JP2730571B2 - Sliding material and piston ring - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding material and a piston ring having a chromium-nitrogen based coating containing CrN as a main component and having excellent wear resistance and seizure resistance.

[0002]

2. Description of the Related Art Conventionally, sliding parts having a film having excellent sliding characteristics formed by surface treatment have been used for sliding parts such as engine parts of automobiles such as piston rings and various mechanical parts. Conventional surface treatment methods include a nitriding treatment, a chromium plating treatment, and a molybdenum spraying treatment.

[0003] A piston ring is incorporated into a ring groove of a piston reciprocally disposed in a cylinder liner of an engine so that an outer peripheral surface thereof is in sliding contact with an inner peripheral surface of the cylinder liner. It functions to control the thickness of the lubricating oil film formed on the cylinder surface, and to cool the piston by transmitting combustion heat from the piston to the cylinder liner. Therefore, a high degree of wear resistance, seizure resistance, heat resistance, oil retention, and suppression of wear on the cylinder side are required as piston ring characteristics. The surface treatment described above is performed to meet these requirements.

[0004] Regarding the coating of the piston ring, Japanese Patent Publication No. 1-52471 and Japanese Patent Application Laid-Open No. 62-120471 disclose a PVD (Physical Vapor Deposition) method.
It discloses that a film such as a metal nitride or a metal carbide is formed on a sliding surface. The metal nitride and metal carbide films exhibit excellent wear resistance and seizure resistance. Titanium nitride, chromium nitride, and the like have attracted attention because of their good compatibility with engines.

However, at present, the conditions of use of the sliding member have become more severe, and even with the use of titanium nitride or chromium nitride, a situation has arisen in which the sliding characteristics cannot be said to be sufficient.
In particular, when the vibration motion in the normal direction of the sliding surface in addition to the sliding motion is synergistic, and the contact surface between the sliding member and the counterpart material is separated and the contact occurs again, or when the striking motion occurs, Under severe operating conditions, such as when the load in the line direction fluctuates, chipping occurs in hard coatings such as chromium nitride coatings by ion plating, which can shorten the life of sliding materials. is there. Further, similar chipping of the hard film is observed even under severe lubricating conditions such as when the operating temperature is high or the lubricating oil film is hardly formed on the sliding portion due to a large contact load. Therefore, a sliding material coated with a ceramic coating film having better peel resistance than the current surface treatment film is desired.

[0006] Further, the ion plating film coated on the piston ring has a problem that chipped peeling which is considered to be caused by pitting fatigue occurs on the outer peripheral film surface of the piston ring.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above points, and does not cause chipped peeling even under severe use conditions and at the same time has sufficient seizure resistance and abrasion resistance. It is an object of the present invention to provide a sliding material and a piston ring coated with an object film.

The present inventors have studied the relationship between the fracture surface structure of a conventional CrN-based film and the chipping-off property of the film. As a result, the conventional fracture surface structure is smooth,
It has been found that the smooth texture is not excellent in the above properties. Furthermore, since it was considered primarily to form a conventional film containing CrN as a main component at a true density, the porosity was almost zero. Such a film has excellent hardness and seizure resistance,
It was found that it was weak against chipped peeling.

[0009]

Means for Solving the Problems and Actions In view of the above problems, as a result of earnest studies, the present inventors have brought a gas phase in which chromium and nitrogen are mixed into contact with a substrate by a PVD method, and When a chromium nitride-based coating containing CrN as a main component is formed on a substrate, the crystal of the fracture surface of the film can be columnar from the substrate surface to the surface of the film, and the columnar layer and the fracture surface are columnar. Instead, conventional layers having a smooth morphology are alternately laminated, or a layer having a porosity limited to 1.5 to 20% by volume and a conventional layer having almost true density are alternately laminated. By doing so, the present inventors have found that a sliding material and a piston ring which are excellent in wear resistance and seizure resistance and in which chipped peeling is less likely to be obtained can be obtained, and have completed the present invention.

That is, the sliding material of the present invention is a sliding material in which a chromium nitride-based coating containing at least CrN is coated on a substrate, wherein the chromium nitride-based coating has a crystal having a fracture surface of the coating. A first sliding material comprising a columnar layer extending from the surface of the substrate toward the surface of the film and a crystal having a fracture surface of the film, wherein a smooth layer is alternately laminated and coated on the substrate; A chromium nitride-based coating containing a base material, wherein the coating has a porosity of 0 to 0.5% by volume or less, and a porosity of 1.5% or less. The present invention relates to a second sliding material, wherein a 20% by volume layer is alternately laminated on a base material and coated.

[0011] Similarly, the present invention comprises alternately laminating at least on the outer peripheral sliding surface a chromium nitride layer having a crystal form having a columnar fracture surface and a chromium nitride layer having a smooth fracture structure instead of a columnar form. A first piston ring, which is formed by forming a film having a total thickness of 1 to 80 µm;
And a chromium nitride layer having a porosity of 1.5 to 20% by volume and a chromium nitride film having a porosity of approximately 0.5% by volume or less and having a substantially true density are alternately laminated to form a total thickness of 1 to 80 μm. The present invention relates to a second piston ring formed by forming a film of (1).

Hereinafter, the structure of the sliding material according to the present invention will be described first. The substrate to be coated with the film is appropriately selected from iron-based materials, aluminum-based materials, titanium-based materials, and the like according to the application. The PVD method described in detail below is based on the CVD (Chemic
Although it is similar to low-temperature treatment as compared with the alVapor deposition method or the like, heat input due to the vapor deposition phenomenon is inevitable. Therefore, it is preferable to use a heat-resistant iron-based material or titanium material as a base material if possible.

The chromium nitride coating in the first sliding material according to the present invention contains at least CrN as a main component, and further contains chromium nitride constituent compounds such as Cr ₂ N, solid solution Cr and N, and atoms. There is. Elements that may be mixed from the PVD atmosphere, such as oxygen, carbon, and hydrogen, may be included in the nitrogen chromium-based coating as long as the CrN crystal structure is maintained. The chromium nitride-based coating has a form in which a layer having a columnar structure in which the crystal of the fracture surface is directed from the surface of the base material to the surface of the substrate and a layer having a smooth shape in which the film fracture surface is not columnar are alternately laminated. Here, the crystal form is identified by an image obtained by observing the fracture surface of the sliding material film with an optical microscope or an electron microscope having a magnification of about 400 to 10,000 times. Further, “smooth” means that no anisotropy in film growth such as columnar shape is observed, and does not exclude that a granular structure is observed at a higher magnification. To prevent the fracture from affecting the crystal morphology of the film, the notch, groove, notch, etc. should be formed on the substrate side, and the film should be destroyed by expanding or reducing the groove, etc. from the substrate side. . The columnar fracture surface crystal morphology which is a feature of the present invention hardly generates chipped separation which is considered to be caused by pitting, and the smooth fracture surface crystal morphology has excellent seizure resistance. By laminating layers having contrasting properties in this manner, the present material is less likely to cause chipped peeling and has excellent scuff resistance.

The reason is considered as follows. The columnar fracture surface crystal can withstand chipping and peeling. However, when scuff wear occurs, it is greatly worn, and the underlying smooth fracture surface crystal layer is exposed to withstand scuffing seizure. Conversely, when the smooth fracture surface crystal layer is chipped by pitting, the columnar fracture surface crystal layer exposed at the chipped portion prevents further progress of chipped separation. At a certain sliding point, one of scuff wear and pitching wear is predominant, and this condition may be maintained for a long period of time. From one to the other. According to the present invention, excellent sliding characteristics can be obtained by compensating for the defect of one of the layers by the other layer. In addition, scuff wear is dominant in the sliding conditions, and when the layer exposed on the surface of the sliding material is a crystal layer having a smooth fracture surface, it goes without saying that this layer stably withstands wear.

When the chromium nitride-based film has a high density, the film has excellent scuffing resistance and abrasion resistance, but the film becomes brittle and chipped peeling is likely to occur. The theoretical density of CrN is 6.14 g / cm ³ , but in order to maintain particularly excellent scuff resistance and wear resistance, the porosity should be 0 to 0.1%.
It is necessary to be 5% by volume. On the other hand, in order to prevent chipping peeling, it is necessary to reduce the denseness of the film and to increase the porosity to 1.5% by volume (hereinafter simply referred to as “%”) or more. At this time, if the porosity of the film is too high, the hardness decreases and the wear resistance deteriorates. Therefore, it is necessary to set the upper limit of the coating porosity to 20%. The coating applied to the second sliding material according to the present invention has a porosity of 0.1.
5% by volume or less film and porosity of 1.5% by volume to 20%
When such layers having different porosity are formed by alternately laminating the coatings of volume%, chipping-like separation hardly occurs and scuff resistance is excellent. The reason is considered as follows.

When the sliding condition changes from the condition (a) in which scuffing and abrasion dominates to the condition (b) in which chipping is dominant, or vice versa, the low porosity layer has a condition (a). In (2), the abrasion is small, but when the condition (a) changes to (b), the abrasion occurs due to chipping and the underlying high porosity layer is exposed, so that chipping does not further progress. Conversely, the low porosity layer easily peels off under the condition (b), and the condition (b)
The high porosity layer, which is highly resistant, is exposed, and the progress of peeling is prevented. As described above, a part or all of the layer which is weak to either the condition (a) or (b) is easily worn by the mating material, and the lower layer which is strong under the condition is exposed and comes into sliding contact with the mating material.

The thickness of one layer of the first and second sliding materials of the present invention is preferably 0.1 to 10.0 μm, and more preferably 0.5 to 5.0 μm.
If the thickness per layer is 0.1 μm or less, the characteristics characteristic of each layer, for example, the scuff resistance of a layer having a smooth fractured surface, are not sufficiently exhibited, and the number of laminated layers increases, making it difficult to form this material. become. On the other hand, when the thickness per layer exceeds 10 μm, the number of laminations is small and only the effect of the outermost layer of the present material can be exerted, and the effect of compensating for each other's weakness by lamination cannot be expected.

The lamination ratio of the two types of coatings in the first and second sliding materials of the present invention, ie, a layer whose fracture surface is not columnar but smooth or a layer whose porosity is 0.5% or less Ratio of the total thickness (A) of the layer having a columnar fracture surface or the layer having a porosity of 1.5 to 20% to the total (B)
/ B) is preferably from 0.2 to 10. The lamination ratio is 0.2
Below, the laminating effect is small and chipping-like peeling of the film is likely to occur. When the lamination ratio is 10 or more, the denseness of the film is low and the scuff resistance and the wear resistance are poor.

The film hardness of the first and second sliding materials of the present invention is affected by the porosity, crystal form, lamination ratio and the like of each film. Generally, the hardness of a CrN film having a porosity of zero and a true density is HmV 1500-200.
On the other hand, the hardness of the coating in the sliding material of the present invention is about 600 to 15 in HmV as measured from the surface.
It is about 00.

The total thickness of the coating in the first and second sliding materials of the present invention is preferably 1 to 80 μm.
Particularly preferably, it is 20 to 60 μm. The film thickness is 1
If it is less than μm, the life of the film is short due to abrasion,
When the thickness of the entire coating exceeds 80 μm, the coating peels off or cracks occur in the coating, and the adhesion to the substrate is reduced. It is not economically preferable to make the film thicker than necessary.

In the film of the present invention, a gas phase in which chromium and nitrogen are mixed is brought into contact with a substrate by a PVD method.
The PVD method is a kind of technology for forming a film, and can be basically classified into three methods of vapor deposition, sputtering, and ion plating. Particularly, in the present invention, a reactive ion plating method in which a chromium nitride film is deposited on a substrate by reacting a chromium vapor substance with nitrogen is most preferable.

The chromium vapor is obtained by irradiating chromium with a high energy beam such as an HCD gun or an electron beam and evaporating it. Alternatively, chromium vapor may be obtained by ejecting chromium particles from the cathode, as in a cathodic arc plasma ion plating method and a sputtering method. When plasma is generated in a gas phase in which nitrogen is mixed with the chromium vapor, chromium is ionized and combined with nitrogen ions to generate chromium nitride. As a result, a chromium nitride film is formed on the substrate surface.

Hereinafter, the ion plating method will be described as an example, but the present invention is not limited to this. First, wash the substrate, remove dirt attached to the surface,
It is sufficiently cleaned and charged into a vacuum chamber of an ion plating apparatus. The pressure in the chamber is 1.3 × 10
^{After evacuating to -3 to} 5 × 10 ^-3 Pa,
The gas contained in the substrate is released by heating with a heater built in the ion plating apparatus. The heating temperature is preferably from 300 to 500C. Then 100 ~
Cool to 400 ° C.

When the pressure in the chamber becomes 4 × 10 ⁻³ Pa or less, chromium as a target is used as a cathode, and an arc discharge is generated on the surface to cause chromium ions to fly out. At this time, a bias voltage is applied to the base material,
A method of colliding metal ions ejected from the cathode with high energy on the substrate surface, that is, so-called bombard cleaning, performs oxide removal and activation treatment of the substrate surface. It is preferable that the bias voltage at that time be -700 to -900V.

Thereafter, the bias voltage is lowered, and nitrogen gas is introduced into the chamber while depositing chromium ions on the surface of the base material, and is passed through the plasma to ionize nitrogen. At this time, the nitrogen partial pressure was set to 1.3 × 10 ^{−1 to} 13.3 P
At about a, a bias voltage of 0 to -100 V is applied to form an ion plating film on the substrate surface. After the film is formed, the sliding material is cooled down to 200 ° C. or lower in a vacuum chamber, and then the sliding material is taken out of the chamber.

The porosity and the crystal morphology of the fracture surface of the film, which are characteristic of the present invention, can be controlled by adjusting the atmospheric pressure or the bias voltage during the coating. By repeating the process, a columnar layer or a layer having a predetermined porosity in which the fracture surface of the film has a columnar shape, and a layer having a fractured surface that is not columnar but smooth or a low porosity layer close to the true density are alternately formed. The laminated chromium nitride coating can be formed on the sliding surface of the sliding material.

If ion plating is performed before the introduction of nitrogen gas during the process of the present invention described above, an underlayer of chromium metal is formed on the substrate. This underlayer of chromium metal
Since the coefficient of thermal expansion is close to that of the substrate and is not easily affected by thermal stress, the adhesiveness is good and the flexibility is high. The chromium metal base layer is preferably formed to a thickness of 0.1 to 2 μm. 0.
If the thickness is less than 1 μm, the effect of improving the adhesion is weak, and 0.1 to 2 μm.
A sufficient effect is shown with a thickness of m. Further, if it exceeds 2 μm, no further effect can be obtained, and it is not economically preferable. Forming an underlayer with high adhesion and flexibility between the film and the substrate in this manner is effective in preventing the film from peeling.

Following the description of the sliding material, the piston ring will be described. Since the configuration of the piston ring of the present invention is almost the same as the above description regarding the sliding material, only the features unique to the piston ring will be described to avoid redundant description.

FIG. 1 shows a piston ring 1 according to the present invention.
FIG. 2 is a cross-sectional view showing a formed film 2A. The surface on which the film is formed is essentially the outer peripheral sliding surface 2 of the piston ring, but may be formed on any other portion, such as the inner peripheral surface 3 or the upper and lower surfaces 4. FIG. 2 is a sectional view showing a part of a state in which a piston 5 equipped with the piston ring 1 according to the present invention is incorporated in a cylinder liner 6. The piston ring body may be of any type known in the art, the material of which is 13Cr and 17Cr stainless steel,
Iron-based materials such as spring steel, tool steel, cast iron, and the like, and those obtained by subjecting these materials to nitriding treatment or chromium plating can be used. The total thickness of the piston ring coating is 1 μm considering the possibility of the surface disappearing due to wear during initial run-in.
As described above, it is necessary to leave the film after the initial adaptation.
On the other hand, if the film thickness is unnecessarily large, it is not economically preferable. If the film thickness exceeds 60 μm, the film is easily cracked and the adhesive strength is reduced. However, in the case of an application that particularly requires wear resistance and durability, it is possible to form a film up to 80 μm.

[0030]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples. (Example 1) In this example, a base material made of SUS440 was subjected to PVD treatment using a cathodic arc plasma type ion plating apparatus, and the basic physical properties of the film were examined.
First, the base material was washed with a hydrocarbon-based solvent, and charged in a vacuum chamber of an ion plating apparatus. After evacuation was performed until the pressure in the chamber reached 1.3 × 10 ⁻³ Pa, the gas contained in the base material was released by heating at 300 to 500 ° C. by a heater built in the ion plating apparatus, Then, it cooled to 200 degreeC.

When the pressure in the chamber becomes 4 × 10 ⁻³ Pa or less, a bias voltage of −800 V is applied to the substrate to generate an arc discharge to cause chromium ions to fly out of the chromium source. Then, a partial pressure of nitrogen gas introduced into the chamber was set to 1.3 × 10 ^{−1 to} 6.7 Pa and an applied bias voltage was set to −100 V to form an ion plating film (smooth layer) having a thickness of 5 μm on the substrate surface. . After that, the coating conditions were changed to a nitrogen gas partial pressure of 6.7 to 13.3P.
a, The bias voltage was changed to −30 V to form a 5 μm thick film (columnar layer). These two conditions were alternately repeated 5 times each to coat a film of a total of 50 μm. After the film was formed, the material was cooled in a vacuum chamber to 200 ° C. or lower to obtain a sliding material.

The morphology, composition, and surface microhardness of the obtained coating were examined. FIG. 3 (magnification: 1000) shows the result of observing a secondary electron image of the fracture surface of the film by using a scanning electron microscope. As shown in this figure, it was confirmed that a crystal layer exhibiting a columnar shape from the base material toward the film surface and a crystal layer exhibiting a smooth fracture surface instead of the columnar shape were alternately laminated. Also, X
As a result of analyzing the composition by line diffraction, it was also confirmed that the composition was a single phase of CrN. The surface hardness was HmV ₍₁₀₀₎ 1024.

Examples 2 and 3, Comparative Example 1 In this example, the seizure resistance of the material of the present invention was evaluated. Vertical 5
mm × 5 mm × height 5 mm pin-shaped projections 20 (FIG. 4,
SKD61 in which three are arranged at equal intervals on a concentric circle
Using the material as a test piece 15, a film according to the present invention was formed to a thickness of about 50 μm on a square end face of 5 mm square, and a seizure resistance test was performed on the obtained test piece using an ultra-high pressure wear tester. The film of the test piece according to Example 2 was formed by the method described in Example 1, and a columnar layer in which the crystal of the fracture surface was directed from the substrate surface to the film surface, and a smooth layer in which the fracture surface was not columnar, respectively. Total thickness 50μ alternately laminated by 5μm
m of CrN single phase coating.

The coating of Example 3 has a layer (a) having a porosity of 0.1% and a thickness of 5 μm, and a layer (a) having a porosity of 3% and a thickness of 3 μm.
(B) were alternately laminated in a total of 48 μm in total of 6 layers (Example 3). Each layer (a),
The conditions for forming (b) were as follows. Layer (a): nitrogen gas partial pressure-6.7 Pa, bias voltage-
-100V layer (b): nitrogen gas partial pressure -26.6Pa, bias voltage --50V The surface microhardness of the film was HmV102 of the film of Example 2.
4. The film of Example 3 had HmV1256.

As a comparative example, a similar test was performed using a chromium plating film having a thickness of 100 μm (Comparative Example 1) on a 5 mm square end face of a test piece.

The equipment and test conditions of the ultrahigh pressure wear tester used in this test are as follows. The test apparatus is schematically shown in FIG. 4 and FIG. 5 which is a cross-sectional view taken along the line AA in FIG. 4, and has a diameter of 80 mm × a thickness of 10 mm detachably attached to the stator holder 11. In the center of the polished disk 12 (counterpart material)
The lubricating oil is supplied through. A pressing force P is applied to the stator holder 11 at a predetermined pressure toward the right in the figure by a hydraulic device (not shown). Disk 12
The rotor 14 is opposed to the rotor 14 and is rotated at a predetermined speed by a driving device (not shown). Rotor 14
, A test piece 15 is slidably attached to the disk 12 with a 5 mm square square end face on which a surface treatment layer is formed as a sliding surface.

In such an apparatus, a predetermined pressing force P is applied to the stator holder 11 so that the disk 12 and the pin-shaped projection 20 of the test piece 15 come into contact with each other at a predetermined surface pressure. Then, the rotor 14 is rotated while oil is supplied to the sliding surface at a predetermined oil supply speed. The pressure acting on the stator holder 11 is increased stepwise at regular intervals, and the torque T generated on the stator holder 11 by the friction between the test piece 15 and the counterpart disk 12 due to the rotation of the rotor 14 is transmitted through the stainless steel fiber 16. The change is read by a dynamic strainmeter 18 and recorded on a recorder 19. Assuming that the seizure occurred when the torque T sharply increased, the quality of the seizure resistance is judged based on the contact surface pressure at this time. The test conditions are as follows.

Friction speed: 8 m / sec Contact surface pressure: After leveling at 20 kgf / cm ² , the pressure was increased by 10 kgf / cm ² until seizure occurred. Hold at each contact pressure for 3 minutes. Lubricating oil: motor oil # 30 Oil temperature 80 ° C, supply amount 250 cc / min Table 1 shows the test results.

[0039]

[Table 1]

The product of the present invention has a contact surface pressure of 28
Seizure occurred at 5 and 290 kgf / cm ² . The chrome plating baking surface pressure of the comparative product is 253 kgf / cm ² or more, and the baking resistance is excellent.

Example 4 and Comparative Example 2 In this example, a corrosion wear test of the material of the present invention was carried out using a Kaken abrasion tester. Using a SKD-61 material having a shape of 5 mm in length x 5 mm in width x 20 mm in length and one end in the longitudinal direction having a curved surface of R6 mm as a test piece, by the method described in Example 1, the tip curved surface of the test piece A film in which a columnar layer in which the crystal of the fracture surface is directed from the substrate surface to the film surface and a smooth layer in which the crystal of the fracture surface is not columnar are alternately laminated so as to have a thickness of 5 μm, respectively, and which is a CrN single phase film ( Example 4) was coated with a thickness of 50 μm. The surface microhardness of the film was HmV1024.

As a comparative example, a thickness of 100
A similar test was performed using a chromium-plated test piece of μm (Comparative Example 2).

In the test, the tip R of the surface-treated test piece was
A curved surface is line-contacted with the outer peripheral portion of the mating material whose part is processed into a drum shape, a predetermined load is applied, the shaft is rotated at a predetermined speed, and a sulfuric acid aqueous solution adjusted to pH = 2 is applied to the contact part by a fixed amount. The test was performed under lubricating conditions in an acid atmosphere.

The test conditions are as follows. Sliding partner material: FC250 material Friction speed: 0.25 m / sec Friction time: 6 hours Contact load: 4 kgf Atmosphere: 1.5 cc / min of sulfuric acid aqueous solution adjusted to pH = 2.0 is dropped on the sliding part Are shown in Table 2. The results are shown as relative values with the friction amount of the chromium plating film as 100.

[0045]

[Table 2]

In comparison with the chrome-plated product, which is a comparative product, the product of the present invention has a significantly reduced wear amount of about 1/25.

Examples 5, 6, and 7 and Comparative Examples 3 and 4 In this example, the peeling resistance of the material coated with the present invention was evaluated using a rolling fatigue tester with roller (roller pitting tester). . The base material of the test piece is carburized SCM material 420 and the shape is φ26mm × 28m
m, and the film of the present invention was applied on the outer peripheral surface thereof to a thickness of about 50 μm. The film of the test piece was formed by the method described in Example 1, and alternately formed a columnar layer in which the crystals of the fracture surface were directed from the substrate surface to the surface of the film, and a layer having a smooth thickness of 5 μm in which the fracture surface crystals were not columnar. Total thickness of 50μm
And a film having a single phase of CrN (Example 5), a film having a porosity of 0.1% and a thickness of 5 μm, and a film having a porosity of 3% and a thickness of 3 μm alternately. 48μ each for 6 layers
m (Example 6). The surface microhardness of the film was HmV1024 in Example 5 and Example 6 was HmV1024.
Was HmV1256.

A columnar layer formed on the outer periphery of the test piece body of the same material as in Examples 5 and 6 by the method described in Example 1 and having a crystal having a fractured surface of 0.5 μm from the substrate surface to the film surface was formed.
m, a film having a total thickness of 55 μm and a single layer of CrN in which a total of 20 layers are alternately stacked in a layer of 5 μm in which the crystal of the fracture surface is not columnar and which is smooth (Comparative Example 3—Comparative Example of Claim 4) ) And a CrN film having a smooth fracture surface and a very low porosity of about 0.2% was coated at 42 μm (Comparative Example 4), and the peel resistance was measured in the same manner as in Examples 5 and 6. did.

The apparatus and test conditions of the pitching tester used in this test are as follows. FIG. 6 schematically shows a main part of the test apparatus. The test apparatus has a load roller 22 opposed to a test roller 21 to which a test piece 23 of φ26 mm × 28 mm is attached, so that a predetermined pressure is applied. It is. The test roller 21 is rotated at a predetermined speed by a driving device (not shown).
On the outer periphery of No. 3, a surface treatment layer is formed. Load roller 22
Has a size of φ130 × 18mm and the outer circumference is R300m
It has a shape of m and makes microscopic point contact with the test piece 23 so that a large pressing force can be applied. The load roller 22 follows the test roller 21 via a gear (not shown), and rotates while sliding relatively. Slip rate specimens peripheral velocity (U ₂₃₎ and the load roller circumferential speed by (U _22), represented by _{(U 23 -U 22) / U} 23, can be arbitrarily selected. Lubricating oil is poured into a contact portion between the test piece 21 and the load roller 22 through a lubrication port (not shown). In such an apparatus, a predetermined pressing force is applied to the test piece 23, the test piece 23 and the load roller 22 are brought into contact with each other at a predetermined surface pressure, and the test is performed while lubricating the contact portion at a predetermined lubrication rate. The roller is rotated at a predetermined speed, and the load roller 22 is rotated at a predetermined slip ratio. During the test, the surface of the test piece is carefully observed regularly, and the quality of the peeling resistance is determined by the total number of rotations until the chipped peeling occurs on the surface of the test piece. The material of the load roller as the mating material was FC250. The test conditions are as follows.

Surface pressure (Hertz stress): 160 kgf / mm ² Test piece peripheral speed: 82 m / s Slip ratio: 20% Oil used: # 30 (base oil) Oil flow rate: 1200 cc / min Oil temperature: 80 ° C. Tested in Table 3 The results are shown.

[0051]

[Table 3] Peeling resistance test results Cumulative number of rotations until peeling occurred Example 5 No peeling occurred even at 2 × 10 ⁷ times or more Example 6 Peeling occurred at 1.8 × 10 ⁷ times Comparative Example 3 3.7 × 10 ⁶ times delamination in delamination Comparative example 4 3.0 × 10 ⁶ times

The product of the present invention is much superior to the comparative example in peel resistance. However, when the lamination ratio (thickness meter of columnar layer / thickness meter of smooth layer) is as small as 0.1 as in Comparative Example 3, peeling is likely to occur.

Examples 7, 8, 9 and Comparative Example 5 In the same manner as in Example 1, the outer peripheral surface of the piston ring had a thickness of 50 μm, and the crystals of the fracture surface of the coating proceeded from the base material surface toward the coating surface. A layer having columnar morphology and a layer having a smooth crystal of the fracture surface of the film were alternately formed by 5 μm each for a total of 10 μm.
The porosity of the coating having a composition of CrN (Example 7, lamination ratio: 1.0) and the outer periphery of the piston ring are 0.
1%, 5 μm thick layer and 3% porosity, 3 μm thick
Were alternately laminated in a total of 48 μm, 6 layers each,
A coating having a composition of a mixture of CrN and Cr ₂ N (Example 8, lamination ratio 0.6) was coated. Further, a coating having an underlayer made of chromium with a thickness of 1 μm was coated between the coating of Example 8 and the piston ring base material (Example 9, lamination ratio 1.0). The film adhesion of the obtained piston ring was measured. The measurement of the adhesion is called a twist test, in which one of the abutting portions of the piston ring is fixed and the other is twisted to measure a torsion angle until peeling of the film occurs.

As Comparative Example 5, a piston ring in which a piston ring body of the same material and dimensions as in Example 7 was coated with a single-phase chromium nitride film of 42 μm consisting of a smooth layer in which the crystal of the film cross section did not have a columnar shape. For Example 7,
The film adhesion was measured in the same manner as in Examples 8 and 9. Examples 7, 8,
Table 4 shows the measurement results of Comparative Example 9 and Comparative Example 5. The measured values are shown in Table 4 as an angle ratio with the torsion angle of Comparative Example 5 set to 1. Table 4 further shows the surface microhardness of the coating.

[0055]

Table 4 Results of adhesion test Specific hardness at torsion angle at which peeling occurred HmV Example 7 1.28 1024 Example 8 1.23 1256 Example 9 1.31 1022 Comparative Example 5 1 1680

As is clear from Table 4, the coating of the present invention has a larger torsion angle until peeling occurs and is excellent in adhesion as compared with the comparative example.

Examples 10 and 11, Comparative Examples 6 and 7 In the same manner as in Example 1, the outer peripheral surface of the piston ring had a thickness of 50 μm, and the crystals of the fracture surface of the film were columnar toward the film surface from the base material surface. CrN has a composition in which a total of 10 layers, each of which has a layer and a fractured surface that is not columnar and has a smoothness of 5 μm each, are alternately laminated.
And a layer having a porosity of 0.1% and a thickness of 5 μm and a layer of a porosity of 3% and a thickness of 3 μm on the outer peripheral surface of the piston ring. Are alternately 6
Film (Example 11, lamination ratio 0.6) having a composition in which the layers by total 48μm laminated is made of a mixture of CrN and Cr ₂ N were coated. In addition, on the outer peripheral sliding surface of the piston ring, first, a crystal having a fractured surface of the coating forms a layer having a smooth thickness of 0.8 μm instead of a columnar shape. A layer having a morphology and a thickness of 12 μm is formed, and a crystal having a fractured surface forms a smooth layer of 0.8 μm, and then a crystal having a fractured surface forms a columnar layer of 12 μm. Thus, the thickness is 51.2 μm and the composition is C
Piston ring coated with a laminated film of rN (Comparative Example 6
-Comparative Example of Claim 4-Lamination ratio 15.0).

The obtained piston ring was assembled into a top ring of a 4-cylinder 4-cycle diesel engine (equipped with a supercharger with an intercooler), and a bench test was performed. The test conditions were as follows. Rotational speed: 4,000 rpm Test time: 100 hours Oil temperature: 120 ° C. Water temperature: 40 ° C. Measurement of the amount of wear on the outer peripheral sliding surface in the actual machine test was performed three times. Table 5 shows the results.

As a comparative example, an actual machine test was performed in the same manner as in Examples 5 and 6 for a piston ring whose outer peripheral sliding surface was plated with chromium to a thickness of 100 μm (Comparative Example 7).

[0060]

[Table 5]

As is apparent from Table 5, the piston ring coated with the coating according to the present invention has a wear amount of about 1/4 to 1 / l as compared with the chromium-plated piston ring (Comparative Example 7).
5, which is a significant decrease. However, in the case of a CrN film having a lamination ratio equal to or more than a preferable value (Comparative Example 6), the wear amount is increased. In diesel engines, the combustion of fuel causes sulfur in the fuel to penetrate into the engine oil, increasing oil oxidation and exposing the piston ring to an atmosphere that promotes not only frictional wear but also corrosive wear.
The piston ring coated with the coating according to the present invention is expected to have excellent friction wear resistance and corrosion wear resistance under such conditions.

Examples 13, 14, 15, 16 and Comparative Example 8 In the same manner as in Example 1, the outer peripheral surface of the piston ring had a thickness of 50 μm, and proceeded from the surface of the crystal base material having the fracture surface to the surface of the film. A film in which the composition is CrN in which a total of 10 columnar layers and a smooth layer in which the crystal of the fracture surface of the film is not columnar, each having a thickness of 5 μm are alternately laminated (Example 13, lamination ratio 1.0), and a porosity on the outer peripheral surface of the piston ring. Is 0.1% and thickness is 5μm
Of CrN and Cr in which a total of 48 μm of a total of 48 μm layers and 3% porosity and 3 μm thick coatings were alternately laminated.
₂ N was mixed film (Example 14, lamination ratio 0.6), further porosity 0.2%, and the film fracture surface crystals are holes and a layer of 0.6μm thickness is smooth of A coating having a thickness of 4.5 μm in which the crystal of the coating fracture surface is columnar at a rate of 15% (Example 15, lamination ratio 7.5), and a porosity of 0.2% at the outer peripheral surface of the piston ring. A film having a composition of CrN, in which nine layers each having a thickness of 5 μm and nine layers each having a porosity of 10% and a thickness of 0.5 μm are alternately laminated to a total of 49.5 μm (Example 16, lamination ratio of 0. 1) was coated. The obtained piston ring was assembled into a top ring of a 4-cylinder 4-cycle diesel engine (equipped with a supercharger with an intercooler), and a bench-based actual machine test was performed. The test conditions were as follows.

Rotation speed: 4,000 rpm Test time: 300 hours Oil temperature: 120 ° C. Water temperature: 100 ° C.

The state of chipped peeling on the outer peripheral sliding surface of the piston ring in an actual machine test was observed. Table 6 shows the results.

As a comparative example, a film coated with a 42 μm-coated CrN composition film in which the crystal in the cross section of the film is not columnar but having only a smooth shape (Comparative Example 8) was subjected to the actual machine test in the same manner as in Examples 13 to 16. Was done.

[0066]

[Table 6] Chipped separation occurrence situation First cylinder Second cylinder Third cylinder Fourth cylinder Example 13 None None None None Example 14 None None None None Example 15 None None None None Example 16 Occurrence None Comparison of occurrence Example 8 Occurrence Occurrence Occurrence Occurrence

As is clear from Table 6, the piston ring coated with the film according to Comparative Example 8 suffered film peeling in all cylinders. However, in Examples of the present invention, improvement was observed as compared with Comparative Example, and chipping resistance was observed. Excellent shape release.

[0068]

As is apparent from the above description,
The present invention relates to a chromium nitride-based coating containing CrN as a main component formed on the surface of a substrate, wherein a layer or porosity of the columnar morphology in which the fracture surface crystal of the coating is from the substrate surface to the coating surface is 1%. By alternately laminating a layer limited to 0.5 to 20% on a layer having a fractured surface having a smooth shape instead of a columnar shape or a layer having a true density, the layer has a higher resistance than conventional hard coatings. An object of the present invention is to provide a sliding material which is excellent in abrasion resistance and seizure resistance and in which chipped peeling is less likely to occur. The material of the present invention is suitable for sliding parts such as engine parts such as piston rings and cam followers, and compressor parts such as shoe disks, and cutting tools.

Similarly, a piston ring having a chromium nitride film alternately laminated as described above has a coating adhesion, abrasion resistance, and abrasion resistance which are lower than those of a conventionally used piston ring. It is excellent in corrosion wear resistance and peel resistance, and can prolong the life of the piston ring.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a piston ring.

FIG. 2 is a sectional view showing a state in which a piston ring is mounted on a piston.

FIG. 3 is a photograph taken by an electron microscope of a metal structure of a film fracture surface of the sliding material according to the first embodiment of the present invention.

FIG. 4 is an explanatory view showing a part of an ultra-high pressure friction tester.

FIG. 5 is a sectional view taken along the line AA of FIG. 1;

FIG. 6 is a schematic sectional view of a rolling fatigue tester.

[Explanation of symbols]

 1: piston ring body 2: outer peripheral sliding surface 2A: coating 3: inner peripheral surface 4: upper and lower surfaces 5: piston ring 6: cylinder liner 11: stator holder 12: disk (partial material) 13: lubrication port 14: rotor 15 : Test piece 16: Stainless steel fiber 17: Load cell 18: Dynamic strain meter 19: Recorder 20: Special pin shape of test piece (5 mm square) 21: Test roller 22: Load roller 23: Test piece

Claims (8)

(57) [Claims] 1. A sliding material comprising a base material coated with a chromium nitride-based coating containing at least CrN. A sliding material comprising a columnar layer directed in a direction and a crystal having a fracture surface of a film, wherein a smooth layer is alternately laminated on a substrate to cover the layer. 2. A sliding material comprising a base material coated with a chromium nitride-based coating containing at least CrN, wherein the coating comprises: a layer having a porosity of 0 to 0.5% by volume; The rate is 1.
A sliding material, wherein 5% to 20% by volume of layers are alternately laminated and coated on a substrate. 3. The sliding material according to claim 1, wherein a ratio (A / B) of the total thickness (A) of the columnar layers to the total thickness (B) of the smooth layers is 0.2 to 10. A sliding material, characterized in that: 4. The sliding material according to claim 2, wherein the porosity is 0 to 0.5% by volume relative to the total thickness (B) of the layer having the porosity of 1.5 to 20% by volume. A sliding material, wherein the ratio (A / B) of the total (A) of the thicknesses of the layers is 0.2 to 10. 5. The sliding material according to claim 1, wherein each layer has a thickness of 0.1 to 10.0 μm. 6. The sliding material according to claim 1, wherein the microhardness of the coating is HmV600 to 1500 measured from the surface. . 7. The sliding material according to claim 1, wherein an underlayer made of chromium is interposed between the film and the base material. 8. The method according to claim 1, wherein at least the outer peripheral sliding surface is provided.
A piston ring, wherein the film according to any one of the above is formed to a thickness of 1 to 80 μm.