JP2006037179A - Pb-FREE COPPER-ALLOY-BASED COMPOSITE SLIDING MATERIAL SUPERIOR IN SEIZURE RESISTANCE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that MoS<SB>2</SB>is oxidized in a process of manufacturing a copper-alloy-based composite sliding material having MoS<SB>2</SB>particles dispersed in a matrix consisting of copper alloy particles through sintering it, and accordingly does not show performance commensurate with an added quantity. <P>SOLUTION: A plated metallic phase exists in a boundary between the alloy particle and the MoS<SB>2</SB>particle, is sinter-bonded to the copper alloy particle, and is previously bonded to the MoS<SB>2</SB>particle before being sintered. Oxidized regions in MoS<SB>2</SB>are controlled to ten parts or less with respect to 100 parts of MoS<SB>2</SB>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a copper-based sintered sliding material. More specifically, the present invention relates to a Pb-free copper alloy-based composite sliding material having excellent seizure resistance.

  As the copper-based sliding material, a Cu—Pb alloy, a Cu—Sn alloy, or a Cu—Sn—Pb alloy sintered material is generally used. Pb in the copper alloy forms a low melting point phase, which melts when the temperature rises during sliding and secures seizure resistance by cooling the sliding surface and the self-lubricating action of Pb. Other than Pb, there is a copper alloy-based sliding material to which a small amount of Ag is added as a component for preventing the copper alloy from adhering to the counterpart during boundary lubrication (see Patent Document 1 (US Pat. No. 6,348,114)). ). In this copper alloy composite sliding material, a small amount of Ag reacts with S in the lubricating oil, and the Ag-S concentrated layer formed on the sliding surface by frictional heat under boundary lubrication extends thinly on the sliding surface. Suppresses adhesion between shaft and bearing.

Copper alloys containing Pb are corroded by components in the lubricating oil, and the sliding properties are reduced. In addition, Pb is an environmentally hazardous substance, and thus there is a high demand for Pb-free. However, Cu and Cu-Sn alloys not containing Pb have poor sliding characteristics, particularly seizure resistance under boundary lubrication. In order to overcome this point, a sintered copper alloy which does not contain Pb and has improved sliding characteristics by adding a tribo material such as MoS ₂ is known as described later.
In addition, for Ag-added copper alloys, Ag-S is produced in environments where high S content lubricants such as ATF and engine oil are used, but sulfides are generated in environments where S content is low such as bushes for fuel injection pumps. There are few, and an effect cannot fully be demonstrated.

A composite alloy composed of Sn: 5 to 16%, MoS ₂ : 5 to 16% and the balance Cu is sintered under conditions of 700 to 900 ° C for 10 to 30 minutes. Patent Document 2 (Japanese Patent No. 3013946) proposes a sliding layer for bushes and washers. MoS ₂ may be plated with Ni or Cu.

Also, a bushing material in which 1 to 10% of graphite, MoS ₂ and WS ₂ and at least 1 to 30% of hard materials such as Fe ₃ P and Fe-Ni are dispersed in a Cu-based sintered alloy (patented) Document 3 (see Patent No. 3042539) and bushing materials (Patent Document 4 (Patent No. 2974738) in which 1 to 10% graphite and 0.05 to less than 1% Al ₂ O ₃ are dispersed are also proposed. Has been.

Patent Document 5 (WO96 / 27685) discloses a copper alloy having the following composition and excellent in sulfidation corrosion resistance. Essential ingredients: Ni: more than 5% and 50% or less, Ag: 0.1-2%. Optional component (1) Sn: 20% or less, P: 0.5% or less, Al: 5% or less, Si: 1% or less, Mn: 5% or less, Zn: 30% or less, Fe: 10% or less, Sb: 1 (2) Pb and / or Bi in a total amount of 30% or less; (3) MoS ₂ , WS ₂ , BN in a total amount of 30% or less; (4) 20% or less in a total amount Al ₂ O ₃ , SiC, SiO ₂ , Fe ₃ P, AlN, Si ₃ N ₄ , TiC, WC, BN, NiB; (5) S: 0.001 to 1%.

Alloys that combine solid lubricants such as graphite and MoS ₂ have insufficient sliding performance with these additives alone, and cannot be used in parts with severe sliding conditions such as high surface pressure and high peripheral speed. In Patent Document 5, Pb is added simultaneously. These Pb, graphite, and MoS ₂ do not form a solid solution in Cu but exist as separate phases. By reducing the hardness of the entire copper alloy, the entire copper alloy is easily deformed and the conformability is improved. However, MoS _{2 as} a solid lubricant has poor adhesion to the copper alloy powder, so chipping may occur during processing of the sliding surface or sliding, but this point is due to solid lubrication plated with Cu and Ni. This can be solved by using an agent (see Patent Document 2).
US Pat. No. 6,348,114 Japanese Patent No. 3013946 Japanese Patent No. 3042539 Japanese Patent No. 2974738 WO96 / 27685 publication JP 2002-220631 A

When a copper alloy composited with graphite and MoS ₂ is sintered in an electric furnace, it is heated in a reducing atmosphere, but even when using a reducing atmosphere, most of the MoS ₂ particles are partially oxidized and MoO It is known to be ₃ . Therefore, the solid lubricating performance corresponding to the added amount of MoS ₂ cannot be exhibited. Furthermore, S decomposed by the oxidation of MoS ₂ reacts with copper to produce copper sulfide, and as a result, the copper alloy becomes brittle.
The present invention appropriately adds an amount of a sulfur-based solid lubricant such as MoS ₂ by a sintering method that limits oxides such as MoO ₃ produced by oxidation during the sintering of a copper alloy, thereby improving seizure resistance. An object is to provide an excellent Pb-free copper alloy composite sintered material.

The present invention provides a copper alloy composite sliding material in which sulfur-based solid lubricant particles are dispersed in a matrix composed of copper alloy particles, wherein the metal-based boundary phase is between the copper alloy particles and the sulfur-based solid lubricant particles. The copper alloy particles are sintered and joined together with the sulfur-based solid lubricant before sintering, and an oxidized portion of the sulfur-based solid lubricant Is controlled to a ratio of 10 parts by mass or less with respect to 100 parts by mass of the sulfur-based solid lubricant. Material)).
In addition, the present invention is a Pb-free copper excellent in seizure resistance, characterized in that a mixture of a copper alloy powder and a sulfur-based solid lubricant powder plated with a film thickness of 0.1 μm or more is subjected to high-frequency induction heating sintering. An alloy composite sliding material (hereinafter referred to as “second sliding member”) is provided.
The present invention will be described in detail below. In the present invention, the sulfur-based solid lubricant refers to one having an oxidized portion in a broad sense, and one having no oxidized portion in a narrow sense.

In the patent document 6 (Japanese Patent Application Laid-Open No. 2002-220631), the present applicant has achieved the achievement achieved by high-frequency sintering of a copper alloy, for example, (1) The steel plate of the back metal is mainly induction-heated below the Curie point. We have announced that rapid heating and short-time heating can be realized by (2) short holding time at sintering temperature, and (3) fine crystal grains of sintered alloy. As a result, a metal-based boundary phase having excellent sulfidation resistance was interposed between the sulfur-based solid lubricant particles and the copper alloy particles, and the metal-based boundary phase and the sulfur-based solid lubricant were previously joined by plating or the like. If found, it is found that even if the sulfur-based solid lubricant is partially oxidized during sintering, it is possible to suppress the influence of free sulfur on the copper alloy particles, and the invention of the first sliding material Was completed.
In addition, since MoS ₂ begins to decompose at about 380 ° C, controlling the sintering conditions indicates that the sulfur-based solid lubricant plated with metal at an appropriate thickness will not be oxidized and will be bonded together with the copper alloy. Found (second sliding material). The temperature rise to the sintering time is preferably within 2 minutes, and the holding time at the sintering temperature is preferably within 3 minutes.

Examples of the type of plating applied to sulfur-based solid lubricants such as MoS ₂ include metal plating such as Cu, Ni, Ag, Sn, and Au. In the present invention, the plating thickness is 0.1 μm or more. If the thickness of the plating is thin, the oxidation of MoS ₂ is not completely suppressed, and MoO ₃ and CuS are generated. Further, since the sulfur-based solid lubricant has a large specific gravity difference from the copper alloy particles and cannot be uniformly dispersed, uniform dispersion becomes possible when the thickness of the plating is increased to 1 μm or more and 5 μm or less.
That is, since the specific gravity difference between the plated MoS ₂ powder and the copper alloy particles is reduced, segregation of MoS _{2 in} the sintered layer is suppressed, and the MoS ₂ particles are uniformly dispersed. In addition, since diffusion of components occurs between the copper alloy particles and the plated metal, the adhesion between the copper alloy and MoS ₂ is improved, and the material strength is increased.
In the second sliding material, by using a sulfur-based solid lubricant that has been subjected to high-frequency sintering and plating of a predetermined thickness, the amount of MoO ₃ produced by oxidation during sintering of the copper alloy is limited, Alternatively, no oxidation is caused.

  In the first sliding material of the present invention, the metal-based boundary phase interposed between the copper alloy particles and the sulfur-based solid lubricant particles (the surface or the whole may be oxidized) is Cu, Ni Such a metal is previously bonded to particles of a sulfur-based solid lubricant. In the absence of this metal-based boundary phase, the sulfur-based solid lubricant is oxidized by a slight amount of oxygen contained in the copper alloy particles, and S generated by this oxidation reaction is combined with the copper alloy particles to produce copper sulfide. . On the other hand, in the present invention, since the metal-based boundary phase is previously bonded to the sulfur-based solid lubricant, the copper alloy particles and the sulfur-based solid lubricant are not in direct contact with each other. As a result, the oxidation of the sulfur-based solid lubricant is suppressed, and the sulfidation of the copper alloy particles can be prevented and delayed. In addition, when a metal-based boundary phase is interposed, sintering proceeds between the metal-based boundary phase and the copper alloy particles, so that a high sintered joint strength can be obtained.

In the first aspect of the present invention, “substantially the whole” means that the boundary between two particles is 90% or more, preferably 100%, in terms of length, and the metallic boundary phase exists. Although the boundary of less than 10% is due to defective plating or the like, if the boundary is at this level, it is possible to avoid significant deterioration of the sliding characteristics even if the sulfur-based solid lubricant is in direct contact with the copper alloy. According to the present invention, the oxidation ratio of the sulfur-based solid lubricant powder can be suppressed to 10/100 or less.
The oxidation ratio is the ratio of the mass of the oxide (MoO _{3 in} the case of MoS ₂ ), where the mass of the sulfur-based solid lubricant in the sintered material is 100. As can be understood from the above description, there are two types of oxides, one in which the entire fine sulfide particles are oxidized and the other in which the sulfide coarse particle surface is an oxide film.
Since the present invention has a low oxidation ratio as described above, a sulfur-based solid lubricant can be used effectively. Further, MoO ₃ is not preferable because it has a low hardness as a hard particle, and therefore has little effect of improving the wear resistance, and acts exclusively in the direction of lowering the bonding strength with the sintered copper alloy material.

As described above, sulfur liberated by oxidation of the sulfur-based solid lubricant sulfidizes the copper alloy. That is, reverse diffusion of oxygen and sulfur occurs through the metallic boundary phase. This sulfidation reaction of the copper alloy by free sulfur is suppressed by the plating metal and the metal-based boundary phase, but can be further suppressed by adding an element that increases the sulfidation resistance such as Sn, Ni, Zn to the copper alloy. it can. The fatigue resistance and wear resistance of the sulfided copper alloy deteriorate, but the conformability improves as the hardness decreases. In order to aim at the latter effect, it is preferable to set the sulfidation ratio of the copper alloy to 2/100 to 5/100.
Subsequently, components of the sliding material of the present invention will be described.

If the addition amount of sulfur-based solid lubricant such as MoS ₂ and WS ₂ (particle surface or the whole may be oxidized) is less than 0.1 parts by mass with respect to 100 parts by mass of the copper alloy, there will be no effect. If it is 10 parts by mass or more, the strength decreases. The addition amount of a preferable sulfur-based solid lubricant is 0.1 to 10 parts by mass, and more preferably 1 to 5 parts by mass. In addition, since the Cu matrix around the sulfur-based solid lubricant is prone to sulfidation and wear resistance and strength are expected to decrease, the above components such as Sn, Ni, Zn are added to the Cu matrix. To prevent. The particle size of these sulfur-based solid lubricants is preferably 10 to 30 μm on average.

  Sn increases the strength of the Cu matrix and is effective in improving fatigue resistance and wear resistance. Furthermore, there is also an effect of preventing sulfidation of the copper alloy due to the addition of the sulfur-based solid lubricant. If the Sn content in the copper alloy exceeds 15% by mass, the copper alloy becomes brittle. Therefore, Sn content is 15 mass% or less, Preferably it is 1-15 mass%, More preferably, it is 3-10 mass%.

  P lowers the melting point of the copper alloy and increases the sinterability. When the content of P in the copper alloy exceeds 0.5% by mass, the copper alloy becomes brittle. Therefore, the P content is 0.5% by mass or less, and preferably 0.01 to 0.2% by mass. Other than the above components, Cu and unavoidable impurities.

Additive elements of copper alloys such as Ag, Ni, Zn, In, and Bi: Ag, Ni, Zn, In, and the like increase the strength of the Cu matrix and are effective in improving fatigue resistance and wear resistance. In addition, it suppresses the copper matrix from undergoing sulfidation corrosion due to heat generated during sliding and S in the lubricating oil. In particular, it is desirable to add Zn or Ni in a sliding material used in a part where the amount of S in the lubricating oil is large or in a part where the temperature is high. Bi does not dissolve in Cu but exists as secondary phase particles. Since Bi has a low melting point, it melts onto the sliding surface by the heat generated during sliding, lowering the temperature of the sliding surface and preventing seizure.
However, when Ag: 5% by mass or more, Ni: 10% by mass or more, Zn: 30% by mass or more, and In: 10% by mass or more, the hardness of the copper alloy is excessively increased and becomes brittle and the conformability decreases. Seizure resistance decreases. If Bi: 20% by mass or more, the melting point of the copper alloy is too low and the strength is lowered. Preferable addition amounts are Ag: 0.1 to 1.2% by mass, Ni: 1 to 5% by mass, Zn: 5 to 30% by mass, and Bi: 1 to 10% by mass.

  Graphite: Graphite is a known solid lubricant that exhibits self-lubricating properties, but supplemental addition in the present invention has no problem. A preferable addition amount is 1 to 5 parts by mass. The average particle size of graphite is preferably 10 to 30 μm.

Fe ₃ P, Fe ₂ P, FeB, AlN, Al ₂ O ₃ , SiC, SiO ₂ , Si ₃ N ₄ : In the present invention, one or more of these hard materials are added to provide wear resistance. Can be increased. If the addition amount of these hard materials exceeds 10 parts by mass with respect to 100 parts by mass of the copper alloy, the strength of the sliding material decreases. A preferable addition amount is 1 to 10 parts by mass. The particle size of these hard materials is preferably 10 to 50 μm on average.

After mixing MoS ₂ powder plated with copper alloy powder and spraying on steel plate, sintering is performed in hydrogen-nitrogen gas reducing atmosphere. After heat-sintering by high frequency, cooling is quickly performed by gas and roll cooling. The sliding material of the present invention can be produced by rolling after sintering, then high-frequency sintering in the same manner at 700 ° C. to 1000 ° C., and then rolling again.
Sintering conditions include the time that is maintained at a temperature equal to or higher than the decomposition temperature of the sulfur-based solid lubricant, that is, the time from the middle of the heating process to the middle of the cooling process as much as possible. A short time is preferable, and specifically, it is preferably within 360 seconds. Further, the temperature raising time to the sintering temperature is preferably within 100 seconds, the holding time at the sintering temperature is within 160 seconds, and the cooling time to room temperature is preferably within 100 seconds. When a sulfur-based solid lubricant is exposed to a temperature above its decomposition temperature for a long time, oxidation proceeds and it becomes impossible to exhibit lubricating performance commensurate with the amount added, and the copper alloy is sulfided by the released sulfur, resulting in sliding performance. descend.
In addition, if the plating layer covers MoS ₂ powder, it will interfere with the contact with the sliding material, so the surface of the sintered material should be polished to expose a part of the MoS ₂ powder on the surface. Is preferred.
Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
After mixing Cu-plated MoS ₂ powder (average particle size 50 μm) at a ratio of 5-10 parts by mass with 100 parts by mass of Cu-Sn copper alloy atomized powder (particle size 180 μm or less) and spraying 1 mm on the steel plate Then, high frequency heating sintering was performed. Sintering conditions for high-frequency heat sintering are as follows. In a reducing atmosphere, the temperature is raised to a sintering temperature of 700 to 1000 ° C. within 2 minutes, the holding time at the sintering temperature is within 3 minutes, and cooling is performed by gas cooling. Or / and quickly cooled to room temperature within 2-3 minutes by roll cooling. Thereafter, rolling was performed, and high-frequency sintering was performed again under the same conditions, and the obtained material was used as a test piece. The thickness of the Cu plating applied to MoS ₂ was 2 μm or less. FIG. 1 shows the results obtained by measuring the amounts of MoO ₃ and MoS _{2 in} the test piece by X-ray diffraction and EPMA, and obtaining the oxidation ratio.
FIG. 1 shows that the oxidation ratio becomes zero when the plating thickness is 1 μm or more. When a sample having a plating thickness of 1 μm or more was observed with an optical microscope, a Cu-based boundary phase was observed around the entire MoS ₂ particle. A diffusion phase formed by sintering was observed between this boundary phase and Cu-Sn copper alloy particles.

Example 2
In the same manner as in Example 1, the compositions shown in Table 1 were sintered, and the surface after sintering was polished to expose MoS ₂ particles. For comparison, electric furnace sintering was performed. Sintering conditions for electric furnace sintering are as follows: in a reducing atmosphere, the temperature is raised to a sintering temperature of 700 to 800 ° C. in 10 to 20 minutes, and the holding time at the sintering temperature is 5 to 10 minutes. Cooled to room temperature in 20-30 minutes. The obtained test piece was tested by the following method.
Testing machine: Pin-on-disk testing machine Load: 4MPa / 10min gradual increase Oil type: Paraffin base oil Oil temperature: Room temperature Counterpart material: SUJ2
The test results are shown in Table 1.

  As shown in Table 1, according to the present invention, a considerably high seizure surface pressure is achieved without containing Pb.

Example 3
The method of Example 1 was performed while changing the high-frequency heating and cooling conditions, and the seizing surface pressure was measured by the test method of Example 2. Test conditions and results are shown in Table 2.

From Table 2, it can be seen that the seizure resistance decreases in the comparative example in which the MoS ₂ decomposition ratio exceeds 10%.

  As described above, since the sliding material of the present invention has excellent seizure resistance even if it does not contain Pb, it is very suitable as a bush for a fuel injection pump and a bush for an automatic transmission.

It is a graph which shows the relationship between plating thickness and an oxidation ratio.

Claims (9)

In a copper alloy composite sliding material in which sulfur-based solid lubricant particles are dispersed in a matrix composed of copper alloy particles, the metal-based boundary phase is substantially the boundary between the copper alloy particles and the sulfur-based solid lubricant particles. The copper alloy particles are sintered and joined to the sulfur-based solid lubricant before sintering, and the oxidized portion of the sulfur-based solid lubricant is the sulfur-based lubricant. A Pb-free copper alloy composite sliding material excellent in seizure resistance, characterized by being suppressed to a ratio of 10 parts by mass or less with respect to 100 parts by mass of a solid lubricant. 2. The Pb-free copper alloy composite sliding material with excellent seizure resistance according to claim 1, wherein the sulfur solid lubricant is 0.1 to 10 parts by mass with respect to 100 parts by mass of the copper alloy. Pb-free copper alloy composite slide with excellent seizure resistance, characterized by high frequency induction heat sintering of a mixture of copper alloy powder and sulfur-based solid lubricant powder plated with a thickness of 0.1μm or more Wood. 3. The seizure resistance according to claim 1, wherein the copper alloy contains Sn: 20% by mass or less and P: 0.5% by mass or less, and the balance substantially consists of Cu and inevitable impurities. Excellent Pb-free copper alloy composite sliding material. The copper alloy contains at least one of Ag: 5 mass% or less, Ni: 10 mass% or less, In: 10 mass% or less, Zn: 30 mass% or less, Bi: 10 mass% or less. The Pb-free copper alloy composite sliding material excellent in seizure resistance according to claim 4. The Pb-free copper alloy system having excellent seizure resistance according to any one of claims 1 to 5, wherein graphite of 10 parts by mass or less is further dispersed with respect to 100 parts by mass of the copper alloy. Composite sliding material. One or more of 10 parts by mass or less of Fe ₃ P, Fe ₂ P, FeB, AlN, Al ₂ O ₃ , SiC, SiO ₂ , Si ₃ N ₄ with respect to 100 parts by mass of the copper alloy 6. The Pb-free copper alloy composite sliding material having excellent seizure resistance according to any one of claims 1 to 5, further dispersed. The Pb-free copper alloy-based composite sliding material having excellent seizure resistance according to any one of claims 1 to 7, wherein the sulfur-based solid lubricant is MoS ₂ and the oxidized portion is MoO ₃ . 9. The Pb-free copper alloy composite sliding material excellent in seizure resistance according to any one of claims 1 to 8, which is sintered on a back metal plate.

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