JP2007010059A - Sliding member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sliding member having a small friction coefficient and superior sliding performance even when used under severe lubricating environment such as the condition of boundary lubrication. <P>SOLUTION: The sliding member has a sliding face to be put in relative sliding contact with the other member. On at least part of the surface forming the sliding face, a solid lubricating coat is formed which has an area percentage of 75% or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sliding member having a sliding surface that is in sliding contact with a mating member.

This type of sliding member is used in various engines for automobiles, bearing cages (retainers), and the like. In recent years, as the social demand for energy problems increases, it is required to improve energy efficiency by further reducing friction of the sliding member.
As a material used for such a sliding member, silicon nitride, silicon carbide or the like having a relatively low friction coefficient is known. Patent Documents 1 to 3 propose a technique for further reducing friction of a sliding member made of silicon nitride, silicon carbide, or the like.

In Patent Document 1, in a sliding member formed by including free carbon in a material composed of silicon nitride and silicon carbide, the content of free carbon in the surface layer portion and the content of free carbon in the interior are specified. Has been proposed.
In Patent Document 2, it is proposed to disperse an iron compound in a non-oxide ceramic containing silicon such as silicon nitride or silicon carbide.

Patent Document 3 proposes that a large number of fine dimples serving as a lubricating oil reservoir are formed on the surface of a sliding member made of a hard material such as silicon nitride or silicon carbide.
Japanese Unexamined Patent Publication No. 7-33527 JP-A-6-122555 JP-A-9-133222

However, the technique described in Patent Document 1 described above shows a remarkable effect in a non-lubricated state, but it is difficult to obtain a sufficient friction reducing effect in a lubricated state where a lubricant is present to some extent. In addition, in the technique described in Patent Document 2, there is a concern that the strength may be reduced due to aggregation of the iron compound dispersed in the non-oxidized ceramic, and the lubricating oil film is not locally retained, and the friction is sufficiently reduced. The effect may not be obtained.
Furthermore, in the technique described in Patent Document 3, it takes time to process a large number of fine dimples, and, as in Patent Document 2 described above, the lubricating oil film is not sufficiently retained except for the dimples. The reduction effect may not be sufficiently obtained.

For this reason, in the technique described in Patent Document 1 to Patent Document 3 described above, the surface pressure is large and sliding with the mating member is performed, for example, between the cam and shim in a valve lifter in various engines for automobiles and the like. There is room for further improvement in terms of reducing friction when applied to a sliding member used in a so-called boundary lubrication state where the speed is relatively small.
Therefore, an object of the present invention is to provide a sliding member having a small friction coefficient and excellent sliding performance even when used in a severe lubrication environment such as a boundary lubrication state.

In order to solve such a problem, according to the present invention, in a sliding member having a sliding surface that is in sliding contact with a counterpart member, an area ratio of 75 is provided on at least a part of the sliding surface. % Or more of the solid lubricant film is formed.
Thereby, since the lubricity on the sliding surface of the sliding member is improved, the friction coefficient of the sliding surface is reduced, and excellent sliding performance can be obtained. Therefore, even if the sliding member is used in a severe lubrication environment such as a boundary lubrication state, a sufficient friction reducing effect can be obtained.

  In the present invention, the sliding member refers to a member having a sliding surface that is in sliding contact with the counterpart member. Specific examples of such a sliding member include mechanical parts that perform contact movement on a cylindrical surface, spherical surface, flat surface, and the like. For example, a cam and a cam follower, a piston ring, a fuel injection device, and a friction that constitute an automobile engine. Examples thereof include a plate, a clutch component, a sliding member constituting a sliding bearing, and a retainer for a rolling bearing and a sliding bearing.

  In the present invention, the material for the solid lubricant film is not particularly limited as long as it provides the strength necessary for the sliding surface of the sliding member and has good adhesion to the material forming the sliding member. For example, molybdenum disulfide, tungsten disulfide, boron nitride, metal soap, fluororesin, nylon, polyacetal, polyolefin, polyethylene, polyester, PTFE (polytetrafluoroethylene), graphite, calcium fluoride, barium fluoride, copper, copper Examples include alloys, zinc, zinc alloys, tin, tin alloys, and metal oxides.

  Examples of the method for forming such a solid lubricating coating include coating, baking, thermal spraying, sputtering, ion plating, and shot peening. In particular, the shot peening method is preferably performed in consideration of improving the hardness of the surface layer portion of the sliding member after the solid lubricating film is formed. Further, in order to form the solid lubricant film in further close contact with the sliding member, it is more preferable to perform the shot peening method in a state where the sliding member as the base material is heated.

Furthermore, the material forming the sliding member is not particularly limited. For example, it can be used for bearing steel such as high carbon chromium bearing steel type 2 (SUJ2), case-hardened steel such as SCM420 and SCR420, and stainless steel such as SUS440. , Quenching and tempering treatment, carburizing or carbonitriding treatment and quenching and tempering treatment.
In the sliding member of the present invention, the area ratio of the solid lubricant film is preferably 95% or less.

This makes it difficult for the solid lubricant film to be peeled off from the sliding surface of the sliding member, so that the friction coefficient of the sliding surface can be further reduced, and acoustic defects and vibration increases caused by peeling of the solid lubricant film are effective. Can be suppressed.
Furthermore, in the sliding member according to the present invention, it is preferable that the thickness of the solid lubricant film is 0.10 μm or more and 8.0 μm or less.

As a result, the lubricity on the sliding surface of the sliding member can be improved, the friction coefficient of the sliding surface can be reduced, and the strength required for the sliding member can be obtained, so that even better sliding performance can be obtained. be able to.
Here, when the thickness of the solid lubricating coating is less than 0.10 μm, good lubricity cannot be obtained, and when it exceeds 8.0 μm, the strength required for the sliding member cannot be obtained.

Furthermore, in the sliding member according to the present invention, it is preferable that the solid lubricant film is formed on a surface having a minute recess having a depth of 0.10 μm to 5 μm.
As a result, the fine recess formed on the surface is filled with the solid lubricant film, and a better lubricity can be obtained by the sliding surface of the sliding member, so that further excellent sliding performance can be obtained.
Here, if the fine dent is less than 0.10 μm, the effect for improving the lubricity cannot be obtained sufficiently, while if it exceeds 5 μm, the obtained effect is saturated.

  In the present invention, the method for forming the minute depressions on the sliding surface of the sliding member is not particularly limited. For example, steel balls having an average particle diameter of 45 μm as defined in JIS R 6001, silicon carbide, Examples thereof include a shot peening method using a shot material such as silicon, alumina, and glass beads, and a method in which a barrel method is used alone or in combination. In particular, it is preferable to apply the shot peening method in consideration of improving the hardness of the surface layer portion of the sliding member after the formation of the minute recess.

Furthermore, in the sliding member of the present invention, it is preferable that the solid lubricant film is formed on a surface having a center line average roughness (Ra) of 0.30 μm or more and 0.70 μm or less.
As a result, even when used in a harsh lubrication environment such as a boundary lubrication state, initial running-in gradually occurs and good lubricity is obtained on the sliding surface of the sliding member. Dynamic performance can be obtained.
Here, when the surface centerline average roughness (Ra) is less than 0.30 μm, the initial run-in is caused gently, and the effect for improving the lubricity cannot be obtained sufficiently, while 5 μm If it exceeds, the obtained effect will be saturated.

  According to the sliding member of the present invention, since the solid lubricating film having a specific area ratio is formed on at least a part of the surface forming the sliding surface, the lubricity on the sliding surface is improved. The coefficient of friction of the moving surface is reduced, and excellent sliding performance can be obtained. Therefore, even if it is a case where it applies as a sliding member used in severe lubrication environments, such as a boundary lubrication state, friction reduction can be aimed at.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In this embodiment, after processing a material composed of two types of high carbon chromium bearing steel (SUJ2) into a predetermined shape, carbonitriding for 3 hours in a mixed gas atmosphere (RX gas + enrich gas + ammonia gas) at 840 ° C., Oil quenching and tempering were performed to produce cylindrical test pieces (outer diameter: 30 mm, inner diameter: 22 mm, width: 8.5 mm) S1, S2. The surface layer part which comprises the outer peripheral surface of obtained test piece S1, S2 was 15-40 volume% of retained austenite, and hardness was HRC58-67 (Hv653-900). And the process shown below was performed only with respect to one test piece S1 among obtained test pieces S1 and S2.

First, in the test piece S1 with the pretreatment “present” shown in Table 1, a pretreatment for forming a minute dimple on the outer peripheral surface forming the sliding contact surface was performed.
The pretreatment “present (shot A)” shown in Table 1 is a shot material using a shot peening apparatus under conditions of an injection pressure of 2.0 to 9.0 kg / cm ² and an injection time of 10 to 20 minutes. As a process in which dimples are formed on the outer peripheral surface of the test piece S1 by accelerating and injecting steel balls having an average particle diameter of 45 μm defined in JIS R 6001 in the atmosphere.

Further, the pretreatment “barrel” shown in Table 1 refers to the roughness of the plateau portion (flat portion) after performing rough processing to form large dimples on the surface by blending various media and additives. Is a process in which dimples are formed on the outer peripheral surface of the test piece S1.
Furthermore, the pretreatment “present (shot B)” shown in Table 1 means that, using a shot peening apparatus, under conditions of an injection pressure of 2.0 to 9.0 kg / cm ² and an injection time of 10 to 20 minutes. Dimples are formed on the outer peripheral surface of the test piece S1 by accelerating and injecting two types of shot materials with different diameters (steel balls having an average particle diameter of 45 μm as defined in JIS R 6001 and glass beads) in the atmosphere. Refers to the process.

Furthermore, the pretreatment “present (SF)” shown in Table 1 refers to a process in which dimples are formed on the outer peripheral surface of the test piece S1 by performing super finishing.
Thereafter, the depth of the dimple formed on the outer peripheral surface of the test piece S1 was measured as follows. First, using a three-dimensional non-contact surface shape measurement system, observation was performed for 30 fields of view at 100 times. Next, the obtained image was converted into a cross-sectional profile, and an average value of results obtained by measuring each of five cross sections in the XY directions was calculated. The results are also shown in Table 1.

Next, a solid lubricating film was formed on the outer peripheral surface of the test piece S1. Specifically, using a shot peening apparatus, tin (product name: SN10104, manufactured by High-Purity Chemical Laboratory, Inc.) is released into the atmosphere under conditions of an injection pressure of 2.0 to 9.0 kg / cm ² and an injection time of 10 to 20 minutes. The solid lubricant film was formed on the outer peripheral surface of the test piece S1 by accelerating and spraying.

  Thereafter, the area ratio of the solid lubricant film formed on the outer peripheral surface of the test side S1 was measured as follows. First, using the EPMA (Electron Probe Microanalyzer), the outer peripheral surface of the test piece S1 was observed (2000 times, 30 fields of view). Next, the 200 μm square of the outer peripheral surface of the test piece S1 is enlarged 1000 times, and the portion where the X-ray intensity 10 times or more of the element characteristic X-ray intensity before the solid lubricant film is formed is detected as the solid lubricant film. It was determined as a region where is formed. And the result for 30 visual fields was image-analyzed and the average value of the area ratio of a solid lubricating film was computed. In addition, the area ratio shown in Table 1 is a value when the area of the observation visual field is 100%. For example, a solid lubricant film with an area ratio of 75% is a hole portion (a solid lubricant film is formed in the observation visual field). This refers to a solid lubricating film in which 25% of the portion is not present. The results are also shown in Table 1.

Moreover, the thickness of the solid lubricating film was measured as shown below using each test piece S1 for destructive inspection in which the solid lubricating film was formed under the same conditions as in each Example. First, the test piece S1 for destructive inspection was cut, mirror-finished by buffing, and then observed for 30 fields of view at 5000 × using an electron microscope (JSM-6360LV, manufactured by JEOL Ltd.). It was.
At this time, as shown in FIG. 1, in one field of view, it is installed so that the cross-sectional layer of the solid lubricating film is observed in the lateral direction, and in six sections along the vertical direction (thickness direction of the solid lubricating film). Dividing and calculating the film thickness of each section. And the average value of the film thickness of 6 sections was made into the average film thickness of 1 visual field, and also the average film thickness for 30 visual fields was computed. The results are also shown in Table 1. FIG. 1 is an electron micrograph of a solid lubricant film formed on the outer peripheral surface forming the sliding surface of the test piece S1, and in FIG. 1, the maximum film thickness is 2.5 μm and the minimum film thickness is 0.00. It was 5 μm.

  Further, a hardness test using a micro hardness tester was performed on the test piece S1 after the solid lubricant film was formed. As a result, a hardness gradient is observed in the surface layer portion (portion from the surface to a depth of 2 to 15 μm) forming the outer peripheral surface of the test piece S1 on which the solid lubricant film is formed, and the maximum hardness of the gradient is Hv780 It was Hv1130, and it was found that the hardness was increased by 5 to 20% compared to the maximum hardness of the surface layer portion of the cage 4 before the solid lubricating film was formed.

The test piece S1 and the test piece S2 thus obtained were respectively mounted on the cylinder 10 of the two-cylinder wear tester shown in FIG. 2, and a wear test was performed under the following conditions.
In this wear test, the test pieces S1 and S2 mounted on the pair of cylinders 10 are rotated in the opposite directions at a low speed while being loaded with a load P from above the pair of cylinders 10 opposed to each other. I went there. In addition, in this wear test, a low-viscosity lubricating oil that easily breaks the oil film during rotation was poured in order to evaluate the wear characteristics particularly in a poorly lubricated state. This result was obtained by calculating the average value of the wear amount (g / m) of both test pieces S1, S2 after rotation. Table 1 also shows the ratio when the wear amount of 27 is 1.00.
[Life test conditions]
Load: 1961N (200kgf)
Rotational speed: 250min ^-1
Rotation time: 200 hoursSlip rate: 30%
Lubricating oil: Mineral oil VG10
Lubricating oil temperature: 60 ° C
Number of tests: 10

  As shown in Table 1, No. 1 in which a solid lubricating film having an area ratio of 75% or more was formed on the outer peripheral surface. 1-No. In the abrasion test using the test piece S1 of No. 26, No. 26 in which a solid lubricating film was not formed on the outer peripheral surface. 27-No. No. 29 test piece S1 and No. No. 75 having a solid lubricating coating area ratio of less than 75%. 30-No. As compared with the case of using the test piece S1 of No. 33, the amount of wear is small. 27 was 0.36 times or less.

In particular, no. 1-No. 6 and no. 7, no. No. 8 result, No. 8 9-No. 15 and No. From the results of 16, it can be seen that the wear amount is further reduced by setting the area ratio of the solid lubricating coating to 75% or more and 95% or less.
No. 3 and no. 17, no. No. 18 result and No. 18 11 and no. 19, no. From the result of 20, it can be seen that the amount of wear is further reduced by setting the thickness of the solid lubricating coating to 0.10 μm or more and 8.0 μm or less.

  Furthermore, no. 11 and no. 21, no. From the result of No. 22, it is understood that the wear amount is further reduced by setting the depth of the dimple to 0.10 μm or more and 5 μm or less by the shot peening method. This is because, by setting the dimple depth within the above range, excellent lubricity can be obtained on the outer peripheral surface of the test piece S1, and the hardness of the surface layer portion forming the outer peripheral surface of the test piece S1 by the shot peening method. This is thought to be due to the improvement.

Furthermore, no. 3 and no. 23, no. 24 and No. 24 11 and no. 25, no. From the result of No. 26, it is understood that the amount of wear is further reduced by setting the surface centerline average roughness (Ra) to 0.30 μm or more and 0.70 μm or less.
Subsequently, among the results shown in Table 1, No. 1-No. 16 and no. 30-No. Using the result of 33, the graph of FIG. 3 showing the relationship between the area ratio of the solid lubricating coating and the wear amount of the test piece was prepared.

As shown in FIG. 3, when using the test piece S1 on which a solid lubricating film having an area ratio of 75% or more is used, compared to using the test piece S1 on which a solid lubricating film having an area ratio of less than 75% is used. It can be seen that the wear amount of the test piece is reduced.
Further, when the test piece S1 in which the solid lubricant film is formed after the pretreatment for adjusting the depth of the dimple is used, the test piece S1 in which the solid lubricant film is formed without performing the pretreatment is used. It can be seen that the amount of wear of the test piece is smaller than that of

  From the above results, by using the test piece S1 in which the solid lubricant film having an area ratio of 75% or more is formed on the outer peripheral surface serving as the sliding surface, the space between the test piece S1 and the test piece S2 is in a severe lubricating environment. It was confirmed that the wear amount of the test specimens S1 and S2 can be reduced even when used in the above. Further, by specifying the thickness of the solid lubricating film formed on the outer peripheral surface of the test piece S1, the depth of the dimple on the surface, and the center line average roughness, the distance between the test piece S1 and the test piece S2 is severe. It was confirmed that the amount of wear of the test pieces S1 and S2 could be further reduced even when used in a lubrication environment.

It is an electron micrograph which shows the solid lubricant film formed in the outer peripheral surface which makes the sliding contact surface of test piece S1. It is a figure which shows the two-cylinder abrasion tester used in embodiment. It is a graph which shows the relationship between the area ratio of the solid lubricating film formed in the outer peripheral surface which makes the sliding surface of test piece S1, and the abrasion loss of test pieces S1, S2.

Explanation of symbols

10 Cylindrical S1 Test piece S2 Test piece

Claims (5)

In the sliding member having a sliding surface that is in sliding contact with the counterpart member,
A sliding member, wherein a solid lubricating film having an area ratio of 75% or more is formed on at least a part of the surface forming the sliding surface.   The sliding member according to claim 1, wherein an area ratio of the solid lubricant film is 95% or less.   3. The sliding member according to claim 1, wherein a thickness of the solid lubricant film is 0.10 μm or more and 8.0 μm or less.   The sliding member according to any one of claims 1 to 3, wherein the solid lubricant film is formed on a surface having a fine recess having a depth of 0.10 µm to 5 µm.   5. The sliding according to claim 1, wherein the solid lubricating film is formed on a surface having a center line average roughness (Ra) of 0.30 μm or more and 0.70 μm or less. Element.