Pb-free copper alloy sliding material

Abstract

When a CuSnBi hadparticle based sliding material is used for sliding, Cu of Cu matrix flows and covers up Bi phase. Seizure resistance lowers as time passes. A Pb-free sliding material preventing the reduction of seizure resistance is provided. (1) Composition: from 1 to 15% of Sn, from 1 to 15% of Bi, from 0.02 to 0.2% of P, and from 1 to 10% of hard particles having an average diameter of from 50 to 70 m, with the balance being Cu and unavoidable impurities. (2) Structure: Bi phase and the hard particles are dispersed in the copper matrix, and all of said hard particles are bonded to the copper matrix.

Claims

1. A method for producing a homogeneous Pb-free sintered sliding material under observation using an optical microscope at a magnification of 100 times, by sintering, comprising: preparing a powder of a CuBi alloy and hard particles, wherein the hard particles have an average particle diameter of from 5 to 70 m and include an FeP based compound, and wherein the FeP based compound comprises at least one selected from the group consisting of Fe.sub.3P and Fe.sub.2P; mixing the CuBi alloy powder and the hard particles, so that a mixture obtained by mixing consists of, by mass %, 1 to 10% of the hard particles, with the balance being CuBi alloy, containing from 1 to 15% of Bi, and unavoidable impurities; heating the mixture of the CuBi alloy powder and the hard particles to a sintering temperature of 700 C. to 900 C., thereby forming a liquid phase of Bi, which is present as a Bi phase around at boundaries of a Cu matrix after sintering, and presenting said hard particles at boundaries of the Cu matrix; and, controlling a temperatureelevating gradient, in terms of C./min, in a temperature range of from room temperature to 600 C., to 300 to 1000 C./min, wherein all of the hard particles are bonded with the Cu matrix without any intermediary of the Bi phase and are bonded with the Bi phase at a length ratio of less than 100%, in a sintered structure in which the Bi phase and the hard particles are present at boundaries of the Cu matrix.

2. The method according to claim 1, wherein said CuBi alloy consists of, by mass %, from 1 to 15% of Bi, with the balance being Cu and unavoidable impurities.

3. The method according to claim 1, wherein said CuBi alloy consists of, by mass %, from 1 to 15% of Bi, 0.02 to 0.2% of P, with the balance being Cu and unavoidable impurities.

4. The method according to claim 1, wherein the Pb-free sintered sliding material is in the form of a sliding member having a sliding surface, on which surface all of said hard particles are bonded with the Cu matrix, at a depth of from 10 to 80 m.

5. The method according to claim 1, wherein the sintering is carried out for 5 to 30 minutes.

6. The method according to claim 5, wherein the sintering is carried out in an electric furnace.

7. The method according to claim 1, wherein the sintering steps are repeated twice with an intermediate rolling.

8. The method according to claim 2, wherein the sintering steps are repeated twice with an intermediate rolling.

Description

BEST MODE FOR CARRYING OUT THE INVENTION

EXAMPLE 1

(1) A preliminary copper alloy having a CuSnBi composition shown in Table 1 was prepared. This alloy was subjected to atomization procedure to obtain a powder having a particle diameter of 150 m or less. In addition, the CuSnBi alloy powder and the hard particles shown in Table 1 were mixed with a V-type blender under ordinary conditions. The mixed powder was dispersed on a steel sheet of 150 mm (width)2000 mm (length) to lay the powder in a 1-mm thickness. Sintering was carried out in an electric furnace under hydrogen atmosphere. The sintering conditions were as follows. The temperature gradient: set at 600 degrees/min in a temperature range of from room temperature to 600 degrees C.; sintering temperature: from 700 to 900 degrees C.; sintering time: from 5 to 30 minutes. Subsequent to sintering, the sintered layer was densified by rolling. The second sintering was then carried out again under the same conditions.

(2) TABLE-US-00001 TABLE 1 Seizure Hard Particles Resistance(#) Bi Sn P Average After mass mass mass Amount Particle Stationary Cu % % % Type mass % Diameter m Initial Sliding I 1 Bal 1 1 0 Fe.sub.3P 3 30 20 20 2 Bal 1 5 0 Fe.sub.3P 3 30 20 20 3 Bal 1 15 0 Fe.sub.3P 3 30 24 24 4 Bal 5 1 0 Fe.sub.3P 3 30 40 36 5 Bal 5 5 0 Fe.sub.3P 3 30 40 36 6 Bal 5 15 0 Fe.sub.3P 3 30 36 36 7 Bal 15 1 0 Fe.sub.3P 3 30 32 28 8 Bal 15 5 0 Fe.sub.3P 3 30 32 28 9 Bal 15 15 0 Fe.sub.3P 3 30 32 32 10 Bal 5 5 0 Fe.sub.3P 1 30 36 36 11 Bal 5 5 0 Fe.sub.3P 10 30 32 32 12 Bal 5 5 0 Fe.sub.3P 3 10 32 28 13 Bal 5 5 0 Fe.sub.3P 3 68 36 36 14 Bal 1 1 0 Fe.sub.2P 3 30 24 24 15 Bal 1 5 0 Fe.sub.2P 3 30 20 20 16 Bal 1 15 0 Fe.sub.2P 3 30 28 24 17 Bal 5 1 0 Fe.sub.2P 3 30 36 40 18 Bal 5 5 0 Fe.sub.2P 3 30 40 40 19 Bal 5 15 0 Fe.sub.2P 3 30 32 32 20 Bal 15 1 0 Fe.sub.2P 3 30 32 32 21 Bal 15 5 0 Fe.sub.2P 3 30 32 28 22 Bal 15 15 0 Fe.sub.2P 3 30 28 32 23 Bal 5 5 0 Fe.sub.2P 1 30 32 28 24 Bal 5 5 0 Fe.sub.2P 10 30 32 32 25 Bal 5 5 0 Fe.sub.2P 3 10 16 32 26 Bal 5 5 0 Fe.sub.2P 3 68 12 32 II 1 Bal 5 0 Fe.sub.3P 3 30 28 12 2 Bal 20 5 0 Fe.sub.3P 3 30 16 8* 3 Bal 5 0.5 0 Fe.sub.3P 3 30 36 12 4 Bal 5 20 0 Fe.sub.3P 3 30 28 12 5 Bal 5 5 0 Al.sub.2O.sub.3 3 30 36 16 6 Bal 5 5 0 36 16 7 Bal 5 5 5 Fe.sub.2P 15 30 24 8* 8 Bal 5 5 0 Fe.sub.2P 3 98 20 8* 9 Bal 5 5 0 Fe.sub.2P 3 0.3 32 8* Remarks: Iinventive example 1, IIcomparative example 1, *Seizure occurred upon step up, (#)Surface Pressure, MPa

(3) Seizure resistance tests were carried out using the following methods and under the following conditions. (1) Test of Initial Seizure Testera pin-on-disc tester Loadstepped up by 4 MPa/10 min Oil Typeparaffin-based oil Oil Temperatureroom temperature Material of Mating MemberSUJ2 (2) Seizure Resistance Test after Stationary Sliding Testera pin-on-disc tester Loadsliding under 8 MPa for 300 minutes, with subsequent step-ups at a rate of 4 MPa/10 min Oil Type: paraffin-based oil Oil Temperatureroom temperature Material of Mating MemberSUJ2

(4) The comparative examples in Table 1 were found to exhibit poor properties. Specifically, since Comparative Example 1 is free of Bi, initial seizure resistance and resistance after stationary sliding are poor. Since Comparative Example 2 has a high Bi content, initial seizure resistance and seizure resistance after initial sliding are poor as well. Since Comparative Example 3 has a low Sn content, although it has good initial seizure resistance, seizure resistance after stationary sliding is poor. Since Comparative Example 4 has a high Sn content, initial seizure and seizure resistance after stationary sliding are poor. Since the hard particles of Comparative Example 5 are Al.sub.2O.sub.3, although initial seizure resistance is good, seizure resistance after stationary sliding is poor. Since Comparative Example 6 is free of hard particles, although initial seizure resistance is good, seizure resistance after stationary sliding is poor. Since Comparative Example 7 has a high additive content of hard particles, the seizure resistance after stationary sliding is poor. Since the average particle diameter of the hard particles is large in Comparative Example 8, although initial seizure resistance is good, seizure resistance after stationary sliding is poor. Since the average particle diameter of the hard particles is small in Comparative Example 9, although initial seizure resistance is good, the seizure resistance after stationary sliding is poor.

(5) Observation of the structure was carried out as follows. A portion of the above-mentioned sliding material which can be applied to actual components was determined. Three locations in such a portion, each having an area of 10 mm10 mm under an optical microscope with a field of 0.50 mm.sup.2 and a magnification of 100. Observation must be repeated six hundred times. First, a preliminary test was carried out six hundred times for No. 1 and No. 22 sample in Table 1 under a PC controlled microscope produced by OLYMPUS Co., Ltd. It was confirmed at each observation that all the hard particles were bonded to the copper matrix on the sliding surface.

(6) Next, the same optical microscopic observation as described above was carried out for the sintered materials of Nos. 11 and 12 samples listed in Table 1 of Patent Document 2. In one of the thirteen observations, hard particles were found to be completely incorporated into the Bi phase.

(7) The above-described preliminarily microscopic observation has confirmed that: no segregation is induced by the sintering method; and, the material is homogeneous in the microscopic field of view mentioned above. Therefore, observation of representative locations under a microscope is sufficient to determine the entire material structure. From these considerations, each of the materials other than Nos. 1 and 22 in Table 1 was subjected to microscopic observation of randomly chosen locations fifty times. The microscopic observation revealed that all the hard particles are bonded to the copper matrix. In addition, the inventive examples exhibited good initial seizure resistance and seizure resistance after stationary sliding.

(8) Sample Nos. 5, 9 and 21, which represent inventive examples, were polished. Microscope photographs of the polished surfaces are shown in FIGS. 1, 2 and 3, respectively. It is clear from these photos that the hard particles are bonded to the copper matrix. These microphotographs are now compared with a microscopic photograph shown in Patent Document 2 (10% Bi-2% Fe.sub.3P-1% Fe.sub.2P-balance Cu). Note that the Bi phase is observed as isolate particles having indefinite shapes. The number of such a Bi phase per identical surface area should be paid attention. However, since the Bi content and the amount of hard particles are not identical in these materials, when this fact is taken into consideration in the comparison, there is a tendency that the number of the Bi phase according to the present invention is smaller than that of Patent Document 2. This comparison in structure also supports the high likelihood that the FeP compound contacts the copper matrix but not the Bi phase.

(9) FIG. 4 shows the results of Comparative Example 2. As is clear from FIG. 4, hard particles are completely surrounded by the Bi phase. Since Comparative Example 3 has a low Sn content and hence a low recrystallizing temperature, several hard particles are completely surrounded by the Bi phase.

EXAMPLE 2

(10) As shown in Table 2, P was added to several of the compositions of Example 1 in Table 1. Test Samples were prepared by the same method employed for those in Table 1, and the same test procedure was followed. In Example 2, in which appropriate amount of P is added, the surface pressure, at which the initial surface pressure occurred, and the surface pressure, at which seizure occurred after stationary sliding, were found to be improved over those of Example 1, in which P is not added. This is because added P further promotes diffusion and hence diffusion bonding between the copper matrix and the hard particles, thereby improving holding of the hard particles. Meanwhile, when P is added excessively as shown in Table 2, Comparative Example 2, the seizure surface pressures of initial sliding and after stationary sliding seriously decreases.

(11) TABLE-US-00002 TABLE 2 Seizure Surface Hard Particles Pressure, MPa Bi Sn P Average After mass mass mass Amount Particle Stationary Cu % % % Type mass % Diameter m Initial Sliding I 1 Bal 1 1 0.04 Fe.sub.3P 3 30 24 24 2 Bal 1 5 0.08 Fe.sub.3P 3 30 28 28 4 Bal 5 1 0.08 Fe.sub.3P 3 30 48 40 5 Bal 5 5 0.08 Fe.sub.3P 3 30 44 44 7 Bal 15 1 0.15 Fe.sub.3P 3 30 36 36 8 Bal 15 5 0.15 Fe.sub.3P 3 30 36 36 10 Bal 5 5 0.08 Fe.sub.3P 1 30 40 48 11 Bal 5 5 0.17 Fe.sub.3P 10 30 40 36 12 Bal 5 5 0.04 Fe.sub.3P 3 10 36 32 13 Bal 5 5 0.08 Fe.sub.3P 3 68 44 44 15 Bal 1 5 0.08 Fe.sub.2P 3 30 28 28 18 Bal 5 5 0.08 Fe.sub.2P 3 30 48 44 21 Bal 15 5 0.15 Fe.sub.2P 3 30 36 40 24 Bal 5 5 0.17 Fe.sub.2P 10 30 32 32 II 1 Bal 1 1 0.25 Fe.sub.3P 3 30 8 16* 4 Bal 5 1 0.30 Fe.sub.3P 3 30 16 8* 8 Bal 15 5 0.25 Fe.sub.3P 3 30 20 8* 10 Bal 5 5 0.25 Fe.sub.3P 1 30 16 8* 11 Bal 5 5 0.35 Fe.sub.3P 10 30 12 8* 13 Bal 5 5 0.25 Fe.sub.3P 3 68 20 8* 21 Bal 15 5 0.25 Fe.sub.2P 3 30 20 8* 24 Bal 5 5 0.35 Fe.sub.2P 10 30 12 8* Remarks: Iinventive example 2, IIcomparative example 2, *Seizure occurred upon step up

INDUSTRIAL APPLICABILITY

(12) As is described hereinabove, the material according to the present invention exhibits little deterioration in seizure resistance caused by sliding and hence exhibits stable performance.

(13) Accordingly, the material of present invention can provide reliable components, such as an automatic transmission (AT) bush, a piston-pin bush, and a bush for general machines.

BRIEF DESCRIPTION OF THE DRAWINGS

(14) FIG. 1 An optical microphotograph (magnification: 250) of a sintered alloy of inventive example No. 5.

(15) FIG. 2 An optical microphotograph (magnification: 250) of a sintered alloy of inventive example No. 9.

(16) FIG. 3 An optical microphotograph (magnification: 250) of a sintered alloy of the inventive example No. 21.

(17) FIG. 4 An optical microphotograph (magnification: 250) of a sintered alloy of the comparative example No. 2.