JP2018135966A - Rolling bearing and hard film deposition method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing which has hard films on slide faces or the like of bearing members, is excellent in peeling resistance of the hard film even when coming into contact with the other member under a condition accompanied by a slide in a poor lubrication state, also excellent in seizure resistance, abrasion resistance and corrosion resistance by exhibiting film original characteristics, and can prevent damage resulting from metallic contact between the bearing members.SOLUTION: A rolling bearing 1 comprises: an inner ring 2 having an inner ring raceway surface 2a at an outer periphery; an outer ring 3 having an outer ring raceway surface 3a at an inner periphery; and a plurality of rolling elements 4 rolling between the inner ring raceway surface 2a and the outer ring raceway surface 3a. Hard films 8 are deposited on the inner ring raceway surface 2a and the outer ring raceway surface 3a, and the rolling bearing is used in a condition that the hard film 8 comes into slide-contact with the other bearing member by boundary lubrication. The hard film 8 has a structure which is composed of an underlayer, a mixture layer having a gradient composition with WC and DLC which are deposited on the underlayer as main bodies, and a surface layer with DLC which is deposited on the mixture layer as a main body, and hydrogen content of the mixture layer is lower than 10 atom%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a rolling bearing in which a hard film containing diamond-like carbon is formed on the surfaces of an inner ring, an outer ring, and rolling elements that are bearing members, and a method of forming a hard film on the bearing member.

  The hard carbon film is a hard film generally called diamond-like carbon (hereinafter referred to as DLC. A film / layer mainly composed of DLC is also referred to as a DLC film / layer). In addition, hard carbon has various names such as hard amorphous carbon, amorphous carbon, hard amorphous carbon, i-carbon, diamond-like carbon, and these terms are not clearly distinguished.

  The essence of DLC in which such terms are used is structurally an intermediate structure of both diamond and graphite mixed. It is as hard as diamond and has excellent wear resistance, solid lubricity, thermal conductivity, chemical stability, and corrosion resistance. For this reason, for example, it is being used as a protective film for molds / tools, wear-resistant mechanical parts, abrasives, sliding members, magnetic / optical parts, and the like. As a method for forming such a DLC film, physical vapor deposition (hereinafter referred to as PVD) such as sputtering or ion plating, chemical vapor deposition (hereinafter referred to as CVD), unbalanced magnetron sputtering ( Hereinafter, a method such as UBMS) is employed.

  Conventionally, attempts have been made to form a DLC film on the raceway surface of a bearing ring of a rolling bearing, the rolling surface of a rolling element, a cage sliding contact surface, and the like. DLC films generate extremely large internal stress during film formation, and have high hardness and Young's modulus, but their deformability is extremely small, so they have the disadvantages of poor adhesion to the substrate and easy peeling. ing. For this reason, when forming a DLC film on each said surface in a rolling bearing, it is necessary to improve adhesiveness.

  For example, assuming that the adhesion of the DLC film is improved by providing an intermediate layer, chromium (hereinafter referred to as Cr), tungsten (hereinafter referred to as W) is formed on the raceway groove formed of a steel material or the rolling surface of the rolling element. ), Titanium (hereinafter referred to as Ti), silicon (hereinafter referred to as Si), nickel, and an underlayer having a composition containing at least one element of iron, and the constituent elements and carbon of the underlayer And an intermediate layer having a carbon content larger than that of the base layer on the opposite side of the base layer, and a DLC layer composed of argon and carbon and having an argon content of 0.02% by mass or more and 5% by mass or less. A rolling device formed in this order has been proposed (see Patent Document 1).

  Also, assuming that the adhesion of the DLC film is improved by the anchor effect, irregularities with a height of 10 to 100 nm and an average width of 300 nm or less are formed on the orbital surface by ion bombardment, and a DLC film is formed on the orbital surface. A rolling bearing has been proposed (see Patent Document 2).

Japanese Patent No. 4178826 Japanese Patent No. 3961739

  However, it is not easy to ensure the peeling resistance of the coating under the high contact surface pressure generated in rolling bearings, and the coating is resistant to lubrication and operating conditions where a strong shearing force can be generated against the coating due to sliding friction. It becomes more difficult to ensure the peelability. The sliding surface for which the application of the DLC film is considered is often in a state where the lubrication state is poor and accompanied by slipping, and is often severer than the operation state in a general rolling bearing.

  Also, in bearings, wear on the outer peripheral surface and end face as well as the rolling surface as well as sliding resistance on the seal groove may be a problem, and the DLC treatment to other than the rolling surface is also the durability and functionality of the bearing. It is an effective means for improvement.

  The technology of each of the above-mentioned patent documents is intended to prevent separation of the hard film, but the film used when applying the DLC film to satisfy the required characteristics according to the use conditions for the obtained rolling bearing. There is room for further improvement in structure and film formation conditions.

  The present invention has been made to cope with such problems. Even when the bearing member has a hard film on the sliding surface or the like and is in a poorly lubricated state and is in contact with other members under slipping conditions, the present invention has been made. Rolling bearings with excellent peeling resistance of hard films, excellent film seizure resistance, wear resistance, corrosion resistance, and damage due to metal contact between bearing members The purpose is to do. It is another object of the present invention to provide a film forming method for forming a hard film having the above characteristics on a bearing member.

  The hard film of the present invention is a rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that roll between the inner ring and the ring, made of an iron-based material, the inner ring, A surface of at least one bearing member selected from the outer ring and the rolling element has a hard film, and the rolling bearing is a bearing used under the condition that the hard film is in sliding contact with other bearing members by boundary lubrication. The hard film includes an underlayer directly formed on the surface, a mixed layer mainly composed of tungsten carbide (hereinafter referred to as WC) and DLC formed on the underlayer. , A film composed of a surface layer mainly composed of DLC formed on the mixed layer, wherein the mixed layer is continuously or stepwise from the base layer side to the surface layer side. The content of the WC in the mixed layer is reduced, and the content in the mixed layer is A layer containing rate increases of LC, and wherein the hydrogen content in the mixed layer is less than 10 atomic%.

  The surface layer has an inclined layer portion whose hardness increases continuously or stepwise from the mixed layer side on the side adjacent to the mixed layer.

  The iron-based material is high carbon chromium bearing steel, carbon steel, tool steel, or martensitic stainless steel.

  The underlayer is a layer mainly composed of Cr and WC.

  The method for forming a hard film of the present invention is a method for forming the hard film on a bearing member in the rolling bearing of the present invention, wherein at least the surface layer and the mixed layer are included in the hard film. It is a layer formed using a UBMS apparatus using argon (hereinafter referred to as Ar) gas as a sputtering gas, and the surface layer comprises a graphite target and a hydrocarbon-based gas as a carbon source for the DLC. In combination, the ratio of the introduction amount of the hydrocarbon-based gas to the introduction amount 100 of the Ar gas into the apparatus is 1 to 10, and carbon atoms generated from the carbon supply source are deposited on the mixed layer. When the mixed layer uses at least a graphite target as a carbon source for the DLC and a hydrocarbon-based gas is used as the carbon source, The ratio of the introduction amount of the hydrocarbon gas to the introduction amount 100 in the apparatus is less than 2.5, and while increasing the sputtering power applied to the graphite target continuously or stepwise, and for the WC The film is formed while lowering the sputtering power applied to the WC target. In particular, the hydrocarbon gas is methane gas.

  The rolling bearing of the present invention is formed by forming a hard film having a predetermined film structure including DLC on the surface of a bearing member made of an iron-based material. Since the intermediate layer is a mixed layer of WC and DLC (WC / DLC) and has a gradient composition, concentration of residual stress after film formation hardly occurs. In addition to this, since the hydrogen content in this mixed layer is less than 10 atomic%, even when it is in a poorly lubricated state and is in contact with other members under slipping conditions, the hard film has excellent peel resistance.

  With the above structure, the hard film has excellent peeling resistance and can exhibit the original characteristics of DLC while being formed on, for example, the inner / outer ring raceway surfaces or the rolling surfaces of the rolling elements. As a result, the rolling bearing of the present invention has excellent seizure resistance, wear resistance, and corrosion resistance, and has a long life with little damage to the raceway surface even under severe lubrication conditions.

  The method for forming a hard film of the present invention is a method for forming the hard film on a rolling bearing member, using a surface layer and a mixed layer in the hard film and an UBMS apparatus using Ar gas as a sputtering gas. In particular, when a mixed layer (WC / DLC) is formed, at least a graphite target is used as a carbon source for DLC, and a hydrocarbon gas is used as the carbon source. By setting the ratio of the introduction amount of the hydrocarbon-based gas to the introduction amount 100 of Ar gas into the apparatus less than 2.5, the hydrogen content in the mixed layer can be adjusted to less than 10 atomic%. This makes it possible to form a hard film that is excellent in peel resistance even when it is in a poorly lubricated state and is in contact with other members under conditions involving slippage.

It is sectional drawing which shows an example of the rolling bearing of this invention. It is sectional drawing which shows the other example of the rolling bearing of this invention. It is a schematic cross section which shows the structure of a hard film. It is a schematic diagram which shows the film-forming principle of UBMS method. It is a schematic diagram of a UBMS apparatus. It is a schematic diagram of a 2-cylinder testing machine.

  A hard film such as a DLC film has a residual stress in the film, and the residual stress varies greatly depending on the film structure and film formation conditions, and as a result, it greatly affects the peel resistance. The peel resistance also varies depending on the conditions under which the hard film is used. As a result of repeated verification under conditions such as rolling and sliding contact under poor lubrication conditions (boundary lubrication conditions) by the two-cylinder test, etc., the present inventors formed on the surface of the bearing member under the conditions. It has been found that, with respect to the hard film to be formed, the film structure is limited, and in particular, by making the hydrogen content within a predetermined range, it is possible to improve the peel resistance under these conditions. The present invention has been made based on such findings.

  The rolling bearing of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a rolling bearing (deep groove ball bearing) in which a hard film described later is formed on the inner and outer ring raceway surfaces, and FIG. 2 is a rolling bearing (deep groove ball bearing) in which a hard film is formed on the rolling surface of the rolling element. ) Are cross-sectional views respectively. The rolling bearing 1 includes an inner ring 2 having an inner ring raceway surface 2a on the outer periphery, an outer ring 3 having an outer ring raceway surface 3a on the inner periphery, and a plurality of rolling elements that roll between the inner ring raceway surface 2a and the outer ring raceway surface 3a. 4. The rolling elements 4 are held at regular intervals by a cage 5. The opening portions in the axial direction of the inner and outer rings are sealed by the seal member 6, and grease 7 is sealed in the bearing space. As the grease 7, a known grease for a rolling bearing can be used.

  In the rolling bearing of FIG. 1 (a), a hard film 8 is formed on the outer peripheral surface (including the inner ring raceway surface 2a) of the inner ring 2, and in the rolling bearing of FIG. 1 (b), the inner peripheral surface ( A hard film 8 is formed on the outer ring raceway surface 3a). In the rolling bearing shown in FIG. 2, a hard film 8 is formed on the rolling surface of the rolling element 4. Since the rolling bearing of FIG. 2 is a deep groove ball bearing, the rolling element 4 is a ball, and its rolling surface is the entire spherical surface.

  As shown in FIGS. 1 and 2, the inner ring raceway surface 2 a of the deep groove ball bearing is a circular curved surface having an arc-shaped cross section in the axial direction in order to guide the balls as the rolling elements 4. Similarly, the outer ring raceway surface 3a is also a circular curved surface having an arc-shaped cross section in the axial direction. The radius of curvature of the arc groove is generally about 0.51 to 0.54 dw when the steel ball diameter is dw. In the case of using a cylindrical roller bearing or a tapered roller bearing as a rolling bearing other than the mode shown in the figure, the inner ring raceway surface and the outer ring raceway surface are curved at least in the circumferential direction in order to guide the rollers of these bearings. It becomes. In addition, in the case of a self-aligning roller bearing or the like, since a cylindrical roller is used as a rolling element, the inner ring raceway surface and the outer ring raceway surface are curved in the axial direction in addition to the circumferential direction. In general, when a hard film is formed on a curved surface, the peel resistance is inferior, but in the present invention, this is improved by limiting the film structure and the hydrogen content.

  In the rolling bearing of the present invention, a hard film is formed on the surface that is in a sliding contact (particularly, rolling sliding contact) with boundary bearing lubrication with other bearing members. The rolling element also slips while rolling between the inner and outer rings. The hard film shown in FIGS. 1 and 2 is used under such conditions. Moreover, the formation location of the hard film is not limited to the location shown in FIG. 1 and FIG. 2, and at least one bearing selected from an inner ring, an outer ring, and a rolling element that satisfies the above conditions according to the application. It can be formed on any surface of the member.

  In the rolling bearing 1, the inner ring 2, the outer ring 3, and the rolling element 4, which are bearing members for which the hard film 8 is formed, are made of an iron-based material. As the iron-based material, any steel material generally used as a bearing member can be used, and examples thereof include high carbon chromium bearing steel, carbon steel, tool steel, martensitic stainless steel, and the like.

  In these bearing members, it is preferable that the surface on which the hard film is formed has a Vickers hardness of Hv650 or more. By setting it as Hv650 or more, a hardness difference with a hard film | membrane (underlayer) can be decreased and adhesiveness can be improved.

  On the surface on which the hard film is formed, it is preferable that a nitride layer is formed by nitriding before forming the hard film. As the nitriding treatment, it is preferable to perform a plasma nitriding treatment in which an oxide layer that hinders adhesion is hardly generated on the surface of the base material. Further, the surface hardness after nitriding is preferably Vickers hardness of Hv1000 or more in order to further improve the adhesion to the hard film (underlayer).

  The surface roughness Ra of the surface on which the hard film is formed is preferably 0.05 μm or less. When the surface roughness Ra exceeds 0.05 μm, it is difficult to form a hard film at the tip of the projection having the roughness, and the film thickness is locally reduced.

  The structure of the hard film will be described with reference to FIG. FIG. 3 is a schematic cross-sectional view showing the structure of the hard film 8 in the case of FIG. As shown in FIG. 3, the hard film 8 includes (1) a base layer 8a directly formed on the inner ring raceway surface 2a of the inner ring 2, and (2) WC and DLC formed on the base layer 8a. (3) and a surface layer 8c mainly composed of DLC formed on the mixed layer 8b. In the present invention, the film structure of the hard film is a three-layer structure as described above, so that sudden changes in physical properties (hardness, elastic modulus, etc.) are avoided.

  The underlayer 8a is an underlayer formed directly on the surface of each bearing member that serves as a base material. The material and structure are not particularly limited as long as the adhesion to the substrate can be ensured. For example, Cr, W, Ti, Si, etc. can be used as the material. Among these, since it is excellent in adhesiveness with the bearing member (for example, high carbon chromium bearing steel) used as a base material, it is preferable to contain Cr.

  In addition, the base layer 8a is preferably a layer mainly composed of Cr and WC in consideration of adhesion with the mixed layer 8b. WC has intermediate hardness and elastic modulus between Cr and DLC, and concentration of residual stress after film formation hardly occurs. In particular, it is preferable to have a gradient composition in which the Cr content is small and the WC content is high from the inner ring 2 side toward the mixed layer 8b side. Thereby, it is excellent in the adhesiveness in both surfaces of the inner ring | wheel 2 and the mixed layer 8b.

  The mixed layer 8b becomes an intermediate layer interposed between the base layer and the surface layer. As described above, the WC used for the mixed layer 8b has an intermediate hardness and elastic modulus between Cr and DLC, and residual stress concentration after film formation hardly occurs. Since the mixed layer 8b has a gradient composition in which the WC content decreases from the base layer 8a side to the surface layer 8c side and the DLC content increases, the both sides of the base layer 8a and the surface layer 8c Excellent adhesion. In addition, WC and DLC are physically coupled in the mixed layer, and damage in the mixed layer can be prevented. Furthermore, since the DLC content is increased on the surface layer 8c side, the adhesion between the surface layer 8c and the mixed layer 8b is excellent.

  The mixed layer 8b is a layer in which non-adhesive DLC is bonded to the base layer 8a side by an anchor effect by WC. As shown in the examples described later, it is important to reduce the hydrogen content in the mixed layer to some extent in order to improve the peel resistance in the case of contact with other members under poorly lubricated conditions with slippage. Become.

  The hydrogen content in the mixed layer is less than 10 atomic%. By setting it as this range, peeling of the hard film can be prevented even under the condition of rolling and sliding contact with boundary lubrication. When the hydrogen content of the mixed layer exceeds 10 atomic%, relatively soft DLC exists in the mixed layer serving as the intermediate layer, and there is a possibility that peeling is likely to occur under the above conditions. Moreover, in order to improve the fatigue characteristics at the time of rolling contact, it is preferable that the hydrocarbon-based gas is used in combination as a carbon supply source for DLC and is within the above range while slightly containing hydrogen.

  Here, the “hydrogen content (atomic%) in the mixed layer” in the present invention can be calculated by a known analysis method. For example, it can be determined by GDS analysis (glow discharge emission spectral analysis). The GDS analysis is an analysis capable of examining the relationship between the depth direction and the element amount, and can be quantified by preparing a calibration curve for each element. The hydrogen amount calibration curve can be created using ERDA analysis (elastic recoil particle detection method) capable of measuring the absolute amount of hydrogen. Since the hydrogen amount output value in the GDS analysis varies depending on the material of the test piece, it is necessary to create a hydrogen amount calibration curve for each of DLC and WC constituting the mixed layer (WC / DLC). For DLC single-layer film test pieces and WC single-layer film test pieces, test pieces with different hydrogen contents can be obtained by adjusting the amount of hydrocarbon gas introduced under conditions that match the film formation conditions of the mixed layer (WC / DLC). An ERDA analysis and a GDS analysis are performed, and a relationship (calibration curve) between a hydrogen amount output value in the GDS analysis and a hydrogen amount (atomic%) measured in the ERDA analysis is examined. Since the hydrogen content obtained with the DLC hydrogen calibration curve is different from the hydrogen content obtained with the WC hydrogen calibration curve, it can be arbitrarily determined by taking the average of the hydrogen content obtained with both calibration curves. The hydrogen content (atomic%) corresponding to the hydrogen content output value can be calculated.

The surface layer 8c is a film mainly composed of DLC. The surface layer 8c preferably has a relaxing layer portion 8d on the side adjacent to the mixed layer 8b. This is because when the film forming condition parameters (hydrocarbon gas introduction amount, vacuum degree, bias voltage) are different between the mixed layer 8b and the surface layer 8c, at least one of the parameters is selected in order to avoid abrupt changes in these parameters. It is a relaxation layer portion obtained by changing one of them continuously or stepwise. More specifically, the film formation condition parameters at the time of forming the outermost layer of the mixed layer 8b are set as the starting points, and the final film formation condition parameters of the surface layer 8c are set as the end points. Change. As a result, there is no abrupt difference in physical properties (hardness, elastic modulus, etc.) between the mixed layer 8b and the surface layer 8c, and the adhesion between the mixed layer 8b and the surface layer 8c is further improved. By increasing the bias voltage continuously or stepwise, the composition ratio of the graphite structure (sp ² ) and the diamond structure (sp ³ ) in the DLC structure is biased toward the latter, and the hardness is inclined (increased). .

  The thickness of the hard film 8 (total of the three layers) is preferably 0.5 to 3.0 μm. If the film thickness is less than 0.5 μm, the abrasion resistance and mechanical strength may be inferior, and if it exceeds 3.0 μm, the film is easily peeled off. Furthermore, the ratio of the thickness of the surface layer 8c to the thickness of the hard film 8 is preferably 0.8 or less. If this ratio exceeds 0.8, the gradient structure for physically bonding WC and DLC in the mixed layer 8b tends to be a discontinuous structure, and the adhesion may be deteriorated.

  By making the hard film 8 have a three-layer structure including the base layer 8a, the mixed layer 8b, and the surface layer 8c having the above composition, the peel resistance is excellent.

  In the rolling bearing of the present invention, by forming a hard film having the structure and physical properties as described above, even when subjected to a load such as rolling and sliding contact during use of the bearing, the film can be prevented from being worn or peeled off. Even in a lubricated state, there is little damage to the raceway surface and the service life is long. In addition, in rolling bearings filled with grease, if the new metal surface is exposed due to damage to the race or the like, grease degradation is promoted by catalytic action. However, in the rolling bearing of the present invention, the raceway surface and rolling due to metal contact are caused by a hard film. Since surface damage can be prevented, this grease deterioration can also be prevented.

  Hereinafter, the formation method of the hard film of this invention is demonstrated. The hard film is obtained by forming the base layer 8a, the mixed layer 8b, and the surface layer 8c in this order on the film formation surface of the bearing member.

  The surface layer 8c is preferably formed using a UBMS apparatus using Ar gas as a sputtering gas. The film forming principle of the UBMS method using the UBMS apparatus will be described with reference to the schematic diagram shown in FIG. In the drawing, the substrate 12 is an inner ring, an outer ring, or a rolling element that is a bearing member to be deposited, but is schematically shown as a flat plate. As shown in FIG. 4, an inner magnet 14 a and an outer magnet 14 b having different magnetic properties are arranged in the central portion and the peripheral portion of the round target 15, and the magnet 14 a, while forming a high-density plasma 19 near the target 15, A part 16 a of the magnetic force lines 16 generated by 14 b reaches the vicinity of the base material 12 connected to the bias power source 11. The Ar plasma generated during the sputtering along the magnetic force lines 16a can be diffused to the vicinity of the base material 12. In such a UBMS method, an ion assist effect that causes Ar ions 17 and electrons to reach the base material 12 in a larger amount than the ordinary sputtering along the magnetic field lines 16a reaching the vicinity of the base material 12 due to the ion assist effect. A dense film (layer) 13 can be formed.

  The surface layer 8c uses this apparatus, uses a graphite target and a hydrocarbon gas in combination as a carbon supply source, and the ratio of the introduction amount of the hydrocarbon gas to the introduction amount 100 of Ar gas into the apparatus. 1 to 10 and carbon atoms generated from a carbon supply source are preferably deposited on the mixed layer 8b. In addition, the degree of vacuum in the apparatus is preferably 0.2 to 0.8 Pa. This preferable condition will be described below.

  The hardness and elastic modulus of the DLC film can be adjusted by using a graphite target and a hydrocarbon-based gas in combination as a carbon supply source. As the hydrocarbon-based gas, methane gas, acetylene gas, benzene and the like can be used, and are not particularly limited. However, methane gas is preferable from the viewpoint of cost and handleability. By setting the ratio of the introduction amount of the hydrocarbon-based gas to 1 to 10 (volume part) with respect to the introduction amount 100 (volume part) of Ar gas into the UBMS apparatus (in the film formation chamber), the surface layer 8c Thus, the adhesion with the mixed layer 8b can be improved without deteriorating the wear resistance.

  The degree of vacuum in the UBMS apparatus (inside the film forming chamber) is preferably 0.2 to 0.8 Pa as described above. More preferably, it is 0.25 to 0.8 Pa. If the degree of vacuum is less than 0.2 Pa, the amount of Ar gas in the chamber is small, so that Ar plasma is not generated and film formation may not be possible. On the other hand, if the degree of vacuum is higher than 0.8 Pa, the reverse sputtering phenomenon tends to occur and the wear resistance may be deteriorated.

  The bias voltage applied to the bearing member serving as the substrate is preferably 50 to 150V. Note that the bias potential to the substrate is applied so as to be negative with respect to the ground potential. For example, the bias voltage of 100 V means that the bias potential of the substrate is −100 V with respect to the ground potential. Show.

  The formation of the base layer 8a and the mixed layer 8b is also preferably performed using a UBMS apparatus using Ar gas as the sputtering gas. When the underlayer 8 a is a layer mainly composed of Cr and WC, a Cr target and a WC target are used in combination as the target 15. Further, when forming the mixed layer 8b, (1) a WC target and (2) a graphite target and, if necessary, a hydrocarbon-based gas are used.

  When the underlying layer 8a has a gradient composition of Cr and WC as described above, it is formed continuously or stepwise while increasing the sputtering power applied to the WC target and decreasing the power applied to the Cr target. Film. Thereby, it can be set as the layer of the structure where the content rate of Cr becomes small toward the mixed layer 8b side, and the content rate of WC becomes high.

  The mixed layer 8b is formed in a continuous or stepwise manner while increasing the sputtering power applied to the graphite target serving as the carbon supply source and decreasing the power applied to the WC target. Thereby, it can be set as the layer of the gradient composition which the content rate of WC becomes small toward the surface layer 8c side, and the content rate of DLC becomes high.

  In order to keep the hydrogen content in the mixed layer 8b within the above range (less than 10 atomic%), the graphite target is used alone as a carbon supply source, or the hydrocarbon gas is introduced using a graphite target and a hydrocarbon gas in combination. Reduce the proportion of quantity. Specifically, when the graphite target and the hydrocarbon gas are used in combination, the ratio of the introduction amount of the hydrocarbon gas is set to the introduction amount 100 (volume part) of Ar gas into the UBMS apparatus (in the film formation chamber). And less than 2.5 (volume part). Preferably it is 0.5-2 (volume part), More preferably, it is 1-1.6 (volume part).

  The degree of vacuum in the UBMS apparatus (inside the film formation chamber) during the formation of the mixed layer 8b is preferably 0.2 to 1.2 Pa. Moreover, it is preferable that the bias voltage applied to the bearing member used as a base material is 20-100V. By setting it as such a range, the peeling resistance can be improved.

  As a hard film formed on the rolling bearing of the present invention, a hard film was formed on a predetermined base material, and the physical properties of the hard film were evaluated. Further, the peel resistance was evaluated by a rolling slip test using a two-cylinder tester.

The test piece, UBMS apparatus, sputtering gas, etc. used for the evaluation of the hard film are as follows.
(1) Physical property of test piece: SUJ2 Quenched and tempered product Hardness 780Hv
(2) Specimen: DLC film formed on each condition on sliding surface of mirror-polished (0.02 μmRa) SUJ2 ring (φ40 × L12 no secondary curvature) (3) Counterpart: Grinding Finish (0.7μmRa) SUJ2 ring (φ40 × L12 secondary curvature 60)
(4) UBMS device: manufactured by Kobe Steel; UBMS202
(5) Sputtering gas: Ar gas

The conditions for forming the underlayer will be described below. The inside of the film forming chamber is evacuated to about 5 × 10 ⁻³ Pa, a test piece serving as a base material is baked with a heater, the base material surface is etched with Ar plasma, and then a Cr target and a WC target are formed by UBMS method The sputtering power applied to the substrate was adjusted, the composition ratio of WC and DLC was inclined, and a Cr / WC gradient layer having a large amount of Cr on the substrate side and a large amount of WC on the surface side was formed.

  The conditions for forming the mixed layer will be described below. The film was formed by the UBMS method in the same manner as the underlayer. Here, for the mixed layer, while supplying methane gas, which is a hydrocarbon-based gas, the sputtering power applied to the WC target and the graphite target is adjusted, the composition ratio of WC and DLC is inclined, and the WC is formed on the base layer side. A WC / DLC gradient layer having a large amount of DLC on the surface layer side was formed. Table 1 shows specific film forming conditions of the mixed layer. The hydrogen content (atomic%) in the mixed layer was determined by the above-described method by GDS analysis (glow discharge emission spectroscopic analysis). The results are also shown in Table 1.

  The conditions for forming the surface layer are as shown in each table.

  FIG. 5 is a schematic diagram of a UBMS apparatus. As shown in FIG. 5, the ion assist effect is increased by increasing the plasma density in the vicinity of the base material 21 by the non-equilibrium magnetic field of the sputter evaporation source material (target) 22 with respect to the base material 21 arranged on the disk 20. By doing this (see FIG. 4), the apparatus has a UBMS function that can control the characteristics of the film deposited on the substrate. With this apparatus, a composite coating in which a plurality of UBMS coatings (including composition gradients) are arbitrarily combined can be formed on a substrate. In this embodiment, a base layer, a mixed layer, and a surface layer are formed as a UBMS film on a ring as a base material.

Examples 1-3, Comparative Examples 1-5
The substrate shown in Table 1 was ultrasonically cleaned with acetone and then dried. After drying, this was attached to a UBMS apparatus, and an underlayer and a mixed layer were formed under the above-described formation conditions. A DLC film, which is a surface layer, was formed on the film formation conditions shown in Table 1 to obtain a test piece having a hard film. Note that “degree of vacuum” in Table 1 is the degree of vacuum in the film forming chamber in the above apparatus. The obtained test piece was subjected to a rolling slip test using a two-cylinder testing machine shown below. The results are also shown in Table 1.

<Rolling and sliding test with 2 cylinder tester>
The obtained specimen was tested for resistance to peeling by rolling and sliding using a two-cylinder testing machine shown in FIG. The two-cylinder tester includes a driven-side test piece 23 and a driven-side test piece 24 that is in rolling contact with each other. Each test piece (ring) is supported by a support bearing 26, and a load is applied by a load spring 27. Is loaded. In the figure, 25 is a driving pulley, and 28 is a non-contact tachometer. Increase the roughness of the mating material to promote the peeling of the hard film, lower the lubricating oil viscosity to make boundary lubrication, cause slippage by applying a rotation difference, and peel off the time (h) until the peeling of the film occurs Evaluation was made as the lifetime. Specific test conditions are as follows.
(Test conditions)
Lubricating oil: VG1.5 equivalent oil (containing additives) Dropping oil temperature: 40-50 ° C
Maximum contact surface pressure: 2.7 GPa
Number of revolutions: (test piece side) 270 min ⁻¹
(Counterpart side) 300 min ^-1
Relative sliding speed: 0.06 m / s
Oil film parameter: 0.006
Abort time: 48h

  Each Example and each Comparative Example have the same base material and surface layer forming conditions, and the surface layer has an average hardness of about 29 GPa. As shown in Table 1, when the methane gas introduction ratio at the time of forming the mixed layer is changed, when the methane gas introduction ratio is high, the peeling life in the two-cylinder rolling slip test tends to be short, and the methane gas introduction ratio is 2. 5. When the hydrogen content was 10.8 atomic%, the lifetime was dramatically shortened. When the methane gas introduction ratio is 2.5 or more, the peeling life is about 1 h, and the presence of a relatively soft DLC with a high hydrogen content in the mixed layer adversely affects the peeling resistance of the film. Conceivable.

  Sliding surfaces and rolling surfaces for which application of DLC is considered are often in a severely lubricated state such as poor lubrication or high sliding speed. The rolling bearing of the present invention has, for example, a DLC film formed on the inner and outer ring raceway surfaces and the rolling surface of the rolling element, and has excellent DL film peeling resistance even when operated in a severely lubricated state. Therefore, it has excellent seizure resistance, wear resistance, and corrosion resistance. For this reason, the rolling bearing of this invention is applicable to various uses including the use in a severe lubrication state.

1 Rolling bearing (deep groove ball bearing)
2 Inner ring 3 Outer ring 4 Rolling element 5 Cage 6 Seal member 7 Grease 8 Hard film 11 Bias power supply 12 Base material 13 Film (layer)
DESCRIPTION OF SYMBOLS 15 Target 16 Magnetic field line 17 Ar ion 18 Ionized target 19 High-density plasma 20 Disc 21 Base material 22 Sputter evaporation source material (target)
23 Drive side test piece 24 Drive side test piece 25 Drive pulley 26 Support bearing 27 Load spring 28 Non-contact tachometer

Claims (6)

A rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements that roll between the inner ring and the outer ring, made of an iron-based material,
The surface of at least one bearing member selected from the inner ring, the outer ring, and the rolling element has a hard film, and the rolling bearing is used under the condition that the hard film is in sliding contact with other bearing members by boundary lubrication. Bearings,
The hard film includes an underlayer formed directly on the surface, a mixed layer mainly composed of tungsten carbide and diamond-like carbon formed on the underlayer, and an upper layer of the mixed layer. A film having a structure composed of a surface layer mainly composed of diamond-like carbon,
In the mixed layer, the content of the tungsten carbide in the mixed layer decreases continuously or stepwise from the base layer side to the surface layer side, and the diamond-like carbon in the mixed layer decreases. A rolling bearing characterized in that it is a layer having a high content rate, and the hydrogen content in the mixed layer is less than 10 atomic%.   The rolling bearing according to claim 1, wherein the surface layer has an inclined layer portion whose hardness increases continuously or stepwise from the mixed layer side on a side adjacent to the mixed layer.   The rolling bearing according to claim 1, wherein the iron-based material is high-carbon chromium bearing steel, carbon steel, tool steel, or martensitic stainless steel.   The rolling bearing according to any one of claims 1 to 3, wherein the underlayer is a layer mainly composed of chromium and tungsten carbide. A method for forming the hard film on a bearing member in a rolling bearing according to any one of claims 1 to 4,
In the hard film, at least the surface layer and the mixed layer are layers formed using an unbalanced magnetron sputtering apparatus using argon gas as a sputtering gas,
The surface layer uses a graphite target and a hydrocarbon gas in combination as a carbon supply source for the diamond-like carbon, and the ratio of the introduction amount of the hydrocarbon gas to the introduction amount 100 of the argon gas into the apparatus 1 to 10, and carbon atoms generated from the carbon source are deposited on the mixed layer to form a film.
The mixed layer uses at least a graphite target as a carbon supply source for the diamond-like carbon, and when using a hydrocarbon-based gas as the carbon supply source, the amount of the argon gas introduced into the apparatus is 100 The ratio of the introduction amount of the hydrocarbon-based gas is less than 2.5, while increasing the sputtering power applied to the graphite target continuously or stepwise, and to the tungsten carbide target for the tungsten carbide A method of forming a hard film, wherein the film is formed while lowering a sputtering power to be applied.   6. The method for forming a hard film according to claim 5, wherein the hydrocarbon-based gas is methane gas.