JP2013014801A - Method for forming hard film on bearing parts, and rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a hard film on the track face or on the rolling face of a bearing part made from bearing steel, formable of a hard film of sufficient durability in a high load environment.SOLUTION: The method for forming a DLC (diamond-like carbon) film 5 comprised of carbon, silicon and hydrogen on a track groove 1a of an upper race 1 and on a track groove 2a of a lower race 2, employs an unbalanced magnetron sputtering process wherein methane gas and argon gas are introduced, using a silicon target and a carbon target. The temperature of a heater heating a specimen support table in the sputtering device is controlled to keep the temperature of the track grooves 1a, 2a of the upper and lower races 1, 2 supported by the specimen support table in a range of 150 to 180°C. The time of forming the film is set so that the thickness of the DLC film 5 becomes 1.0 to 1.6 μm.

Description

  The present invention relates to a method for forming a hard film on a raceway surface or a rolling surface of a bearing component made of bearing steel.

  The diamond-like carbon (hereinafter abbreviated as “DLC”) film has a hardness equivalent to diamond (plastic deformation hardness of 10 GPa or more), and the friction coefficient is 0.2 or less. And as small as molybdenum disulfide and fluororesin. Therefore, the DLC film is attracting attention as a new wear-resistant coating formed on the raceway surface and rolling surface of the bearing component. The DLC film formed on the raceway surface or the like of a rolling bearing has a problem that it is easily peeled off from the raceway surface or the like due to high contact stress, and many proposals have been made for improving the adhesion of the DLC film.

  Patent Document 1 discloses that a hard amorphous carbon-hydrogen-silicon film having a silicon content is formed on a raceway portion of a rolling bearing that is in rolling contact with a nitride layer having a thickness of 30 μm or more having irregularities on the surface. Describes that a DLC film having a thickness of 30 at% or less is formed. The nitride layer is formed by gas nitriding, and the surface irregularities are formed by ion bombardment at a height of 10 to 100 nm and an average width of 300 nm or less. The DLC film is formed by a plasma CVD method.

However, since the nitriding treatment is generally performed at a high temperature of 400 ° C. or higher, the material of the base material that can be used is limited.
Patent Document 2 discloses an intermediate layer made of at least one element of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Si, or a carbide thereof, between the DLC film and the substrate. Is provided with a thickness of 0.5 nm or more and less than 10 nm. However, even if such an intermediate layer is provided, peeling of the DLC film may not be prevented in an environment where the contact surface pressure reaches several GPa where a rolling bearing is used.

Patent Document 3 discloses an internal stress composed of a carbon layer that does not contain hydrogen in order to prevent a hard carbon layer composed of a DLC film containing hydrogen from peeling off or warping the substrate due to its internal stress. The provision of a relaxation layer is described. It is described that the hard carbon layer is formed by a plasma CVD method using a hydrocarbon gas as a raw material, and the internal stress relaxation layer is formed by a sputtering method.
However, in an environment where the base material is greatly elastically deformed, such as a rolling bearing, even if the internal stress relaxation layer is present, there is a possibility that peeling of the hard carbon layer from the substrate or warping of the substrate cannot be prevented. .

Japanese Patent No. 3961739 JP 2001-316800 A Japanese Patent Laid-Open No. 11-10061

  An object of the present invention is to provide a method of forming a hard film having sufficient durability even in a high load environment as a method of forming a hard film on a raceway surface or a rolling surface of a bearing component made of bearing steel. It is.

In order to solve the above-mentioned problems, a method for forming a hard film on a bearing component according to the present invention is a method for forming a hard film on a raceway surface or a rolling surface of a bearing component made of bearing steel, comprising carbon, silicon and hydrogen. The thickness of the DLC film is 1.6 μm or less by controlling the temperature of the raceway surface or the rolling surface within a range of 150 to 180 ° C. by sputtering using a silicon target and a carbon target and introducing hydrocarbon gas. It is characterized by forming a film. The lower limit of the effective thickness of the DLC film made of carbon, silicon and hydrogen formed by this method is 0.8 μm.
The linear expansion coefficient of the DLC film is generally 1 to 7 × 10 ⁻⁶ / ° C., but the linear expansion coefficient of the bearing steel is about 12 × 10 ⁻⁶ / ° C. The higher the temperature, the greater the difference in volume expansion between the DLC film and the film formation surface.

  In addition, when a film is formed by sputtering using a silicon target and a carbon target and hydrocarbon gas is introduced, not only “C—H” bonds but also “Si—H” bonds exist in the DLC film. Since “Si—H” has a low binding energy, unbonded “H” is positively bonded to “Si”. As a result, it is considered that the residual stress of the DLC film is reduced as compared with the case where no hydrocarbon gas is introduced. However, when the temperature of the base material (film formation surface) during film formation is high, the “Si—H” bond tends to be broken, and the unbonded “H” exists in the DLC film. Volume expansion occurs and compressive residual stress increases.

Further, when the temperature of the base material (deposition surface) during film formation is high, silicon tends to be formed in a crystalline state.
On the other hand, in the method of the present invention, the temperature of the raceway surface or the rolling surface of the bearing part, which is the film formation surface, is controlled in the range of 150 to 180 ° C., so that the DLC film composed of carbon, silicon, and hydrogen. The volume expansion of is suppressed. In addition, a decrease in the hardness of the bearing steel is suppressed, and the adhesion and durability of the DLC film made of carbon, silicon, and hydrogen with respect to the film formation surface is improved.

  Even if the temperature of the film formation surface is controlled within the range of 150 to 180 ° C., the residual stress becomes extremely large when the thickness of the DLC film made of carbon, silicon and hydrogen becomes 2.0 μm or more. By setting the thickness to 1.6 μm or less, the residual stress of the DLC film is small, and a favorable state as a bearing component can be obtained.

  According to the method of the present invention, a hard film having sufficient durability even in a high load environment can be formed on the raceway surface or rolling surface of the bearing component.

It is sectional drawing which shows the thrust ball bearing provided with the bearing ring in which the DLC film was formed by the method of embodiment. It is a graph which shows IR spectrum of the DLC film of sample No.2 and No.5 formed into a film in the Example.

Embodiments of the present invention will be described below.
The thrust ball bearing (rolling bearing) of FIG. 1 is composed of an upper race (race ring) 1, a lower race (race ring) 2, balls (rolling elements) 3, and a cage 4. The upper race 1, the lower race 2, and the ball 3 are made of SUJ2, and are produced by a normal method. A DLC film 5 made of carbon, silicon, and hydrogen is formed on the raceway groove (track surface) 1 a of the upper race 1 and the raceway groove (track surface) 2 a of the lower race 2.

  The DLC film 5 is formed by a non-equilibrium magnetron sputtering method using a silicon target and a carbon target and introducing methane (hydrocarbon) gas and argon gas. At that time, the temperature of the raceway grooves 1a and 2a of the upper and lower races 1 and 2 supported by the sample support is controlled by heating the sample support in the sputtering apparatus with a heater and controlling the temperature of the heater. Hold in the range of 180 ° C. Further, the DLC film 5 is formed by setting the time so that the thickness becomes 1.0 to 1.6 μm. Other points follow the normal magnetron sputtering method.

By this method, the DLC film 5 made of carbon, silicon and hydrogen formed on the upper race 1 and the lower race 2 is rotated by rotating the thrust ball bearing of FIG. 1 with a load of 8820 N (900 kgf), a rotational speed of 2000 rpm, and oil lubrication. In this case, almost no peeling occurs and good adhesion and durability can be obtained.
The Young's modulus of the DLC film formed on the raceway surface and the rolling surface of the bearing component is preferably 150 to 200 GPa. When the Young's modulus of the DLC film is less than 150 GPa, the hardness of the DLC film becomes insufficient as the hardness of the raceway surface and the rolling surface of the bearing component. When it exceeds 200 GPa, it becomes more difficult to deform than a bearing component made of bearing steel, and therefore, it is easy to peel off in a high load environment.

Further, a metal intermediate layer made of chromium or the like may be provided between the raceway surface and rolling surface of the bearing component made of bearing steel and the DLC film.
In addition, it is preferable to form the DLC film so that the proportion of carbon becomes higher than the proportion of silicon as it goes to the surface from the viewpoint of reducing the compressive residual stress of the DLC film.

  A DLC film 5 made of carbon, silicon and hydrogen is introduced into the raceway grooves 1a and 2a of the upper race 1 and the lower race 2 constituting the rolling bearing of FIG. 1, and methane gas and argon gas are introduced using a silicon target and a carbon target. The film was formed by non-equilibrium magnetron sputtering. At that time, by gradually increasing the voltage applied to the carbon target and gradually decreasing the voltage applied to the silicon target, the composition of the DLC film 5 is such that the proportion of carbon becomes higher than the proportion of silicon toward the surface. A film was formed.

  In addition, the temperature of the track grooves 1a and 2a during film formation is 150 ° C. (sample No. 1), 180 ° C. (sample No. 2), 200 ° C. (sample No. 3), 250 ° C. (sample No. 4), The temperature of the sample support was controlled so that each temperature of 300 ° C. (sample No. 5) was ± 5 ° C. The film formation time was set so that the film thickness was the same 1.0 μm. Except for these points, the films were formed under the same conditions.

In Samples Nos. 6 to 8, DLC5 having different film thicknesses was formed by changing the temperature of the track grooves 1a and 2a during film formation at the same temperature of 180 ° C. and changing the film formation time. Except for these points, the conditions were the same as those of No. 1 to No. 5.
The IR spectra of the sample No. 2 and No. 5 DLC films 5 thus obtained were measured. The resulting graph is shown in FIG. In this graph, a peak of “Si—H” in the vicinity of a wavelength of 2100 cm ⁻¹ is observed in the No. 2 DLC film 5 having a track groove temperature of 150 ° C. during film formation. It is not observed in the No. 5 DLC film 5 having a groove temperature of 300 ° C. That is, when the temperature of the track groove at the time of film formation is 300 ° C., the “Si—H” bond is broken and a large amount of unbonded “H” exists. It is assumed that the residual stress has increased.

Further, the upper race 1 and the lower race 2 of each sample obtained were combined, and three SUJ2 balls 3 made by a normal method were arranged at equal intervals between the raceway grooves 1a and 2a, and an oil bath (VG10 ), And a test of rotating 10 million times (10 ⁷ times) under the conditions of a load of 8820 N (900 kgf) and a rotational speed of 2000 rpm.
After completion of the test, the state of the DLC film 5 formed in the raceway grooves 1a and 2a was observed with a microscope. Then, image processing was performed to examine the ratio of the area where the DLC film 5 was peeled off. In addition, when peeling occurs in the raceway grooves 1a and 2a before the end of the test (before the rotation reaches 10 million times), the DLC film is within the range excluding the peeling portion of the raceway grooves 1a and 2a at that time. The ratio of the area where 5 was peeled was examined. The results are shown in Table 1 below.

  In addition, a test piece for measuring Young's modulus and residual stress was formed under the same conditions as those for the track grooves 1a and 2a of samples No. 1 to No. 8, and the Young's modulus and residual stress were measured. did. Young's modulus was measured by the nanoindentation method. The residual stress was calculated by a shape measurement method using metal flakes. The results are also shown in Table 1 below. A value with a sign “−” in the residual stress indicates a compressive stress. Unsigned values indicate tensile stress.

As can be seen from Table 1, Nos. 1, 2, 6, and 7 formed by the method corresponding to the embodiment of the method of the present invention have an absolute value of the residual stress of the DLC film 5 of 0.12 GPa or less. It was small and the peeling rate was as small as 4% by area or less. Further, no peeling occurred on the raceway groove surface.
On the other hand, No. 3 to No. 5 in which the temperature of the track groove during film formation is higher than 180 ° C., No. 7 and No. 8 in which the temperature is 180 ° C. but the film thickness is 2.0 μm or more The absolute value of the residual stress of the DLC film 5 was as large as 0.32 GPa or more, and the peeling rate was as large as 7 area% or more. In addition, peeling occurred on the raceway groove surface.
From the above, it is possible to form a hard film with good adhesion and durability by adopting a method satisfying the temperature of the track groove during film formation of 150 to 180 ° C. and the thickness of the DLC film 5 of 1.6 μm or less. I understand.

1 Upper race (Raceway)
1a Track groove (track surface)
2 Lower race (Raceway)
2a Track groove (track surface)
3 balls (rolling elements)
4 Cage 5 DLC film made of carbon, silicon and hydrogen

Claims (2)

A method of forming a hard film on a raceway surface or a rolling surface of a bearing component made of bearing steel,
By using a silicon target and a carbon target, a DLC film composed of carbon, silicon, and hydrogen, by using a silicon target and a carbon target, and controlling the temperature of the raceway surface or the rolling surface within a range of 150 to 180 ° C., A method of forming a hard film on a bearing component, wherein the film is formed to a thickness of 1.6 μm or less.   A rolling bearing having a bearing component in which a hard film is formed on a raceway surface or a rolling surface by the method according to claim 1.

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