Patent Application
20230160425
The present invention relates to a sliding member and a sliding bearing in which a counterpart member slides on a sliding surface.
Sliding bearings in which 0.3 to 25 vol % of inorganic particles are dispersed in a plating film are known (see Patent Literature 1). In Patent Literature 1, wear resistance can be improved by the inorganic particles contained in the plating film.
However, there is a problem of technical difficulty in dispersing inorganic particles in a plating film as in Patent Literature 1. Specifically, there is a problem that agglomeration of the inorganic particles occurs and that it is difficult to control the eutectoid rate, at the time of plating. As a result, it is not possible to stably control the dispersion state of the inorganic particles in the plating film and to realize good wear resistance.
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of realizing good wear resistance with a simple structure.
To achieve the above object, a sliding member and a sliding bearing according to the present invention are a sliding member and a sliding bearing each including a base layer and a coating layer formed on the base layer, the coating layer having a sliding surface with a counterpart member, in which the base layer is formed of a hard material that is harder than the coating layer, and in which the average concentration of a diffusion component of the hard material diffused from the base layer is 4 wt % or more in an evaluation range, in the coating layer, in which the distance from an interface with the base layer is 1 μm or more and 2 μm or less.
In the above structure, the coating layer is formed of a material softer than the hard material for the base layer, but the diffusion component from the base layer diffuses into the coating layer, whereby wear resistance can be improved. Further, by diffusing the hard material from the base layer into the coating layer, it is possible to easily improve the wear resistance. By diffusing the hard material from the base layer into the coating layer, it is possible to maintain the surface side of the coating layer far from the base layer in a soft state, and to obtain good initial conformability. By setting the average concentration of the diffusion component in the evaluation range in which the distance from the interface with the base layer is 1 μm or more and 2 μm or less to 4 wt % or more, good wear resistance can be exhibited at the latest at the stage where wear has progressed to the evaluation range. It is more desirable that the average concentration of the diffusion component in the evaluation range be 8.2 wt % or more.
Here, the coating layer may be formed of Bi, Sn, Pb, In, or Sb. Bi, Sn, Pb, In, and Sb all have low hardness (for example, Mohs' hardness) and are suitable as materials softer than the hard material for the base layer. On the other hand, the hard material for the base layer may be any material as long as it is harder than these materials for the coating layer and can diffuse into the coating layer. The base layer may be formed of a single element metal, an alloy, or a material in which various particles are dispersed in the matrix.
Further, the diffusion component from the base layer may diffuse into the coating layer at least by grain boundary diffusion at the crystal grain boundaries of the coating layer. This strengthens a portion of the sliding surface where the grain boundaries of the crystal grains of the coating layer are exposed, while the flexibility can be maintained at a portion thereof where the portion (intragranular) other than the grain boundaries of the crystal grains of the coating layer is exposed. Therefore, it is possible to achieve both wear resistance and conformability. Incidentally, it suffices that the diffusion component includes at least a component diffused by grain boundary diffusion, and the diffusion component may include an intragranular diffusion component and a grain boundary diffusion component.
Furthermore, in the evaluation range, the standard deviation of the concentration of the diffusion component in a direction parallel to the interface may be 3 wt % or more. When the standard deviation of the concentration of the diffusion component in the direction parallel to the interface between the base layer and the coating layer is 3 wt % or more in this manner, it can be determined that the diffusion of the diffusion component is biased toward the grain boundaries.
Embodiments of the present invention will be described in the following order.
(1-1) Structure of Sliding Member:
(1-2) Measurement Method:
(1-3) Method for Manufacturing Sliding Member:
(1-1) Structure of Sliding Member:
The sliding member 1 has a structure in which the back metal 10, the lining 11, and the overlay 12 are laminated in an order of being distant 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 constant thickness in the circumferential direction. The thickness of the back metal 10 is 1.8 mm, the thickness of the lining 11 is 0.2 mm, and the thickness of the overlay 12 is 10 μm. The diameter of the surface on the curvature center side of the overlay 12 (the inner diameter of the sliding member 1) is 73 mm. Hereinafter, the term “inner side” means the curvature center side of the sliding member 1, and the term “outer side” means the side opposite to the center of curvature of the sliding member 1. The inner surface of the overlay 12 constitutes the sliding surface for the counter shaft 2.
The back metal 10 is formed of steel containing 0.15 wt % of C, 0.06 wt % of Mn, and the balance Fe. It suffices that the back metal 10 is formed of a material that can support the load from the counter shaft 2 via the lining 11 and the overlay 12, and the back metal 10 may not necessarily be formed of steel.
The lining 11 is a layer laminated on the inner side of 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 consisting of Cu and unavoidable impurities. The unavoidable impurities of the lining 11 are Mg, Ti, B, Pb, Cr, and the like, and are impurities mixed in refining or scrapping. The content of the unavoidable impurities 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. The overlay 12 is composed of Bi, the diffusion component from the lining 11 and unavoidable impurities, and the content of the unavoidable impurities is 1.0 wt % or less.
As shown in
In the overlay 12, as the distance from the interface with the lining 11 increases, the concentration of Cu as the diffusion component from the lining 11 decreases. Note that Sn contained in the lining 11 also diffuses into the overlay 12 similarly to Cu.
In
In the present embodiment described above, the diffusion component from the lining 11 diffuses into the overlay 12, so that the wear resistance can be improved. Further, by diffusing Cu serving as the hard material into the overlay 12 serving as the coating layer from the lining 11 serving as the base layer, it is possible to easily improve the wear resistance. By diffusing Cu into the overlay 12, it is possible to maintain the surface side of the overlay 12 far from the lining 11 in a soft state, and to obtain good initial conformability. Further, by setting the average concentration of the diffusion component (Cu) in the evaluation range E where the distance from the interface between the lining 11 and the overlay 12 is 1 μm or more and 2 μm or less to 8.2 wt %, good wear resistance can be exhibited at the latest at the stage where wear has progressed to the evaluation range E. The present inventor has confirmed that, by managing the average concentration of the diffusion component in the evaluation range E in which the distance from the interface between the lining 11 and the overlay 12 is 1 μm or more and 2 μm or less to be 4 wt % or more, the wear resistance is improved as compared with the case where the average concentration of the diffusion component is less than 4 wt %.
Further, the diffusion component from the lining 11 is diffused in the overlay 12 by grain boundary diffusion. This strengthens a portion of the sliding surface S where the grain boundaries of the crystal grains 12a of the overlay 12 are exposed, while the flexibility can be maintained at a portion thereof where the portion (intragranular) other than the grain boundaries of the crystal grains 12a is exposed. Therefore, it is possible to achieve both wear resistance and conformability. Furthermore, in the evaluation range E, the standard deviation of the concentration of the diffusion component in the direction parallel to the interface between the lining 11 and the overlay 12 is 5.6 wt % which is 3 wt % or more. When the standard deviation of the concentration of the diffusion component in the direction parallel to the interface is 3 wt % or more in this manner, it can be determined that the diffusion of the diffusion component is biased toward the grain boundary, of grain boundary diffusion and intragranular diffusion. The present inventor has confirmed that, by managing the standard deviation of the concentration of the diffusion component in the direction parallel to the interface between the lining 11 and the overlay 12 to be 3 wt % or more, the conformability is improved as compared with the case where the standard deviation of the concentration of the diffusion component is less than 3 wt %.
(1-2) Measurement method:
Each of the numerical values shown in the above embodiment was measured by the following method. The mass of the element constituting each of the layers of the sliding member 1 was measured by an ICP emission spectroscopic analyzer (ICPS-8100 manufactured by Shimadzu Corporation).
The thickness of each of the layers was measured by the following procedures. First, the vertical cross section in the axial direction of the sliding member 1 was polished with a cross section polisher (IB-09010CP manufactured by JEOL Ltd.). Image data of an observation image (backscattered electron image) was obtained by photographing the cross section of the sliding member 1 with an electron microscope (JSM-6610A manufactured by JEOL Ltd.) at a magnification of 7000 times. Then, the film thickness was measured by analyzing the observation image with an image analyzer (Luzex AP manufactured by NIRECO).
Further, an analysis image was obtained by photographing the cross section of the sliding member 1 with the electron microscope (JSM-6610A manufactured by JEOL Ltd.) at a magnification of 15000 times. Then, the analysis image was analyzed by the image analyzer (Luzex AP manufactured by NIRECO). Specifically, the average line of the waviness curve (JIS B 0601) forming the interface between the lining 11 and the overlay 12 was specified as the boundary line X by the image analyzer. Further, the grain boundaries of the respective crystal grains 12a in the overlay 12 were detected by the image analyzer, and the long axis LA, the short axis SA, and the crystal growth direction of each of the crystal grains 12a were specified. The grain boundaries of the respective crystal grains 12a can be detected by edge detection, for example. Further, the average value of the ratio obtained by dividing the length of the long axis LA in each of the crystal grains 12a by the short axis SA was calculated as the average aspect ratio. Note that the crystal grains 12a having a circle equivalent diameter of less than 0.1 μm were excluded from the target for calculation of the aspect ratio.
Further, the concentration of Cu in the evaluation range E in
(1-3) Method for Manufacturing Sliding Member:
First, a flat plate of low carbon steel having the same thickness as the back metal 10 was prepared.
Next, powder of a material constituting the lining 11 was scattered on the flat plate formed of low carbon steel. Specifically, Cu powder, Bi powder, and Sn powder were scattered on the flat plate of low carbon steel so as to attain the mass ratio among the respective components in the lining 11 described above. It suffices that the mass ratio among the respective components in the lining 11 can be satisfied, and alloy powder such as Cu—Bi or Cu—Sn may be scattered on the flat plate of low carbon steel. The particle sizes of the powders were adjusted to 150 μm or less by a test sieve (JIS Z 8801).
Next, the flat plate of low carbon steel and the powders sprayed on the flat plate were sintered. The sintering temperature was controlled to 700 to 1000° C., and the sintering was performed in an inert atmosphere. After the sintering, the sintered flat plate was cooled. The lining 11 is not necessarily formed by sintering, and may be formed by casting or the like.
After completion of the cooling, a Cu alloy layer is formed on the flat plate of the low carbon steel. The Cu alloy layer contains soft Bi particles precipitated during the cooling.
Next, the low carbon steel having a Cu alloy layer formed thereon was pressed so as to have a shape obtained by dividing a hollow cylinder into two equal parts in diameter. At this time, the pressing process was performed so that the outer diameter of the low carbon steel matched 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. Thereby, the lining 11 can be formed by the Cu alloy layer after the cutting process. The cutting process was carried out by a lathe with a cutting tool material made, for example, of sintered diamond set. The surface of the lining 11 after the cutting process constitutes the interface between the lining 11 and the overlay 12.
Next, Bi was laminated to a thickness of 10 μm on the surface of the lining 11 by electroplating, whereby the overlay 12 was formed. The electroplating procedures were as follows. First, the surface of the lining 11 was washed with water. Further, unnecessary oxides were removed from the surface of the lining 11 by pickling the surface of the lining 11. Thereafter, the surface of the lining 11 was again washed with water.
Upon completion of the above pretreatment, electroplating was performed by supplying a current to the lining 11 immersed in a plating bath. A bath composition of the plating bath containing methane sulfonic acid: 50 to 250 g/l, methane sulfonic acid Bi: 5 to 40 g/l (Bi concentration), and a surfactant: 0.5 to 50 g/l. The bath temperature of the plating bath was set to 20 to 50° C. Further, the current supplied to the lining 11 was a direct current, and the current density was set to 0.5 to 7.5 A/dm2. In the electroplating, the plating bath (liquid) was put in a stationary state without liquid flow. As a result, the crystal grains 12a can be crystal-grown from the surface of the lining 11 toward the center of curvature. After completion of the electroplating, water washing and drying were carried out.
Next, the components (mainly, Cu) of the lining 11 were diffused into the overlay 12 by heat treatment for 50 hours in a state where the temperature was maintained at 150° C. As a result, as shown in the graph of
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.
In the above embodiment, the sliding member 1 constituting the sliding bearing A for bearing the crankshaft of the engine has been illustrated, but sliding bearings A for other purposes may be formed by the sliding member 1 of the present invention. For example, a radial bearing such as a transmission gear bush or a piston pin bush/boss bush may be formed by the sliding member 1 of the present invention. Furthermore, 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 it suffices that the material of the matrix is selected according to the hardness of the counter shaft 2. It suffices that the material for the coating layer is softer than the lining 11, and the material for the coating layer may be, for example, any of Pb, Sn, In, and Sb.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-121114 | Jun 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/020347 | 5/28/2018 | WO |
