A sliding member and an internal combustion engine equipped with the sliding member.

Abstract

A sliding member according to the present invention includes, at least at the surface thereof, a particulate aggregate of base material particles and hard particles.　Because the hard particles are iron alloy particles containing molybdenum silicide at 35 to 90 surface area%, a sliding member having an abrasion resistance equivalent to that in the case where cobalt-based hard particles are used can be provided.

Description

Technical Field

[0001] The present invention relates to a sliding member, and more particularly, to a sliding member including an aggregate of particles in which hard particles are dispersed in a particle group in a base material particle phase, and an internal combustion engine including the sliding member.

Background Art

[0002] In order to cope with the high performance and high output of automobile engines, members that require wear resistance at high temperatures, such as valve seats, generally have cobalt-based hard particles having a hard phase imparted to the base material particle phase to satisfy performance such as the above wear resistance.

[0003] In addition to the high cost of the cobalt-based hard particles, in recent years, it has become difficult to obtain them. Therefore, a sliding member having wear resistance up to a high temperature range without using cobalt is desired.

[0004] Patent Document 1 discloses that, as an alternative material for cobalt-based hard particles having a hard phase, hard particles in which a hard phase of molybdenum silicide is dispersed in an iron-based alloy matrix phase at 3 to 30 area% are used, and a sintered alloy of a mixed powder containing this can improve the wear resistance of the sliding member.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the case of what is described in Patent Document 1, wear resistance equivalent to that of a sliding member using cobalt-based hard particles having a hard phase has not been obtained, and there is room for improvement.

[0007] This invention has been made in view of the problems of the prior art, and its objective is to provide a sliding member that has the same wear resistance as a conventional material using hard particles of cobalt groups, without using hard particles of cobalt groups having a hard phase. [Means for solving the problem]

[0008] The inventors of the present invention have conducted extensive research to achieve the above objectives and have found that these objectives can be achieved by using hard particles of an iron-based alloy containing 35% to 90% molybdenum silicide, thereby completing the present invention.

[0009] In other words, the sliding member of the present invention comprises a particle aggregate of base material particles and hard particles on at least its surface. And the hard particles mentioned above, Molybdenum (Mo) at 33.5-40% by mass, Silicon (Si) at 2.39-15% by mass, It contains 0-8% by mass of chromium (Cr), The remainder consists of iron (Fe) and unavoidable impurities. Contains 2.6% or more of the Raves phase of molybdenum silicide by area. It is characterized by being an iron-based alloy particle.

[0010] Furthermore, the internal combustion engine of the present invention is characterized by comprising the above-mentioned sliding member. [Effects of the Invention]

[0011] According to the present invention, since hard particles of an iron-based alloy containing a desired amount of molybdenum silicide are used, it is possible to provide a sliding member having wear resistance equivalent to that of a case in which hard particles of cobalt groups having a hard phase are used. [Brief explanation of the drawing]

[0012] [Figure 1] This is the Fe-Mo phase diagram. Here, MoFe2 is the Laves phase, Mo5.1Fe7.9 is the μ phase, and Mo0.38Fe0.62 is the R phase. [Modes for carrying out the invention]

[0013] A detailed description will be given of the sliding member of the present invention. The sliding member of the present invention has a particle aggregate of base material particles and hard particles at least on the surface, and the hard particles are iron-based alloy particles containing 35 area% or more and 90 area% or less of molybdenum silicide.

[0014] In the present invention, the "particle aggregate" is one in which the surfaces of the particles are partially softened or melted without completely melting the particles, and the contact portions between adjacent particles are solidified and bonded to be integrated. The sliding member of the present invention may be entirely formed of the above particle aggregate or may have a coating film formed of the above particle aggregate on the surface of the base material.

[0015] In the above particle aggregate, the hard particles are dispersed in the base material particle group, thereby improving the wear resistance of the sliding member.

[0016] <Hard particles> In the particle aggregate of the present invention, the hard particles are iron-based alloy particles, and these iron-based alloy particles contain hard molybdenum silicide. The iron-based alloy particles have a molybdenum silicide content of 35 area% or more and 90 area% or less. Since the molybdenum silicide content is high, wear resistance equivalent to that of hard particles containing cobalt can be exhibited.

[0017] When the molybdenum silicide content is less than 35 area%, the hard particles do not have sufficient hardness. When it exceeds 90 area%, the silicon (Si) content of the hard particles increases, and the toughness of the hard particles themselves decreases and becomes brittle, resulting in a decrease in wear resistance.

[0018] The hard particles of the above iron-based alloy contain iron (Fe) as the first element, molybdenum (Mo) as the second element, and silicon (Si) as the third element in order from the most contained elements. The silicon content is preferably 2.3 mass% or more and 16 mass% or less.

[0019] When the silicon content is 2.3% by mass or more, molybdenum silicide is likely to precipitate in the hard particles, increasing the hardness of the hard particles. When it is 16% by mass or less, it is possible to prevent a decrease in the toughness of the hard particles.

[0020] The above molybdenum silicide preferably contains a Laves phase (Mo(Fe,Si)2 or Mo(Fe,Si), where these (Fe,Si) may contain a metal element with a content of the fourth element or less). Since the Laves phase is a metastable phase that decomposes at a relatively low temperature near 900 °C, it is oxidized by being exposed to the sliding surface of an internal combustion engine such as a valve sheet, forming molybdenum oxide with lubricity and improving wear resistance.

[0021] The content of the Laves phase molybdenum silicide (hereinafter sometimes simply referred to as the "Laves phase") in the above hard particles is preferably 2.0% by area or more and 90% by area or less, more preferably 10% by area or more and 85% by area or less, and still more preferably 30% by area or more and 80% by area or less.

[0022] All of the molybdenum silicide in the hard particles may be the Laves phase. Therefore, the upper limit of the content of the Laves phase in the hard particles is 90% by area.

[0023] The hard particles containing the Laves phase can be formed by melting and homogenizing an iron-based alloy mainly composed of iron (Fe) and containing molybdenum (Mo) and silicon (Si), and then precipitating molybdenum silicide.

[0024] As shown in the Fe-Mo phase diagram of Figure 1, the molybdenum silicide forms a μ phase and an R phase in addition to the Laves phase. Since the above Laves phase precipitates at a lower temperature than the molybdenum silicide of the μ phase and the R phase, it is necessary to appropriately adjust the cooling rate to form the Laves phase.

[0025] Specifically, the material can be formed by crushing a cast piece made by melting and slowly cooling an iron-based alloy of the above composition, or by water atomization or gas atomization, where water or gas is sprayed onto the molten iron-based alloy and the finely atomized droplets are solidified to form particles. However, it is preferable to produce it using water atomization or gas atomization.

[0026] When the hard particles obtained by crushing the iron-based alloy castings mentioned above are crushed, a Laves phase is formed because the cooling rate during casting is slow. However, the molybdenum silicide precipitates tend to become coarse, so the hardness of the crushed hard particles and the molybdenum silicide content tend to vary.

[0027] Furthermore, water atomization and gas atomization are generally used to rapidly cool and solidify molten metal, thereby trapping components dissolved in the matrix metal without allowing them to precipitate. Therefore, under normal conditions, the Laves phase is not formed.

[0028] In the water atomization and gas atomization methods of the present invention, by adjusting the pressure of the water or gas sprayed onto the molten metal, the dropping rate of the molten metal, and the size of the droplets, the cooling rate can be slowed down compared to the conventional atomization method, thereby forming hard particles with a precipitated Raves phase.

[0029] Specifically, it depends on the composition of the iron-based alloy, especially the silicon content, but 10 4 ~10 2 By cooling at K / second, molybdenum silicides with a crystallite size of 0.1 to 3 μm precipitate, forming hard particles with uniform hardness in which these molybdenum silicides are finely dispersed.

[0030] The mesh size of the sieve used to adjust the particle size of the hard particles is preferably adjusted to 100 to 500. In particular, when the particle aggregate is manufactured using a sintered alloy as described later, the mesh size of the sieve is preferably adjusted to 100 to 150, and when formed by cold spraying, the mesh size of the sieve is preferably adjusted to 350 to 500. By increasing the mesh size of the sieve and reducing the particle size of the hard particles, a dense particle aggregate can be formed.

[0031] <Base material particles> As the base material particles, metal or alloy particles that have been conventionally used in components requiring wear resistance at high temperatures, such as valve seats, can be used. However, copper-based alloy particles or iron-based alloy particles, with copper (Cu) or iron (Fe) as the main component (50% by mass or more), are preferred.

[0032] In copper-based alloy particles, heat transfer paths are formed by the highly thermally conductive copper, increasing the thermal conductivity of the particle aggregate and improving cooling performance, which in turn improves heat resistance.

[0033] Examples of copper-based alloy particles include Cu-Ni-Si alloy particles, Cu-Cr alloy particles, Cu-Zr alloy particles, and Cu-Ti alloy particles, but Cu-Ni-Si alloy particles are preferred among them.

[0034] Cu-Ni-Si alloy particles readily precipitate with nickel through bonding with silicon, forming a structure in which nickel silicide precipitates within the matrix phase. This precipitation strengthens the matrix particles themselves, increasing their hardness, and in combination with the aforementioned hard particles, improves wear resistance.

[0035] Furthermore, as iron-based alloy particles, Fe-Mo alloy particles, Fe-Cr alloy particles, and high-speed steel such as SKH53 can be used. In addition, pure Fe particles can be used, which become an Fe-C alloy when mixed with graphite particles and sintered, causing carbon to diffuse.

[0036] Furthermore, if the copper-based alloy particles and iron-based alloy particles are solid solution particles, when forming particle aggregates by cold spraying as described later, the particles will bond strongly to each other and undergo precipitation hardening, further improving wear resistance.

[0037] The above-mentioned solid solution particles can be produced by water atomization or gas atomization.

[0038] The average particle size (D50) of the base material particles is preferably 20 μm to 40 μm. The average particle size was measured using the laser diffraction / scattering method with the MT3000 from Microtrac-Bell Co., Ltd.

[0039] <Method for manufacturing sliding members> The above-mentioned sliding member can be manufactured by coating the surface of the substrate with a particle aggregate using a cold spray, warm spray, or the like, which involves spraying raw material particles containing the base material particles and hard particles onto the substrate surface without melting, or by press molding and sintering the raw material particles.

[0040] When manufacturing by press-molding and sintering raw material particles, the hard particle content in the raw material particles is preferably 50% or less by area. When coating the substrate surface with a cold spray or the like, the hard particle content in the particle aggregate is preferably 20% or less by area. Within these ranges, hardness, strength, and cooling properties can be achieved simultaneously, and wear resistance can be improved.

[0041] (Cold spray) Cold spraying is a method of forming a coating layer of particle aggregates by impacting a substrate with raw material particles in a non-molten solid state in a supersonic flow along with an inert gas, without melting or gasifying the particles.

[0042] Unlike methods such as thermal spraying, which melt and integrate raw material particles, cold spraying prevents changes in the properties of raw material particles due to heat, thus allowing the formation of a coating layer on the particle aggregate without altering the molybdenum silicides in the hard particles.

[0043] Furthermore, if the base material particles are solid solution particles, the base material particles have not yet precipitated and hardened before they collide with the substrate in a solid state. Therefore, the base material (substrate) particles undergo plastic deformation to absorb the stress of the collision, preventing the hard particles from cracking or bouncing back.

[0044] Furthermore, within the base material particles, the components in solid solution precipitate due to the collision energy, forming crystallites with a crystallite size of 5 to 50 nm. As a result, the base material particles become precipitation-hardened copper-based alloy particles or iron-based alloy particles, improving wear resistance.

[0045] Then, due to the collision of raw material particles, some of the kinetic energy is converted into thermal energy, causing the surface of the raw material particles to melt and solidify locally, which causes the raw material particles to bond together and form a particle aggregate in which hard particles are dispersed within the base material particle group.

[0046] At this time, the surface of the raw material particles melts locally, causing diffusion and the formation of precipitates such as intermetallic compounds. However, since the temperature of the substrate and raw material particles is below the melting point of the raw material particles, the locally melted portion is rapidly cooled, leaving no time for the precipitates to crystallize.

[0047] Therefore, nanocrystals or amorphous materials are formed near the bonding interface between the substrate and the particles, and near the bonding interface between the particles themselves.

[0048] The amorphous or crystallite forms at particle interfaces can be identified by electron backscatter diffraction (EBSD) 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.

[0049] The spraying speed of the raw material particles, which include the base material particles and hard particles, is preferably 300 to 1200 m / s, and more preferably 500 to 1200 m / s.

[0050] Furthermore, the pressure of the working gas used to blow the above-mentioned raw material particles is preferably 2 to 7 MPa, and more preferably 3.5 to 7 MPa. If the working gas pressure is less than 2 MPa, the particle velocity may not be obtained, and the porosity may increase.

[0051] Furthermore, the temperature of the working gas is preferably 400 to 1000°C, and more preferably 600 to 1000°C, although this depends on the type and particle size of the raw materials. If the working gas temperature is below 400°C, the raw material particles may not undergo plastic deformation easily, leading to increased porosity and reduced wear resistance. Conversely, if the working gas temperature exceeds 1000°C, it approaches the melting point of the raw material particles, making the throat of the injection nozzle more prone to clogging.

[0052] Examples of working gases include nitrogen gas and helium gas, which may be used individually or in mixtures.

[0053] The thickness of the coating film described above depends on the temperature and sliding environment of the area where the sliding member is used, but is preferably 0.05 to 5.0 mm, and more preferably 0.1 to 1.0 mm.

[0054] If the thickness is less than 0.05 mm, the strength of the coating film itself may be insufficient, and plastic deformation may occur if the strength of the substrate is low. Furthermore, if it exceeds 5.0 mm, the relationship between residual stress generated during coating film formation and interfacial adhesion may make the coating film more prone to peeling.

[0055] There are no particular restrictions on the above-mentioned base material; metals conventionally used as sliding members in internal combustion engines can be used, but aluminum alloys are preferable due to their high thermal conductivity.

[0056] Examples of the above-mentioned aluminum alloys include AC2A, AC8A, AC4CH, and ADC12, which are specified in the Japanese Industrial Standards.

[0057] (sintering) As a sintering method, a sliding member can be formed by press-molding base material particles and hard particles, and then sintering them at a temperature below the melting point of the base material particles and hard particles.

[0058] <Particle aggregate> The above particle aggregate preferably has a porosity of 20 area% or less, more preferably 4 area% or less, and even more preferably 1 area% or less. The low porosity and dense structure improve the strength of the particle aggregate and enhance the wear resistance of the sliding member.

[0059] The porosity of the above-mentioned particle aggregate, as well as the area ratio of base material particles and hard particles, can be calculated by binarizing scanning electron microscope (SEM) images using image processing and then performing image analysis.

[0060] Because the above-mentioned sliding member exhibits excellent wear resistance at high temperatures, it can be suitably used as a sliding member in internal combustion engines, for example, in valve seats, valve lifters, pistons, piston rings, piston pins, cylinders, crankshafts, camshafts, and connecting rods. [Examples]

[0061] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples.

[0062] (Cold spray method) The hard particles and solid solution-state base material particles shown in Table 1 below were cold-sprayed under the following conditions to form a coating layer on the surface of a valve seat-shaped substrate. After that, finishing processes were performed to manufacture the sliding member. Cold spray device: PCS-1000, manufactured by Plasma Giken Kogyo Co., Ltd. Working gas: Nitrogen Operating gas temperature: 600℃~1000℃ Operating gas pressure: 4MPa~7MPa Spray distance: 20mm~35mm

[0063] (Sintering method) The hard particles and solid solution-state base material particles shown in Table 1 below are molded at a molding pressure of 6.5 ton / cm². 2 The valve seat was then compression-molded into a shape with an outer diameter of 30 mm, an inner diameter of 22 mm, and a height of 8 mm. This molded body was then sintered at 1130°C for 60 minutes in ammonia decomposition gas, and subsequently machined to produce a sliding component.

[0064] <Rating> The above sliding members were evaluated using the following method. The evaluation results, along with the manufacturing conditions, are shown in Table 1.

[0065] (Abrasion test) Test conditions Test method: Valve seat single-unit tapping abrasion test (Test equipment: manufactured by Takachiho Seiki Co., Ltd.) Test temperature: 300℃ Number of sittings: 1.44 million (3000 cpm x 8hr) Mating material (valve): JIS SUH35 Evaluation items: Valve seat and valve face wear (shape measurement)

[0066] (Molybdenum silicides in hard particles) Analytical method: The phase ratio of molybdenum silicide was measured by X-ray diffraction (XRD). The crystal structure was identified from the distribution of diffraction angle peaks, and the abundance (mass %) of each phase was calculated from the peak size. It goes without saying that volume %) is equivalent to area %). Analytical equipment: Rigaku Corporation's SmartLab horizontal X-ray diffractometer Detector: 2D detector (HyPix3000) After measuring the ratio of each phase using the method described above, the Raves phase, μ phase, R phase, other silicides, and matrix phase were identified using STEM+EDX and nanodiffraction within a radius of several nanometers, and the proportion of each phase was obtained.

[0067] (porosity) Cross-sections of the particle aggregate were captured using SEM composition imaging, with five fields of view within a field of view of 350 μm x 263 μm. The images were binarized using an image processing device, and the porosity was calculated. In addition, the area ratio of hard particles was calculated from the same images, and the area ratio of base material particles was obtained as the remainder.

[0068] [Table 1]

[0069] [Table 2]

[0070] [Table 3]

[0071] A comparison of Comparative Examples 1-7 and Examples 1-14 shows that when hard particles contain 35% or more molybdenum silicide, wear resistance improves, becoming comparable to components containing TRIBALOY® T-400, a hard particle with a cobalt group having a hard phase. A comparison of Examples 6-11 shows that as the Si content of the hard particles increases, the amount of molybdenum silicide also increases, improving wear resistance. Comparative Example 2 had a low Si content, and molybdenum silicate was not detected in the analysis. Example 6 exhibits superior wear resistance despite having less molybdenum silicide than Examples 1 and 2, indicating that a higher amount of molybdenum silicide in the Raves phase improves wear resistance.

Claims

1. A sliding member having a particle aggregate of base material particles and hard particles at least on its surface, wherein the hard particles are Molybdenum (Mo) in a concentration of 33.5 to 40% by mass. Silicon (Si) in a quantity of 2.39 to 15% by mass, It contains 0 to 8% by mass of chromium (Cr), The remainder consists of iron (Fe) and unavoidable impurities. A sliding member characterized by being an iron-based alloy particle containing 2.6 area percent or more of the Raves phase of molybdenum silicate.

2. The sliding member according to Claim 1, characterized in that the hard particles contain 90% or less of the Raves phase.

3. The sliding member according to Claim 1, characterized in that the hard particles contain 10% to 85% of the Raves phase.

4. The sliding member according to Claim 1, characterized in that the hard particles contain 30% to 80% of the Raves phase.

5. The sliding member according to claim 1, characterized in that the base material particles are copper-based alloy particles or iron-based alloy particles.

6. The sliding member according to claim 1, characterized in that the base material particles and the hard particles are sprayed onto a substrate, deformed, and laminated.

7. The sliding member according to claim 1, characterized in that the base material particles and the hard particles are sintered.

8. An internal combustion engine characterized by comprising the sliding member described in any one of Claims 1 to 7 above.

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