JPS6315987B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sliding member that can be used for a shift fork pawl, an inner surface of a cylinder liner, a piston ring, an inner surface of a synchronizer ring, a transmission friction plate, etc. Hypereutectic silicon-aluminum alloys have excellent wear resistance and are therefore used in various sliding members. This alloy has primary silicon particles dispersed in an aluminum-silicon eutectic structure, and the presence of these primary silicon particles contributes greatly to wear resistance. This is clear from the comparison of wear resistance with a eutectic aluminum-silicon alloy. However, conversely, the presence of these primary silicon particles has some aspects that are undesirable as a sliding member. In other words, there is a problem of the aggressiveness of the primary silicon particles to the other material. Because primary silicon particles are hard with a Vickers hardness of about 1000, the matrix selectively wears out faster during friction, and the primary silicon (Si) particles stand out on the surface of the sliding member, causing damage to the sliding member. Easy to wear out the material. As the wear progresses further, the primary Si particles floating on the surface may peel off from the matrix, and in such a state, the wear of the mating material becomes even more severe. In addition, in this regard, the presence of primary silicon particles causes wear of the cutting tool, which is a major obstacle in the production of sliding members. In order to solve the above problems, it is necessary to reduce the size of primary Si particles to suppress their extrusion and peeling from the matrix, reduce the aggressiveness of the particles themselves, and reduce the amount of primary Si particles. It is also necessary to avoid excessive amounts. Conventionally, a specific method for this purpose has been to increase the cooling rate after casting, die casting, forging, etc. in order to make the primary Si particles finer. There is no known practical method for obtaining it. Additionally, methods such as thermal spraying and alloy piece methods that form a hypereutectic silicon-aluminum alloy only on sliding parts can increase the cooling rate compared to the above-mentioned integrated product methods such as casting, die casting, and forging. However, it has previously been impossible to make the particles sufficiently fine, less than 10 μm in size. The present invention is intended to solve the above problems,
By making the primary Si particles of the hypereutectic silicon-aluminum alloy fine, it is less aggressive to the mating material, has excellent wear resistance and seizure resistance, and is easy to cut and economically produced. This provides a possible sliding member. The sliding member of the present invention is made of hypereutectic silicon in which primary Si particles with a particle size of 5 μm or less are dispersed in an area ratio of 2 to 20% in a matrix on a sliding surface made of iron-based metal or light metal. It is characterized by having a sprayed aluminum alloy layer with a thickness of 50μ or more. In the sliding member of the present invention, the primary Si particle diameter is specified to be 5μ or less, as will be explained later in Example 1 with a wear test example. In order to improve machinability, etc., the thickness was set to 5μ or less. The reason why the area ratio of primary Si particles was specified to be 2 to 20% is because if it is less than 2%, the wear resistance of the sprayed layer cannot be obtained.
On the other hand, if it exceeds 20%, the seizure resistance of the sprayed layer will deteriorate, so in order to prevent these disadvantages, the content is set at 2 to 20%. The reason why we specified the thickness of the sprayed layer to be 50μ or more is because the surface of a normal sprayed layer has irregularities of 30 to 50μ, so if it is not sprayed to a sufficient thickness, the base material may be exposed.
Since the adhesion between the sprayed layer and the base material becomes weak, the thickness was set to 50μ or more. To manufacture the sliding member of the present invention, for example, a hypereutectic silicon alloy material preferably having a silicon content of 15 to 30% is sprayed onto a substrate from a thermal spray gun at a temperature above the melting point of the alloy. It can be produced by heating to completely melt it and spraying the melt onto a substrate preferably maintained at a temperature below 300°C. In the above method, the reason why it is preferable to use a hypereutectic silicon alloy material with a silicon content of 15 to 30% is that a sprayed layer with a primary Si area ratio of 2 to 20% can be easily obtained. . In addition, if the thermal spray material (hypereutectic silicon alloy) is used with unmelted components remaining, not only will the primary Si particles in the resulting thermal spray layer not be sufficiently refined, but the strength of the thermal spray layer itself will deteriorate. It is desirable to completely melt the thermal spray material before use, as poor results are likely to occur. Thermal spray materials can be used in either powder or wire form, but if powdered materials manufactured by the atomization method are used, primary Si crystals can be formed by atomization.
Since the particles are made relatively fine in advance to a size of 20 to 30 μm or less, they can be easily melted, which is convenient. Furthermore, if the temperature of the substrate to be thermally sprayed is high, the cooling rate of the melt will be slow, making it impossible to sufficiently refine the primary Si particles, so it is convenient to thermally spray the substrate at a temperature of 300° C. or lower. Any of the following thermal spraying methods may be used: gas wire, gas powder, plasma, and explosion methods. The sprayed material is sufficiently melted in the high-temperature frame portion, and cools rapidly once it leaves the frame portion, which is advantageous for obtaining a sprayed layer containing fine primary Si particles. EXAMPLES The present invention will be explained in detail below with reference to Examples, but the present invention is not limited to these Examples. Example 1 As a thermal spray material, the particle size was
An aluminum-silicon alloy powder with 100 to 400 meshes and a silicon content of 23.9% was prepared. The primary Si particle size of the obtained powder was 3 to 25μ, and the area ratio of primary Si was 10.
~12%, Bitskers hardness (load 300g) is 130~
It was 145. This thermal spraying material was sprayed from a spraying distance of 120mm using a METCO 3M plasma spraying device.
Carbon steel with dimensions 30 x 30 x 5 mm kept at various temperatures
A S45C plate-shaped test piece (substrate) was thermally sprayed to a thickness of 200μ to produce plate-shaped test pieces made of sliding members of the present invention and non-inventive sliding members shown in Table 1. Plasma gas used was N ₂ 70.8/min and H ₂ 4.7/min, and the temperature of the substrate was controlled by preheating the substrate before starting thermal spraying and controlling cooling during thermal spraying. In Table 1, the sliding members whose symbols are circled are the sliding members of the present invention, and the others are sliding members other than the present invention. As a characteristic of the sprayed layer of the obtained sliding member, the primary crystal
The Si particle size, primary Si area ratio, and Vickers hardness were investigated, and the relationship with thermal spraying conditions was investigated. These values are also shown in Table 1.

[Table] ○ Sliding member of the present invention From the relationship between the spraying conditions and the properties of the sprayed layer shown in Table 1, the following can be seen. (1) The finer the particle size of the spray material powder, the larger the spray current, and the lower the powder supply rate, the more a sliding member having a spray layer with smaller primary Si particles can be obtained. (2) The lower the substrate temperature is, the easier the primary Si particles in the sprayed layer are to be refined, and when the substrate temperature is 400°C or higher, the primary Si particles are not sufficiently refined. (3) Considering (1) and (2) together, if the thermal spray material powder is sufficiently melted and the substrate temperature is low (that is, the thermal spray material cools quickly), the Si particles will become finer. A thermally sprayed layer is obtained. (4) In the sprayed layer where the primary Si particles have become finer, the area ratio of primary Si in the layer decreases slightly. This is thought to be due to the fact that the cooling effect during crystallization was large as the size of the crystallization progressed, so that some Si that did not crystallize was exposed. (5) The hardness of the sprayed layer increases as the substrate temperature decreases. As representative examples of the sliding members manufactured above, micrographs of the cross-sectional structures of the sprayed layers of the sliding member W of the present invention and the sliding member G other than the present invention are shown in FIGS. 1 and 2, respectively. . In the sliding member of the present invention shown in Fig. 1, all the primary Si particles have a fine diameter of 5 μ or less, whereas in the sliding member of the present invention shown in Fig. 2, the primary Si particles have a particle size of 5 μ or less and much larger. It can be seen that crystalline Si particles are mixed. Next, among the above sliding members, G,
A wear test was conducted using plate-shaped test pieces made of H, L, W, and X. As the other side test piece,
The test conditions were set as follows using a carburized and quenched cylindrical specimen of SCr420 (JIS G4104) (inner diameter φ20, outer diameter φ25.6, length 16 mm). Wear tester: Mechanical laboratory type Friction and wear tester Sliding speed: 2.4 m/sec Lubricating oil: Low viscosity gear oil Temperature: 35 to 45°C Surface pressure and time (1) Surface pressure for the first 10 minutes: 12.5 Run at Kg/ ^cm2 . (2) Afterwards, increase the surface pressure to a maximum of 12.5Kg/ ^cm2 every 2 minutes.
Raise to 250Kg/cm ² . If the product seizes during the ascent, the test will end at that stage. (3) After the test, determine the wear weight of the plate-shaped test piece and the mating test piece. The results of this wear test are shown in Table 2. Also,
For comparison, abrasion tests were also conducted on sliding plate specimens made of an aluminum-silicon alloy (Al-24%Si) having the same composition as the above-mentioned thermal sprayed material and manufactured to the same size by die-casting. The results are also listed in Table 2. In addition, the primary Si particle diameter of the test piece produced by the die-casting method is 12 to 115μ, the area ratio is 13.6%, and the Vickers hardness is 125 to 115μ.
It was 136.

[Table] As is clear from Table 2, the primary Si particle diameter is 5μ
The following plate-shaped test pieces made of the sliding members L, W, and X of the present invention are far superior in seizure resistance and wear resistance (of the sliding members themselves and especially the mating material) than other plate-shaped test pieces. Ta. Example 2 In order to investigate the relationship between the silicon content of the thermal spray material and the properties of the thermal spray layer, thermal spray material powders with a silicon content of 10%, 30%, and 35% were used on the same base material test piece as in Example 1. A sliding member was prepared by thermal spraying using the same powder particle size and thermal spraying conditions as the sliding member W in Table 1. A wear test was conducted on this sliding member under the same conditions as in Example 1. Table 3 summarizes the characteristics of the thermal spray material powder, the characteristics of the thermal spray layer, and the results of the wear test.

[Table] * Wear weight of plate specimen (mg)
** Cylindrical (mating side) test piece wear weight (mg)
As is clear from Table 3, the thermal sprayed layer obtained from the Al-10Si thermal sprayed material with low Si content and no primary Si crystals in the powder form does not have any primary Si particles in the matrix, and has poor seizure resistance. Although good, the wear resistance was poor. Also, Al−15Si, Al−
As explained in Example 1, 30Si and Al-35Si thermal spray materials can be melted sufficiently and then thermally sprayed under rapid cooling conditions, so that the fine primary Si particles in the sprayed layer can be formed regardless of the amount of Si. The anti-seizure properties and abrasion resistance were also good. However, in the sprayed layer obtained from Al-35Si, although the degree of refinement of the primary Si particles was the same as in the case of other sprayed materials, the amount of primary Si particles increased and the area ratio was 21%. , seizure resistance, and wear resistance decreased. Therefore, in order to obtain a sliding member with good properties, the Si content of the sprayed material should be kept below 35%, preferably below 30%, thereby reducing the primary crystallization of the sprayed layer.
It was necessary to suppress the Si area ratio to 20% or less. Example 3 A shift fork main body part was manufactured by forging carbon steel material (S55C) for machine structural use, and the same powder as in Table 1 W of Example 1 was applied to the pawl part corresponding to the sliding surface as an example of the present invention. A thermal sprayed layer with a thickness of 0.15 mm was formed under thermal spraying conditions. This shift fork was attached to an automobile drive transmission and evaluated on an actual machine using low viscosity gear oil. At this time, the amount of wear on the shift fork pawl and the amount of wear on the mating hub sleeve
Shown in the table. As a comparative example, Table 4 also shows the results of a similar evaluation of a shift fork of the same composition produced by the die-casting method described in Example 1.

[Table] As is clear from Table 4, the shift fork in which the claw portion was formed from the sliding member of the present invention had significantly better wear resistance than the comparative shift fork, and also had significantly less wear on the mating material. . As is clear from the above results, the sliding member of the present invention has excellent seizure resistance and wear resistance (including wear of the mating material). In this specification, an example in which the sliding member of the present invention is used in a shift fork is shown in Example 3, but as is clear from the results of Example 1, the sliding member of the present invention can be used on the inner surface of a cylinder liner, a piston ring, a transmission friction plate, etc. It is also useful as a sliding member for various parts. It is particularly suitable as a member for sliding surfaces conventionally manufactured using hypereutectic silicon-aluminum alloys, or sliding surfaces manufactured in such a manner but with problems in mechanical properties.
Furthermore, since the sliding member of the present invention is less likely to attack others, the problem of tool wear can be significantly improved by forming the sliding surfaces of parts that require good machinability, etc., with the sliding member of the present invention. Furthermore, since the sliding member of the present invention is manufactured using a thermal spraying method, there is a large degree of freedom in the base material, and various base materials such as aluminum alloy, steel, and cast iron can be used. productivity, strength,
It has the advantage of being able to meet a wide range of requirements such as wear resistance.

[Brief explanation of the drawing]

FIG. 1 shows a microscopic photograph (×1000) of the cross-sectional structure of the sliding member of the present invention, and FIG. 2 shows a microscopic photograph (×400) of the cross-sectional structure of the sliding member of the comparative example. 1...Primary silicon particles (small), 2...Primary silicon particles (large), 3...pores.

Claims (1)

[Claims] 1 A hypereutectic silicon-aluminum alloy sprayed layer with a thickness of 50 μm or more is provided on the surface of the sliding part of the base material, in which primary silicon particles with a particle size of 5 μm or less are dispersed in a matrix with an area ratio of 2 to 20%. A sliding member characterized by: