JP6944019B2 - Sliding members and plain bearings - Google Patents

Description

The present invention relates to a sliding member and a slide bearing in which a mating material slides on a sliding surface.

A tin-based overlay in which Cu is added to Sn, which is a soft metal, is known (see Patent Document 1). In Patent Document 1, by adding Cu as a reinforcing element to Sn, wear resistance and fatigue resistance are improved.

Japanese Unexamined Patent Publication No. 2002-310158

However, there is a problem that fatigue resistance is lowered when a heat load is applied when the tin overlay of Patent Document 1 is used. When a heat load is applied to the tin overlay of Patent Document 1, a hard intermetallic compound is formed by Sn and Cu. Then, an interface having a significantly different hardness difference is formed between the hard intermetallic compound and the soft Sn, and fatigue cracks are likely to occur at the interface. Further, the fatigue cracks propagate at the interface between the intermetallic compound and Sn, so that the fatigue resistance is lowered.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of improving fatigue resistance.

In order to achieve the above object, the sliding member and the sliding bearing of the present invention are sliding members in which a base layer, an intermediate layer and a coating layer are laminated in this order, and the coating layer is Sn as a first metal element. Cu as a second metal element that is harder than the first metal element and forms an intermetal compound with the first metal element, and C of 0.015 wt% or more and 0.100 wt% or less. The base layer is composed of Sn, Bi, and Cu.

In the above configuration, even if an intermetallic compound is formed by Sn which is the first metal element and Cu which is the second metal element when a heat load is applied, an appropriate amount of C serves as a diffusion barrier. The possibility of coarsening of the intermetallic compound can be reduced. Therefore, the interface between the soft Sn and the hard intermetallic compound can be kept in a small size. Therefore, even if fatigue cracks occur at the interface between the soft Sn and the hard intermetallic compound, the possibility that the fatigue cracks will greatly develop can be reduced and the fatigue resistance can be improved. Further, in the above configuration, the intermediate layer can suppress the diffusion of the elements contained in the base layer into the coating layer.

By setting C to 0.015 wt% or more, coarsening of the intermetallic compound can be suppressed, and it is more desirable to set C to 0.02 wt% or more. Further, it is possible to prevent the coating layer from becoming brittle by setting C to 0.100 wt% or less, and it is more desirable to set C to 0.075 wt% or less. The second metal element may be any element that is harder than Sn and forms an intermetallic compound with Sn, and may be, for example, Ag, Sb, Ni, or the like. The second metal element may be 0.5 wt% or more and 10.0 wt% or less, and preferably 1.0 wt% or more and 5.0 wt% or less. Sn as the first metal element constitutes the second metal, C and the rest of the unavoidable impurities.

It is a perspective view of the sliding member which concerns on embodiment of this invention. It is explanatory drawing of a fatigue test. It is a graph of carbon concentration and fatigue damage area ratio in overlay.

Here, embodiments of the present invention will be described in the following order.
(1) First embodiment:
(1-1) Configuration of sliding member:
(1-2) Measurement method:
(1-3) Manufacturing method of sliding member:
(2) Experimental results:
(3) Other embodiments:

(1) First embodiment:
(1-1) Configuration of sliding member:
FIG. 1 is a perspective view of a sliding member 1 according to an embodiment of the present invention. The sliding member 1 includes a back metal 10, a lining 11, and an overlay 12. The sliding member 1 is a metal member having a semicircular shape obtained by dividing a hollow cylinder into two equal parts in the diameter direction, and has a semicircular arc shape. The slide bearing A is formed by combining the two sliding members 1 so as to form a cylinder. The slide bearing A bearings a columnar mating shaft 2 (crankshaft of an engine) at a hollow portion formed inside. The outer diameter of the mating shaft 2 is formed to be slightly smaller than the inner diameter of the slide bearing A. Lubricating oil (engine oil) is supplied to the gap formed between the outer peripheral surface of the mating shaft 2 and the inner peripheral surface of the slide bearing A. At that time, the outer peripheral surface of the mating shaft 2 slides on the inner peripheral surface of the slide bearing A.

The sliding member 1 has a structure in which a back metal 10, a lining 11, and an overlay 12 are laminated in this order in order of distance from the center of curvature. Therefore, the back metal 10 constitutes the outermost layer of the sliding member 1, and the overlay 12 constitutes the innermost layer of the sliding member 1. The back metal 10, the lining 11, and the overlay 12 each have a certain thickness in the circumferential direction. The back metal 10 has a thickness of 1.8 mm, the lining 11 has a thickness of 0.2 mm, and the overlay 12 has a thickness of 10 μm. Twice the radius of the surface of the overlay 12 on the center side of the curvature (inner diameter of the sliding member 1) is 73 mm. Hereinafter, the inside means the curvature center side of the sliding member 1, and the outside means the side opposite to the curvature center of the sliding member 1. The inner surface of the overlay 12 constitutes the sliding surface of the mating shaft 2.

The back metal 10 is made of steel containing 0.15 wt% of C, 0.06 wt% of Mn, and the balance of Fe. The back metal 10 may be formed of a material capable of supporting the load from the mating shaft 2 via the lining 11 and the overlay 12, and may not necessarily be formed of steel.

The lining 11 is a layer laminated inside the back metal 10, and constitutes the base layer of the present invention. The lining 11 contains 10 wt% of Sn, 8 wt% of Bi, and the balance is composed of Cu and unavoidable impurities. The unavoidable impurities in the lining 11 are Mg, Ti, B, Pb, Cr and the like, which are impurities mixed in refining or scrap. The content of unavoidable impurities in the lining 11 is 1.0 wt% or less as a whole.

The overlay 12 is a layer laminated on the inner surface of the lining 11 and constitutes the coating layer of the present invention. In the overlay 12, the coating layer is composed of Sn as a first metal element, Cu and C as a second metal element forming an intermetallic compound with the first metal element, and unavoidable impurities. In the overlay 12 of the present embodiment, the Cu content is 3.0 wt%, the C content is 0.05 wt%, the total content of unavoidable impurities is 1.0 wt% or less, and the balance is It is Sn.

When a fatigue test piece (connecting rod R) having the same overlay 12 as the sliding member 1 described above was prepared and the fatigue damage area ratio was measured, the fatigue damage area ratio was as good as 3.0%. Even if an intermetallic compound is formed by the first metal element and the second metal element when a heat load is applied in the fatigue test described later, an appropriate amount of C acts as a diffusion barrier and the intermetallic compound becomes coarse. The possibility of doing so can be reduced. _{In the present embodiment, Cu 6} Sn ₅ and Cu ₃ Sn are precipitated in the overlay 12 as an intermetallic compound, but C serves as a diffusion barrier and can suppress the coarsening of _{Cu 6} Sn ₅ and Cu _{3 Sn.} As a result, the interface between the soft Sn and the hard intermetallic compound can be kept in a small size. Therefore, even if fatigue cracks occur at the interface between the soft Sn and the hard intermetallic compound, the possibility that the fatigue cracks will greatly develop can be reduced and the fatigue resistance can be improved.

(1-2) Measurement method:
The fatigue damage area ratio was measured by the following procedure. First, as shown in FIG. 2, a connecting rod R having columnar through holes formed at both ends in the length direction was prepared, and a test shaft H (hatching) was supported by the through holes at one end. An overlay 12 (black) similar to that of the sliding member 1 was formed on the inner peripheral surface of the through hole of the connecting rod R bearing the test shaft H. The test shaft H was supported on both outer sides of the connecting rod R in the axial direction of the test shaft H, and the test shaft H was rotated so that the sliding speed was 6.6 m / sec. The sliding speed is the relative speed between the surface of the overlay 12 and the test shaft H. The end of the connecting rod R on the opposite side of the test shaft H was connected to the moving body F that reciprocates in the length direction of the connecting rod R, and the reciprocating load of the moving body F was 57 MPa. Further, engine oil at 120 ° C. was supplied between the connecting rod R and the test shaft H.

The fatigue test of the overlay 12 was performed by continuing the above state for 50 hours. Then, after the fatigue test, the inner surface (sliding surface) of the overlay 12 is photographed from a position on a straight line orthogonal to the surface so that the straight line is the main optical axis, and the photographed image. An evaluation image was obtained. Then, a damaged portion of the surface of the overlay 12 projected on the evaluation image is observed and identified with a binocular (magnifying mirror), and the damaged portion area, which is the area of the damaged portion, is the overlay projected on the evaluation image. The percentage of the value divided by the area of the entire surface of 12 was measured as the fatigue damage area ratio.

Each numerical value shown in the above-described embodiment was measured by the following method. The mass of the elements constituting each layer of the sliding member 1 was measured by an ICP emission spectrophotometer (ICPS-8100 manufactured by Shimadzu Corporation). However, the carbon concentration in the overlay 12 was measured by a high-frequency induction heating furnace combustion infrared absorption method (JISG1211 carbon content analysis method for steel).

The thickness of each layer was measured by the following procedure. First, the axially vertical cross section of the sliding member 1 was polished with a cross section polisher (IB-09010CP manufactured by JEOL Ltd.). Then, the cross section of the sliding member 1 was photographed with an electron microscope (JSM-6610A manufactured by JEOL Ltd.) at a magnification of 7000 times to obtain image data of an observation image (reflected electron image). Then, the film thickness was measured by analyzing the observed image with an image analysis device (Luzex AP manufactured by Nireco Corporation).

(1-3) Manufacturing method of sliding member:
First, a low carbon steel flat plate having the same thickness as the back metal 10 was prepared.
Next, the powder of the material constituting the lining 11 is sprayed on the flat plate made of low carbon steel. Specifically, Cu powder, Bi powder, and Sn powder were sprayed on a flat plate of low carbon steel so as to have a mass ratio of each component in the lining 11 described above. As long as the mass ratio of each component in the lining 11 is satisfactory, alloy powders such as Cu—Bi and Cu—Sn may be sprayed on a flat plate of low carbon steel. The particle size of the powder was adjusted to 150 μm or less by a test sieve (JIS Z8801).

Next, the flat plate of low carbon steel and the powder sprayed on the flat plate were sintered. The sintering temperature was controlled to 700 to 1000 ° C., and sintering was performed in an inert atmosphere. After sintering, it was cooled. The lining 11 does not necessarily have to be formed by sintering, and may be formed by casting or the like.

When cooling is complete, a Cu alloy layer is formed on the flat plate of low carbon steel. The Cu alloy layer contains soft Bi particles precipitated during cooling.
Next, the low carbon steel on which the Cu alloy layer was formed was press-processed so that the hollow cylinder was divided into two equal parts in the diameter direction. At this time, press working was performed so that the outer diameter of the low carbon steel coincided with the outer diameter of the sliding member 1.

Next, the surface of the Cu alloy layer formed on the back metal 10 was cut. At this time, the cutting amount was controlled so that the thickness of the Cu alloy layer formed on the back metal 10 was the same as that of the lining 11. As a result, the lining 11 can be formed by the Cu alloy layer after cutting. The cutting process was performed by, for example, a lathe set with a cutting tool material made of sintered diamond. The surface of the lining 11 after cutting constitutes an interface between the lining 11 and the overlay 12.

Next, the overlay 12 was formed by laminating Sn on the surface of the lining 11 by electroplating to a thickness of 10 μm. The procedure for electroplating was as follows. First, the surface of the lining 11 was washed with water. Further, by pickling the surface of the lining 11, unnecessary oxides were removed from the surface of the lining 11. Then, the surface of the lining 11 was washed with water again.

When the above pretreatment was completed, electroplating was performed by supplying an electric current to the lining 11 immersed in the plating bath. The bath composition of the plating bath was composed of stannous nitrate: 28 g / l (Sn concentration), copper sulfate: 3 g / l (Cu concentration), inorganic ammonium salt: 100 g / l, and organic carboxylic acid: 80 g / l. The bath temperature of the plating bath was set to 30 ° C. Further, the current supplied to the lining 11 was a direct current, and the current density was 2.0 A / dm ² . After the electroplating was completed, it was washed with water and dried.

When the sliding member 1 was completed as described above, the sliding bearing A was formed by combining the two sliding members 1 in a cylindrical shape and attached to the engine.

(2) Experimental results:
In the same electroplating as in the first embodiment, Example 1 in which the concentration of the organic carboxylic acid was changed to 20 g / l, Example 2 in which the concentration of the organic carboxylic acid was changed to 40 g / l, and the concentration of the organic carboxylic acid. Example 3 (first embodiment) in which the concentration of organic carboxylic acid was changed to 80 g / l, Example 4 in which the concentration of organic carboxylic acid was changed to 100 g / l, and Comparative Example 1 in which the concentration of organic carboxylic acid was changed to 200 g / l. And prepared. Further, Comparative Example 2 in which electroplating was performed in a plating bath of a borofluoride bath (tin borofluoride, copper borofluoride) was prepared.

表１は、実施例１〜４と、比較例１，２におけるオーバーレイ１２中の炭素濃度と疲労損傷面積率とを示す。炭素濃度と疲労損傷面積率とは、第１実施形態と同様の手法によって計測した。表１に示すように、めっき浴における有機カルボン酸の濃度を大きくことにより、オーバーレイ１２中の炭素濃度を大きくすることができた。また、比較例２のように、有機物を含まないめっき浴を使用することにより、オーバーレイ１２中の炭素濃度をほぼ０とすることができた。

Table 1 shows the carbon concentration and the fatigue damage area ratio in the overlay 12 in Examples 1 to 4 and Comparative Examples 1 and 2. The carbon concentration and the fatigue damage area ratio were measured by the same method as in the first embodiment. As shown in Table 1, the carbon concentration in the overlay 12 could be increased by increasing the concentration of the organic carboxylic acid in the plating bath. Further, by using a plating bath containing no organic matter as in Comparative Example 2, the carbon concentration in the overlay 12 could be made almost 0.

FIG. 3 is a graph showing the relationship between the carbon concentration and the fatigue damage area ratio. As shown in the figure, it was found that in the carbon concentration range of 0.05 wt% or less, the higher the carbon concentration, the better the fatigue resistance. It is considered that the larger the carbon concentration, the more effectively _{the coarsening of Cu 6} Sn ₅ and Cu ₃ Sn could be suppressed. It was found that in the range of carbon concentration larger than 0.05 wt%, the smaller the carbon concentration, the better the fatigue resistance. It is considered that the smaller the carbon concentration, the more the overlay 12 could be prevented from becoming brittle due to C.

Further, in the graph of FIG. 3, as shown by hatching, it was found that it is desirable that C is 0.015 wt% or more and C is 0.100 wt% or less. Further, it is more desirable to set it to 0.02 wt% or more, and it is more desirable to set it to 0.075 wt% or less.

(3) Other embodiments:
In the first embodiment, Cu is adopted as the second metal element, but other elements (Ag, Sb, Ni, Au, etc.) that are harder than Sn (for example, have a higher moth hardness) are adopted as the second metal element. You may. Further, the intermetallic compound is not always formed when the sliding member 1 is used. For example, the precipitation of the intermetallic compound may be completed by performing a heat treatment in advance before using the sliding member 1. In this case as well, coarsening of the intermetallic compound can be suppressed by an appropriate amount of C.

Further, an intermediate layer may be inserted between the lining 11 and the overlay 12. The intermediate layer is preferably formed of a material that can prevent the elements of the lining 11 from diffusing into the overlay 12, and may be formed of, for example, Ni. The carbon concentration of the overlay 12 does not necessarily have to be adjusted by the carbon concentration in the plating bath of electroplating, and the method of forming the overlay 12 is not limited to electroplating. For example, the overlay 12 may be formed by sputtering or thin film deposition, or the carbon concentration may be adjusted during sputtering or thin film deposition. Further, after forming the overlay 12 having a low carbon concentration, the carbon concentration may be increased by diffusion or the like.

In the above embodiment, the sliding member 1 constituting the sliding bearing A bearing the crankshaft of the engine has been illustrated, but the sliding member 1 of the present invention may be used to form the sliding bearing A for other purposes. For example, the sliding member 1 of the present invention may be used to form a radial bearing such as a gear bush for a transmission, a piston pin bush, or a boss bush. Further, the sliding member of the present invention may be a thrust bearing, various washers, or a swash plate for a car air conditioner compressor. Further, the matrix of the lining 11 is not limited to the Cu alloy, and the material of the matrix may be selected according to the hardness of the mating shaft 2. Further, the back metal 10 is not essential and may be omitted.

1 ... sliding member, 2 ... mating shaft, 10 ... back metal, 11 ... lining, 12 ... overlay, A ... bearing, F ... moving body, H ... test shaft, R ... connecting rod

Claims (2)

A sliding member in which a base layer, an intermediate layer, and a coating layer are laminated in order.
The coating layer is
Sn as the first metal element and
Cu as a second metal element that is harder than the first metal element and forms an intermetallic compound with the first metal element,
0.015 wt% or more and 0. With C less than 02 wt%,
Inevitable impurities and
Characterized by consisting of
The base layer is
Sn and
Bi and
Cu and
A sliding member characterized by being composed of. A plain bearing in which a base layer, an intermediate layer, and a coating layer are laminated in order.
The coating layer is
Sn as the first metal element and
Cu as a second metal element that is harder than the first metal element and forms an intermetallic compound with the first metal element,
0.015 wt% or more and 0. With C less than 02 wt%,
Inevitable impurities and
Characterized by consisting of
The base layer is
Sn and
Bi and
Cu and
A plain bearing characterized by consisting of.

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