JP7116360B2 - sliding member - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sliding member provided with a film, and more particularly to a sliding member that prevents film defects from occurring due to thermal stress.

Sliding members used in internal combustion engines are exposed not only to friction but also to combustion heat and oxidation by combustion products. is formed, and a film such as a copper-based alloy is formed on the counterbore groove.

In Patent Document 1, a metal powder supplied to a counterbore groove is irradiated with a laser beam, and gas is blown to a gas rectifying wall provided in the counterbore groove to flow from the inside to the outside of the counterbore groove, thereby forming a film. It is disclosed that it is possible to prevent the lack of thickness caused by the formed molten metal sagging downward in the vertical direction.

International publication 2015/001698 pamphlet

However, in the case of Patent Document 1, since the coating is formed by melting the metal powder, the volume shrinks due to the solidification of the molten metal, and the tensile stress remains in the coating. When the grooves expand due to the heat of combustion, etc., the coating is stretched and defects such as cracks and peeling occur, resulting in a decrease in wear resistance.

The present invention has been made in view of such problems of the prior art, and the purpose thereof is to prevent the occurrence of film defects such as cracks and peeling due to thermal expansion impact, and to provide excellent wear resistance. An object of the present invention is to provide a sliding member.

As a result of intensive studies aimed at achieving the above object, the present inventor found that by forming a coating of particle lumps without melting the metal powder, compressive stress remains in the coating, and the above object can be achieved. , have completed the present invention.

That is, the sliding member of the present invention includes a base material having an annular groove, and a coating provided in the groove.
The coating is made of agglomerates of alloy material containing copper alloy particles containing 50% by mass or more of copper , and at least a part thereof has a compressive residual stress of 1 MPa or more in at least one of the circumferential direction and the radial direction. characterized by

According to the present invention, since a film having a compressive residual stress of 1 MPa or more is formed, film defects due to thermal expansion impact do not occur, and a sliding member having excellent wear resistance can be provided.

It is a schematic sectional view showing an example of a section of a sliding member of the present invention. FIG. 4 is a schematic enlarged cross-sectional view showing an example of a coating structure; 4 is a cross-sectional SEM image of the sliding member of Example 1. FIG.

The sliding member of the present invention will be described in detail.
The sliding member includes a base material having an annular groove and a coating provided in the groove, the coating being made of agglomerates of alloy material and having a compressive residual stress in at least one of the circumferential direction and the radial direction. have. In FIG. 1, the direction from the front to the back of the paper surface is the circumferential direction of the ring, and the horizontal direction of the paper surface is the radial direction of the ring.

The compressive residual stress at the center of the coating at room temperature (25° C.) is 1 MPa or more, preferably 100 MPa or more, and more preferably 400 MPa or more.

The coating provided in the grooves of the base material has compressive residual stress, and stress is applied in the direction in which the coating expands the grooves of the base material. Even if there is, the compressive residual stress of the coating cancels the tensile stress from the substrate, so the coating is not subjected to tensile stress. Therefore, the coating does not crack or separate from the substrate.

In the present invention, the particle mass means, as shown in FIG. Refers to an aggregate of alloy particles that are bonded and integrated to form an interface without being harmoniously integrated with each other, and are harmoniously integrated by completely melting or dissolving and solidifying the alloy particles It does not refer to aggregates of particles.

The coating can be formed by spraying alloy particles into the grooves of the substrate by a cold spray method.

The cold spray method is a method in which the alloy material is collided with the substrate in a solid phase state with a supersonic flow together with an inert gas without melting or gasifying, and the coating is formed by melting the alloy particles. It is possible to minimize the property change and oxidation of the alloy particles due to heat and the like, unlike the film formation method in the liquid phase such as the thermal spraying method that forms the .

The reason why the compressive stress remains in the film formed by the cold spray is not clear, but when the alloy particles collide with the substrate, the kinetic energy of the alloy particles is converted into stress in the direction of crushing and expanding the alloy particles in the lateral direction. be. However, since the alloy particles are in a solid state and are not sufficiently deformed, the stress cannot be completely eliminated by deformation.
In particular, when a film is formed inside the groove, deformation of the alloy particles is restricted by the inner wall of the groove, and compressive stress tends to remain.

In addition, part of the kinetic energy of the alloy particles is converted into thermal energy, and the surfaces of the alloy particles are locally melted and solidified, so that the alloy particles are bonded together to form particle agglomerates, and a coating is formed. be.

At this time, since the temperature of the base material and the alloy particles is lower than the melting point of the alloy particles, the surfaces of the locally melted alloy particles are quenched, and as shown in FIG. An amorphous phase is formed at the interface, and the alloy particles are plastically deformed to refine the crystal grains in the alloy particles.

At least some of the alloy particles preferably contain crystal grains having a particle size of less than 1 μm. The inclusion of fine crystal grains in the alloy particles improves the coating strength.

In the coating, the ratio of crystal grains having a grain size of less than 1 μm is preferably 30 area % or more, more preferably 50 area % or more, and more preferably 70 area % or more.
In the present invention, the proportion of crystal grains having a grain size of less than 1 μm was calculated by measuring the film at multiple locations and averaging them.

Moreover, in the present invention, an annular shape is sufficient if it can be regarded as a circular shape, and includes not only perfect circles but also elliptical shapes and elliptical shapes. Moreover, it includes not only a closed circular shape having no ends in the circumferential direction, but also a discontinuous annular shape having ends due to a partial cut in the circumferential direction.

It is preferable that the annular groove has a substantially trapezoidal cross-sectional shape cut in the radial direction, with the opening wider than the bottom. Since the opening has a broad trapezoidal cross-sectional shape, the alloy particles colliding with the side wall of the groove are easily subjected to stress in the direction of the center of the groove. Higher stress can prevent coating defects.

The coating preferably has compressive residual stress in the radial direction. Interfacial delamination between the coating and the substrate occurs mainly when the annular groove expands in the radial direction and applies tensile stress to the coating.

The compressive residual stress in the radial direction can be imparted by making the coefficient of linear expansion of the alloy particles forming the coating smaller than the coefficient of linear expansion of the substrate.
When the sliding member cools down after forming the coating, the base material shrinks and the grooves of the base material decrease in diameter, so the coating existing inside the base material is compressed from the base material. However, if the coefficient of linear expansion of the coating is small, it does not shrink as much as the base material and resists compression from the base material, so compressive residual stress is generated in the radial direction.

In the sliding member, the compressive stress remaining on the surface of the base material preferably exists from the end of the coating to a point that is 20% or more of the width of the coating, and is 50% or more of the width of the coating. It is more preferable that the compressive residual stress in the radial direction exists up to the point.

Not only the film but also the base material has residual compressive stress, and the range of the compressive residual stress extends to the surface of the base material. is improved and peeling of the film is prevented.

In addition, when the sliding member after forming the coating is cooled, the amount of shrinkage differs between the outer peripheral side and the inner peripheral side in the circumferential direction. easy to become

By having a compressive residual stress in the radial direction from the edge of the coating on the surface of the base material to a point that is 80% or more of the width of the coating, the adhesion between the coating and the base material is further improved and the peeling of the coating is prevented. prevented.

The thickness of the film depends on the temperature and sliding environment of the place where the sliding member is used, but for example, it is preferably 0.05 to 5.0 mm, and preferably 0.1 to 2.0 mm. is more preferred. If it is less than 0.05 mm, the strength of the film itself may be insufficient, and if it exceeds 10 mm, the film may easily peel off due to the relationship between the residual stress generated during film formation and the interfacial adhesion.

As the alloy particles, it is sufficient that the alloy particles can form particle agglomerates and form a film by the cold spray method without being completely melted. Copper alloys containing 50% by mass or more of copper, such as alloys and Cu--Ti alloys, tend to be plastically deformed so that alloy particles are bound together to form particle agglomerates.
In particular, Cu--Ni--Si alloys can be preferably used because the particles are strongly bonded to each other and film defects are less likely to occur.

Moreover, the alloy particles preferably contain alloy particles harder than the copper alloy particles.
Since the alloy particles contain copper alloy particles and hard alloy particles, the relatively soft copper alloy particles are plastically deformed and deposited and bonded without gaps, and amorphous is formed at the interface between the copper alloy particles and the copper alloy particles. form agglomerates of copper alloy having Then, the hard alloy particles sink into the particle agglomerates, and as shown in FIG. 1, a coating is formed in which the hard alloy particles are dispersed in the form of islands in the copper alloy particle agglomerates, thereby improving the wear resistance of the coating. improves.

As the hard alloy particles, an alloy containing at least one metal selected from the group consisting of cobalt (Co), chromium (Cr) and nickel (Ni) can be used.
For example, hard cobalt-based alloys such as TRIBALOY® T-400 and Stellite® 6, and TRIBALOY® T-700 and Ni700® (Ni-32Mo-16Cr-3.1Si). and particles of hard nickel-based alloys such as

The base material is not particularly limited, and metals conventionally used as sliding members of internal combustion engines can be used, but aluminum alloys are preferably used because of their high thermal conductivity.

Examples of the aluminum alloy include AC2A, AC8A, ADC12, etc. specified by Japanese Industrial Standards.

Next, conditions for forming a film by the cold spray method will be described.
The speed at which the alloy particles are sprayed by the cold spray method is preferably 300 to 1200 m/s, more preferably 500 to 1000 m/s.

The pressure of the working gas for spraying the alloy particles is preferably 2-5 MPa, more preferably 3.5-5 MPa. If the pressure of the working gas is less than 2 MPa, the particle velocity may not be obtained and the porosity may increase.

The temperature of the working gas is preferably 400 to 800.degree. C., more preferably 600 to 800.degree. C., depending on the alloy particles.
If the temperature of the working gas is less than 400° C., the bonding between the alloy particles may become weak and the strength of the coating may be lowered. On the other hand, if the temperature of the working gas exceeds 800° C., the alloy particles colliding with the base material become too soft, and the compressive residual stress becomes small, and the coating may easily peel off.

Examples of the working gas include nitrogen gas and helium gas, and these may be used singly or in combination.

Since the sliding member is excellent in wear resistance and heat resistance, it can be suitably used for valve seats, and by forming the coating on the inner surface of the hole, it can be applied to cylinder bores, connecting rods, bearing metals of crankshafts, etc. .

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[Example 1]
In the completed state of machining of the seating portion of the engine valve in the cylinder head, assuming a target film thickness of 0.2 mm, an aluminum base material (Japanese Industrial Standards H 4040 A5056) was coated with a diameter of 25.3 mm, a depth of 0.4 mm, and a width of 0.4 mm. A 2.7 mm annular groove was formed.

The following alloy particles were cold-sprayed under the following conditions while rotating the aluminum base material to form a coating having a thickness of 1.0 m.

Copper alloy particles: Cu-2.9Ni-0.7Si alloy particles (average particle size 30 μm)
Hard alloy particles: Co alloy particles (Tribaloy T-400 manufactured by Kennametal: average particle size 45 μm)
Copper alloy particles/hard alloy particles (volume ratio): 90/10

High-pressure cold spray device: Kinetics 4000 manufactured by CGT
Working gas: Nitrogen gas Gas temperature: 600°C,
gas pressure: 3.6 MPa,
Particle velocity: 680-720m/s

The aluminum substrate having the film formed thereon was machined into the shape of the seating portion of the engine valve of the cylinder head to obtain a sliding member having a film thickness of 0.45 mm.

[Example 2]
In the state where the engine valve seating portion of the cylinder head has been processed, assuming a target film thickness of 0.2 mm, an aluminum substrate (Japanese Industrial Standard H 4040 A5056) is coated with a diameter of 25.3 mm, a depth of 0.15 mm, and a width of 0.15 mm. A 2.1 mm annular groove was formed.

A film having a thickness of 1.0 m was formed in the same manner as in Example 1, except that the above aluminum substrate was used.
The aluminum substrate on which the film was formed was machined into the shape of the seating portion of the engine valve of the cylinder head to obtain a sliding member having a film thickness of 0.20 mm.

[Reference example 1]
A film having a thickness of 1.0 m was formed in the same manner as in Example 1, except that no annular groove was formed on the aluminum substrate.
The aluminum substrate on which the coating was formed was machined into the shape of the seating portion of the engine valve of the cylinder head to form an annular coating having a diameter of 25.3 mm, a thickness of 0.20 mm and a width of 1.9 mm.

[Comparative Example 1]
In the state where the engine valve seating portion of the cylinder head has been processed, assuming a target film thickness of 0.2 mm, an aluminum base material (Japanese Industrial Standard H 4040 A5056) is coated with a diameter of 25.3 mm, a depth of 0.7 mm, and a width of 0.7 mm. A 3.2 mm annular groove was formed.

While supplying Cu-12Ni-9.7Co-3Si-1.4Fe-2V-1.7Nb-0.9Al alloy particles (average particle size 30 μm) at 0.7 g/sec, to prevent oxidation and plume, In an Ar gas environment, laser build-up, that is, laser cladding was performed while irradiating a laser beam with a wavelength of 960 nm and an output of 2.0 kW. After laser cladding, a coating with a thickness of 1.0 mm was formed through finishing.

The aluminum substrate on which the coating was formed was machined into the shape of the seating portion of the engine valve of the cylinder head to form an annular coating having a diameter of 25.3 mm, a thickness of 0.80 mm and a width of 3.2 mm.

[Comparative Example 2]
Cu-14Ni-3Si-1.5Fe-2V-2Cr-1Al-0.5P alloy particles (average particle diameter 30 μm) were used in the same manner as in Comparative Example 1, and a A ring-shaped coating with a width of 3.2 mm was formed.

[Comparative Example 3]
A Ni--P film was formed by electroplating, and the shape of the engine valve seating portion of the cylinder head was finished by machining to form an annular film with a diameter of 25.3 mm, a thickness of 0.20 mm, and a width of 1.5 mm. .

[Comparative Example 4]
A TiO film is formed by a plasma electrolytic deposition method, and finished to the shape of the seating portion of the engine valve of the cylinder head by machining to form an annular film with a diameter of 25.3 mm, a thickness of 0.02 mm, and a width of 1.4 mm. did.

<Evaluation>
The sliding members of Examples 1-8 and Comparative Examples 1-5 were evaluated by the following methods.
Table 1 shows the evaluation results.

(Measurement of residual stress)
Using an X-ray residual stress measuring device, the residual stress was measured at arbitrary multiple locations on the central portion of the coating surface, the vicinity of the interface between the coating and the substrate, and the substrate surface, and the average value was calculated.

(Observation of coating structure)
A sample was embedded in resin and polished to prepare a cross section. A composition image of SEM was obtained and binarized by image processing to determine the area ratio of the voids displayed in black and the portions displayed in dark and light gray to calculate the porosity.
Next, by changing the binarization threshold, the area ratio of the black part + dark gray part and the light colored part was obtained, and by twice binarizing, the copper alloy part, the hard alloy part, and the holes An area ratio was obtained.

In addition, electron beam backscatter diffraction (EBSD) is performed using a scanning electron microscope (SEM), the diffraction pattern is projected onto the detector surface, and the crystal orientation is analyzed from the projected pattern. The presence or absence of grains and the size of crystal grains in the grains were observed.
A cross-sectional SEM image of the sliding member of Example 1 is shown in FIG.

(Thermal expansion impact test)
The sliding member was heated to 200° C. in an electric furnace, submerged in hot water of 80° C., and color-checked before heating and after submersion to confirm the presence or absence of cracks.
For those with no cracks, the setting of the electric furnace was further increased by 50° C., the sliding member was heated to 250° C., submerged in hot water at 80° C., and the color was checked again to confirm the presence or absence of cracks.
Thereafter, the heating temperature was raised in 50° C. increments and submerged in water to confirm the presence or absence of cracks, and the heating temperature and the cumulative occurrence rate of cracks were measured.

(wear resistance)
Using a valve seat wear tester manufactured by Takachiho Seiki Co., Ltd., the amount of wear was measured under the following conditions.
Specifically, using a shape measuring device, the shape of the engine valve seating portion of the cylinder head before and after the test was obtained, the amount of wear at four locations was measured, the average value was calculated, and the wear was calculated. Quantity.

Mating valve material: SUH35
Test temperature: 300°C
Vertical speed: 3000 times/min
Valve rotation speed: 5 rpm
Seating times: 540,000 times

From the results shown in Table 1, the sliding members of Examples 1 and 2, in which the films had compressive residual stress, did not peel off in the thermal expansion impact test compared to the sliding members of Comparative Example, which had tensile residual compressive stress. , excellent heat resistance, less wear amount, and excellent wear resistance.
Further, from the comparison between the examples and the reference examples, it can be seen that forming the grooves in the base material increases the compressive residual stress on the surface of the base material in the radial direction, thereby preventing separation between the coating and the base material.

REFERENCE SIGNS LIST 1 sliding member 2 coating 21 copper alloy particles 22 hard alloy particles 23 amorphous 3 base material 31 holes

Claims (7)

a substrate having an annular groove;
and a coating provided in at least the groove, wherein the coating comprises agglomerates of alloy material containing copper alloy particles containing 50% by mass or more of copper, and at least one of circumferential and radial compressive residual stress is present. A sliding member characterized by being 1 MPa or more. 2. The sliding member according to claim 1, wherein the compressive residual stress at the center of the coating surface is 100 MPa or more. At least a part of the alloy particles forming the particle agglomerates has amorphous and crystal grains with a particle size of less than 1 μm,
3. The sliding member according to claim 1, wherein the crystal grains are contained in the coating in an amount of 70 area % or more. The sliding member according to any one of claims 1 to 3, wherein the coating has a compressive residual stress in the radial direction. The sliding according to any one of claims 1 to 4, wherein compressive residual stress exists from the edge of the coating on the surface of the base material to a location that is 20% or more of the width of the coating. Element. 6. The compressive residual stress according to any one of claims 1 to 5, wherein a compressive residual stress in the radial direction exists from the edge of the coating on the surface of the base material to a point separated by 50% or more of the width of the coating. sliding member. The substrate has pores,
The sliding member according to any one of claims 1 to 3, wherein the coating is provided on the inner surface of the hole.

Images