JP6756995B1 - Copper-based sintered alloy and its manufacturing method - Google Patents

Abstract

By using the member of the present invention made of brass containing hard lubricating particles in which MnS having excellent lubricity is finely dispersed and held by reaction sintering in αFe-Fe2Mo-Fe7Mo6 particles which are relatively hard and have high toughness. Due to the wear resistance and self-lubrication effect of the hard particles, the amount of wear of the sliding members is significantly reduced. For example, when used for bearings of rotating parts of turbochargers, further improvement in output, higher efficiency and longer life are achieved. This makes it possible to reduce fuel consumption and purify exhaust gas.

Description

The present invention is suitably used for floating bush bearings and thrust bearings used in turbochargers for automobile engines, and sliding members such as bearings for automobile fuel pumps and bearings for home appliances, which are constantly supplied with lubricating oil. The present invention relates to a copper-based sintered alloy that can be used for oil-impregnated sliding members and the like impregnated with the lubricating oil of the above, and a method for producing the same.

Initially, turbochargers used in automobile engines were aimed at obtaining high output by sending compressed air into the engine. However, since around 1990, downsizing turbos that have an exhaust gas purification function while compensating for the decrease in engine output have become mainstream along with the reduction of engine weight (smaller exhaust volume) for the purpose of improving fuel efficiency. The smaller the displacement of an engine, the greater the rate of increase in rotational speed and the easier it is for the exhaust temperature to rise, so the ambient temperature in the engine room also rises. Therefore, if fuel efficiency is required to be improved, the temperature at which the lubricating oil and bearings used are exposed becomes higher.

The turbocharger includes a turbine blade that rotates by combustion exhaust gas from the engine and a compressor blade that compresses air by the rotation and blows air to the engine, and both blades are connected by a rotating shaft made of chrome molybdenum steel or the like. The rotating shaft of the turbocharger is supported by a floating bush bearing that receives a load in a direction perpendicular to the rotating shaft and a thrust bearing that receives a load in a direction parallel to the rotating shaft. Alloys based on lead bronze and high-strength brass, which have excellent sliding characteristics, have been used for all bearings.

Although lead bronze has excellent seizure resistance and sliding characteristics, it is inferior in sulfide corrosion resistance. Therefore, when exposed to high-temperature lubricating oil containing sulfur, a fragile black copper sulfide layer is formed on the alloy surface. Wear of the bearing surface is promoted. Therefore, when used for floating bush bearings and thrust bearings that receive the rotating shaft of a turbocharger exposed to high temperatures, it was difficult to use it stably for a long period of time (Yuka Iwama, Masaaki Yamane, Kiyokazu Iizuka, Mt. Wada). Katsuya: "Study on the blackening phenomenon of bearing materials for vehicle turbochargers by automobile lubricating oil", Proceedings of the Society of Automotive Engineers of Japan, 47 (2016), p.615-619).

Since high-strength brass has excellent sulfurization and corrosion resistance, a black sulfide layer is not formed even when exposed to a high-temperature lubricating oil containing sulfur. However, there is a problem in abrasion resistance, and therefore, it has been widely used for sliding members used at low speed rotation as compared with bearings of turbochargers (see paragraph [0052] of Japanese Patent No. 3718147).

Japanese Patent No. 2745696 discloses one or more of Zn: 5 to 25% by mass, Si: 0.1 to 2% by mass, Fe, Ni and Co in order to solve the problem of conventional copper-based molten alloys. : 0.1 to 3% by mass, oxygen: 0.01 to 0.5% by mass, Al: 0.1 to 0.3% by mass, one or more of Cr, Mo and W: 0.1 to 2% by mass, and the balance is Cu and A metal having a composition consisting of unavoidable impurities, in which oxides distributed in a particle size range of 1 to 40 μm are uniformly dispersed in an area ratio of 0.1 to 7%, and also distributed in a particle size range of 1 to 25 μm. Copper base firing having a structure in which intermetallic compounds are uniformly dispersed at an area ratio of 1 to 8%, fine oxides and intermetallic compounds are uniformly dispersed in the substrate, and pores are distributed by 1 to 15% by volume. The bond money is disclosed.

When trying to further improve output and efficiency in order to enable lower fuel consumption and exhaust gas purification with a downsized turbocharged automobile engine, the atmosphere inside the engine room with turbocharger bearings is 180 ° C or higher. In many cases, the temperature becomes high (see paragraph [0013] of Japanese Patent No. 3718147). As a result, since the sintered alloy for bearings of Japanese Patent No. 2745696 is brass having a Zn content of 25% or less, when applied to bearings of turbochargers used at high temperatures of 180 ° C or higher, sulfur contained in lubricating oil As a result, corrosion easily progresses, causing abnormal wear in the bearing portion (see paragraph [0012] of Japanese Patent No. 3718147).

Therefore, in Patent No. 3718147, brass with a Zn content of about 40%, which is resistant to sulfide corrosion, is used as the sintered alloy for bearings of the turbocharger, and needle-shaped hard MnSi phase particles are oriented and dispersed in the brass in the direction of rotation axis. The aim was to improve the wear resistance of the MnSi phase while preventing corrosion.

However, according to Japanese Patent Application Laid-Open No. 2016-169434, when used for a long period of time, the MnSi phase breaks down and falls off from the bearing surface, damaging the sliding surface, which causes a problem of seizure (paragraph). (See [0004]). In order to alleviate this, Japanese Patent Application Laid-Open No. 2016-169434 focuses on the α phase of a copper-zinc alloy (α-β two-phase alloy) in which hard particles of the MnSi phase are dispersed, and has a lower hardness than the β phase. Bi particles are dispersed so as to be encapsulated in the α phase, Bi remains in the recess formed by the wear of the α phase, and slidability is imparted by Bi to improve seizure resistance.

However, since the MnSi phase itself is not prevented from falling off at all, the problem that the MnSi phase breaks down and falls off from the bearing surface and damages the sliding surface as the wear progresses, which causes seizure, can be solved. Not done.

As described above, proposals have been made for sintered alloys for turbocharger bearings for harsher operating environments, but if there is any prior art that discloses bearing alloys that can prevent wear-resistant phases from falling off. Absent. Therefore, the inventors of the present application consider that it is important to solve the following two points at the same time in order to improve the performance of the copper-based sintered alloy so as to be suitable for the bearing of the turbocharger. It was.

First, the hard particles dispersed in the bearing member have high toughness to withstand the stress generated during sliding and high toughness that does not fall off from the copper alloy base material in order to prevent destruction and falling off due to microscopic impact during sliding. Must have interfacial strength.

Second, the bearing material needs to maintain a low coefficient of friction even during harsh sliding. Lubricating oil is always supplied when driving the turbocharger, but under harsh conditions, the oil film at the bearing / rotating shaft interface is not sufficiently formed, and the bearing material and rotating shaft material come into direct microscopic contact with each other. Depending on the material, the brass part of the bearing (hardness: brass <steel) may be scratched, and the friction coefficient may increase sharply, causing seizure. Not limited to bearings for turbochargers, the sliding characteristics of bearing materials under boundary lubrication affect the performance and life of products such as pumps and motors. Therefore, a bearing material that can maintain a low coefficient of friction even in a harsh sliding environment is required.

As a means to solve the problem, if the hard particles dispersed in the bearing member have self-lubricating property, even if the oil runs out temporarily, the friction coefficient at the bearing / rotating shaft interface is prevented from increasing and stable sliding is performed. Can be maintained.

From the above, the hard particles dispersed in the copper-based sintered alloy used for sliding materials used in harsh environments such as bearing members have high toughness, high interfacial strength with the copper alloy base material, and self-lubricating property. It is desirable to have.

Japanese Patent No. 5229862 describes a Fe ₇ Mo ₆ intermetallic compound phase obtained by mixing Fe powder and Mo powder so that Fe powder is 55 to 60 atomic% and the rest is Mo powder, and pressure sintering. A Fe ₇ Mo _6-element alloy (hereinafter referred to as "alloy A") which is composed of three phases of Fe-7 atomic% Mo phase and Mo phase and exhibits low friction and low wear is disclosed. Patent No. 5229862 further states that, of the three phases constituting Alloy A, the Fe ₇ Mo ₆ intermetallic compound phase contributes to low friction and low wear, and the Fe-7 atomic% Mo phase functions as a fracture toughness strengthening phase. It states that it will be done. Therefore, although the alloy A is produced by pressure sintering and has a drawback that the productivity is slightly inferior, it is promising as a hard lubricating particle.

Japanese Patent Application Laid-Open No. 10-317002 clarifies that mechanical structural parts such as automobile parts manufactured by using Fe-Mo-S ternary alloy powder have a low coefficient of friction. That is, a Mo _x S _y- type compound (FeMo _x S _y ) is finely precipitated inside the alloy powder particles themselves, and the powder particles themselves, and thus powder sintering, are based on the lubricating action of the Mo _x S _y- type compound. It is said that the coefficient of friction of the body can be effectively reduced. The inventors of the present application thought that the sliding characteristics of the alloy A disclosed in Japanese Patent No. 5229862 could be further improved by using this concept.

That is, one aspect of the present invention is a sintered alloy in which hard particles containing αFe, Fe ₂ Mo, Fe ₇ Mo ₆ and MnS are dispersed in a brass alloy base material containing Cu, Zn and Mn. The total content of Fe and Mo is 7 to 25% by mass, and the contents of Fe, Mo, Mn and S (% by mass) are C _Fe , C _Mo , C _Mn and C _Mn , respectively. Assuming C _S , C _Mn / (C _Fe + C _Mo ) is 0.15 to 0.47, C _Mo / (C _Fe + C _Mo ) is 0.20 to 0.30, and C _S / (C _Fe + C _Mo ) is 0.01 to 0.04. der is, the hard particles, when the volume of the entire hard particles is 100%, 40 to 60 vol% of αFe phase, 10-30 vol% of Fe ₂ Mo phase, 10-30 vol% of Fe ₇ Mo It is a copper-based sintered alloy having ₆ phases, 10 to 20% by volume MnS phase, and less than 4% by volume ZnS phase, and the average particle size of the hard particles is in the range of 10 to 40 μm .

The ratio of the Zn content to the total Cu and Zn content in the brass alloy base material is preferably 0.38 to 0.42.

It is preferable that the brass alloy base material further contains 6.0% by mass or less of Al and 1.0% by mass or less of Sn, or 1.2% by mass or less of Al , 1.0% by mass or less of Sn and 1.0% by mass or less of Ni. ..

The relative density of the copper-based sintered alloy is preferably 96% or more. When used as an oil-impregnated bearing, the relative density of the copper-based sintered alloy is preferably 82% or more and 88% or less.

As the starting raw material powder for the hard particles, it is preferable to use Fe—Mo—S alloy powder and Mn powder and / or copper alloy powder containing Mn.

The sintered alloy of the present invention is a brass alloy containing hard particles M in which MnS having excellent lubricity is finely dispersed and held in αFe-Fe ₂ Mo-Fe ₇ Mo ₆ particles, which are relatively hard and have high toughness. When a sliding member is manufactured from the sintered alloy of the present invention, the amount of wear of the sliding member is significantly reduced due to the wear resistance and self-lubricating effect of the hard particles M. Therefore, for example, when it is used for a sliding member or a bearing for an engine auxiliary such as a floating bush bearing or a thrust bearing of a turbocharger, it is possible to improve the output and the efficiency, and further reduce the fuel consumption and purify the exhaust gas. The sintered alloy of the present invention uses lead bronze or high-strength brass for sliding members or bearings for engine accessories such as bearings for turbochargers, industrial equipment, compressors, home appliances, and OA equipment. It is self-evident that it can be used as an alternative.

It is a vertical sectional view of Fe-MoS ₂ of the Fe-Mo-S ternary phase diagram. It is a Cu-Zn-Mn ternary phase diagram. It is a graph which shows the relative density of the comparative alloys 6 and 7 and the invention alloys 2 and 4. It is a figure which shows the distribution of each element in comparative alloys 6 and 7 and invention alloys 2 and 4 analyzed by SEM-EDX. It is an X-ray diffraction pattern of the comparative alloy 6 and the invention alloy 4. It is a figure which compares FIGS. 4 and 5, determined the compound / metal phase of the dispersed particle, and shows the image-processed distribution. It is a figure which shows the TG-DTA curve when the starting material powder of the comparative alloy 6 and the invention alloy 4 was formed, respectively, and heated from room temperature to 1,000 degreeC at 10 degreeC / min in an Ar flow (atmospheric pressure) atmosphere. The TG-DTA curve when 100% by mass powder F and mixed powder with 16.7% by mass Mn added to powder F were molded and heated from room temperature to 1,000 ° C at 10 ° C / min in an Ar flow (atmospheric pressure) atmosphere. It is a figure which shows.

The copper-based sintered alloy of the present invention (hereinafter referred to as "invention alloy") can be produced by a powder metallurgy method. The invented alloy is a brass alloy base material composed of Cu, Zn and Mn, and αFe phase and Fe by reaction sintering. ₂Mo phase, Fe₇Mo₆It is a sintered alloy in which hard particles M containing a phase and an MnS phase as main components are dispersed. As the raw material powder of the copper alloy base material, a mixed powder obtained by blending copper or copper-zinc alloy powder so that the copper alloy has a predetermined zinc amount can be used. As raw material powders for hard lubricating particles, αFe and Fe produced by the atomization method or the like₂Mo and FeMo₃S_FourA mixed powder composed of a mixture of powder F (composition: Fe-24% by mass Mo-2.7% by mass S) and Mn powder can be used, and a copper alloy powder containing Mn can be used instead of Mn powder. You may use it.

The above raw material powders are blended to have a predetermined composition and mixed with a ball mill to obtain a starting raw material powder. This starting material powder is molded with a mold and then reaction-sintered to form MnS inside the hard particles to obtain an invention alloy. Sintering may be performed by filling a predetermined mold with the starting material powder or a molded product thereof and hot-press sintering or energization sintering, or sintering HIP which pressurizes at the time of sintering, but ordinary sintering is preferable. In the case of ordinary sintering, the porosity of the sintered body can be changed depending on the sintering conditions, which is advantageous in terms of cost. Since the amount of zinc volatilized in the copper alloy increases when ordinary sintering is performed under reduced pressure, it is preferable to use an inert gas such as Ar as the atmospheric gas to increase the pressure to atmospheric pressure or higher.

The total content of Fe and Mo is 7 to 25% by mass when the total mass of the sintered alloy is 100%. If the total amount is less than 7% by mass, the amount of hard particles M to be dispersed is insufficient and the wear resistance is lowered. If the total amount is more than 25% by mass, the strength is lowered and seizure occurs when used as a bearing. It will be easier to do.

The average particle size of the hard particles M dispersed in the alloy of the invention is in the range of 10 to 40 μm . If the average particle size of the hard particles M is less than 10 μm, the self-lubricating effect of the hard particles M during sliding cannot be sufficiently exhibited, and the wear resistance is not sufficiently improved. If the average particle size of the hard particles M is more than 40 μm, the strength of this material is reduced and chipping or cracking may occur when used as a bearing, resulting in reduced reliability. The average particle size of the hard particles M can be obtained by taking a 300-fold SEM microstructure photograph in 9 fields and analyzing the image. The particle size of the hard particles M is preferably in the range of 2 μm to 90 μm. Hard particles M having a particle size of less than 2 μm do not have a sufficient self-lubricating effect, and hard particles M having a particle size of more than 90 μm may cause chipping or cracking when used as a bearing.

When the contents (% by mass) of Fe, Mo, Mn and S of the invented alloy are C _Fe , C _Mo , C _Mn and C _S , respectively, the ratio of the content of Mn to the total content of Fe and Mo C _Mn / (C _Fe + C _Mo ) is 0.15 to 0.47. Mn is formed by finely dispersing the MnS phase by combining with S in the hard particles M, and when the reacting S disappears, it dissolves in the brass alloy base material. If C _Mn / (C _Fe + C _Mo ) is less than 0.15, the amount of MnS phase is small, so the self-lubricating effect of hard particles M is not sufficient, and if it exceeds 0.47, the amount of Mn that dissolves in the brass alloy base material. As a result, the temperature at which the liquid phase of the brass alloy appears decreases, and the liquid phase becomes excessive during sintering, causing deformation. C _Mn / (C _Fe + C _Mo ) is preferably 0.46 or less, and preferably 0.20 or more.

Ratio of S content to total Fe and Mo content C_S/ (C_Fe+ C_Mo) Is 0.01 to 0.04. S hardly dissolves in the brass alloy base material, and forms an MnS phase and a ZnS phase described later in the hard particles M. C _S/ (C_Fe+ C_Mo) Is less than 0.01, it cannot combine with Mn in the hard particles M to generate a sufficient amount of MnS phase, and if it is more than 0.04, the fragile sulfide phase increases and it is hard depending on the usage situation. Abrasion resistance cannot be maintained due to cracking or breakage of particles M.

The ratio of the Mo content to the total Fe and Mo content C _Mo / (C _Fe + C _Mo ) is 0.20 to 0.30. Mo hardly dissolves in the brass alloy base material and forms Fe ₇ Mo ₆ phase and Fe ₂ Mo phase in the hard particles M. If C _Mo / (C _Fe + C _Mo ) is less than 0.20, the amount of Fe ₇ Mo ₆ phase or Fe ₂ Mo phase is too small, so the self-lubricating effect of hard particles M is reduced, and if it is more than 0.30, the toughness is low. Machinability is reduced because the amount of Fe ₇ Mo ₆ phase and Fe ₂ Mo phase is too large.

The content of each component in the entire sintered alloy, which is the sum of the content of each component in the brass alloy base material and the content of each component in the hard particles M, is the addition of each component contained in the starting material powder. Since the amounts are almost the same, the content ratio of each component of the above-mentioned sintered alloy can be calculated by calculation based on the amount added at the time of blending the starting material powder. The calculated value is basically the same as the result of analyzing the sintered alloy with an ICP emission spectroscopic analyzer (for example, ICPV-1017 manufactured by Shimadzu Corporation).

Since the Fe ₇ Mo ₆ phase and the Fe ₂ Mo phase exhibit excellent wear resistance as well as a self-lubricating effect, the Fe ₇ Mo ₆ phase and the Fe ₂ Mo phase have a total of 20 to 46% by volume with respect to the total hard particle M. Good to contain. When the volume ratio of Fe ₇ Mo ₆ phase and Fe ₂ Mo phase is within this range, excellent wear resistance and strength can be obtained. The Fe ₇ Mo ₆ phase is preferably contained in an amount of 10 to 30% by volume, and the Fe ₂ Mo phase is preferably contained in an amount of 10 to 30% by volume based on the total amount of the hard particles M.

The MnS phase is preferably contained in an amount of 10 to 20% by volume based on the total amount of the hard particles M. When the volume ratio of the MnS phase is within this range, the hard particles M have good self-lubricating property and interfacial strength, are excellent in sliding characteristics, and do not seize even in a harsh sliding environment.

When the hard particles M contain a ZnS phase, it indicates that the amount of the MnS phase is not sufficient, which causes a problem in sinterability and the like. Therefore, even if the hard particles M contain the ZnS phase, it is desirable that the amount is less than 4% by volume.

The brass alloy base material in which the hard particles M are dispersed is based on a copper-zinc alloy (brass). The ratio of the amount of Zn to the total amount of Cu and Zn is preferably 0.38 to 0.42. In this composition range, when the alloy comes into contact with a sulfur-containing lubricating oil at high temperature, a dense film containing ZnS as the main component is formed on the surface to suppress the CuS formation reaction, as if stainless steel is dense in an aqueous solution. It exhibits excellent sulfurization and corrosion resistance under high temperature lubricating oil containing sulfur, just as it forms a passivation film and exhibits excellent corrosion resistance. In addition, β-phase formation is promoted to increase hardness and wear resistance.

The amount of Mn contained in the brass alloy base material is preferably in the range of 0.1 to 5% by mass. When Mn is added to brass, the β phase increases as in the effect of Zn, the hardness increases, and the wear resistance can be improved. If the amount is 0.1% by mass or less, the increase in hardness is not sufficient, and if it is more than 5% by mass, the machinability is lowered.

The brass alloy base material may further contain 6.0% by mass or less of Al and 1.0% by mass or less of Sn, and may further contain 1.2% by mass or less of Al , 1.0% by mass or less of Sn, and 1.0% by mass or less of Ni. .. It also contains unavoidable impurities derived from each raw material.

The invention alloy should have a relative density of 96% or more when used in a harsh usage environment such as a turbocharger bearing. If it is less than 96%, the oil film formed during sliding is easily broken and seizure is likely to occur. Further, it can also be used as an oil-impregnated bearing by forming a certain amount of pores in the sintered alloy and impregnating the pores with oil. At this time, the relative density of the invention alloy is preferably 82% or more and 88% or less. If it exceeds 88%, the amount of oil discharged from the alloy is insufficient, and if it is less than 82%, the contact area with the mating material decreases, resulting in a high surface pressure and easy seizure.

The present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

(Example 1)
A powder in which the amount of Fe is increased as compared with alloy A to increase the ratio of αFe phase, and the amount of S is decreased as compared with the Fe-Mo-S alloy powder of JP-A-10-317002 to reduce the amount of Mo _x S _y- type compounds. F (composition: Fe-24% by mass Mo-2.7% by mass S) was prepared. When the constituent phase of powder F was examined by X-ray diffraction, it was found to consist of αFe, Fe ₂ Mo and Fe Mo ₃ S ₄ .

A sintered body obtained by adding powder F and powder F to brass was prepared by the following procedure. A dry ball mill (powder) in which brass powder (average particle size 10 μm), powder F (average particle size 25 μm), and Mn powder (average particle size 10 μm) are blended into the compositions of Comparative Alloys 1 to 9 and Invention Alloys 1 to 6 shown in Table 1. : Ball = 1: 1) was mixed for 30 minutes to obtain a starting material powder. Subsequently, this starting material powder was molded (5 t / cm ² ), and finally sintered (900 ° C.-1 hour) in an inert gas (Ar). The commercially available alloy 1 (brass C2801) and the commercially available alloy 2 (high-strength brass C6782) were obtained from the market.

* 1: Cu and Zn are added as Cu-40 mass% Zn brass alloy.
* 2: F refers to powder F.
* 3: Other elements are Fe, Al, and Pb.
* 4: N is normal sintering, H is hot press sintering, and C is casting.

Table 1 (continued)
* 5: During sintering, it drips due to excessive liquid phase.
* 6: Not tested because the specified shape could not be obtained due to excessive liquid phase during sintering.
* 7: "Not broken" indicates that the product was not bent and torn, and the bending strength is not high.
* 8: Discoloration in engine oil S (200 ° C), ○ indicates no discoloration, ● indicates discoloration to black, and △ indicates discoloration to gray.
* 9: Test using a pin-on disk tester.
* 10: ◎ is 20% or more superior to the non-seizure surface pressure of commercially available alloy 1. ○ is better than equivalent to less than 20%. △ is equivalent. ○ △ is the one that varies and has both results.

Table 1 shows the ingredients, fabrication methods and alloy properties. The dimensions of each alloy test piece used for the relative density, flexural strength and corrosion test were width x thickness x length of 8 mm x 4 mm x 25 mm. In the corrosion test to examine the sulfurization corrosion resistance, the test piece was immersed in engine oil S (Zepro Ecomedalist SN / GF5 0W-20 manufactured by Idemitsu Kosan Co., Ltd.) containing sulfur heated to 200 ° C for 20 hours. The color change was observed. ○ indicates no discoloration, ● indicates discoloration to black, and △ indicates discoloration to gray. Only ○ can be considered to be corrosion resistant and suitable for this application.

A pin-on disk tester is used for the sliding test and the practical mock test, the mating material is a disk made of SCM435 (HRC47) (φ35 mm × 15 mm), and the pin is each alloy test piece (8 mm × 8 mm × 16). The mm and the angle were 0.2 R).

In the sliding test, the sliding speed was set to 0.4 m / s at room temperature, 0.5 cc of engine oil S was applied only to the sliding surface of the disc for the first time, and the surface pressure was 20 MPa and the mixture was slid for 1 hour. The coefficient of friction is the value in the steady state, and the wear dimension is the value after sliding for 1 hour. "- ^{* 6} " indicates that the alloy was not tested because it was deformed due to excessive liquid phase during sintering. The reason why the engine oil was not supplied all the time was that the conditions were harsh.

The practical practice test is a seizure test that simulates the usage environment when it is put into practical use. At room temperature, the sliding speed was 0.4 m / s, and 0.2 cc of engine oil S was applied only to the sliding surface of the disc at the beginning, and the surface pressure was gradually increased to determine the load immediately before seizure. If the load immediately before seizure is equivalent to the value of the commercially available alloy 1, it is marked with Δ, if it is equal to or more than 20%, it is marked with ○, and if it is 20% or more superior, it is marked with ◎. “-” Indicates that the test was not performed due to insufficient densification of the alloy and large deformation during sintering. The reason why 0.2 cc of engine oil was applied to the disc only at the beginning was because the conditions were as harsh as the friction coefficient measurement.

The test temperature was set to room temperature for the following reasons. The temperature inside the engine room, which is said to be seized in the practical test, is 180 ° C or higher, but when the temperature when seized with a thermocouple in contact with the opposite side of the disk was measured in this mock test, the temperature was about 200. It was ° C. Therefore, it was judged that the actual environment could be reproduced even in the mock test at room temperature.

Comparative Alloy 1 was composed of powder F only, was difficult to sinter, had a low relative density in ordinary sintering, and lacked corrosion resistance. Comparative Alloy 2 in which 40% by mass of powder F was added to brass also showed difficulty in sintering, and the relative density was as low as 75.6% in normal sintering. Therefore, Comparative Alloy 3 was densified by hot press sintering. Since the corrosion resistance of Comparative Alloy 3 was improved, a practical mock test was conducted and both judgment results of 〇 and △ were obtained. However, hot press sintering is not practical because the production cost becomes too high.

Therefore, the improvement of sinterability in ordinary sintering was examined. In addition to the poor sinterability of brass itself, it was thought that the powder F added to brass also reduced the sinterability, so comparative alloys 4 to 6 in which the amount of powder F added was gradually reduced. Was prepared and evaluated. As a result, the relative density of Comparative Alloy 6 was improved to about 90%, so the amount of powder F added was set to 10% by mass.

It was considered from the phase diagram whether the sinterability could be further improved in ordinary sintering. Vertical section of Fe-MoS _{2 in} the Fe-Mo-S ternary phase diagram shown in Fig. 1 (P. Villars, A. Prince, H. Okamoto: Handbook of Ternary Alloy Phase Diagrams, Volume 1-10, ASM International From 1995, p.10480), since powder F is a solid phase at the sintering temperature (~ 900 ° C), improvement in sinterability cannot be expected with powder F as it is. Therefore, in order to improve the sinterability, it is the first priority to consider how to improve the sinterability of the brass itself at this sintering temperature. Figure 2 is a Cu-Zn-Mn ternary phase diagram (see P. Villars, A. Prince, H. Okamoto: Handbook of Ternary Alloy Phase Diagrams, Volume 1-10, ASM International, 1995, p.9710). , The numbers in the figure indicate the temperature at which the liquid phase appears. Two small circles near Cu-39.3 atomic% Zn indicate the positions of each element in the compositions of Comparative Alloys 6 and 7 in Table 1, excluding powder F. From this, it is estimated that the liquid phase appearance temperature drops by about 5 ° C with the addition of 1% by mass Mn. That is, it is considered that the addition of Mn lowers the liquid phase appearance temperature and improves the sinterability of brass itself.

The addition of Mn is also considered to have the following effects on powder F. Under the sintering temperature (~ 900 ° C), MnS is energetically lower and more stable than both FeS and MoS ₂ (The Iron and Steel Institute of Japan: 3rd Edition, Steel Handbook, Volume I, Basic, Maruzen Co., Ltd.) Company, 1981, see Ellingham diagram on p.12), MnS is also considered to be more stable than FeMo ₃ S _{4, which} is also a Fe-Mo-S compound. Therefore, if Mn is added and sintered, it can be inferred that MnS is produced by reacting with FeMo ₃ S ₄ in the powder F, and if the production of MnS is an exothermic reaction, the temperature around the powder F rises. , It is considered that the wettability with brass is improved and the sinterability can be improved.

From the above, it was considered that the addition of Mn was effective in improving the sinterability. Furthermore, if Fe Mo ₃ S ₄ in the powder F becomes α Fe, Fe ₇ Mo ₆ and Mn S by the addition of Mn, the constituent phases of the dispersed particles are closer to the alloy A. Then, it was considered that the sliding characteristics could be improved if MnS having excellent lubricity (see paragraph [0060] of Japanese Patent No. 4823183) was finely generated in the dispersed particles.

Therefore, 10% by mass of powder F was added to the Cu-40% by mass Zn brass alloy powder by a predetermined mixing method, and a mixed powder having a composition of 0 to 5% by mass Mn was further formed (5 t / cm ² ). Normal sintering was carried out in an inert gas (under atmospheric pressure) at 900 ° C. for 1 hour to prepare comparative alloys 6 to 8 and invention alloys 1 to 5.

In order to make it easier to understand the relationship between the relative density of the sintered alloy and the amount of Mn added, the relative densities of the comparative alloys 6 and 7 and the invention alloys 2 and 4 are shown in FIG. It can be seen that the relative density reaches 96.0% when 1% by mass of Mn is added, and then tends to increase gradually. The addition of Mn succeeded in improving the sinterability as expected.

In order to confirm whether MnS formation occurred in the dispersed particles, X-ray diffraction analysis of the sintered alloy, SEM observation of the cross-sectional structure, and EDX analysis were performed. In X-ray diffraction, it is often not detected when only a small amount of substance is contained, so first, a sintered alloy (comparative alloys 6 and 7 and invention alloys 2 and 4) to which 0 to 4% by mass of Mn is added is ground and polished. After that, it was analyzed by EDX (FlatQUAD manufactured by Bruker) attached to SEM (Regulus8100 manufactured by Hitachi High-Technologies Corporation) (acceleration voltage 15 kV, secondary electron detection time constant for 30 minutes). The results obtained are shown in Fig. 4. The amount of Mn added is shown at the left end of each stage. The leftmost column is the secondary electron image of SEM, and the right side shows the distribution of elements shown at the bottom of each figure in white to gray. The whiter the color, the stronger the detection energy, indicating that the elemental component is higher. Focusing on the distribution of Mn, most of it was distributed in the brass alloy base material when 1% by mass Mn was added, but it was also slightly generated around the dispersed particles.

Figure 5 shows the X-ray diffraction patterns of the 0% by mass and 4% by mass Mn-added sintered alloys (comparative alloy 6 and invention alloy 4). Using RINT-Ultima III manufactured by Rigaku Co., Ltd., the measurement conditions are tube voltage: 40 kV, tube current: 30 mA, X-ray type: CuKα, divergence slit: 2/3 °, scattering slit: 2/3 °, light receiving. Slit: 0.3 mm, step width: 0.01 °, scan speed: 0.25 ° / min, graphite curved crystal monochromometer was used. The constituents of the sintered alloy are (Cu-Zn) -αFe-Fe without the addition of Mn.₂Mo-Fe₇Mo₆-It was ZnS. On the other hand, with the addition of 4% by mass Mn, (Cu-Zn) -αFe-Fe₂Mo-Fe ₇Mo₆-It became MnS. That is, ZnS disappeared by adding 4% by mass Mn, and MnS was newly generated.

Fig. 4 and 5 are compared, the compound / metal phase in the dispersed particles is determined, and the image-processed distribution is shown in FIG. It is binarized for easy understanding. The black to gray part shows the distribution of each phase displayed at the bottom, and the blacker the color, the larger the amount of the component. As shown in FIG. 6, the constituent phase of the dispersed particles of the alloy after sintering was αFe-Fe ₂ Mo-Fe ₇ Mo ₆ -ZnS without Mn addition. With the addition of 1% by mass Mn, MnS was observed around the dispersed particles, which was a little difficult to understand, but was slightly generated in the dispersed particles. With the addition of 2% by mass Mn, ZnS disappeared, and conversely, MnS became clear, and the same was true with the addition of 4% by mass Mn. Although MnS was also produced in the 5 mass% Mn-added alloy (comparative alloy 8), it could not be used for various evaluations due to the remarkable sintering deformation as described above. Therefore, FIG. 6 shows only the results of addition of 0 to 4% by mass Mn. In any case, by adding Mn, the desired MnS could be produced in the dispersed particles.

As described above, it can be seen from FIG. 6 that ZnS is generated in the dispersed particles when Mn is added in an amount of 1% by mass or less. Since this is energetically stable in the order of FeS <ZnS <MnS (MnS is the most stable), it is considered that ZnS is present when the amount of Mn added is small, and only MnS is present when the amount of Mn added is large. Considering this together with Table 1 and Fig. 3, it seems that ZnS formation, unlike MnS formation, hardly improves the sinterability deterioration due to the addition of powder F. In any case, ZnS generation may not have a great meaning for the present invention.

Simultaneous measurement of thermogravimetric (Thermo Gravimeter: TG) and differential thermal (DT) using a differential thermal analyzer TG8120 manufactured by Rigaku Co., Ltd. to confirm whether the formation of MnS is an exothermic reaction (hereinafter, "TG-DTA"). ”) Was carried out in an Ar flow atmosphere (atmospheric pressure) from room temperature to 1,000 ° C.

In Fig. 7, the starting material powders of the comparative alloy 6 without Mn added and the invention alloy 4 with 4 mass% Mn added were molded and heated from room temperature to 1,000 ° C at 10 ° C / min in an Ar flow (atmospheric pressure) atmosphere. The TG-DTA curve of the case is shown. The starting material powder was molded at 5 t / cm ² , and the reference material was alumina. As shown in Fig. 7, a sharp endothermic reaction was observed around 900 ° C. This indicates the liquid phase appearance temperature of the brass alloy, which was 890 ° C. when Mn was not added, but was 880 ° C. when 4% by mass Mn was added. That is, as shown in the Cu-Zn-Mn ternary phase diagram of FIG. 2, it is considered that the addition of Mn lowered the temperature at which the liquid phase of the brass alloy appeared, and the sinterability of the brass itself was improved.

FIG. 8 shows the TG-DTA curve measured in the same manner as in FIG. 7 for a mixed powder of 100% by mass powder F and F-16.7% by mass Mn. The value of 16.7% by mass Mn corresponds to the ratio of the Mn content to the total F + Mn content of the invention alloy 2. As estimated, MnS formation was found to be an exothermic reaction. When an exothermic reaction, that is, reaction sintering occurs, the temperature around the powder F rises, so that the wettability with brass is improved and the adhesion is improved. This seems to make it difficult for hard particles (composition is different from that of powder F) to fall off during sliding.

It should be noted that the reason why the powder F has difficulty in sintering is that the powder F is a coarse-grained powder and the mixing conditions of the powder are light pulverization.

Furthermore, as shown in the results of the invention alloy 5 with 4.5% by mass Mn added and the comparative alloy 8 with 5% by mass Mn added, if the amount of Mn added is larger than 4.5% by mass, the liquid phase will be too large due to sintering. The sintered body has been deformed. Therefore, in order to obtain an alloy without sintering deformation, 1.5% by mass or more and 4.5% by mass or less is preferable.

The mass change of the sintered body is relatively large because the zinc on the surface layer of the sintered body volatilizes during sintering. However, since that part is in the category of replacement allowance when processing into bearings and sliding members, there is no particular problem in production.

As a result of quantitative analysis by EDX of the brass part of the base material when observing Fig. 4, it was confirmed that the brass part contained a small amount of Mn by adding Mn, and in the invention alloy 4 with 4% by mass Mn added, it was confirmed. A content of about 2% by mass of Mn was observed. As a result, the hardness and strength of brass as an α-β two-phase alloy will increase (Masa Nemoto, Mitsuya Kamada, Kazuo Tanozaki: "Structure and Machinery of Cu-Zn-Mn-Al-Fe-based Copper Alloy for Casting" Properties ”, Hitachi Review, 44 (1962), 1755-1760), and wear resistance seems to be improved.

From Table 1, it can be seen that the sintered body of the powder F and the powder F-added alloy has an extremely excellent friction coefficient of 0.07. In that case, the wear size does not fall below 20 μm unless the relative density is 96% or more, excluding powder F. Specifically, in the sintered body of the powder F-added alloy having a relative density of 96% or more, the wear rate is higher than that of the mating material at the beginning of the test, but after that, the wear is caused by the lubrication effect of the hard particles M. It was suppressed, and even after sliding for 1 hour, the wear size was less than 20 μm, and it was confirmed that there was almost no wear. The comparative alloys 9 and the commercially available alloys 1 and 2 were worn at the same wear rate from the start of the wear test until 1 hour had passed, and the wear size was finally increased.

In any case, in a practical mock test that reproduces a harsh environment where bearings for turbochargers and bearings for fuel pumps are used, it is practically used that the load immediately before seizure exceeds that of commercially available alloys. It is an index to judge whether it can be done. In Table 1, the invention alloys 1 to 6 achieved this.

From the above results, the following can be said. Hard particles M containing αFe, Fe ₂ Mo, Fe ₇ Mo ₆ and Mn S as main components obtained by decomposing Fe Mo ₃ S ₄ in powder F by adding Mn are dispersed particles having both wear resistance and lubricity. Yes, the reaction that changes from powder F to hard particles M is an exothermic reaction, so it has good adhesion to the surroundings and does not easily fall off when sliding. Therefore, the invention alloys 1 to 6 in which the hard particles M are dispersed in brass are extremely stable in the presence of high-temperature lubricating oil containing sulfur when used in bearings for turbochargers, bearings for fuel pumps, etc. It can exhibit corrosiveness and sliding characteristics.

Table 2 shows the αFe phase, Fe ₂ Mo phase, Fe ₇ Mo ₆ phase, MnS phase, and ZnS phase when the total amount of hard particles present in the comparative alloys 6 to 8 and the invention alloys 1 to 6 is 100% by volume. Indicates the volume fraction. The amount of MnS produced increases sharply when the Mn content is increased from 0% by mass to 1% by mass and 1.5% by mass (when the relative density exceeds 96%), and when the Mn content is 2% by mass or more. It becomes constant by about 15% by mass. Since the Mn content of the other phases is almost constant at 2% by mass or more, the composition of the invention alloys 2 to 6 is particularly stable and can be said to be industrially advantageous.

(Example 2)
Among the invention alloys 2 to 6 in Table 1, an alloy having the same composition as the invention alloy 2 having the largest wear size was selected, and an oil-impregnated alloy test was conducted. The starting material powder was obtained in the same manner as in Example 1. The starting material powder is molded at 1 to 5 t / cm ² , then sintered at 800 to 900 ° C, and the relative densities are 80%, 82%, 85%, 88% and 90%. Reference alloy 1, Invention alloy 7 ~ 9 and reference alloy 2 were prepared respectively. Cu-10% Sn commercial alloy 3 (bronze alloy P4013Z) was obtained from the market. The obtained alloy was immersed in lubricating oil and vacuum defoamed to impregnate the alloy with lubricating oil to obtain an oil-containing alloy. For the measurement of relative density and the oil impregnation method, Japanese Industrial Standards: "Sintered metal material-density, oil content and open porosity test method", Z2501: 2000, p.3-6 were referred to.

The seizure test was performed with a pin-on disk type tester using SUS304 (HV250), SUS440C (HV700) and SCM435 (HV470) as the mating material of each alloy. The sliding speed is constant at 0.1 m / s, which is a low speed at which the lubricating oil impregnated in the alloy does not easily spread to the sliding surface and tends to be boundary lubrication. In that state, the surface pressure is gradually increased and the surface pressure seizure on the mating material. Was compared.

Table 3 shows blend composition, porosity of the commercial and the invention alloy 2 different relative density in the same composition Reference Alloy 1 and 2 and invention alloy 7-9 alloy 3, the relative density, the seizure test results. The results of the seizure test were judged in the same manner as in Table 1.

As a result of the test, the invention alloys 7 to 9 did not seize even at a surface pressure 1.8 times higher than that of the commercially available alloy 3. Some alloys did not seize even at twice the surface pressure of commercially available alloy 3. From this, by substituting the oil-impregnated alloy of the present invention with the bronze oil-impregnated alloy, seizure does not occur even if boundary lubrication occurs after long-term use, and the life of the product using the invention alloy can be extended.

Reference alloys 1 and 2 showed almost no difference in surface pressure from the commercially available alloy 3. As a cause, since the reference alloy 1 has a high porosity, the oil content is sufficient, but the area actually in contact with the mating material is smaller than the apparent contact area, and the surface pressure is high. Therefore, it is considered that boundary lubrication is likely to occur and the seizure surface pressure is lowered. Since the reference alloy 2 has a low porosity, the oil content is low, and it is probable that the alloy 2 was seized because sufficient lubricating oil was not supplied to the sliding surface.

From the above results, it is clear that when the invention alloy is an oil-impregnated alloy, a relative density of 82% to 88%, which has a sufficient oil content and excellent mechanical strength, is suitable. Further, when the invention alloys 3 to 6 having less wear dimensions than the invention alloy 2 are made into oil-containing alloys by the same method as the invention alloy 8, it is clear that at least the same performance as the invention alloys 7 to 9 can be obtained.

* 1: Cu and Zn are added as a Cu-40 mass% Zn brass alloy.
* 2: F is αFe-Fe ₂ Mo-FeMo ₃ S ₄ alloy powder F (composition: Fe-24 mass% Mo-2.7 mass% S).
* 3: ◎ is 20% or more superior to the non-seizure surface pressure of commercially available alloy 3. ○ is better than equivalent to less than 20%. △ is equivalent.
* 4: Since the results of the seizure test with the mating materials SUS304, SUS440C and SCM435 were all in the same category, the notation of the category was summarized into one.

As described above, since MnS having excellent lubricity is finely dispersed in the hard particles M, the MnS particles are prevented from falling off during use and exhibit a long-term lubrication effect. In addition to the above method, various studies were conducted to see if there was another method for finely dispersing MnS in M.

When MnS particles were dispersed in a molten metal containing Fe and Mo in advance to prepare Fe-Mo-MnS particle powder by an atomization method or the like, the eutectic temperature of the Fe-Mo system was 1,450 ° C and the eutectic temperature of the Fe-Mo system was 1,450 ° C. Due to the large temperature difference of 1,580 ° C., the MnS particles segregated in the Fe-Mo alloy powder and could not be finely dispersed.

We also considered using MnS powder (average particle size of about 5 μm) as the raw material powder when preparing the mixed powder, but dispersed it coarsely (about 10 μm or more) as the MnS phase in the brass alloy base material of the sintered alloy. However, it could not be finely dispersed in the hard particles.

After all, it was confirmed that the best method is to mix Mn powder and powder F instead of MnS powder and react-sinter. The powder used when adding Mn may be Mn powder or a copper alloy powder containing Mn.

The sintered alloy of the present invention having the above-mentioned characteristics is not limited to bearings used for turbochargers, but also for sliding members to which lubricating oil is constantly supplied or oil-impregnated bearing materials containing lubricating oil inside the alloy. Can be used. As an example of bearings to which lubricating oil is supplied, there are bearings for automobile engine auxiliary equipment, industrial machinery, and the like.

Specifically, examples of automobile engine auxiliary equipment include turbochargers, sliding members or bearings for fuel pumps and fuel injection pumps. Examples of industrial machines include sliding members or bearings for supporting spindles of gear pumps and machine tools and for air compressors.

An example of an oil-impregnated sliding member in which oil is contained inside an alloy is a sliding member or bearing for home appliances and OA equipment. Specifically, for home appliances, it is incorporated into compressors used in refrigerators and air conditioners, magnetic or optical recording devices such as HDDs and Blu-rays (registered trademarks), ventilation devices, washing machines, electric cookware, etc. Examples include sliding members or bearings. Examples of OA equipment include sliding members such as multifunction devices or bearings. When the sintered alloy of the present invention is used for these sliding members or bearings, the output and efficiency can be improved, and the life can be extended.

The turbocharger using the bearing made of the sintered alloy of the present invention enables further downsizing of the engine, and can improve the output and efficiency, thus promoting low fuel consumption and exhaust gas purification, and global warming. It can contribute to the prevention of climate change and energy saving.

Claims (6)

In a sintered alloy in which hard particles containing αFe, Fe ₂ Mo, Fe ₇ Mo ₆ and MnS are dispersed in a brass alloy base material containing Cu, Zn and Mn.
When the total mass of the sintered alloy is 100%, the total content of Fe and Mo is 7 to 25 mass%, and the contents (mass%) of Fe, Mo, Mn and S are C _Fe and C _Mo , respectively. , C _Mn and C _S , C _Mn / (C _Fe + C _Mo ) is 0.15 to 0.47, C _Mo / (C _Fe + C _Mo ) is 0.20 to 0.30, and C _S / (C _Fe + C _Mo ). There Ri der 0.01 to 0.04,
The hard particles are 40 to 60% by volume αFe phase, 10 to 30% by volume Fe ₂ Mo phase, 10 to 30% by volume Fe ₇ Mo ₆ phase, 10 when the total volume of the hard particles is 100%. It has ~ 20% by volume MnS phase and less than 4% by volume ZnS phase.
A copper-based sintered alloy characterized in that the average particle size of the hard particles is in the range of 10 to 40 μm . The copper-based sintered alloy according to claim 1 , wherein the ratio of the Zn content to the total Cu and Zn content in the brass alloy base material is 0.38 to 0.42. The brass alloy base material is characterized by further containing 6.0% by mass or less of Al and 1.0% by mass or less of Sn, or 1.2% by mass or less of Al , 1.0% by mass or less of Sn and 1.0% by mass or less of Ni. The copper-based sintered alloy according to claim 1 or 2 . The copper-based sintered alloy according to any one of claims 1 to 3 , wherein the relative density is 96% or more. The copper-based sintered alloy for an oil-impregnated bearing according to any one of claims 1 to 3 , wherein the relative density is 82% or more and 88% or less. The method for producing a copper-based sintered alloy according to any one of claims 1 to 5 , wherein the starting raw material powder of the hard particles includes Fe—Mo—S alloy powder, Mn powder and / or Mn. A method characterized by using a copper alloy powder.