Sliding body

Abstract

Sliding body (1), with: a base material layer (3); and an alloy top layer (9) formed on the base material layer (3), where the alloy cover layer (9) has a soft metal phase (11) which is deposited in a metallic matrix phase (10), and the alloy top layer (9) is formed as a layer on the base material by electron beam evaporation or boat heating evaporation, wherein, if an average particle diameter of the soft metal phase (11) is defined as C and its standard deviation as Cσ, C + Cσ is 0.70 µm or less, and wherein where an average elongation ratio of particles of the soft metal phase (11) is defined as A and its standard deviation as Aσ, A + Aσ is 3.0 or less, wherein the elongation ratio is a ratio of a principal axis (b) to a minor axis (a) of the individual particles, wherein the alloy cover layer (9) is cut in its thickness direction and an image of the cut surface is taken with an electron microscope, wherein the obtained image is analyzed to extract corresponding ellipses of the soft metal phase, wherein all corresponding ellipses within a range of 10 µm × 10 µm in the processed image are extracted, and the elongation ratio of each of the corresponding ellipses is calculated.

Description

Technical field

[0001] The present invention relates to a sliding body. In particular, the present invention relates to an improvement of a sliding body having an alloy covering layer whose matrix phase is a metal, such as aluminum. State of the art

[0002] An aluminum alloy layer disclosed in JP 2006-45677 A is known as an example of an alloy topcoat.

[0003] This alloy coating consists of a hard phase, made of silicon or a similar material, and a soft metal phase, made of tin, lead, or a similar material, deposited as phases in an aluminum matrix. Controlling the size of this soft metal phase (miniaturization) and ensuring its coexistence with the hard phase improves the coating's strength, allowing it to reliably exhibit high wear resistance.

[0004] Such an alloy coating is generally formed by atomization. This is because the use of atomization (e.g., DC magnetron sputtering) makes it possible to obtain a stable coating composition while reducing production costs.

[0005] The use of a different vapor deposition process, such as PVD, has also been suggested. Summary of the invention: Technical problems

[0006] The current inventors have found the following problem when an alloy coating layer is formed by atomization, in particular when a soft metal phase made of tin or the like is deposited in a matrix phase made of aluminum or the like.

[0007] In particular, it has often been observed that particles of the soft metal phase intended for deposition are coupled together by agglomeration within the matrix phase, causing the soft metal phase to elongate in a specific direction. When particles of the soft metal phase, which were originally intended to be miniaturized, are coupled together, resulting in elongation of the soft metal phase, the soft metal phase takes on a knife-like shape. Therefore, when a load is applied to the alloy coating, the stress is concentrated on knife-shaped sections, limiting the strength of the alloy coating. Modern sliding components are required to have higher fatigue resistance, and such a limitation in strength can therefore hinder improvements in fatigue resistance.

[0008] For a better understanding of the present invention, reference is also made to EP 1 888 798 B1, US 2006 / 0029827 A1 and EP 2 105 512 B1. Problem solving

[0009] Under the above circumstances, the present inventors have conducted intensive research to improve the fatigue resistance of an alloy coating layer. As a result, the present inventors have conceived the following aspects of the present invention.

[0010] A first aspect of the present invention is defined as follows. According to the invention, a sliding body comprising: a base material layer; and an alloy cover layer formed on the base material layer, wherein the alloy top layer has a soft metal phase that is deposited in a metallic matrix phase, and the alloy top layer is formed as a layer on the base material by electron beam evaporation or boat heating evaporation, wherein, if an average particle diameter of the soft metal phase is defined as C and its standard deviation as Cσ, C + Cσ is 0.70 µm or less, and wherein, where an average elongation ratio of particles of the soft metal phase is defined as A and its standard deviation as Aσ, A + Aσ is 3.0 or less, wherein the elongation ratio is a ratio of a principal axis (b) to a minor axis (a) of the individual particles, wherein the alloy cover layer (9) is cut in its thickness direction and an image of the cut surface is taken with an electron microscope, wherein the obtained image is analyzed to extract corresponding ellipses of the soft metal phase, wherein all corresponding ellipses within a range of 10 µm × 10 µm in the processed image are extracted, and the elongation ratio of each of the corresponding ellipses is calculated.

[0011] In the sliding body, according to the first aspect defined above, the soft metal phase does not have a shape that extends in a specific direction, but rather a shape close to a sphere. When a load is applied to the alloy cover layer, the stress is applied and thus distributed evenly across this soft metal phase, which has a near-spherical shape. Therefore, the alloy cover layer can reliably exhibit high mechanical strength, which improves its fatigue resistance. In the sliding body, the average particle diameter of the soft metal phase is as small as C + Cσ ≤ 0.70 µm. The soft metal phase is deposited at the crystal grain boundary of the matrix phase; therefore, a reduction in the particle diameter of the soft metal phase corresponds to a reduction in the crystal grain size of the matrix phase.Therefore, the mechanical strength of the matrix phase increases according to Hall-Petch's law, thus increasing the mechanical strength of the alloy coating. Consequently, the alloy coating can reliably exhibit high fatigue resistance.

[0012] A second aspect of the present invention is defined as follows. In the sliding body according to the first aspect, if a standard deviation of regions of Voronoi polygons around the particles of the soft metal phase, with centroids of the particles as centers, obtained by processing a cross-sectional image in a thickness direction of the alloy cover layer, is defined as Bσ, Bσ ≥ 0.80 µm 2 or less.

[0013] If the Voronoi polygons are uniform within a region, development points within that region are uniformly spaced. This indicates excellent dispersibility. When the cross-sectional image of the alloy coating is processed to form Voronoi polygons using particles of the soft metal phase as development points, the standard deviation Bσ of the resulting Voronoi polygon regions is 0.80 µm, according to the second aspect. 2or less. If the alloy coating has such a small standard deviation Bσ of the regions of Voronoi polygons, that is, if the soft metal phase is uniformly distributed within the alloy coating, then the soft metal phase is also uniformly exposed on the surface of the alloy coating. As a result, when a counterpart part comes into sliding contact with the alloy coating, the soft metal phase is uniformly in contact with the entire surface of the counterpart part. Additionally, compared to a case where the soft metal phase is unevenly distributed (that is, particles of the soft metal phase form clumps), the area of ​​contact between the soft metal phase and the counterpart part is increased.

[0014] When the soft metal phase, exposed on the surface of the alloy coating, comes into sliding contact with the mating part, its contact surface immediately reaches a high temperature and melts. The molten soft metal acts as a lubricant, thus preventing a subsequent increase in the temperature of the contact surface. This, in turn, prevents an increase in the temperature of the alloy coating itself, thereby preventing a reduction in its hardness. Consequently, the mechanical strength of the alloy coating is maintained, and a reduction in fatigue resistance is prevented. According to the second aspect of the present invention, the area of ​​the soft metal phase exposed on the surface of the alloy coating is increased, thus improving its function as a lubricant.

[0015] Additionally, if the soft metal phase is uniformly distributed, the stress on the alloy coating, generated by applying a load to the alloy coating, is reduced to the soft metal phase. Therefore, combined with the condition defined as the first aspect (spheronization of the soft metal phase), the alloy coating can reliably exhibit higher mechanical strength, thereby also improving its fatigue resistance.

[0016] A third aspect of the present invention is defined as follows. In the sliding body according to one of the first and second aspects, the matrix phase is preferably made of aluminum, copper, or an alloy thereof, and the soft metal phase is preferably made of at least tin and / or lead and / or bismuth.

[0017] In the sliding body according to the third aspect described above, a material or combination of materials forming each of the phases is suitably selected, and therefore the alloy coating is suitable for a sliding body for vehicles or similar applications for use in a harsh environment. Brief description of the drawings Fig. Figure 1 is a sectional view showing a sliding body according to a first embodiment of the present invention. Fig. 2A to 2D are schematic diagrams to explain the elongation ratio properties of a soft metal phase, in which Fig. 2A is a cross-sectional image of an alloy top layer that meets the requirement specified in the first aspect. Fig. 2B is a histogram showing the elongation ratio distribution of a soft metal phase appearing in the cross-sectional image. Fig.2C is a cross-sectional image of an alloy top layer that does not meet the requirement specified in the first aspect. Fig. 2D is a histogram showing the elongation ratio distribution of a soft metal phase as it appears in the cross-sectional image. Fig. Figure 3 is an illustration to explain Voronoi polygons. Fig. 4A to 4D are schematic diagrams to explain properties based on the standard deviation of regions of Voronoi polygons in which Fig. 4A is a cross-sectional image of an alloy top layer that meets the requirement specified in the second aspect. Fig. Figure 4B is a histogram showing the distribution of areas of Voronoi polygons of a soft metal phase appearing in the cross-sectional image. Fig.4C is a cross-sectional image of an alloy top layer that does not meet the requirement specified in the second aspect. Fig. 4D is a histogram showing the distribution of areas of Voronoi polygons of a soft metal phase that appears in the cross-sectional image. Fig. 5A and Fig. 5B are schematic diagrams showing the average particle diameter properties of a soft metal phase, in which Fig. 5A is a histogram showing the distribution of particle diameter of a soft metal phase captured by the cross-sectional image of an alloy cover layer that meets the requirements specified in the third aspect. Fig.5B is a histogram showing the particle diameter distribution of a soft metal phase composed of the cross-sectional image of an alloy cover layer that does not meet the requirements specified in the third aspect. Description of the exemplary implementations

[0018] The present invention will now be described in detail based on exemplary embodiments.

[0019] Fig. Figure 1 shows the layer structure of a sliding bearing 1 as a sliding body according to a first embodiment of the present invention.

[0020] The sliding bearing 1 contains a back metal layer 3 as a base material layer, a bearing alloy layer 7 and an alloy cover layer 9.

[0021] The back metal layer 3 consists of a steel plate formed into a cylindrical or semi-cylindrical shape. The bearing alloy layer 7, made of an alloy of Al, Cu, Sn, etc., is laminated to the upper surface of the back metal layer 3 by a process such as sintering, casting, or pressure welding.

[0022] To improve adhesion between the bearing alloy layer 7 and the alloy cover layer 9, the bearing alloy layer 7 is preferably subjected to a surface treatment. One method used for surface treatment can be, for example, ion milling, such as argon bombardment.

[0023] As in Fig. As shown in Figure 2A, the alloy top layer 9 is formed by dispersing a soft metal phase 11 in a matrix phase 10.

[0024] Aluminum, copper, or an alloy thereof can be used as matrix phase 10.

[0025] A hard phase, made of silicone or similar material, can be used in combination with the soft metal phase 11.

[0026] The soft metal phase 11 can be made of a metallic material that has the same or a lower hardness than the metallic material of the matrix phase and a lower melting point than the metallic material of the matrix phase. Examples of such a metallic material include tin, lead, and bismuth.

[0027] The percentage of the amount of the soft metal phase to the amount of the matrix phase can be appropriately chosen depending on the intended use of the sliding body, but is, for example, 10 wt.% to 40 wt.%.

[0028] The thickness of the alloy cover layer 9 can also be selected appropriately depending on the intended use of the sliding body, but is e.g. 5 to 40 µm.

[0029] If an average elongation ratio of the soft metal phase 11 is defined as A and its standard deviation is defined as Aσ, then A + Aσ is 3.0 or less.

[0030] Here, a stretching relationship can be captured in the following way.

[0031] The alloy cover layer 9 is sectioned in its thickness direction, and an image of the sectioned surface is acquired using an electron microscope. The resulting image is analyzed to extract corresponding ellipses of the soft metal phase. All corresponding ellipses within a specific area (e.g., 10 µm x 10 µm) in the processed image are extracted, and the scaling ratio b / a of each corresponding ellipse is calculated, where a and b represent the minor and major axes, respectively, of the corresponding ellipse. An average scaling ratio A and a standard deviation Aσ are calculated from the scaling ratios of all extracted ellipses.

[0032] In the present invention, the sum of the average stretch ratio A and the standard deviation Aσ is 3.0 µm or less. Preferably, the sum is 2.0 µm or less.

[0033] Fig.Figure 2B shows an example of a histogram obtained when the sum of the average scaling ratio A and the standard deviation Aσ is 3.0 µm or less. As shown in the drawing, the histogram obtained when A + Aσ ≤ 3.0 µm corresponds to a bimodal histogram. In either case, the scaling ratio distribution is narrow. Therefore, the soft metal phase 11 in the matrix phase 10 has a shape close to a sphere.

[0034] When particles of a soft metal are coupled together, such that a soft metal phase extends in a specific direction, as in the case of a conventional alloy coating (see Fig. 2C), A + Aσ ≥ 3.0 µm. It should be noted that a histogram obtained when A + Aσ ≥ 3.0 µm is a bimodal histogram (see Fig.2D) corresponds. In any case, many particles of a soft metal phase 21, which have a large elongation ratio, are present. If such a soft metal phase, which elongates in a particular direction, is present, the stress on a matrix phase is concentrated on knife-shaped sections of the soft metal phase, which is not preferred, as described above.

[0035] Fig. Figure 3 shows the result of a Voronoi polygon mosaic with the centers of the soft metal phase 11. This processing was performed using versatile image processing software, and the area of ​​each Voronoi polygon was also calculated. Then, a standard deviation Bσ of the areas of all the Voronoi polygons obtained within a given image area was calculated.

[0036] In this invention, the standard deviation Bσ is preferably 0.80 µm. 2 or less. The value of Bσ is preferably 0.45 µm.2 or less.

[0037] If the standard deviation of regions of Voronoi polygons is such a small value, the distances between the centers of mass of particles of the soft metal phase 11 are uniform. That is, the soft metal phase is uniformly distributed in the matrix phase.

[0038] Fig. Figure 4A shows a state where the soft metal phase 11 (which has a shape close to a sphere) is uniformly distributed in the matrix phase 10. Fig. 4B is a histogram of regions of Voronoi polygons in this case.

[0039] On the other hand, it shows Fig. 4C schematically shows how particles of the soft metal phase 11 are distributed (particles of the soft metal phase 11 are agglomerated) when the standard distribution of a histogram of regions B of the Voronoi polygons is 0.80 µm 2 exceeds. The histogram of regions of Voronoi polygons in this case is in Fig.4D shown. The reference symbol 20, which is in Fig. 4A and Fig. 4C shows a counterpart part that comes into sliding contact with the sliding body.

[0040] The comparison between Fig. 4A and Fig. Figure 4C shows that the soft metal phase 11, which is exposed at the surface of the alloy cover layer 9, certainly has a larger area in the previous case. In particular, if the soft metal phase has a shape close to a sphere, the area of ​​the soft metal phase exposed at the surface of the alloy cover layer 9 is proportional to the number of particles of the soft metal phase exposed at the surface of the alloy cover layer 9, and therefore the area of ​​the soft metal phase exposed at the surface of the alloy cover layer 9 can be increased by achieving high dispersibility, as in Fig. 4A shown, can be maximized.

[0041] Additionally, the stress on the matrix phase 10 is uniformly distributed across the soft metal phase 11, and therefore the alloy cover layer 9 can have stable mechanical strength across its entire area; that is, the alloy cover layer 9 has no fragile sections. As a result, the alloy cover layer 9 has increased mechanical strength.

[0042] In the cross-sectional image obtained as described above, the length of a line connecting two points on the outer circumference of a particle of the soft metal phase and passing through the particle's center of mass is measured as a diameter at 2° intervals. From the averages of the diameters measured in this way, an average particle diameter C and its standard deviation Cσ are calculated.

[0043] In this invention, the sum of the average particle diameter C and its standard deviation Cσ is 0.70 µm or less. Preferably, the sum is 0.55 µm or less.

[0044] Fig. Figure 5A shows an example of a histogram obtained when the sum of the mean particle diameter C and the standard deviation Cσ is 0.7 µm or less. As shown in the drawing, the histogram obtained when C + Cσ ≤ 0.70 µm corresponds to a bimodal histogram. In either case, the mean particle diameter is small. Therefore, the alloy coating has improved mechanical strength due to the Hall-Petch effect, resulting in high fatigue resistance.

[0045] On the other hand, a histogram that is obtained when the requirement is not met, that is, C + Cσ > 0.70 µm, corresponds to a bimodal histogram (see. Fig.2D). In any case, many particles of the soft metal phase 21, which have a large particle diameter, are present.

[0046] Particles of the soft metal phase deposited in the matrix phase have a near-spherical shape due to surface tension when the particles themselves are individually separated. Therefore, the soft metal phase can be given a near-spherical shape by preventing the particles from coupling together during deposition. Studies by the current inventors have shown that coupling of soft metal phase particles can be prevented by increasing the rate of layer formation, such as the alloy top layer 9, to a certain extent (e.g., 15 µm / min). Additionally, there are concerns that if there is a thermal history during and after the formation of a layer such as the alloy top layer 9, soft metal phase particles with a lower melting point than those of the matrix phases may be coupled together.

[0047] From this perspective, an electron beam evaporation or boat-type evaporation process according to the invention, which achieves a high layer formation rate, can be used as a method for forming a layer such as the alloy top layer, in which the soft metal phase, which has a shape close to a sphere, is deposited in the matrix phase. However, in order to reduce the influence of radiant heat from a heat source (i.e., a thermal history during and after layer formation), the shape of a boat-type heat source is preferably adapted so that a virtual normal line of its surface does not intersect with a workpiece. This is to prevent the workpiece from being directly irradiated with radiant heat from the heat source during layer formation and thus prevent excessive thermal transfer to the workpiece.

[0048] If the alloy coating is produced in the manner described above, coupling of particles from the soft metal phase can be prevented. In addition, a high dispersion and miniaturization of the particles in the soft metal phase can also be achieved by increasing the coating formation rate. Examples

[0049] Examples are described below.

[0050] Plain bearings of examples and comparative examples were formed in the following way.

[0051] A so-called bimetal was produced by forming a Cu-based bearing alloy layer 7 as a lining on a steel backing metal layer 3. This bimetal was formed in a semi-cylindrical shape and the surface of the bearing alloy layer 7 was drilled and surface-finished.

[0052] Then, as a pretreatment, an argon bombardment was carried out before an alloy top layer 9 was formed.

[0053] A layer was formed as an alloy coating on the workpiece thus obtained by boat-type vapor deposition. The following conditions for layer formation were generally described in examples and comparative examples. (evaporation material)

[0054] The vapor deposition material was an aluminum-tin alloy, and the aluminum-tin alloy has a composition of Al : Sn = 75 : 25 (mass%). (Effusion source temperature)

[0055] The evaporation source temperature was 1300°C. (Ambient pressure)

[0056] The ambient pressure was 5.0 × 10 -3 Pa (Temperature of the workpiece) Examples 1 and 2: 170 to 190°C Examples 3 and 4: 140 to 160°C Examples 5 and 6: 70 to 90°C Comparison examples 1 and 2: 240 to 260°C

[0057] It was found that the temperature of the workpiece has a significant influence on the profile of the soft metal phase of the alloy's surface layer.

[0058] Results are shown in Table 1. [Table 1] Stretch ratio property (µm) Dispersion property (µm) 2 ) Average particle diameter property (µm) Evaluation of fatigue resistance (MPa) A Aσ A + Aσ Bσ C Cσ C + Cσ Example 1 2,5 0,5 3,0 1,25 0,70 0,28 0,98 130 Example 2 0,4 1,6 2,0 1,15 0,90 0,25 1,25 130 Example 3 1,5 0,5 1,8 0,80 0,80 0,30 1,20 150 Example 4 1,5 0,5 1,8 0,45 0,25 0,90 1,15 150 Example 5 1,5 0,5 1,8 0,45 0,40 0,30 0,70 170 Example 6 1,5 0,5 1,8 0,45 0,25 0,30 0,55 170 Comparative example 1 3,0 0,5 4,0 2,00 0,70 0,30 1,00 110 Comparative example 2 1,5 2,5 4,0 2,00 0,80 0,20 1,00 110 Comparative example 3 3,0 2,5 5,8 2,30 1,00 0,90 1,90 110

[0059] It should be noted that in comparative example 3, the alloy coating layer was formed by atomization at a low layer formation rate in accordance with a conventional example.

[0060] An AlSn alloy (75 : 25 wt.%) was used as a atomizing source and the temperature of the workpiece was 140°C.

[0061] A fatigue resistance test was performed in the following manner.

[0062] A bearing, used as a sliding element in each example and comparison example, had a width of 15 mm, an outer diameter of 55 mm, and a thickness of 1.5 mm. The thickness of the alloy coating was 15 µm.

[0063] A rotating shaft made of high-carbon steel (S55C) was selected as the mating component of the bearing. The rotating shaft was subjected to a predetermined surface pressure and oil at a temperature of 100°C for 20 hours. After the test, the alloy coating of the sliding element was visually inspected to determine whether or not cracking had occurred.

[0064] The surface load applied to the rotating shaft, as described above, was increased in 10 MPa increments from 100 MPa. Fatigue resistance was evaluated based on the maximum surface pressure before cracking occurred in the alloy coating.

[0065] The properties of the soft metal phase of the alloy coating (elongation ratio property, dispersion property, average particle diameter property) were determined in the following way.

[0066] The bearing of each sample and comparison sample was sectioned axially using a wet cutter, and a cross-sectional image of the alloy cover layer 9 was acquired using an electron microscope. The resulting image was processed using image processing software "Image-Pro" from Media Cybernetics to determine the average elongation ratio A, its standard deviation Aσ, the standard deviation Bσ of Voronoi polygon areas, the average particle diameter C, and its standard deviation Cσ. It should be noted that the processed image area was 10 µm × 10 µm.

[0067] The present invention is not limited to the description of the above embodiment. A bearing mechanism utilizing device, such as an internal combustion engine, which uses the sliding element according to the present invention, exhibits excellent sliding properties.

[0068] The above embodiment was described with reference to a case in which a sliding bearing is used as a sliding body, but the present invention can also be applied to other sliding bodies, such as plate-shaped pressure plates. Reference symbol list 1 sliding body 3 Backside metal layer 7 Bearing alloy layer 9 Alloy top layer 10 Matrix phase 11, 21 Soft metal phase 20 Counterpart part

Claims

[1] Sliding body (1), with: a base material layer (3); and an alloy covering layer (9) formed on the base material layer (3), where the alloy covering layer (9) has a soft metal phase (11) which is deposited in a metallic matrix phase (10), and the alloy covering layer (9) is formed as a layer on the base material by means of electron beam vapor deposition or boat heating vapor deposition, wherein, when an average particle diameter of the soft metal phase (11) is defined as C and its standard deviation as Cσ, C + Cσ is 0.70 µm or less, and wherein when an average aspect ratio of particles of the soft metal phase (11) is defined as A and its standard deviation as Aσ, A + Aσ is 3.0 or less, the aspect ratio being a ratio of a major axis (b) to a minor axis (a) of the individual particles, wherein the alloy covering layer (9) is cut in its thickness direction and an image of the cut surface is taken with an electron microscope, the obtained image is analyzed to extract corresponding ellipses of the soft metal phase, all corresponding ellipses within a range of 10 µm × 10 µm in the processed image are extracted, and the aspect ratio of each of the corresponding ellipses is calculated. [2] The sliding body (1) according to claim 1, wherein when a standard deviation of areas of Voronoi polygons of the soft metal phase (11) obtained by processing a cross-sectional image of the alloy covering layer is defined as Bσ, Bσ 0.80 µm 2 or less. [3] Sliding body (1) according to claim 1 or 2, wherein the matrix phase (10) contains aluminum, copper or an alloy thereof and the soft metal phase (11) contains at least one of tin or lead and bismuth or a combination thereof.

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