Sliding member, method for manufacturing same, and method for manufacturing hard material

Abstract

In a sliding member, fatigue resistance of a surface layer formed by dispersing a hard material in a soft metal matrix is improved. A sliding member includes a base material layer and a surface layer, the surface layer includes a metal matrix and a hard material harder than the matrix and dispersed in the matrix, the hard material has a gradient in hardness, and the gradient in hardness gradually decreases from an inner side to a surface of the hard material.

Claims

1. A sliding member comprising a base material layer and a surface layer, wherein the surface layer includes a metal matrix and a hard material harder than the matrix and dispersed in the matrix, the hard material has a continuous gradient in hardness with the gradient in hardness gradually decreasing from an inner side to a surface of the hard material.

2. The sliding member according to claim 1, wherein the hardness of the surface of the hard material is equal to a hardness of the metal matrix.

3. The sliding member according to claim 1, wherein the hard material includes a first metal material and a second metal material, the second metal material is softer than the first metal material, a concentration of the second metal material has a gradient, and the gradient in the concentration gradually increases from an inner side toward the surface of the hard material.

4. The sliding member according to claim 3, wherein a material of the metal matrix is identical or of an identical kind to a material of the second metal material.

5. The sliding member according to claim 3, wherein in the hard material, an area rate of a region where a rate of the second metal material is less than or equal to 9% by mass is greater than or equal to 1% and less than or equal to 35%.

6. The sliding member according to claim 5, wherein in the hard material, a distance from the surface of the hard material to the region where the rate of the second metal material is less than or equal to 9% by mass is greater than or equal to 0.07 ?m.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram of a sliding member of the present invention.

(2) FIG. 2 is a schematic diagram illustrating a hard material of the present invention.

(3) FIG. 3 is a schematic diagram illustrating a relationship between a ratio of hard region A to soft region B in the hard material and characteristics thereof.

(4) FIG. 4 is a schematic diagram illustrating a relationship between a distance from a surface of the hard material to hard region A and characteristics thereof.

DESCRIPTION OF EMBODIMENT

(5) Hereinafter, the present invention will be described in more detail with reference to an embodiment.

(6) A base material layer that constitutes a sliding member is generally made of a metal material.

(7) In a bearing as an example of the sliding member, a base material layer has a configuration in which a copper-based bearing alloy layer is formed on a back metal layer made of a steel material. An intermediate layer made of Ag or Ni, for example, may be formed on the bearing alloy layer.

(8) The surface layer that constitutes the sliding member has a soft metal as a matrix, and a hard substance is dispersed in the metal matrix.

(9) Examples of the material of the metal matrix include indium (In), tin (Sn), lead (Pb), bismuth (Bi), and antimony (Sb). The metal matrix has a thickness of 1 ?m to 50 ?m.

(10) The average particle diameter of the hard material dispersed in the metal matrix can be 0.2 ?m to 50 ?m. A preferable average particle diameter is shorter than the film thickness of the surface layer and is 1 ?m to 5 ?m. In addition, the blending amount of the hard material with respect to the metal matrix is preferably 0.5 to 60.0% by volume. The blending amount is more preferably 5.0 to 40.0% by volume.

(11) The average particle diameter, the blending amount, and the quality of material of the hard material can be appropriately selected according to the use of the sliding member.

(12) The hard material dispersed in the surface layer has a gradient in hardness, and the gradient in hardness gradually decreases from the inner side toward the surface.

(13) By gradually decreasing the hardness, the external force applied to the surface layer can be efficiently absorbed. In other words, when the change in the hardness is stepwise in the radial direction, it is not preferable because the external force may be repelled at the interface where the hardness changes. Further, it takes time and effort to provide a stepwise hardness change in a minute hard material.

(14) By gradually changing the quality of material (chemical property) of the hard material, a continuous gradient in hardness can be imparted to the hard material. In addition, it is also possible to impart a gradient in hardness to the hard material by gradually changing the physical property of the hard material.

(15) In order to gradually change the quality of material of the hard material, a material that is softer than the material of the base material that constitutes the hard material is diffused from the surface of the particles serving as the base material. Accordingly, in the particles made of a material whose quality is hard, a diffusion state of the soft material in which the concentration of the soft material gradually increases from the inner side toward the surface is obtained. As a method of diffusing the soft material, it is preferable to diffuse the soft material into the material of the base material by bringing the soft material and the base material into contact with each other under a high-temperature condition (the base material is solid, and the soft material is liquid). In addition, diffusion can also be achieved by physically injecting the fine particles of the latter into the former.

(16) In the hard material, the gradient in hardness may be formed in the entire hard material or a part of the hard material. Further, the gradient in hardness may be uniform or non-uniform as viewed from the center of the hard material. Here, the term uniform means that hardnesses at an equal distance as viewed from the center are the same.

(17) Even when a gradient in hardness is formed in the entire hard material, since the unique role of the hard material is to improve abrasion resistance, a portion maintaining original hardness is required of the hard material. In this specification, such a portion is referred to as hard region A, and for example, when a hard material is made of a first metal material having its original hardness and a relatively soft second metal material, a region in which the rate of the second metal material to the entire hard material is less than or equal to 9% by mass is referred to as hard region A.

(18) When hard region A occupies a predetermined size in the hard material, an original abrasion resistance function can be imparted to the hard material. The size to be occupied by hard region A can be appropriately selected according to on the hardness of hard region A itself or the use of the sliding member, for example.

(19) In this specification, the proportion of hard region A is defined with an area rate in a desired cross section, and it is preferable that the area rate be greater than or equal to 1%. A method of calculating the area rate is not particularly limited, but for example, a pixel is virtually set in a desired cross section of a hard material, elemental analysis is performed for each pixel, and the number of pixels in which the rate of the second metal material is within the above range (less than or equal to 9% by mass) is counted. The ratio between the number of counted pixels and the number of entire pixels of the hard material is taken as the area rate.

(20) From such a viewpoint, the area rate of hard region A is more preferably greater than or equal to 20%.

(21) When the rate of hard region A in the hard material is too large, that is, when the area rate of hard region A is too large, the stress relaxation function is affected, and thus, in the present invention, the area rate of the hard region is preferably less than or equal to 355.

(22) From such a viewpoint, the area rate of hard region A is more preferably less than or equal to 30%.

(23) In order to make a change to the quality of material of the hard material, the hard material is preferably formed of two or more kinds of metal materials. It is assumed that the first metal material has a hardness originally required of the hard material. A material softer than the first metal material is selected as the second metal material, and is infiltrated into the particles made of the first metal material from the surface side, thereby forming the gradient of a concentration (that is, the gradient of the hardness) of the second metal material.

(24) Here, as the first metal material, metals such as copper (Cu), silver (Ag), manganese (Mn), and nickel (Ni), or alloys of these metals can be used. The first metal material is harder than the material of the metal matrix.

(25) As the second metal material, a material that is softer than the first metal material and diffusible into the first metal material is selected. Examples of the second metal material include metals such as In, Sn, Pb, Bi, Sb, and Zn, and alloys of these metals.

(26) In addition to the first and second metal materials, a third component can also be added to the hard material.

(27) A third metal material can be added as the third component. The third metal material may diffuse into the first metal material or the second metal material, or may exist alone.

(28) An inorganic material may be added as the third component. For example, by incorporating porous silica in the hard material, the heat resistance of the hard material is improved.

(29) The shape of the hard material can also be arbitrarily selected. The shape is not limited to the spherical shape as illustrated in FIG. 2, and an elliptical spherical shape or a rod shape can also be adopted.

(30) Hereinafter, a method for forming a surface layer on a base material layer will be described.

(31) <Method of Preparing Particles with Gradient in Hardness, i.e. Hard Material, Separately from Metal Matrix>

(32) Particles made of a first metal material harder than a metal matrix are prepared.

(33) A molten in which the second metal material is melted is prepared. The second metal material can form a solid solution with the first metal material and is softer than the first metal material. The molten of the second metal material is maintained at a predetermined temperature, the particles of the first metal material are immersed in the molten, and the molten is stirred by a predetermined method for a predetermined time. Accordingly, the second metal material diffuses from the surface of the particles made of the first metal material to the inside thereof, and particles having a concentration gradient, that is, particles having a gradient in hardness in the second metal material, in other words, a hard material is obtained.

(34) When the metal matrix is formed on the surface of the base material layer by electrolytic plating, by forcibly supplying the hard material to the base material layer side, the hard material is taken into and dispersed in the metal matrix.

(35) In the above, a porous inorganic material such as porous silica can be incorporated in the hard material as a third material. In this case, by immersing the porous inorganic material in a molten of the first metal material, the particles of the first metal material incorporating the porous inorganic material are prepared in advance, and as described above, the particles are immersed in a molten of the second metal material.

(36) <Method for Forming Eutectoid of Hard Material in Metal Matrix>

(37) A first metal material (for example, Cu) that secures hardness of a hard material and a second metal material (for example, Bi) that is softer than the first metal material and does not form a solid solution with the first metal material are prepared. The second metal material serves as a metal matrix.

(38) Using the first metal material and the second metal material as plating sources, electrolytic plating is simultaneously performed on the surface of the base material layer. Since both the metal materials do not form a solid solution, in the formed plating layer (the precursor layer of the surface layer), by adjusting the plating conditions (methanesulfonic acid bath, Cu concentration in the bath (g/L), the bath temperature, current density, and the storage period from completion of bath adjustment to use for plating), a particle form of the first metal material is dispersed in the second metal material as a matrix.

(39) The ratio between the first metal material and the second metal material can be arbitrarily designed according to characteristics required of the sliding member, but for example, a volume ratio of the first metal material:the second metal material of 1:1.5 to 1:10 is preferred.

(40) A layer of a third metal material (for example, Sb) capable of forming a solid solution with the first metal material and the second metal material is formed by electrolytic plating on the precursor layer as obtained above.

(41) The ratio between the third metal material and (first metal material+second metal material) can be arbitrarily designed according to the characteristics required of the sliding member, but for example, a volume ratio of the former (third metal material):the latter (first metal material+second metal material) of 1:3 to 1:15 is preferred.

(42) When the temperature of the layered product is increased to a predetermined temperature and maintained for a predetermined time, owing to the third metal material, the second metal material is diffused together with the third metal material into the particle form of the first metal material. Accordingly, the hard material is dispersed in the metal matrix made of the second metal material. Since the hard material is a material in which the second metal material and the third metal material that are relatively soft are diffused from the surface side of the hard first metal material, in the hard material, the second metal material and the third metal material that are softer than the first metal material are diffused with a gradient of a concentration in the first metal material, and the gradient of the concentration gradually increases from the inner side toward the surface. Here, the third metal material is also preferably softer than the first metal material.

(43) In the above description, the metal matrix and other layers are formed by electrolytic plating, but these layers can also be formed by a sputtering method or other methods.

EXAMPLES

(44) The sliding members of the examples had a cross-sectional structure illustrated in FIG. 1, for example. More specifically, a copper-based bearing alloy layer was lined on a steel back metal to produce a bimetal, and the bimetal was formed into a semi-cylindrical shape or a cylindrical shape. Thereafter, the surface of the bearing alloy layer was subjected to boring to finish the surface. Next, the surface of the semi-cylindrical or cylindrical formed product was cleaned (electrolytic degreasing and acid cleaning). In this manner, a base material layer 3 (thickness: 1.5 mm) was formed.

(45) A surface layer (about 15 ?m) was formed on the upper surface of the base material layer 3 obtained as described above.

(46) The surface layer of Examples 1 to 3 was formed as follows.

(47) Particles (average particle diameter: 3.6 ?m) made of the first metal material were prepared, immersed in a molten made of the second metal material in a liquid form for 1 hour, and stirred. As a result, the second metal material was diffused into the particles made of the first metal material. Note that the average particle diameter of the particles formed of the first metal material is based on a catalog from a material provider (material manufacturer) (the same is applies hereinafter).

(48) When the metal matrix material was electrolytically plated on the base material layer, the hard material obtained as described above was supplied to a portion near the base material layer. The supply method is a method of engulfing the hard material in the supplied air when the plating bath is bubbled.

(49) Note that, in Comparative Examples 1 to 3, alloy particles made of the first metal material and the second metal material were prepared, and the alloy particles were engulfed in the same manner as described above when the metal matrix material was electrolytically plated.

(50) The surface layers of Examples 4 to 9 were prepared as follows.

(51) A Cu plating source, a Bi plating source, and an Sb plating source were prepared as the first metal material, the second metal material, and the third metal material, respectively.

(52) Electrolytic plating was performed using both the Cu plating source and the Bi plating source with the surface of the base material layer as a surface to be plated.

(53) In this manner, a precursor layer (13 ?m) of the surface layer was formed on the surface of the base material layer. In the precursor layer, Cu particles formed a eutectoid with Bi as a metal matrix. Cu and Bi had a volume ratio of Cu:Bi=7:13.

(54) Next, an Sb layer (2 ?m) was formed on the surface of the precursor layer using the Sb plating source.

(55) The layered product obtained as described above was heat-treated under the conditions shown in Table 2.

(56) It goes without saying that the heat treatment can be arbitrarily selected according to the material to be selected and the conditions required of the surface layer.

(57) In the layered product whose temperature is increased by the heat treatment, Sb is diffused into the precursor layer, and concentrated on Cu in a particle form and diffused into Cu. This is because Sb has better compatibility (higher reactivity) with Cu than Bi does. It is considered that when Sb diffuses into Cu particles, surrounding Bi is engulfed. As a result, as shown in Table 1, Bi was diffused, in addition to Sb, in the Cu particles.

(58) In Comparative Example 4-1, alloy particles made of Cu, Bi, and Sb were prepared, and a surface layer was formed in the same manner as in Comparative Examples 1 to 3 by using Bi and Sb as plating sources.

(59) In Comparative Example 4-2, heating was performed under the same conditions as in Example 4 (140? C.?5 hours (in air)) in a state where Sb was not formed on the precursor layer. Diffusion of the Bi material into the hard material made of Cu was not observed.

(60) Table 1 shows the test results of the sliding members of Examples and Comparative Examples.

(61) TABLE-US-00001 TABLE 1 Fatigue Characteristics of hard material resistance of Material of surface layer Hard material Hard Hard sliding member Material of hard material infiltration region region Maximum First Second Third Inorganic Material treatment A A contact metal metal metal porous of metal Immersion Heat Area rate Distance pressure material material material material matrix treatment treatment (%) (?m) (MPa) Example 1 Cu In Bi yes 80 Comparative Cu In Bi no 60 Example 1 Example 2 Cu Sn Sn yes 70 Comparative Cu Sn Sn no 50 Example 2 Example 3 Cu Pb porous Pb, In, yes 125 silica Cu Comparative Cu Pb porous Pb, In, no 100 Example 3 silica Cu Example 4 Cu Bi Sb Sb, Bi yes 0.7 0.05 110 Comparative Cu Bi Sb Sb, Bi no 90 Example 4-1 Comparative Cu Bi Bi yes 100 0 90 Example 4-2 Example 5 Cu Bi Sb Sb, Bi yes 50 0.05 110 Example 6 Cu Bi Sb Sb, Bi yes 20 0.05 115 Example 7 Cu Bi Sb Sb, Bi yes 1 0.05 115 Example 8 Cu Bi Sb Sb, Bi yes 35 0.05 115 Example 9 Cu Bi Sb Sb, Bi ves 19 0.07 120

(62) TABLE-US-00002 TABLE 2 Infiltration heat treatment conditions Treatment Treatment temperature time Environment Example 4 140? C. 5 hours in the atmosphere Example 5 160? C. 20 hours in the atmosphere Example 6 160? C. 10 hours in the atmosphere Example 7 160? C. 5 hours in the atmosphere Example 8 160? C. 15 hours in the atmosphere Example 9 170? C. 15 hours in the atmosphere

(63) In Table 1, the hard materials of Examples 1 to 4 having a gradient in hardness have improved fatigue resistance as compared with the hard materials of Comparative Examples 1 to 4 having no gradient in hardness.

(64) Further, from the results of Examples 4 and 5 and Examples 6 to 9, when the area rate of a hard region is 1 to 35%, the fatigue resistance is improved.

(65) Furthermore, comparison between Example 6 and Example 9 illustrates that when distance L from the surface of the hard material to hard region A is greater than or equal to 0.07 ?m, the fatigue resistance is improved.

(66) In Table 1, the area rate of hard region A was determined as follows.

(67) First, the interface between the base material layer and the surface layer was identified.

(68) The cross section of the sliding member was observed with an electron microscope. Ten measurement points were set at equal intervals along the sliding direction on the outermost surface of the sliding member, and ten vertical lines perpendicular to the outermost surface were drawn from the points. Next, the length to a point where each vertical line intersects the base material layer, that is, the thickness of the surface layer was measured, and the average of the measured values was calculated. At this time, when any of the measured thicknesses of the surface layer was greater than or equal to ?5% of the average, the value was excluded as an abnormal value, and the average was calculated again.

(69) The abnormal value mainly appeared when the quality of material of the base material and the quality of material of the hard material in the surface layer were similar. When the hard material is in contact with the base material layer, the hard material may be recognized as the roughness of the surface of the base material layer. For convenience of the measurement method, such a case has to be detected as an abnormal value. In this way, the interface between the base material layer and the surface layer was identified, and then the area rate of the region where the concentration of the second metal material was less than or equal to 9% (that is, hard region A) was calculated.

(70) Elemental analysis was performed on the range of the surface layer in which the base material layer and the interface were identified. For elemental analysis, JXA-8530F Field Emission Electron Probe Microanalyzer (manufactured by JEOL Ltd.) was used. The resolution of elemental analysis was 0.05 ?m?0.05 ?m for one pixel. Next, the concentration of the second metal material was divided into three sections, and a region having a concentration of 100 to 95% (region of metal matrix), a region having a concentration of less than 95% and greater than 9% (soft region B), and a region having a concentration of 9 to 0% (hard region A) were detected. The area rate of the region having a concentration of the second metal material of 9 to 0% (that is, hard region A) was calculated by the following calculation formula.
Area rate of region having concentration of second metal material of 9 to 0% (that is, hard region A) in hard material=(area of region having second metal material concentration of 9 to 0% (that is, hard region A)?100)/(area of region having concentration of less than 95% to greater than 9% (that is, soft region B)+region having concentration of 9 to 0% (area of hard region A)

(71) Here, the area corresponds to the number of pixels.

(72) In Table 1, the distance from the surface of the hard material to hard region A was determined as follows.

(73) An interface between a region having a Bi concentration of 100 to 95 (region of metal matrix) and a region having a Bi concentration of less than 95% to greater than 9% (soft region B) was subjected to image analysis, and the interface was defined as a hard material first interface. The hard material first interface is defined as a surface of the hard material. Similarly, an interface between a region having a concentration of less than 95% to greater than 9% (that is, soft region B) and a region having a concentration of 9 to 0% (that is, hard region A) is detected, and the interface is defined as the hard material second interface.

(74) Next, the distance from the first interface to the second interface of the hard material is measured, and the minimum value among them is defined as the distance from the surface of the hard material to the region where the concentration of the second metal material is 9 to 0% (that is, hard region A).

(75) The fatigue resistance strength is determined as follows.

(76) A test is performed under the following conditions to evaluate fatigue resistance.

(77) Bearing inner diameter: 53 mm

(78) Bearing width: 15 mm

(79) Rotation speed: 3250 rpm

(80) Lubricating oil: VG22

(81) Quality of shaft material: S55C

(82) Test time: 20 hours

(83) In the test, the contact pressure was increased by 5 MPa, and the maximum contact pressure at which no crack occurred was used as an evaluation value.

(84) The maximum contact pressure is a value of the contact pressure immediately before a crack occurs in the sliding surface. When a crack occurs in the surface layer of the sample surface, it is determined that the sample is fatigued.

(85) The present invention is not limited to the description of the embodiment of the invention described above. Various modifications that can be easily conceived by those skilled in the art without departing from the scope of the claims are also included in the present invention. A device including a bearing mechanism, such as an internal combustion engine including the sliding member of the present invention, exhibits good sliding characteristics.