acts as a support member for sliding. As shown in Figure 1, carbon is added as a solid lubricant to significantly improve sliding properties, and carbon content is reduced from the surface layer to the interior of the sintered body. shall be.

[0008] As the aggregate constituting the sintered body of the present invention,
It may be silicon carbide, silicon nitride, or a composite of silicon carbide and silicon nitride, and these ceramics themselves have high strength and superior sliding properties compared to other ceramics. It is something that you have. In addition, it is desirable that carbon as a solid lubricant exists at a volume ratio of about 5 to 30% in the surface layer of the sintered body, and if it is less than 5%, the desired sliding characteristics cannot be obtained. First, if it exceeds 30%, the strength of the surface layer portion decreases, making it easy for damage to the sliding surface to occur. On the other hand, the inside of the sintered body does not need to contain substantially carbon from the viewpoint that it does not affect sliding properties, and is preferably made of silicon carbide or silicon nitride, which are aggregate components.

However, if the composition or structure of the sintered body suddenly changes from the surface layer to the inside, stress is likely to occur at the boundary due to the difference in characteristics, which may cause cracks or chips. As shown in FIG. 1, the amount of solid lubricant is preferably configured to gradually decrease toward the inside.

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

To explain the method for obtaining the sliding member of the present invention, the conventional method of mixing carbon powder with aggregate components such as silicon carbide and silicon nitride and firing the mixture results in a uniform structure, which results in the sliding member of the present invention. A structure with different carbon contents is not formed between the surface layer and the interior.

According to the present invention, silicon carbide powder is first prepared as a raw material powder. The silicon carbide powder used may be either α-SiC or β-SiC, or a mixture thereof. The average particle size of the silicon carbide powder is suitably 0.1 to 2 μm. Additionally, additives for the silicon carbide powder include carbon powder such as carbon black and graphite, organic materials such as phenol resin that can generate carbon through thermal decomposition, coal tar pitch, and sucrose, and boron such as B4C. Contains 10 compounds
It can be added in a proportion of % by weight or less.

After the silicon carbide powder and optionally the additives are sufficiently added and mixed, a binder or the like is added to the powder, and the powder is subjected to a known molding method such as press molding, extrusion molding, casting molding, or cold isostatic pressing. Form 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-generating compound such as a phenol resin.

[0014] Next, the molded body obtained as described above is fired, and according to the present invention, this firing is performed according to the following equation 1.

[Math. 1] 3SiC+2N2 → Si3 N
4 +3C, firing is carried out in an atmosphere in which silicon nitride and carbon can be produced by a reaction between silicon carbide and nitrogen. Specifically, by firing at a temperature of 1000°C or higher, especially 1500°C or higher, containing nitrogen gas as an essential component in the atmosphere, and at a nitrogen gas pressure of 500 atmospheres or higher, especially 1000 atmospheres or higher, The reaction can proceed.

[0015] According to this firing, high densification is achieved in both the interior and the surface layer, and the above reaction occurs particularly actively in the surface layer of the sintered body, so that carbon is more concentrated in the surface layer of the sintered body than in the interior. A specific sintered body is formed that increases in number.

Although the mechanism of this sintering is not clear, in a nitrogen atmosphere under high temperature and high pressure, a reaction progresses from the surface of silicon carbide particles to silicon nitride, resulting in volumetric expansion, which results in some degree of densification. As the sintering progresses and once a dense layer is formed in the surface layer, the entry of nitrogen gas into the interior of the sintered body is suppressed, resulting in a dense body with a porosity of 10% or less in both the surface layer and the interior. It is thought that different structures are formed almost continuously between the surface layer and the inside.

[0017] Therefore, according to the above-described firing, by controlling the firing temperature, firing time, etc., it is possible to increase the amount of carbon produced in the surface layer portion and to suppress the production of carbon inside the sintered body. Preferably, the reaction proceeds completely in the surface layer of the sintered body, and it is desirable that the surface layer is composed of silicon nitride and carbon. In this case, a structure is formed in the surface layer in which silicon nitride is used as aggregate and carbon is uniformly dispersed at a ratio of about 26% by volume.

[0018] Another feature of this sintered body is that the quantitative ratio of silicon carbide and silicon nitride, which are aggregates, changes from the surface layer to the inside. The composition ratio expressed by ) increases from the surface layer to the inside. According to such a structure, the surface layer portion has characteristics similar to silicon nitride, that is, characteristics excellent in thermal shock resistance and toughness. Furthermore, in a normal silicon nitride sintered body, a metal oxide used as a sintering aid exists between silicon nitride crystal grains as a grain boundary phase, but in the surface layer of this sintered body, nitride Another major feature is that there is substantially no metal oxide between silicon crystal particles, which improves chemical resistance and expands the range of applications for sliding members.

It is preferable that the thickness of the surface layer containing at least 20% by volume of carbon is 10 to 2000 μm. If the thickness is thinner than 10 μm, the long-term stability of the sliding properties will be lacking, and if it is thicker than 2000 μm, the surface layer will be damaged. The strength of the parts decreases and chips are more 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 in the interior. It is desirable that there be.

Next, the sintered body obtained by the above method is impregnated with lubricating oil. The method for impregnating is to immerse the sintered body in a lubricating oil bath to be impregnated.
The sintered body is heated to about 0 to 120°C and left in a vacuum with the oil clay lowered to defoam the sintered body, and then taken out from the lubricating oil bath, the lubricating oil is poured into the open pores in the sintered body. Impregnated.

[0022]

[Function] According to the present invention, a large amount of carbon, which is a solid lubricant in the surface layer, is present only in the surface layer of the sintered body, and by impregnating the sintered body with lubricating oil, the lubricating oil is removed when used as a sliding member. Since it exudes onto the sliding surface and liquid lubrication can also be used, it is possible to have both solid lubricating action and liquid lubricating action, and it is possible to lower the coefficient of friction in the surface layer. In addition, the presence of a large amount of carbon only in the surface layer does not reduce the strength of the sintered body as a whole, and even if a relatively large amount of carbon exists in the surface layer, the internal strength is high, so sliding members It can also exhibit stable sliding characteristics. Moreover, since the structural changes from the surface layer to the inside are almost continuous, it is possible to reduce stress caused by differences in characteristics within the sintered body.

Furthermore, 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 thereby the heat generated during sliding can be efficiently dissipated. can. Furthermore, by allowing an appropriate amount of carbon to exist inside the sintered body, the electrical resistance of the entire sintered body can be reduced, thereby allowing electric discharge machining to be performed.

Furthermore, by forming the aggregate in the surface layer mainly of silicon nitride, the thermal shock resistance of the surface layer of the sliding member can be improved.

[0025]

[Example] Various additives as shown in Table 1 are added and mixed to β-SiC powder (average particle size 0.4 μm, oxygen content 0.1% by weight) as a binder for molding. A suitable amount of a 20% resol type phenol resin solution was added, and a suitable amount of acetone was further added as a solvent, and after kneading and drying, the mixture was passed through a sieve to obtain moldable granules. These granules were molded using a mold press at a molding pressure of 2000 kg/cm2 to an outer diameter of 20 mm.
A disc-shaped molded body with a thickness of 10 mm was prepared. Next, the molded body was calcined in an inert atmosphere (in a N2 stream) at 600°C to carbonize the phenol resin, and the composition of the calcined body was analyzed. Then, this calcined body was fired under the conditions shown in Table 1, and 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 out the surface layer and the inside of the sintered body and crushing it, LE
Total carbon and total nitrogen were measured by the CO method, nitrogen was calculated as silicon nitride, bound carbon was determined assuming that the remaining silicon existed as silicon carbide, and the remainder was calculated as free carbon. In addition, the constituent phases of the sintered body were analyzed by X-ray analysis. In addition, in the sample to which B4 C was added as an additive, B4 C was also nitrided and became BN, but the amount added was so small that it was not detected by X-ray diffraction measurement.

Each of the obtained sintered bodies was polished into a disk shape of φ50×t10, the surface was lapped, washed and dried, and then immersed in a general-purpose lubricating oil bath using paraffinic ultra-low pour point base oil. and 110℃ in a vacuum (20mmtorr) container.
It was heated for 1 hour. The oil content of the sample was determined from the weight change before and after impregnation.

Next, the sliding characteristics were evaluated using the ball-on-disc method in which a SUJII steel ball was brought into contact with the sample disk as a fixed pin and the sample disk was rotated. The contact load and friction force were measured and the friction coefficient was calculated.

[0029]

[Table 1]

[0030]

[Table 2]

According to Tables 1 and 2, the friction coefficient of the conventional sliding member (sample No. 4) made of SiC sintered material is 0.
．． On the other hand, all the sliding members of the present invention exhibited excellent characteristics with a coefficient of friction of about 0.1. Also,
As a comparison, it showed excellent sliding properties when compared with a sample that was not impregnated with lubricating oil.

[0032]

[Effects of the Invention] As detailed above, according to the present invention,
By using silicon carbide or silicon nitride as aggregate, and by making the surface layer of the sintered body contain more carbon than the inside, and by impregnating it with lubricating oil, the sintered body as a whole maintains high strength and has excellent properties. This results in better sliding properties. In addition, by having a large amount of carbon as a solid lubricant present in the surface layer, the thermal conductivity and electrical conductivity of the sintered body itself can be increased, thereby efficiently dissipating the heat generated during sliding. It is also possible to perform electrical discharge machining.

[Brief explanation of drawings]

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

Claims (3)

[Claims] 1. A sliding member that uses silicon carbide and/or silicon nitride as an aggregate and contains carbon dispersed therein as a solid lubricant, wherein the carbon is present in a larger amount in the surface layer than in the interior and is impregnated with lubricating oil. A sliding member characterized by: [Claim 2] The amount of carbon in the surface layer of the sintered body is 5 to 3.
The sliding member according to claim 1, wherein the content is 0% by volume. 3. The sliding member according to claim 1, wherein the inside is mainly made of silicon carbide, and the surface layer contains at least silicon nitride and carbon.