WO2015186790A1

WO2015186790A1 - Piston ring

Info

Publication number: WO2015186790A1
Application number: PCT/JP2015/066201
Authority: WO
Inventors: 雅之佐藤; 祐一村山; 琢磨関矢
Original assignee: 株式会社リケン
Priority date: 2014-06-06
Filing date: 2015-06-04
Publication date: 2015-12-10
Also published as: JP5980841B2; JP2015230086A

Abstract

The objective of the present invention is to provide a laminated hard-film-coated piston ring which can be used in an environment in which an engine is subjected to high mechanical and thermal loads, and which has superior scuffing resistance, abrasion resistance, and resistance to coating film separation. Therefore, a hard film is deposited on the outer circumferential surface of a piston ring, said hard film containing at least one layer which is a metal layer comprising at least one type of a metal (M) in a CrN/TiN laminated film formed by alternately laminating a CrN-type chromium nitride and a TiN-type titanium nitride. In this case, the metal (M) is selected such that the standard free energy of formation (ΔG_M-N) of the nitride of the metal (M) and the standard free energy of formation (ΔG_CrN) of the chromium nitride satisfy the relationship ΔG_M-N > ΔG_CrN.

Description

piston ring

The present invention relates to a piston ring for an automobile engine, and more particularly to a piston ring in which a laminated hard film excellent in scuffing resistance, abrasion resistance and film peeling resistance is coated with PVD (Physical Vapor Deposition).

In recent years, piston rings have increased in combustion temperature and surface pressure load due to higher engine output and compliance with exhaust gas regulations, the use of low-viscosity lubricants, diversification of fuels such as bioethanol, Due to high-pressure fuel injection and the like, the usage environment has become severe year by year. Even with a hard chromium nitride (CrN) coated piston ring with ion plating, which is said to have the best scuffing and wear resistance, there is a situation where sufficient performance cannot be achieved due to film peeling problems including cracks and chipping. It has come to be scattered. Accordingly, there is a strong demand for a piston ring that is superior in scuff resistance, wear resistance, and film peeling resistance.

Chromium nitride by the above ion plating generally has a problem that it is hard but easily chipped. Until now, crystal orientation, structure control, porosity (porosity) control, or addition of a third element, coating Various improvements have been made, such as stacking of layers.

Regarding the addition of the third element to chromium nitride, JP-A-62-265023 teaches to dissolve oxygen (O) and JP-A-6-300130 to dissolve carbon (C) in order to improve the toughness of CrN. ing. Furthermore, in WO 2008/059791, the chromium nitride film has a columnar shape toward the film surface, the carbon concentration is 4 to 8% by weight with respect to the total of the main components consisting of chromium, nitrogen and carbon, and the Vickers hardness is A CrCN film with excellent wear resistance of 1600 or more and fracture toughness of 3 MPa√m or more is disclosed.

Regarding the lamination of the film, for example, in Japanese Patent Laid-Open No. 8-312779, in order to solve the problem of chip-like peeling due to pitting fatigue on the surface of the outer peripheral film of the piston ring, A film in which a columnar layer and a smooth layer are alternately laminated in the direction from the surface to the film surface, or a layer having a porosity of 0 to 0.5% by volume and a layer having a porosity of 1.5 to 20% by volume are alternately laminated. A film is disclosed. Furthermore, in JP 2005-187859, from a similar viewpoint, for example, for a composite nitride film of CrSiN or TiSiN, a high bias voltage condition that allows columnar crystals and a low bias voltage condition that does not allow columnar crystals are set at regular intervals. By repeating alternately, a stress relaxation layer of the composite nitride having a structure that is not a columnar crystal having a constant thickness is sandwiched in a hard film of a columnar crystal composite nitride at regular intervals to reduce internal stress, and high A hard thick film having adhesion is disclosed.

JP-A-8-312779 and JP-A-2005-187859 both have different structures (columnar structure layer / non-columnar structure layer or porous structure layer / dense structure layer) within the same nitride range. JP-A-2005-82822 discloses a laminate film containing different compositions using a metal layer as a stress relaxation layer, as disclosed in JP-A-2005-187859.

Patent 5372760 was proposed for the purpose of providing a piston ring having a laminated film with excellent crack resistance, and by introducing a metal layer into the laminated film of two or more different types of nitrides, It is taught that since the progress is suppressed and the crack extends, it extends only to the nearest phase boundary, so that it is difficult to cause large peeling across the entire laminated film.

However, in the above patent 5372760, although the metal layer is intended to suppress the progress of cracks by introducing a metal layer into a laminate film of two or more different types of nitrides, the metal layer is Ti, Zr, Hf, Since it is selected from V, Nb, Ta, Cr, Mo and W, the metal layer tends to partially change due to diffusion of nitrogen (N) from the adjacent nitride, for example, adjacent to the CrN layer. When a metal Ti layer is introduced, Ti ₂ N and Cr ₂ N are formed, and these have a hard and brittle property and have a problem that cracks are likely to progress.

The present invention solves the above-described problems and provides a laminated hard film excellent in scuffing resistance, abrasion resistance, and film peeling resistance that can be used in an environment where the mechanical and thermal loads of the engine are high. The object is to provide a piston ring coated with PVD.

The present inventors have introduced a metal layer in addition to a CrN / TiN laminated hard film, particularly for a PVD laminated hard film excellent in scuffing resistance, abrasion resistance, and film peeling resistance coated on a piston ring. As a result of diligent research to improve peelability, pistons coated with a laminated hard film with excellent film peel resistance by introducing a metal layer that does not diffuse from CrN and TiN even when adjacent to CrN and TiN. I came up with the idea that it could be a ring.

That is, the piston ring of the present invention is a piston ring whose outer peripheral sliding surface is coated with a hard film, and the hard film includes a film in which CrN type chromium nitride and TiN type titanium nitride are alternately laminated, The laminated film has at least one metal layer composed of at least one kind of metal M, and the standard formation free energy ΔG _MN of the metal nitride and the standard formation free energy ΔG _{CrN of the} chromium nitride are ΔG _MN > It is characterized by satisfying the relationship of ΔG _CrN .

The metal M is preferably at least one selected from Co, Ni and Cu. The thickness of the metal layer is preferably 10 to 1000 nm.

The metal layer-containing CrN / TiN laminated hard film-coated piston ring having excellent scuff resistance, abrasion resistance and film peeling resistance of the present invention is, for example, a metal layer-containing laminated nitride film-coated piston ring disclosed in Patent 5372760. Unlike CrN, the standard free energy of formation ΔG _CrN is lower and more stable than the standard free energy of formation of metal M nitride, ΔG _MN (more stable because the standard free energy of formation of TiN ΔG _TiN is lower than ΔG _CrN ). Nitrogen diffusion to the layer does not occur (ΔG _TiN is lower than ΔG _CrN , so nitrogen diffusion from the TiN layer to the metal layer does not naturally occur), so maintain the original stress relaxation characteristics of the metal layer The film peel resistance can be further improved.

It is the figure which showed typically an example of the film | membrane cross section of the metal layer containing CrN / TiN lamination | stacking hard film coating | coated piston ring of this invention. It is the figure which showed typically another example of the film cross section of the metal layer containing CrN / TiN lamination | stacking hard film coating piston ring of this invention. It is the schematic of the PVD apparatus used by this invention. It is the schematic of a rolling sliding fatigue testing machine.

The piston ring of the present invention is a piston ring in which a hard film is coated on an outer peripheral sliding surface, and the hard film includes a laminated film in which CrN type chromium nitride and TiN type titanium nitride are alternately laminated. . Further, the piston ring of the present invention has at least one metal layer composed of at least one kind of metal M in the laminated film, and a standard free energy of formation ΔG _MN of the nitride of the metal M and a standard of the chromium nitride. The free energy of generation ΔG _CrN satisfies the relationship of ΔG _MN > ΔG _CrN .

The CrN / TiN multilayer coating is formed by arc ion plating (hereinafter also referred to as “AIP”), but in the present invention, a metal layer made of metal M during the manufacturing process of the CrN / TiN multilayer coating. A CrN / TiN laminated hard film containing a metal layer is formed by introducing the formation process of The metal layer composed of the metal M of the present invention has a standard formation free energy ΔG _{MN of} the nitride MN larger than the standard formation free energy ΔG _{CrN of CrN} , so even if the metal layer is formed adjacent to the CrN layer, the CrN layer Is thermodynamically stable and is formed as a metal layer made of metal M without diffusion of nitrogen from the CrN layer to the metal layer. Since the TiN layer is thermodynamically more stable than the CrN layer, naturally, even if the metal layer is adjacent to the TiN layer, nitrogen does not diffuse from the TiN layer to the metal layer.

It is preferable that ΔG _MN is at least one selected from Co, Ni and Cu as the metal M which is larger than ΔG _CrN . If Cu is selected as the metal M, a metal layer with extremely high thermal conductivity is more preferable.

FIG. 1 is a diagram schematically showing a cross section of a piston ring of the present invention, in which a CrN / TiN laminated film (2) is formed on a base material (1), and is composed of metal M therein. At least one metal layer (3) in FIG. 1 is formed. Metal layer (3) is CrN / TiN / M / CrN / TiN / M ..., CrN / TiN / CrN / M / TiN / CrN / TiN / M ..., CrN / TiN / CrN / TiN ... / M / Any arrangement of CrN / TiN... / M / CrN / TiN... May be used, and the thickness of the metal layer (3) is preferably 10 to 1000 nm. The thickness of the metal layer (3) is more preferably 25 to 500 nm, and further preferably 50 to 300 nm. The metal layer (3) emphasizes the function as a stress relaxation layer, and in order to reduce the residual stress (compressive stress) of the entire hard coating and suppress crack propagation, it is preferable to have a thickness exceeding 100 nm. In order to further improve the film peeling resistance by the metal layer by utilizing the scuff resistance and wear resistance of the CrN / TiN multilayer coating as the entire hard coating of the present invention (3-10 μm CrN / TiN multilayer coating) It is preferable to form a hard film in which / (a metal layer of 10 to 1000 nm) is repeated.

The CrN / TiN multilayer coating consisting of alternating CrN type chromium nitride and TiN type titanium nitride, which form the basis of the hard coating of the present invention, has a higher thermal conductivity than the CrN coating and a high piston ring thermal conductivity function A film that contributes to That is, not only the heat of the piston head is efficiently released to the cooled cylinder wall, but also the reduction of the generated thermal stress is suppressed, and the generation of cracks and chips is suppressed. Here, CrN type chromium nitride means that the main chromium nitride may be CrN type although it may contain Cr ₂ N type chromium nitride, and TiN type titanium nitride means Ti ₂ N type nitride. Although it may contain titanium, it means that the main titanium nitride is of the TiN type.

When cracks or chipping occur in the hard film coated on the piston ring by PVD, the crack is caused by the tensile stress on the outermost surface of the film generated by sliding or the shear stress inside the film, starting from defects on the surface or inside of the film. Propagates and breaks down in the form of chipping, dropping or peeling of the film. In addition, a laminated film in which different phases are laminated generally tends to cause cracks to propagate along the interface because strain remains at the interface. However, in the present invention, the CrN / TiN multilayer coating forms a strong interface with high consistency because the lattice constants of CrN and TiN are very close to 0.414 nm and 0.424 nm, respectively. Here, the unit thickness of the layer consisting of the sum of the thickness of each layer in the CrN / TiN multilayer coating, that is, the sum of the thickness of one CrN layer and the thickness of one TiN layer is 20 to 100 nm. It is preferable. From the viewpoint of crack resistance propagation, it is preferably 20 to 80 nm, and more preferably 20 to 60 nm. Furthermore, if the thicknesses of the CrN layer and the TiN layer correspond to the crystallite size of CrN and TiN, it can be regarded as a single crystal at least in the film thickness direction, and the rigidity is remarkably improved as compared with the polycrystal. It is considered as a polycrystal having a small tilt boundary in the direction parallel to the coating surface, and these configurations suppress the propagation of cracks both at the interface of the laminated film and within the layer. When paying attention to the crystallite size, the stack unit thickness composed of one CrN layer and one TiN layer is preferably 1 to 1.3 times the sum of the crystallite sizes of CrN and TiN.

In the present invention, the CrN / TiN laminated film having excellent crack propagation resistance described above has at least one metal layer made of metal M in order to further improve the crack propagation resistance. The CrN layer and the metal layer in which nitrogen is not diffused from the TiN layer have sufficient ductility, and even if the crack propagates through the CrN / TiN laminated film, the presence of the metal layer is the crack at the interface. Propagation is stopped, and it is possible to avoid chipping or falling off of the film.

When the thickness of the CrN layer and TiN layer approaches the crystallite size of CrN and TiN, respectively, as described above, the CrN layer and the TiN layer with few defects are formed, so that the Young's modulus and strength are improved. Furthermore, phonon scattering due to grain boundaries is reduced, and thermal conductivity is improved. Therefore, in the present invention, not only from the viewpoint of strength but also from the viewpoint of thermal conductivity, the laminated unit thickness is set to 20 to 100 nm, and 1 to 1.3 times the sum of the crystallite sizes of CrN and TiN. It is preferable. The inclusion of a metal layer having a higher thermal conductivity in the CrN / TiN multilayer coating also contributes to further improving the thermal conductivity of the hard coating.

The thermal conductivity of CrN and TiN formed by AIP is 0.0261 to 0.0307 cal / cm · sec · deg (SI unit), respectively, according to Oki (Surface Technology, Vol. 41, No. 5, (1990), pages 464-470). 10.9-12.9 W / m · K) and 0.07 cal / cm · sec · deg (29.3 W / m · K when converted to SI), and TiN is about 2.5 times higher than CrN. . On the other hand, TiN has a problem that it is inferior in corrosion resistance compared to CrN. Therefore, it is preferable to increase the titanium ratio if the thermal conductivity is considered, and increase the chromium ratio if the corrosion resistance is considered. Considering the balance between the two, it is more preferable that the range is 3: 7 to 7: 3.

The growth orientation of the stacked CrN layer and TiN layer varies depending on the film formation conditions. Although not particularly limited, it is preferable that the CrN layer has the maximum diffraction intensity on the (200) plane, and the TiN layer also has the maximum diffraction intensity on the (200) plane.

Further, the piston ring of the present invention preferably has a composite structure composed of CrN and TiN or a composite structure composed of CrN, TiN and metal M on the outermost sliding surface. In consideration of scuff resistance and wear resistance, only the metal layer made of metal M should be exposed on the outermost surface. In that respect, if the thickness of the metal layer is close to the thickness of the CrN layer and the TiN layer, the metal-containing CrN / TiN multilayer coating basically exhibits a composite structure composed of CrN, TiN and metal M on the outermost surface. That is, as shown in FIG. 2, if a laminated film is formed on the surface of the substrate (1) on which irregularities are formed, the laminated film is also formed in a wave shape, and if the outer peripheral sliding surface is polished to a flat surface, CrN (5) A composite structure consisting of TiN (6) metal M (7) is obtained on the outermost surface. In general, it is preferable to form irregularities on the substrate surface and form a metal layer-containing CrN / TiN laminated hard film thereon.

The composite structure consisting of CrN (5), TiN (6) and metal M (7) appearing on the outermost surface depends on the lamination thickness, the angle between the lamination surface and the polishing surface, the wavelength of the wavy laminated film, etc. It is preferable to include a contoured structure. If the conditions are set, a layered ring shape is obtained.

A metal intermediate layer (4) for improving the adhesion may be formed between the laminated film and the substrate. The metal intermediate layer (4) is preferably made of Cr.

Furthermore, the hardness of the hard coating of the piston ring of the present invention is preferably 1000 ある HV0.1 or more. The high hardness side is preferably 1450 HV0.1 or less. 1100 より HV0.1 to 1300 HV0.1 is more preferable. The residual stress of the film is preferably -500 to 1500 MPa (compressive residual stress). It is more preferable if it is -600 MPa to -1400 MPa. Such a balanced compressive residual stress of the coating reduces the tensile stress and shear stress due to friction and suppresses the propagation of cracks.

In the present invention, the metal-containing CrN / TiN laminated hard coating is formed using, for example, a PVD apparatus having a schematic diagram (plan view from above) as shown in FIG. In this PVD system, a workpiece (18) (with a piston ring superimposed) is set in a vacuum vessel (10) having a process gas inlet (11) and a process gas outlet (12), and a rotary table. The metal Cr cathode (13) and metal Ti cathode (14) of arc ion plating and the cathode (15, 16) of metal M of sputtering are arranged at positions facing each other with (17) interposed therebetween. The rotary table (17) has a mechanism for rotating the workpiece (18), and is further connected to a bias power source (not shown). A heater (19) is installed on the wall of the apparatus.

In the arc ion plating method, nitrogen (N ₂ ) gas is introduced into the vacuum vessel (10), and an arc is generated on the surface of the metal Cr cathode and / or the metal Ti cathode in a low-pressure atmosphere, so that the metal Cr and / or Metal Ti is instantaneously dissolved, ionized in nitrogen plasma, and drawn into the coated surface as chromium ions, titanium ions, or CrN or TiN reacted with nitrogen plasma by a negative bias voltage applied to the workpiece (18). This is a method of forming a CrN layer or a TiN layer. In arc ion plating, a high ionization rate of metallic Cr and metallic Ti can be achieved with a high energy density. Therefore, a high film formation rate can be obtained, and the film formation of 10 to 60 μm required for the piston ring can be industrially performed.

Sputtering is a glow discharge plasma generated by applying a high voltage to a metal cathode while introducing an inert gas such as Ar. , The metal atoms / molecules are blown off and deposited on the object to be processed (18) to form a film. If magnetron sputtering using a magnetic field (not shown) placed on the back side of the metal cathode (15, 16) is used to generate a non-equilibrium magnetic field in which the magnetic field of the outer magnetic pole is stronger than that of the inner magnetic pole, it converges near the target. A part of the plasma that has been used is easily diffused to the vicinity of the substrate along the magnetic field lines, increasing the plasma density in the vicinity of the workpiece (18), and irradiating the workpiece (18) during film formation The amount of ions can be increased to enhance the film interface.

The CrN / TiN multilayer coating can be formed alternately by performing arc discharge at the metal Cr cathode and arc discharge at the metal Ti cathode at different times. In order to increase the speed and productivity, it is preferable to perform arc discharge of the metal Cr cathode and the metal Ti cathode simultaneously. The metal (M) layer is formed by stopping the arc discharge of the metal Cr cathode and the metal Ti cathode, replacing the N ₂ atmosphere with the Ar atmosphere, and performing glow discharge of the metal M cathode for a predetermined time.

Since the composition of chromium nitride and titanium nitride is determined by the amount of evaporation from the metal Cr cathode and metal Ti cathode and the nitrogen gas partial pressure, it is adjusted in the present invention to be mainly composed of CrN type chromium nitride and TiN type titanium nitride. . In addition, the amount of metal evaporation from the cathode depends on the vapor pressure and arc current (temperature) at the metal's inherent melting point, so the composition does not change (for example, the CrN-based composition does not become the Cr ₂ N-based composition). The ratio of Cr and Ti can be changed by changing the arc current. Therefore, the thicknesses of the CrN layer and the TiN layer can be controlled by the arc current and the rotation speed of the rotary table (17). The thickness of the CrN layer and the TiN layer can be measured by direct observation using FE-SEM (Field Emission-Scanning Electron Microscope), etc., but at least the sum of the CrN layer and the TiN layer, that is, the rotary table is 1 The thickness of the stacked unit formed during the rotation is a value obtained by dividing the film formation speed (μm / min) by the rotation speed (rpm) of the table. Here, since the film formation rate increases as the arc current increases, the unit thickness of the stack decreases as the arc current is decreased or the rotation speed of the table is increased.

The film thickness and film quality of the metal layer formed by sputtering depend on the sputtering power and the pressure of the atmospheric gas. In general, if the sputtering power is increased and the pressure of the atmospheric gas is reduced, collision and scattering with the atmospheric gas are reduced and the film formation rate is increased.

The crystal structure of the film formed by PVD can generally be adjusted by the furnace pressure and bias voltage. When the furnace pressure is raised and the bias voltage is lowered, it becomes columnar crystals, and conversely, the furnace pressure is lowered and the bias voltage is lowered. It is said that a granular structure can be obtained by increasing the value. However, as disclosed in Japanese Patent Laid-Open No. 6-300130, there is a teaching that when a bias voltage is increased, a columnar crystal is formed. The film deposition environment for ion plating and sputtering is very complex.For example, if the same discharge power, furnace pressure, and bias voltage are selected, there is no guarantee that the same structure can be obtained if the equipment is changed. It is a fact. Of course, although it is also related to the material of the base material, crystal structure, temperature, surface condition, etc., the structure in the furnace (arrangement of workpiece and cathode, etc.) has a relatively large influence, and the film formation conditions are the equipment. Must be set every time.

Example 1
A piston ring with a rectangular face with a nominal diameter (d) of 96 mm, radial thickness (a1) of 3.8 mm, and axial width (h1) of 2.5 mm from a wire equivalent to SWOSC-V. 50 piston rings were stacked, the outer peripheral surface was adjusted to a surface roughness (Ry) of several μm by shot blasting, and set in a composite apparatus having both arc ion plating and sputtering functions. The target was 99.9% pure metal Cr, 99.9% pure metal Ti, and 99.9% pure metal Cu. The inside of the apparatus was evacuated to 1.0 × 10 ⁻² Pa, Ar gas was introduced to 1.0 Pa, and a bias voltage of −900 V was applied to clean the outer peripheral surface of the piston ring as a base material by bombardment treatment. Ar gas having a purity of 99.99% was used. Then, N ₂ gas with a purity of 99.999% was introduced up to 4 Pa, the arc current of the metal Cr cathode was 120 A, the arc current of the metal Ti cathode was 170 A, the bias voltage was -9 V, the table rotation speed was 2 rpm, 100 A CrN / TiN multilayer coating was formed by ion plating for a minute. Subsequently, the arc discharge of the metal Cr cathode and the metal Ti cathode was stopped, the N ₂ gas was evacuated, Ar gas was introduced to 0.4 Pa, the metal Cu cathode voltage was 400 V, and UBM (Unbalanced Magnetron) sputtering. A metal layer of metal Cu was formed by treatment. Here, the processing time was set to 5 minutes without changing the bias voltage and the table rotation speed. Under the above conditions, CrN / TiN multilayer coating by ion plating and Cu metal layer formation by sputtering were repeated, and finally a hard coating containing two Cu metal layers in the CrN / TiN multilayer coating was coated. A piston ring was made. For the purpose of improving adhesion, a metal intermediate Cr layer was formed between the substrate and the laminated film. The obtained metal (Cu) layer-containing CrN / TiN laminated hard film-coated piston ring was subjected to the following various measurements.

[1] Thickness measurement Thickness measurement was performed by measuring the length from the substrate surface to the surface of the coating on a mirror-polished piston ring cross section perpendicular to the coated surface, using a scanning electron microscope (SEM) photograph. Film thickness. The film thickness of Example 1 was 22.8 μm, and the thicknesses of the Cu metal layer observed at a high magnification were 0.16 μm (160 nm) and 0.14 μm (140 nm). The film thickness of the CrN / TiN multilayer coating is 22.5μm, and the unit thickness of the stack (one chromium nitride layer + one titanium nitride layer) formed during one rotation of the rotary table is 22.5μm and the coating time ( It was calculated to be 0.0375 μm (37.5 nm) from 300 minutes) and the number of rotations of the table (2 rpm).

[2] Hardness measurement Hardness measurement was performed on a surface parallel to the mirror-polished coating surface using a micro Vickers hardness tester with a test force of 0.9807 N. The hardness of the metal layer-containing CrN / TiN laminated hard film of Example 1 was 1210 HV0.1.

[3] Residual Stress Measurement The residual stress σ of the film was calculated by the following Stoney equation.
σ =-{E _s (1-ν _s ) h _s ² } / 6h _f Δ R …………………………………… (1)
Where E _s is the Young's modulus (N / mm ² ) of the substrate, ν _s is the Poisson's ratio of the substrate, h _s is the thickness of the substrate, h _f is the film thickness, and ΔR is the amount of change in curvature. is there. Incidentally, E _s and [nu _s, respectively, was 200,000 N / mm ² and 0.3. The residual stress of the metal layer-containing CrN / TiN laminated hard film of Example 1 was -1170 MPa (1170 MPa in compression).

[4] X-ray diffraction measurement X-ray diffraction intensity is measured in the range of 2θ = 35 to 70 ° using Cu-Kα rays with a tube voltage of 40 kV and a tube current of 30 mA on the surface parallel to the mirror-polished coated surface. It was measured. The X-ray diffraction pattern of the metal layer-containing CrN / TiN laminated hard film of Example 1 shows the maximum peak intensity on the TiN (200) plane, followed by the CrN (200) plane, TiN (111) plane, CrN (111) The diffraction peak of the Cu (111) surface was also detected, although it was slight, followed by the surface, the TiN (220) surface, and the CrN (220) surface. The crystallite size D _hkl was calculated using the following Scherrer equation on the TiN (200) plane and the CrN (200) plane.
D _hkl = Kλ / β cosθ …………………………………………………… (2)
Here, K is Scherrer's constant of 0.94, λ is the X-ray wavelength (Cu: 1.5406Å), β is the full width at half maximum (FWHM), and θ is the Bragg angle. The crystallite size of the CrN layer of Example 1 is 10.2 nm, and the crystallite size of the TiN layer is 20.8 nm. Therefore, the sum of the crystallite sizes of the CrN layer and the TiN layer is 31.0 nm. The laminated unit thickness 37.5 nm calculated from the film thickness was 1.21 times the sum of the crystallite sizes of chromium nitride and titanium nitride.

[5] Coating composition measurement The composition of the CrN / TiN multilayer coating was analyzed using EPMA (Electron Probe Micro Analyzer). The atomic ratio of Cr: Ti: N was 17.2: 29.3: 53.5, and the atomic ratio of Cr and Ti was 3.7: 6.3.

[6] Rolling sliding fatigue test A rolling sliding fatigue test was conducted as an evaluation to make it possible to reproduce the film dropout in the actual machine test. Fig. 4 shows the outline of the testing machine. In the rolling sliding fatigue test, a repeated load was applied to the rotating drum (21) and the sliding test piece (20), and the film was removed in a relatively short time. It is reproduced. The removal of the film depends on the friction coefficient, the load (maximum Hertz stress) and the number of repetitions under the same lubrication condition. The test conditions are as follows.
Test piece: Metal ring containing CrN / TiN multilayer coating coated piston ring cut piece,
Load: 98-196 N, sine curve 50 Hz,
Counterpart material (drum): 80 mm diameter SUJ2 material,
Sliding speed: Forward / reverse rotation pattern operation (± 2 m / sec), hold for 10 seconds at speed ± 2 m / sec.
Acceleration 0.08 m / sec ^2,
Lubricant: pure water, 4 cc / min,
Temperature: drum surface temperature 80 ℃,
Test time: 1 hour.
In addition, the test result was determined by the presence or absence of film removal. As a result of the rolling sliding fatigue test of Example 1, there was no film falling off.

Examples 2-3
CrN / TiN multilayer film deposition time and number of times 50 minutes x 6 times (Example 2), 5 minutes x 60 times (Example 3), and Cu metal layer deposition time and number of times 5 minutes each x A metal (Cu) layer-containing CrN / TiN laminated hard film was formed under the same conditions as in Example 1 except that it was changed to 5 times (Example 2) and 1 minute × 59 times (Example 3).

Example 4
Under the same conditions as in Example 2, except that the arc current in ion plating was changed to 160 A for the metal Cr cathode, 130 A for the metal Ti cathode, and the deposition time and frequency of the Cu metal layer to 10 minutes x 5 times. A (Cu) layer-containing CrN / TiN laminated hard film was formed.

Example 5
A CrN / TiN laminated hard material containing a metal (Ni) layer under the same conditions as in Example 4 except that the sputtering target was changed from Cu to Ni, the cathode voltage was changed to 500 V, and the deposition time and number of times were changed to 5 minutes × 5. A film was formed.

Example 6
A metal (Co) layer-containing CrN / TiN laminated hard film was formed under the same conditions as in Example 5 except that the sputtering target was changed from Ni to Co.

Table 1 shows the film forming conditions of Examples 1 to 6 above.

In all examples, the bias voltage was −9 V and the table rotation speed was 2 rpm.

Table 2 shows the results of film thickness measurement, Table 3 shows the results of X-ray diffraction measurement, and Table 4 shows the results of composition measurement of CrN / TiN laminated film by EPMA. Crystals of film hardness, residual stress, and lamination unit thickness Table 5 shows the ratio of the child size to the sum (T / S) and the results of the rolling sliding fatigue test. However, the composition measurement of the CrN / TiN multilayer coating was performed only for Examples 1 and 4 with different ion plating conditions.

* The thickness of one metal layer of Examples 2 to 4 is a value estimated from the measured value of Example 1 based on the film formation time.

* T / S indicates (stacking unit thickness / sum of crystallite sizes of CrN and TiN).

The thickness of each of the CrN / TiN multilayer coatings in Examples 1 to 6 is 600 units, and the thickness of the metal layer is 2 to 59 in the range of 30 to 300 mm by changing the deposition time. The thickness of the entire film was 19.7 to 24.8 μm. The laminated unit thickness calculated from the film thickness of the CrN / TiN laminated film part excluding the metal layer was 31.8-39.1 nm.

The film structure is composed of CrN type chromium nitride and TiN type titanium nitride and metal Cu, metal Ni or metal Co in each example, chromium nitride is CrN (200) face, titanium nitride is TiN (200) and has the maximum peak. was gotten. The crystallite sizes of CrN and TiN were 10.2 to 15.8 nm for CrN and 11.5 to 22.4 nm for TiN. The sum of the crystallite sizes of CrN and TiN was 25.7 to 37.9 nm.

The composition ratio of Cr and Ti in the CrN / TiN multilayer coating was an atomic ratio, and Example 1 was 3.7: 6.3 and Example 4 was 5: 5.

The film hardness is 1072 HV0.1 ~ 1276 HV0.1, the residual stress is -682 ~ -1170 MPa (negative symbol indicates compression), and the thickness of the metal layer in Example 4 is 300 nm And the residual stress was the smallest. The ratio (T / S) of the stack unit thickness to the sum of the crystallite sizes of CrN and TiN was between 1.03 and 1.26. As a result of the rolling sliding fatigue test, none of the examples produced minute dropouts or surface cracks.

Comparative Examples 1 and 2
As Comparative Examples 1 and 2, using a commercially available piston ring coated with CrN and TiN instead of the metal layer-containing CrN / TiN laminated hard film, film thickness measurement, hardness measurement, residual stress measurement, X-ray diffraction measurement A rolling sliding fatigue test was conducted. The results are shown in Table 6. Comparative Example 1 is a film having a relatively high porosity, which is said to be excellent in chipping resistance, and the film hardness is as low as Hv 930, while Comparative Example 2 is a film having a relatively high film hardness. In both cases, film falling off was observed in rolling sliding fatigue tests under severe conditions.

Claims

A piston ring in which a hard coating is coated on an outer peripheral sliding surface, wherein the hard coating includes a laminated coating in which CrN type chromium nitride and TiN type titanium nitride are alternately laminated, and at least one kind in the laminated coating A standard formation free energy ΔG MN of the nitride of the metal M and a standard formation free energy ΔG CrN of the chromium nitride satisfy a relationship of ΔG MN > ΔG CrN. Piston ring characterized by
2. The piston ring according to claim 1, wherein the metal M is at least one selected from Co, Ni and Cu.
3. The piston ring according to claim 1, wherein the metal layer has a thickness of 10 to 1000 nm.
The piston ring according to any one of claims 1 to 3, wherein a lamination unit thickness composed of a sum of thicknesses of each of the laminated chromium nitride and titanium nitride is 20 to 100 nm, and the nitride A piston ring characterized by being 1 to 1.3 times the sum of the crystallite sizes of chromium and titanium nitride.
5. The piston ring according to claim 1, wherein an atomic ratio of chromium to titanium in the laminated film is 3: 7 to 7: 3.
6. The piston ring according to claim 1, wherein the X-ray diffraction intensity of the coated surface of the multilayer coating is maximized on the CrN (200) surface for chromium nitride and maximized on the TiN (200) surface for titanium nitride. Piston ring characterized by
The piston ring according to any one of claims 1 to 6, wherein the residual stress of the hard film is -500 to 1500 MPa.
The piston ring according to any one of claims 1 to 7, wherein the hardness of the hard coating is 1000 HV0.1 or more.