Bismuth-based overlay layer for sliding member

Abstract

To provide a bismuth-based overlay layer having high fatigue resistance even when additive particles are included.SOLUTION: A bismuth-based overlay layer for a sliding member comprises a polycrystalline matrix containing crystal particles composed of a material containing bismuth or a bismuth alloy, and additive particles dispersed in the matrix. The matrix includes a region where crystal particles having a Grain Orientation Spread (GOS) of 1 degree or less account for 85% or more of all crystal particles.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an improvement in a bismuth-based overlay for a slide member, a method for producing the same, and a slide member provided with the overlay. [Background technology]

[0002] From the viewpoint of reducing the environmental load, bismuth is used as a matrix for overlay layers for sliding members. Such bismuth-based overlay layers can contain hard particles or solid lubricant particles, which gives the overlay layers wear resistance and low friction (Patent Document 1, Patent Document 2). For other prior art documents related to the present invention, please refer to Patent Document 3. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-156046 A [Patent Document 2] Patent No. 6905926 [Patent Document 3] British Patent Publication No. 2534120 Summary of the Invention [Problem to be solved by the invention]

[0004] When the sliding member is used as a bearing for today's high-power engines, it has been found that the bismuth-based overlay containing hard particles and solid lubricant particles as described above has the following problems. That is, since the overlay layer is made of a bismuth-based matrix, the brittleness due to the characteristics of bismuth affects the overlay layer, making the overlay layer more susceptible to fatigue. It has generally been believed that the fatigue resistance of a bismuth-based overlay containing hard particles or solid lubricant particles is inferior to the fatigue resistance of a bismuth-based overlay not containing these particles.

[0005] The additive particles, such as hard particles and solid lubricant particles, impart wear resistance and low friction to the bismuth-based overlay, and therefore, when the bismuth-based overlay is applied to a sliding member such as a bearing of a high-power engine, it is required that the bismuth-based overlay contains the additive particles. [Means for solving the problem]

[0006] The present inventors have conducted extensive research to solve the above problems, and have come up with the following invention by focusing on the misorientation of crystal grains constituting the matrix of a bismuth-based overlay. That is, a first aspect of the present invention is defined as follows. A bismuth-based overlay for a slide member, comprising: The present invention comprises a polycrystalline matrix including crystal grains made of a material including bismuth or a bismuth alloy, and additive grains dispersed in the matrix, The matrix of the bismuth-based overlay includes a region in which the crystal grains having a grain orientation spread (GOS) of 1 degree or less account for 85% or more of all the crystal grains.

[0007] The bismuth-based overlay of the first aspect thus defined improves fatigue resistance while maintaining the properties (wear resistance, low friction, etc.) imparted to the overlay by the additive particles. It is believed that because crystal particles with a GOS of 1 degree or less are unlikely to become the starting point of cracks, adjusting their ratio to 85% or more makes it less likely that fatigue caused by cracks will occur in the matrix. Here, the ratio of crystal grains refers to the ratio of the number of crystal grains.

[0008] The thickness of the overlay layer is not particularly limited and may be appropriately selected depending on the application of the sliding member, etc. The bismuth alloy is a material containing bismuth (Bi) as a main component and one or more elements selected from lead (Pb), indium (In), tin (Sn), antimony (Sb), etc., or an alloy of these elements. The average grain size of the crystal grains that make up the matrix can be 0.1 μm to 5.0 μm. This average grain size was measured by using any grain observation method on the cross section of the overlay sample, and then measuring the "maximum ferret diameter" (the longest distance between any two points on the outline of the grain) using image analysis software to calculate the average value. GOS refers to the average value of misorientation between a certain measurement point and all other measurement points within a crystal grain. For more details, see Kimura et al., "Analysis of Misorientation in Plastic Deformation of Stainless Steel by EBSD and X-ray Diffraction Methods," Transactions of the Japan Society of Mechanical Engineers (Series A), Vol. 71, No. 712 (2005-12). The contents of this paper are incorporated herein by reference.

[0009] The hard particles as additive particles enhance the mechanical properties of the bismuth-based overlay layer. As additive particles for reinforcing the wear resistance of the bismuth-based overlay, particles harder than bismuth or a bismuth alloy are used. As such hard particles, one or more selected from carbon fiber, glass fiber, boron nitride, aluminum oxide, silicon carbide, silicon oxide, aluminum nitride, and titanium oxide can be used. The average particle size of the hard particles can be 1 nm to 10 μm, and more preferably 0.1 μm to 3.0 μm. The average particle size of such hard particles can be obtained by measuring with a laser diffraction / scattering method before being added to the plating solution.

[0010] The additive particles for reinforcing the low friction properties of the bismuth-based overlay are solid lubricant particles, which may be one or more of the plate-like crystal particles of molybdenum disulfide, graphite, tungsten disulfide, and boron nitride. The average particle size of the solid lubricant can be 1 nm to 5.0 μm. More preferably, it is 0.1 μm to 3.0 μm. The solid lubricant is easier to control the GOS when it is in a granular shape than in a plate shape. The average particle size of the solid lubricant can be measured by a laser diffraction / scattering method before being added to the plating solution.

[0011] The additive particles are not limited to hard particles or solid lubricants, and any other additive particles can be contained in any amount to improve the overlay functions such as adhesion, corrosion resistance, lipophilicity, and oil repellency.

[0012] The content of the additive particles in the matrix may be 1.0 to 15.0 vol %. By setting the content of the additive particles in this range, the properties derived from the additive particles can be suitably exhibited in the bismuth-based overlay (second aspect). When a matrix is ​​used in which 85% or more of crystal grains containing bismuth or a bismuth alloy with a GOS of 1 degree or less are used, the proportion of crystal grains with a GOS of 1 degree or less can be increased more in a matrix containing additive particles within the above range than in a matrix not containing additive particles.

[0013] The hardness of the bismuth-based overlay is preferably 20 HV or more (third aspect). An overlay having such a hardness has excellent abrasion resistance. The hardness of the bismuth-based overlay can be adjusted by changing the content of the hard particles. As described above, the amount of the hard particles is preferably selected from the range of 1.0 to 15.0 vol% in order to control the proportion of crystal grains with a GOS of 1 degree or less.

[0014] The method for producing the bismuth-based overlay can be defined as follows. treating the surface of the additive particles to control the wettability of the surface; The surface-treated additive particles are introduced into a plating solution for bismuth or a bismuth alloy and stirred; Providing a substrate for a slide member; a lamination step of laminating a bismuth-based overlay on a surface of the substrate of the sliding member using the plating solution containing the additive particles; A method for producing a sliding member comprising the steps of:

[0015] In the above, in order to control the wettability of the surface of the additive particle, any treatment method such as plasma treatment or UV irradiation treatment can be selected for the surface. By controlling and enhancing the wettability of the surfaces of the additive particles, the additive particles are prevented from agglomerating together in the plating solution, thereby enhancing the dispersibility of the additive particles. The amount of particles added to the plating solution is preferably 15g to 150g per 1L of plating solution. More preferably, it is 40g to 120g / 1L. This makes it easy to achieve that crystal particles with a GOS of 1 degree or less account for 85% or more of all crystal particles in the bismuth or bismuth alloy that constitutes the matrix of the bismuth-based overlay. Although the plating solution is required to be sufficiently stirred, there is no need to strictly control the stirring conditions. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram showing a sliding member according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An embodiment of the present invention will be described below. As shown in FIG. 1, a slide member 1 according to an embodiment of the present invention has a structure in which a bearing alloy layer 3 and a bismuth-based overlay layer 5 are laminated in this order on a back metal layer 2. The backing metal layer 2 applied to the sliding member 1 is made of a general steel material, and a soft metal material such as copper or a copper alloy is used for the bearing alloy layer 3. An intermediate layer made of Ag, Ni, etc. may be formed on the bearing alloy layer. The shape of the sliding member 1 can be arbitrarily designed according to the diameter and movement of the other member (sliding member) that it slides against.

[0018] The matrix 5a of the bismuth-based overlay 5 is a polycrystal made of bismuth or a bismuth alloy, and additive particles 5b are uniformly dispersed in the matrix 5a. This bismuth-based overlayer 5 can be applied by known methods such as electroplating, vacuum sputtering, thermal and cold spray.

[0019] In this example, an electroplating technique was employed to create the bismuth-based overlay layer. First, prepare the plating solution for bismuth. There are no particular restrictions on the plating solution, and a solution that can be used for composite plating should be selected taking into consideration the compatibility with the additive particles. In this example, a sulfonic acid bath was used. The reinforcing particles are also UV-treated to make their surfaces more wettable by the plating solution. The UV treatment equipment is a UV surface cleaning and modification equipment ASM1101N manufactured by Asumi Giken Co., Ltd. The conditions are a total output irradiator of 5W to 250W and 0.1mW / cm 2 ~30mW / cm 2 The illuminance was controlled by 100 nm and the treatment time was controlled by 5 minutes to 48 hours. The wavelength was selected in the range of 185 nm to 365 nm.

[0020] The amount of additive particles added to the plating solution is 15 g / L to 150 g / L, and preferably 40 g / L to 120 g / L. The plating solution to which the additive particles have been added is thoroughly stirred to prevent the additive particles from agglomerating. The stirring conditions are not particularly limited, but it is preferable to use ultrasonic stirring and mechanical stirring in combination for 0.2 to 2.0 hours, preferably 1.0 hour. The ultrasonic stirrer used was QS12 manufactured by Ultrawave Ltd, and the stirring conditions were an ultrasonic frequency of 32 to 38 kHz and an ultrasonic output of 200 W. On the other hand, the mechanical stirrer used was MICROSTAR 7.5 control manufactured by IKA England Ltd, and stirring was performed at 110 to 2000 rpm, preferably 600 to 1000 rpm.

[0021] The bismuth-based overlay 5 was formed as follows. The surface of the bearing alloy layer 3 is cleaned and degreased by a general-purpose method. The surface of the bearing alloy layer 3, which is the substrate, is brought into contact with the plating solution to which additive particles have been added and which has been sufficiently stirred, and a current density of 1 to 6 A / dm 2 Electroplating was carried out under the following conditions: plating bath temperature: 20 to 50°C. Those skilled in the art will understand that these plating conditions are not fixed, but are appropriately selected based on the experience of the plating operator. The thickness of the bismuth-based overlay 5 was set to 15 μm. Although the thickness is not limited to this, it is preferable that the thickness is set to a maximum of 30 μm from the viewpoint of fatigue resistance.

[0022] The properties of the bismuth-based overlays 5 of the examples and comparative examples are shown in Tables 1 and 2. [Table 1] In the above, the integrated light amount is the illuminance (mW / cm 2 ) multiplied by time (seconds). [Table 2]

[0023] From the results of Example 3 and Comparative Example 1 in Table 1, it can be seen that when the ratio of crystal grains with a GOS of 1 degree or less is 85% or more of all crystal grains, the fatigue area is narrowed and fatigue resistance is improved. It is more preferable to set the ratio to 90% or more (see Examples 2 and 3).

[0024] As shown in Table 2, the results of Examples 6 to 11, in which the additive particles were SiC and the content (vol%) was varied, showed that when the additive particle content was 0.5 vol% to 20.3 vol%, the proportion of crystal particles with a GOS of 1 degree or less could be made 85% or more of the total crystal particles. As the content of hard particles such as SiC increased, the proportion of particles with GOS below 1 increased, and when the content exceeded a certain amount, the proportion decreased. On the other hand, in terms of wear resistance, a content of 1.0 vol% or more was superior. From the above, according to the study by the present inventors, the content of the additive particles is preferably set to 1.0 vol % to 15.0 vol %.

[0025] In the above, GOS was obtained as follows. Before the fatigue test, the samples of the examples and comparative examples were prepared as follows. The specimen was cut at the desired area (the area expected to be most heavily loaded in the examples and comparative examples), and the cut surface of the resin-embedded specimen was mechanically polished. The mechanical polishing process consisted of paper polishing, buff polishing (diamond slurry), and polishing (colloidal silica). A conductive coating (carbon, gold, etc.) was applied to the polished surface, and then ion milling was performed. EBSD Instrument: FEI Versa 3D DualBeam SEM equipped with a Symmetry-2 EBSD detector Measurement conditions: Scan area: 100 μm × 22.9 μm, step size: 30 nm, collection speed: approximately 2000 cps, magnification: 4000 times, crystal grain definition: orientation difference 10 degrees or more In the above, the step size was set so that 10 or more measurement points could be obtained within the smallest crystal grain. The scanning pattern can be either a square lattice or a hexagonal lattice, but can be determined arbitrarily depending on the crystal structure. The measurement area (scan area) can be arbitrarily set so as to include 1000 or more crystal grains in the overlay in order to improve measurement accuracy. The EBSD image obtained in this way was processed with data analysis software to obtain the GOS of all crystal grains contained in the scan area, and the percentage of crystal grains contained therein with a GOS of 1 degree or less was calculated. When obvious noise was confirmed, noise removal processing was performed (in the examples and comparative examples, the Auto Clean-up function of the EBSD data analysis software AZtecCrystal manufactured by Oxford was used). According to the investigations of the present inventors, in the bismuth-based overlay produced by electroplating, the proportion of crystal grains with a GOS of 1 degree or less was approximately the same in all observed regions.

[0026] The fatigue test conditions were as follows: Bearing dimensions: Φ56×L14.2×t1.5 (mm) Oil clearance: 0.060 (mm) Rotational speed: 3600 (rpm) Load: 100 (MPa) Frequency: 60 (Hz) Lubricating oil: VG68 Oil temperature: 110 (°C) Shaft material: S55C hardened Shaft roughness: Ra0.05±0.01 (μm) Exam duration: 20 (hours) Load application: The load was increased every 15 minutes starting from 0 load, and after 1.5 hours a load of 100 MPa was applied continuously for 20 hours.

[0027] After repeatedly applying a load from the radial direction to a cylindrical sliding member (bearing) into which a rotating shaft is fitted, the surface of the overlay layer of the sliding member sample is observed. Any cracked areas on this surface are fatigued areas. The overlay surface of the sliding member is photographed with a microscope (Keyence VHX-8000), and the resulting images are processed using the attached software to calculate the area ratio of the cracked areas to the entire surface. The obtained area ratios are shown in Tables 1 and 2 as fatigue area ratios. A fatigue area ratio of 20% or less is considered to be fatigue resistant.

[0028] The amount (vol%) of the added particles in the coating is the area ratio (the area ratio of the added particles to the entire overlay) obtained by cross-sectional observation. Hardness HV was measured from cross-sectional samples using a micro Vickers hardness tester (Mitutoyo HM-220). The amount of wear was obtained as follows. The thickness of the overlay layer was measured 1 mm from the edge before and after the test using a thickness gauge (manufactured by our company) to obtain the amount of change in thickness (amount of wear) after the test. The results in Table 2 are the average values ​​of two locations, 1 mm from the left edge and 1 mm from the right edge.

[0029] The present invention is not limited to the above-mentioned embodiment of the invention. Various modifications within the scope of the claims and within the scope of those skilled in the art are also included in the present invention. [Explanation of symbols]

[0030] 1 Sliding member 2 Backing layer 3 Bearing alloy 5 Bismuth-based overlay

Claims

1. A bismuth-based overlay for a slide member, comprising: The present invention comprises a polycrystalline matrix including crystal grains made of a material including bismuth or a bismuth alloy, and additive grains dispersed in the matrix, The matrix includes a region in which the crystal grains having a grain orientation spread (GOS) of 1 degree or less account for 85% or more of all crystal grains.

2. 2. The bismuth-based overlay of claim 1, wherein the content of the additive particles in the matrix is ​​1.0 vol % to 15.0 vol %.

3. 2. The bismuth-based overlay of claim 1 having a hardness of at least 20 HV.

4. A sliding member comprising the bismuth-based overlay according to any one of claims 1 to 3.

5. treating the surface of the additive particles to control the wettability of the surface; Adding the treated additive particles to a plating solution for bismuth or bismuth alloy and stirring the solution; Providing a substrate for a slide member; a lamination step of laminating a bismuth-based overlay on a surface of the substrate of the sliding member using the plating solution containing the additive particles; A method for producing a sliding member comprising the steps of:

6. 6. The method according to claim 5, wherein the amount of the additive particles added to the plating solution is 15 g to 150 g per 1 L of the plating solution.

7. The method according to claim 5 , further comprising the step of subjecting a surface of the additive particles to a plasma treatment or a UV irradiation treatment to improve wettability of the surface with respect to the plating solution.

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