Bismuth-based overlay layer for sliding member

Abstract

Provided is a bismuth-based overlay layer having high fatigue resistance even when additive particles are contained.　A bismuth-based overlay layer for a sliding member according to the present invention includes: a polycrystalline matrix including crystal particles made of a material containing bismuth or a bismuth alloy; and additive particles dispersed in the matrix. The matrix includes a region in which crystal particles having one degree or less of grain orientation spread (GOS) accounts for 85% or more of all the crystal particles.

Description

Bismuth-based overlays for sliding components.

[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.

[0002] From the viewpoint of reducing environmental impact, bismuth is used as the matrix of an overlay for a sliding member. Such a bismuth-based overlay can contain hard particles or solid lubricant particles. This provides the overlay with wear resistance and low friction (Patent Document 1, Patent Document 2). For other prior art documents related to the present invention, see Patent Document 3.

[0003] Japanese Patent Publication No. 2003-156046 Japanese Patent Publication No. 6905926 British Patent Publication No. 2534120

[0004] When the sliding member is used as a bearing in 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 problem: Since the overlay uses a bismuth-based matrix, the brittleness inherent in the properties of bismuth affects the overlay, making it prone to fatigue. It has generally been thought that the fatigue resistance of bismuth-based overlays containing hard particles and solid lubricant particles is inferior to that of bismuth-based overlays that do not contain 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 used in a bearing of a high-power engine, it is required that the bismuth-based overlay contain the additive particles.

[0006] The present inventors have conducted extensive research to solve the above-mentioned 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 sliding member, comprising: a polycrystalline matrix containing crystal grains made of a material containing bismuth or a bismuth alloy; and additive particles dispersed in the matrix, wherein 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 the crystal grains.

[0007] The bismuth-based overlay of the first aspect thus defined improves its fatigue resistance while maintaining the properties (wear resistance, low friction, etc.) imparted to the overlay by the additive particles. Since crystal particles with a GOS of 1 or less are unlikely to become crack initiation points, adjusting their ratio to 85% or more is thought to reduce the likelihood of fatigue caused by cracks in the matrix. Here, the ratio of crystal particles refers to the ratio of the number of crystal particles.

[0008] The thickness of the overlay layer is not particularly limited and can be selected appropriately depending on the application of the sliding member. Bismuth alloys are composed primarily of bismuth (Bi) and one or more elements selected from lead (Pb), indium (In), tin (Sn), and antimony (Sb), or alloys thereof. The average grain size of the matrix crystal grains can be 0.1 μm to 5.0 μm. This average grain size was measured by observing the cross section of the overlay sample using any grain observation method and then using image analysis software to measure the "maximum ferret diameter" (the longest distance between any two points on the grain outline) and calculate the average value. GOS refers to the average misorientation between a given measurement point and all remaining measurement points within a crystal grain. For more details, see Kimura et al., "Analysis of Misorientation During Plastic Deformation of Stainless Steels by EBSD and X-ray Diffraction Methods," Transactions of the Japan Society of Mechanical Engineers (Part A), Vol. 71, No. 712 (2005-12). The contents of this paper are incorporated herein by reference.

[0009] The hard particles used as additive particles reinforce the mechanical properties of the bismuth-based overlay. Particles harder than bismuth or a bismuth alloy are used as additive particles to reinforce the wear resistance of the bismuth-based overlay. Such hard particles can be one or more selected from carbon fiber, glass fiber, boron nitride, aluminum oxide, silicon carbide, silicon oxide, aluminum nitride, and titanium oxide. 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 the hard particles can be measured by laser diffraction / scattering before adding them to the plating solution.

[0010] Solid lubricant particles are used as additive particles to reinforce the low friction properties of the bismuth-based overlay. These solid lubricant particles can be one or more selected from the group consisting of molybdenum disulfide, graphite, tungsten disulfide, and boron nitride platelet crystal particles. The average particle size of the solid lubricant can be 1 nm to 5.0 μm. It is more preferably 0.1 μm to 3.0 μm. Controlling GOS is easier when the solid lubricant is granular rather than platelet-shaped. The average particle size of the solid lubricant can be measured by laser diffraction / scattering before adding it 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 overlay functions such as adhesion, corrosion resistance, lipophilicity, and oil repellency.

[0012] The content of the additive particles in the matrix can 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 favorably exhibited in the bismuth-based overlay (second aspect). When a matrix is ​​used in which 85% or more of crystal particles containing bismuth or a bismuth alloy with a GOS of 1 degree or less are used, the proportion of crystal particles with a GOS of 1 degree or less can be increased more in a matrix containing additive particles in the above range than in a matrix not containing the additive particles.

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

[0014] The method for producing a bismuth-based overlay can be defined as follows: a step of treating the surfaces of additive particles to control the wettability of the surfaces, a step of introducing the surface-treated additive particles into a plating solution for bismuth or a bismuth alloy and stirring the same, a step of preparing a substrate for a slide member, and a laminating step of laminating a bismuth-based overlay on the surface of the substrate for the slide member using the plating solution containing the additive particles.

[0015] In the above, to control the surface wettability of the additive particles, any treatment method can be selected, such as plasma treatment or UV irradiation treatment. By controlling and increasing the surface wettability of the additive particles, aggregation of the additive particles in the plating solution is prevented. This improves the dispersibility of the additive particles. The amount of additive particles in the plating solution is preferably 15 g to 150 g per 1 L of plating solution. More preferably, it is 40 g to 120 g / 1 L. This makes it easy to achieve that 85% or more of all crystal particles in the bismuth or bismuth alloy that constitutes the matrix of the bismuth-based overlay have a GOS of 1 or less. While sufficient stirring of the plating solution is required, strict control of the stirring conditions was not necessary.

[0016] FIG. 1 is a schematic diagram showing a sliding member according to an embodiment of the present invention.

[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 sequentially laminated on a backing metal layer 2. The backing metal layer 2 used in the slide 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, or the like may be formed on the bearing alloy layer. The shape of such a slide member 1 can be arbitrarily designed depending on the diameter and operation of the sliding counterpart (sliding member).

[0018] The matrix 5a of the bismuth-based overlay 5 is a polycrystalline material made of bismuth or a bismuth alloy. The matrix 5a contains uniformly dispersed additive particles 5b. The bismuth-based overlay 5 can be formed by known methods such as electroplating, vacuum sputtering, thermal spraying, and cold spraying.

[0019] In this example, a bismuth-based overlay layer was created using electroplating. First, a plating solution for bismuth was prepared. There are no particular restrictions on the plating solution, and one that is compatible with the additive particles and allows for composite plating was selected as appropriate. In this example, a sulfonic acid bath was used. The reinforcing particles were also UV-treated to make their surfaces more wettable to the plating solution. The UV treatment device was a UV surface cleaning and modification device manufactured by Asumi Giken Co., Ltd. (Model: ASM1101N). The conditions were a 5W to 250W total output irradiator with 0.1mW / cm ２ ~30mW / cm ２ The irradiation intensity was controlled by 185 nm to 365 nm, and the treatment time was controlled by 5 minutes to 48 hours.

[0020] The amount of additive particles added to the plating solution is 15 g / L to 150 g / L, 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 a combination of ultrasonic stirring and mechanical stirring for 0.2 to 2.0 hours, preferably 1.0 hour. The ultrasonic stirrer used was a 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 a 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 was cleaned and degreased by a general-purpose method. The surface of the substrate, the bearing alloy layer 3, was brought into contact with a plating solution to which additive particles had been added and which had been thoroughly stirred, and a current density of 1 to 6 A / dm ２ Electroplating was performed under the following conditions: plating 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 15 μm. Although the thickness is not limited to this, it is preferable that it be up to 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. In the above, the integrated light amount is the illuminance (mW / cm ２ ) and time (seconds).

[0023] The results of Example 3 and Comparative Example 1 in Table 1 show that the fatigue area is narrowed and fatigue resistance is improved when the proportion of crystal grains with a GOS of 1 degree or less is 85% or more of all crystal grains. It is even more preferable to set this proportion 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 all crystal particles. As the content of SiC, which is a hard particle, increased, the proportion of GOS of 1 degree or less tended to decrease when the content exceeded a certain amount. 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 inventors' investigations, it is preferable that the additive particle content be 1.0 vol% to 15.0 vol%.

[0025] The GOS was obtained as follows. Before fatigue testing, samples for the Examples and Comparative Examples were prepared as follows. The samples were cut at the desired area (the area expected to be subjected to the highest load in the Examples and Comparative Examples), embedded in resin, and mechanically polished on the cut surface. Mechanical polishing included paper polishing, buffing (diamond slurry), and polishing (colloidal silica). A conductive coating (carbon, gold, etc.) was applied to the polished surface, followed by ion milling. EBSD equipment: FEI Versa 3D DualBeam SEM (registered trademark) 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; 4000x, grain definition; orientation difference; 10° or greater. The step size was set to ensure 10 or more measurement points within the smallest grain size. The scanning pattern can be either a square or hexagonal lattice, but can be arbitrarily determined depending on the crystal structure. To improve measurement accuracy, the measurement area (scan area) can be arbitrarily set to include 1,000 or more crystal grains in the overlay. The EBSD images obtained in this manner were processed using data analysis software to obtain the GOS of all crystal grains in the scan area, and the percentage of crystal grains with a GOS of 1 or less was calculated. If significant noise was observed, noise removal was performed (using the Auto Clean-up function of AZtecCrystal, an EBSD data analysis software manufactured by Oxford Electronics, Inc., for both the examples and comparative examples). Furthermore, according to the inventors' investigations, in bismuth-based overlay layers fabricated by electroplating, the percentage of crystal grains with a GOS of 1 or less was approximately the same in all observed areas.

[0026] The fatigue test conditions were as follows: Bearing dimensions: Φ56 x L14.2 x t1.5 (mm) Oil clearance: 0.060 (mm) Rotation speed: 3600 (rpm) Load: 100 (MPa) Frequency: 60 (Hz) Lubricating oil: VG68 Oil supply temperature: 110 (°C) Shaft material: S55C hardened Shaft roughness: Ra 0.05 ± 0.01 (μm) Test time: 20 (hours) How the load was applied: The load was increased from 0 load every 15 minutes, 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 sample sliding member 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 of added particles in the coating (vol%) is the area ratio (the area ratio of the added particles to the entire overlay) obtained by cross-sectional observation. Hardness HV was measured on 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 measuring device (manufactured in-house), and the amount of change in thickness (amount of wear) after the test was obtained. 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-described embodiments of the invention, and various modifications within the scope of the claims and within the scope that can be easily conceived by a person skilled in the art are also included in the present invention.

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

Claims

1. A bismuth-based overlay for a sliding member, comprising: a polycrystalline matrix containing crystal grains made of a material containing bismuth or a bismuth alloy; and additive particles dispersed in the matrix, the matrix including an area in which the crystal grains having a GOS (Grain Orientation Spread) of 1 degree or less account for 85% or more of all crystal grains.

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

3. The bismuth-based overlay of claim 1, having a hardness of 20 HV or greater.

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

5. A method for manufacturing a slide member, comprising: a step of treating surfaces of additive particles to control wettability of the surfaces; a step of introducing the treated additive particles into a plating solution for bismuth or a bismuth alloy and stirring the same; a step of preparing a base body of a slide member; and a lamination step of laminating a bismuth-based overlay on the surface of the base body of the slide member using the plating solution into which the additive particles have been introduced.

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

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