JPH0570706B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a sliding member that has excellent wear resistance and seizure resistance even under high surface pressure. (Prior Art) In recent years, due to the demand for higher output and lower heating costs for automobiles, various sliding members such as shift fork pawls, inner surfaces of synchronizer rings, inner surfaces of cylinder liners,
Piston rings, transmission friction plates, etc. are being used under higher surface pressure. In such cases, the sliding parts are prone to seizure and abnormal wear, so it is required to improve the performance of the sliding members, especially the seizure resistance and wear resistance, more than ever. Among sliding parts, for example, regarding shift forks, the pawls have traditionally been induction hardened, hard chrome plated, or sprayed with aluminum bronze, but these are no longer applicable under the harsh sliding conditions of recent times. It's coming. For this reason, a method of improving the sliding characteristics by spraying a material with excellent sliding characteristics on the surface of the sliding part by plasma spraying or the like is widely used. Conventionally used thermal spray materials include, for example, molybdenum (Mo), iron-chromium (Fe-Cr), iron-carbon (Fe-0.8C; carbon content 0.8
weight%), alumina-titania (Al ₂ O ₃ −TiO ₂ )
etc. However, when using the above-mentioned conventional thermal spray materials, the following problems occurred. That is,
Mo spraying and Fe-Cr thermal spraying have excellent wear resistance of the sprayed material itself, but are highly aggressive towards the mating material and easily wear the mating material. In addition, Fe-0.8C thermal spraying has a problem with the wear resistance of the thermal spraying material itself. Furthermore,
Thermal spraying using ceramic powder, typified by Al ₂ O ₃ -TiO ₂ thermal spraying, has excellent wear resistance, but is highly aggressive towards the mating material, so it tends to wear out the mating material, and it also causes damage to the metal base material. It is difficult to obtain sufficient adhesion, and it is easy to separate from the metal base material in parts that are subjected to shock loads, vibrations, etc. Therefore, recently, a sliding member has been proposed in which a sprayed layer comprising 2 to 30% by weight of molybdenum and the balance aluminum alloy or copper alloy is provided on a base material. (See Special Publication No. 58-10986). This is an Al alloy sprayed layer such as hypereutectic Al-Si with a hardness of about 100 to 200 Hv, and a single sprayed layer of Mo, which has a hardness of about 500 to 600 Hv and has good seizure resistance. By adding ~30% by weight, it was intended to give the thermal sprayed layer the same performance as a single Mo layer. Automobile parts such as shift forks and synchronizer rings obtained using such members exhibit excellent wear resistance and seizure resistance under normal sliding conditions, that is, under surface pressures of about 2 Kgf/mm ² or less. (Problem to be solved by the invention) However, in this case, at a Mo content of 2 to 30% by weight,
The distribution state is such that Mo is scattered in the Al-Si alloy, and the sliding conditions with higher surface pressure that will be required in the future, such as surface pressure of 5 kgf/mm ² or more, synchronized rotation speed
It has been found that the above sliding member cannot be said to have sufficient wear resistance under the condition of 6000 rpm.
This is due to the low hardness (Hv: 90 to 100) of the Al-Si alloy that makes up most of the sprayed layer, so under high surface pressures of 5 Kgf/mm ² or more, the sliding surface becomes smooth due to compressive stress and wear resistant. It was found that this is because the friction coefficient decreases due to wear caused by low friction. As a countermeasure to this, it is possible to increase the Mo content in the Al-Si layer. However, the Mo content is 50
%, it is unable to withstand compressive stress under a surface pressure of 7 to 8 Kgf/mm ² , and wear resistance and seizure resistance remain low. Therefore, if the Mo content is further increased, the wear resistance of the material itself will be improved, but the aggressiveness toward the mating member will be significantly increased. This is because if the Mo content in the sprayed layer is less than 50%, the surface of the sliding part with a surface hardness of Hv450 or less will sink due to high compressive force, and the wear resistance will not be sufficiently exhibited, and if it is more than 50%, the Mo content on the surface This is because the amount of distribution increases and its hardness (approximately Hv650) causes wear on the mating member. The present invention was made to solve the above problems, and its purpose is to
It is an object of the present invention to provide an inexpensive sliding member that has excellent wear resistance even when placed under high surface pressure of up to f/mm ² , is less aggressive to mating materials, and has excellent anti-seizure properties. (Means for Solving the Problems) The sliding member of the present invention for achieving the above object consists of 70 to 100% by weight molybdenum and the balance aluminum alloy or copper alloy on the sliding part surface of the base material. A thermally sprayed layer (hereinafter referred to as "lower layer") is provided, and on top of this thermally sprayed layer, a layer of 5 to 50% by weight consisting of 30 to 50% by weight of molybdenum and the balance aluminum alloy or copper alloy is provided.
It is characterized by having a thermally sprayed layer (hereinafter referred to as "upper layer") with a thickness of 50 μm. The present invention will be explained in more detail below. In addition, hereinafter, "%" refers to % by weight unless otherwise specified. Regarding the Mo content, the reason why the Mo content in the upper layer is preferably 30 to 50% is because if it is less than 30%, the effect of improving wear resistance is small, and if it is more than 50%, it will attack the mating member. Furthermore, if the Mo content of the lower layer is 70% or less, the back-up effect on the upper layer due to hardening the lower layer will not be seen, and the wear resistance will decrease. Aluminum alloys used in the present invention include aluminum-silicon (Al-Si) alloys and aluminum-lead (Al-Pb) alloys, but hypereutectic Al-Si alloys are particularly preferred. Further, as the copper alloy, an aluminum bronze alloy or a phosphor bronze alloy is used, and an aluminum bronze alloy is particularly preferred. To adjust the thermal spraying material, each powder thermal spraying material (100 to 400 mesh) of aluminum alloy, copper alloy, and Mo as a matrix material is separately supplied to the thermal spraying device and simultaneously sprayed to form the desired thermal sprayed layer. Alternatively, the matrix material and Mo powder may be mixed in advance before being supplied to the thermal spraying apparatus, or a composite material may be used in which Mo powder is adhered to the surface of the matrix material. Also, in order to maintain the surface pressure during sliding of the base material, 25 μRZ
Since it is necessary to have surface irregularities of a certain degree or higher, the matrix material for the lower layer is preferably an Al--Si type having an irregularity of 30 to 70 μRZ after thermal spraying. The thermal spraying method may be any of the gas wire method, gas powder method, plasma method, and explosion method. In these cases, it is necessary to thermal spray to create a difference between the Mo content of the upper layer and the Mo content of the lower layer, but this can be done by changing the supply ratio of the aforementioned matrix material and Mo powder, and by changing the supply amount of both powders midway through. This can be achieved by changing the mixing ratio or by using a composite material in which the amount of Mo powder attached to the surface of the matrix material is changed. Regarding the thickness of the sprayed layer, if the thickness of the upper layer is less than 5 μm, the lower layer will be exposed and the attack on the mating member will be greater, and if it is more than 50 μm, the back-up effect of the lower layer will be small and the wear resistance will be reduced. .
The base material used is iron-based alloys such as cast iron and steel, or light alloys such as aluminum alloys, but the surface of these base materials usually has irregularities of about 30 to 50 μm, so it is necessary to spray the material to a sufficient thickness. The base material may be exposed or the adhesion between the sprayed layer and the base material may become weak.
The thickness of the sprayed layer (upper layer + lower layer) is preferably 50 μm or more. (Example) The present invention will be explained in more detail with reference to Examples below. A reference example in which only one thermal spray layer is used, its performance test, and a comparative test to confirm the effects of the present invention are also listed. Reference example 1 Steel with an outer diameter of 35 mm, an inner diameter of 30 mm, and a width of 10 mm (JIS standard
Mixed powder of various compositions with varying mixing ratios of Al-Si alloy and Mo as shown in Table 1 was sprayed onto the outer peripheral surface of a cylindrical specimen made of SUJ2 (equivalent to SUJ2) by plasma spraying.
Friction and wear test pieces (sprayed ring materials) B to J, each having a different surface hardness, were prepared by thermal spraying to a thickness of 200 μm. Here, Al as a hypereutectic Al-Si alloy
-23%Si alloy and Mo were both within the range of 100 to 400 mesh. A cylindrical specimen with only Cr plating was also prepared as a comparative material.

[Table] Thermal spraying was carried out under the following conditions, after degreasing the base material and pre-treating it for shotplast, preheating it to 150-200°C. The gas used was N ₂ (7.08/min) + H ₂ (4.7/min), and the spraying distance was set to 120 mm and the powder supply rate was set to 50 g/min. The thermal spraying device used was a 3M plasma spraying device manufactured by METCO. As described above, test thermal sprayed ring materials B to J and Cr metal coating ring material A were obtained to be subjected to the following performance test 1. Performance Test 1 Test pieces A to J obtained in Example 1 were subjected to an LFW (friction and wear) test, and the amount of wear between the thermal sprayed layer and the mating material of each test piece was measured. A plate specimen of SUJ2 was used as the mating material, and the wear conditions were a surface pressure of 7 kgf/
mm ² , the rotation speed of the cylindrical test piece was 200 rpm, transmission oil was used, and measurements were taken 1 hour after the start of the test. The results of this wear test are shown in FIG. In FIG. 1, the numbers below the bar graph indicate the Mo content in the sprayed layer. Comparison material A, which was plated with Cr, developed seizure in about 30 minutes, whereas thermal sprayed products B to J did not experience seizure until the end of the test (until one hour later). As can be seen from Figure 1, specimens with a Mo content of less than 60% (B to E) exhibited significantly more wear, and as the Mo content increased, the wear decreased, but with Mo content of 60% or more, content (F to J),
Particularly, those with 80% or more (H to J) significantly abraded the mating material. Further, when the cross section of the thermal sprayed layer was observed under a microscope after the test, it was found that in B to E, which had a low Mo content, the Al--Si layer was significantly scratched off, resulting in a smooth surface. On the other hand, high Mo
At content rates F to J, most of the initial unevenness of the sprayed layer remained, but many scratches due to hard Mo were generated on the mating material. Reference Example 2 A sprayed layer with a thickness of 200 μm was formed on the sliding surface of the synchronizer ring with the gear in the same manner as in Reference Example 1. As a result, the sprayed layer composition is B~ in Table 1.
Various single-layer thermal spray synchronizer rings corresponding to J: B′ to J′ were obtained. Performance test 2 B′ to J′ obtained in reference example 2 were all subjected to a surface pressure of 7 kg.
It was subjected to a synchro shift durability test at f/mm ² and synchro rotation speed of 6000 rpm. As a result, it was found that in B' to E', the friction coefficient suddenly decreased from 10 to 900 times, causing gear noise. On the other hand, with F' to J', there was no gear noise, but there was a lot of wear on the mating gear, and the gear and synchronizer ring were in contact with the back, causing the synchronizer to malfunction after 30 to 950 cycles. These synchronizers were investigated and the results shown in Table 2 were obtained.

[Table] Example 1 According to the method of Reference Examples 1 and 2, Mo content was 5
The lower layer is 60% to 100% in % increments, and the same is 10% to 60.
% upper layer and a two-layer thermal sprayed layer were formed on the sliding surface of the synchronizer ring with the gear. The matrix material of the sprayed layer is Al-23%Si alloy, and the thickness of the upper layer is 10μm and the thickness of the lower layer is 190μm.
It is m. Comparative Test The two-layer thermal sprayed synchronizer ring obtained in Example 1 was subjected to a test similar to Performance Test 2. The results are shown in Figure 2. In the figure, the ○ mark indicates that no gear noise or synchronization malfunction occurred until the 1000th shift.
Indicates that no abnormality was observed. Also, the x mark indicates that synchronizer malfunction or gear noise occurred after shifting less than 1000 times. From this result, the upper
The Mo content is 30 to 50%, and the Mo content in the lower layer is
It can be seen that those with a sprayed layer of 70 to 90% have the best sliding properties. As a result of investigating the synchronizer rings used in this test, all of the synchronizer rings according to the present invention had a wear amount of 26 μm or less, and a wear amount of the mating gear.
18 μm or less, which was clearly superior to the best performing single-layer thermal spray synchronizer ring (listed in Table 2). The surface hardness of the upper layer of the products of the present invention was often about Hv450 to 500, while most of the products that caused gear noise were less than Hv450. In addition, many of the items that caused synchro malfunction had an upper layer hardness of Hv500 or more, and the gears were worn by approximately 20 μm or more. Those that caused gear noise, that is, those with too low Mo content in the upper or lower layer, had low back-up effects in the lower layer and could not withstand compression under high surface pressure, resulting in low wear resistance. I found out. In addition, if the synchronizer malfunctions,
The hardness of the upper layer is too high or there is hardness on the upper layer surface.
It was found that the wear of the mating gear was severe due to the large distribution of the Mo layer. Example 2 The Mo content in the upper and lower layers of the sprayed layer was kept constant at 40% and 80%, respectively, and the thickness of the upper layer was 2, 3, 5, 7, 10, 15, 20, 25, 30. ,35,40,
Thermal sprayed layers were formed on the sliding surfaces of the synchronizer ring in the same manner as in Example 1 so that the thicknesses were 45, 50, 55, 60, 70 μm, and the thickness of the upper layer + lower layer was 200 μm. The obtained product was tested in the same manner as in the comparative test above, and the sliding parts were examined, and the thickness of the upper layer was found to be
It was found that when the thickness exceeds 50 μm, no backup effect of the lower layer is observed, and the wear resistance decreases. It was also found that when the thickness of the upper layer is less than 5 μm, a portion of the lower layer is exposed, and the sliding properties of the lower layer are exhibited, increasing the aggressiveness towards the mating material. Therefore, it can be seen that the thickness of the upper layer is preferably 5 to 50 μm in order to exhibit the effects of the present invention. (Effect of the invention) The thermal spray layer is the same as the lower layer with a Mo content of 70 to 100%.
By creating a two-layer structure consisting of a 30% to 50% upper layer, the back-up effect of the hard lower layer is used to improve the wear resistance of the upper layer, and the covering effect of the upper layer suppresses the aggressiveness of the lower layer. The sliding member of the invention exhibits excellent wear resistance, anti-seizure properties, and non-aggressiveness against mating members even under severe surface pressure of 7 to 8 Kgf/mm ² . Therefore, the present invention can be applied to various sliding parts that are required to be subjected to higher surface pressure than conventional ones, such as piston rings, cylinder bores, pistons, air compressor parts, piston rods, shift forks, synchronizer rings, etc. Wear resistance, seizure resistance, corrosion resistance,
It has the effect of improving various physical properties such as heat resistance.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the Mo content in the sprayed layer, the wear resistance of the sprayed sliding area, and the aggressiveness of the mating material.
The figure shows the optimum range of Mo content in the upper and lower layers of the sprayed layer.

Claims (1)

[Claims] 1 A sprayed layer consisting of 70 to 100% by weight of molybdenum and the balance aluminum alloy or copper alloy is provided on the surface of the sliding part of the base material, and a 30 to 50% by weight layer is further formed on this sprayed layer.
1. A sliding member comprising a sprayed layer with a thickness of 5 to 50 μm consisting of % by weight of molybdenum and the balance of aluminum alloy or copper alloy.