BRONZE ALLOY, AND SLIDING MEMBER USING THE BRONZE ALLOY

Abstract

To provide a bronze alloy and a sliding member, to which high seizure resistance and high adhesive wear resistance against fluctuating high speed/high surface pressure sliding are imparted, while having a lead-free composition. A bronze alloy of the present application characteristically contains 8 to 15 mass % of Sn, 0.5 to 7.0 mass % of Bi, 0.5 to 5.0 mass % of Ni, 0.08 to 1.2 mass % of S, 0.5 to 6.0 mass % of Fe, and a balance of Cu and inevitable impurities; and the bronze alloy has a eutectoid structure in which a fine flaky copper-tin-based intermetallic compound precipitates in the -copper matrix and also an iron-nickel-based intermetallic compound and a copper-iron-based sulfide complex are dispersed.

Claims

1. A bronze alloy containing copper (Cu), tin (Sn), bismuth (Bi), nickel (Ni), sulfur (S), and iron (Fe), wherein: the bronze alloy contains 8 to 15 mass % of Sn, 0.5 to 5.0 mass % of Bi, 0.5 to 5.0 mass % of Ni, 0.08 to 1.2 mass % of S, 0.5 to 6.0 mass % of Fe, and a balance comprised of Cu and inevitable impurities; and the bronze alloy has a eutectoid structure in which a fine flaky copper-tin-based intermetallic compound precipitates in the -copper and an iron-nickel-based intermetallic compound and a copper-iron-based sulfide complex are dispersed.

2. The bronze alloy according to claim 1, wherein the bronze alloy contains 1.5 to 6.0 mass % of Fe.

3. The bronze alloy according to claim 1, wherein a mass ratio of an Fe content to an Ni content (Fe/Ni) is 0.7 to 1.5.

4. A sliding member, wherein a sliding surface is formed of the bronze alloy according to claim 1.

5. A multi-layer sliding member, wherein the bronze alloy according to claim 1 is melt-joined with a sliding surface of an iron-based material, or only the bronze alloy is melted and the sliding surface of the iron-based material is lined with the bronze alloy by a method such as thermal spraying.

6. A multi-layer sliding member, wherein powder of the bronze alloy according to claim 1 is sintered and joined on a sliding surface of an iron-based material.

Description

DESCRIPTION OF EMBODIMENTS

[0036] The bronze alloy to which the present invention is applied contains Cu and Sn as main components, and besides, Ni, Fe, Bi and S (sulfur) as essential elements, and other components are composed of inevitable impurities (less than 0.3 mass % of elements, with the proviso that the S content is less than 0.08 mass %). The reason for limiting these ranges is as follows.

[Sn: 8 to 15 Mass %]

[0037] Sn dissolves in a Cu matrix to improve a tensile strength and a hardness of the bronze alloy. If the Sn content is less than 8 mass %, a strength and a hardness required for a sliding member cannot be obtained and a wear resistance is decreased. If the Sn content is more than 15 mass %, a large amount of CuSnNi-based intermetallic compound is produced, and the alloy becomes brittle, and as a result, a microcrack resistance is decreased. A lower limit of the Sn content is preferably 9.0 mass %, and an upper limit is preferably 13.5 mass %. A range of 10.0 to 13.0 mass % is more preferable.

[Ni: 0.5 to 5.0 Mass %]

[0038] Ni causes an Fe primary crystalline austenite generated in a liquid phase to change into an FeNi-based intermetallic compound to prevent decrease in machinability. Also, Ni has an effect of uniformly dispersing a crystallization phase in a structure, and dissolves together with Sn in a Cu matrix to improve a Brinell hardness (HB) of the bronze alloy. If the Ni content is less than 0.5 mass %, there is no effect of preventing decrease in machinability and no effect of uniformly dispersing the crystallization phase in the structure. If the Ni content is more than 5.0 mass %, fluidity of a molten metal is decreased, and then castability becomes poor. A range of the Ni content is preferably 0.5 to 1.5 mass % for a high-speed sliding application with an importance on initial conformability. For an application of refining and homogenizing a cast structure with an importance on the microcrack resistance, the range of the Ni content is preferably 2.0 to 4.5 mass %.

[Fe: 1.5 to 6.0 Mass %, or 0.5 to 1.5 Mass %]

[0039] Fe in bronze produces a primary crystalline austenite (free iron) by a peritectic-eutectic reaction. The free iron hinders growth of a Cu primary crystalline -dendrite, and becomes a heterogeneous solidification nucleus to refine the cast structure. If the Fe content is less than 1.5 mass %, there is no effect of refining the cast structure. If the Fe content is more than 6.0 mass %, the primary crystalline austenite is coarse, and there is no effect of refining the cast structure. The range of the Fe content is more preferably 2.0 to 5.5 mass %. On the other hand, if the Fe content is 0.5 mass % or more, the FeNi-based intermetallic compound required for improving a frictional wear property crystallizes in the bronze alloy, and if the Fe content is 1.5 mass % or more, the bronze alloy becomes hard, and the initial conformability decreases. Consequently, the range of the Fe content is preferably 0.5 to 1.5 mass % for a high-speed sliding application with an importance on initial conformability.

[Bi: 0.5 to 5.0 Mass %]

[0040] Bi is a low melting point metal element which has properties similar to those of Pb and does not dissolve in Cu, and improves the machinability and the frictional wear property of the bronze alloys. However, Bi tends to segregate at a grain boundary to decrease a high-temperature strength, and if Bi is excessively contained, cracks are generated due to heat generation during machining to decrease a mechanical property. If the Bi content is less than 0.5 mass %, there is no effect of improving the machinability and the frictional wear property. If the Bi content is more than 5.0 mass %, the Bi phase excessively increases to decrease the mechanical property. The range of the Bi content is more preferably 1.0 to 3.5 mass %.

[S: 0.08 to 1.2 Mass %]

[0041] S binds with Cu and Fe to form a sulfide complex of copper and iron, and the sulfide complex acts as an extreme-pressure additive for preventing seizure of a sliding surface. If the S content is less than 0.08 mass %, an amount of the produced sulfide complex is small, resulting in a low effect. If the S content is more than 1.2 mass %, a reactant gas is generated during solidification, and a robust casting cannot be manufactured. The range of the S content is more preferably 0.15 to 0.6 mass %.

EXAMPLES

[0042] Next, specific examples of the bronze alloy and the sliding member according to the present invention will be explained based on experimental results.

[0043] Bronze alloys having compositions presented in Table 1 were smelted in a high-frequency melting furnace, and casted into shell sand molds for JIS tensile test pieces No. A, and then machined into JIS tensile test pieces No. 4. These test pieces were measured for tensile strength (MPa), braking elongation (%), and Brinell hardness (HB), and metal structure crystal grain size.

TABLE-US-00001 TABLE 1 No. Cu Sn Ni Fe Bi S P Pb Zn Mn 1 Balance 11.03 1.47 3.38 1.24 0.36 0.07 0.02 <0.005 <0.005 2 Balance 11.22 1.60 1.48 1.91 0.34 0.06 0.05 0.01 0.01 3 Balance 11.23 1.46 3.39 2.31 0.35 0.09 0.02 <0.005 <0.005 4 Balance 9.81 3.65 3.65 2.11 0.35 0.09 0.03 <0.005 0.01 5 Balance 11.69 3.42 3.72 2.46 0.40 0.085 0.01 <0.005 <0.005 6 Balance 11.50 5.96 6.16 2.27 0.46 0.08 0.01 <0.005 <0.005 7 Balance 10.80 2.46 2.80 2.09 0.37 0.08 0.04 0.18 <0.005 8 Balance 11.02 1.06 1.88 1.97 0.28 0.03 0.05 <0.005 <0.005 9 Balance 9.59 0.97 0.89 2.04 0.28 0.02 0.02 0.01 <0.005 10 Balance 10.09 0.97 0.80 1.87 0.34 0.04 0.02 0.23 <0.005 11 Balance 10.17 0.98 0.41 2.00 0.35 0.04 0.04 0.01 <0.005 Comparative Material 1 Balance 11.44 1.57 <0.005 0.92 0.31 0.06 0.03 0.01 <0.005 Comparative Material 2 Balance 9.03 0.94 <0.005 2.01 0.25 0.07 0.01 <0.005 <0.005 Comparative Material 3 Balance 9.45 1.54 <0.005 2.08 0.26 0.10 0.01 <0.005 <0.005 Comparative Material 4 Balance 9.66 2.50 <0.005 2.00 0.31 0.07 <0.005 <0.005 <0.005 Comparative Material 5 Balance 9.5 3.52 <0.005 2.11 0.30 0.07 <0.005 <0.005 <0.005 Comparative Material 6 Balance 10.9 1.47 0.01 0.12 0.72 0.08 0.02 <0.005 <0.005 Comparative Material 7 Balance 11.53 1.68 <0.005 3.82 0.33 0.06 0.04 0.04 <0.005 Comparative Material 8 Balance 13.08 1.69 0.01 0.01 0.01 0.03 9.66 0.08 <0.005 Comparative Material 9 Balance 10.56 0.19 <0.005 0.02 0.01 0.03 9.86 0.02 <0.005

[0044] Comparative Material 1 has a lead-free composition and is different from Examples in that it does not contain Fe. Comparative Materials 8 and 9 are existing lead-bronze-based alloys. FIG. 2 shows a metal structure of Example 5, and FIG. 3 shows a metal structure of Comparative Material 1.

[0045] In the metal structure of Example 5, Fe precipitated while forming a compound with Ni, and an intermetallic compound and a sulfide complex were uniformly dispersed in a particulate form in the metal structure. A primary crystal of an -copper became fine and the whole had a fine eutectoid structure. On the other hand, in Comparative Material 1, the primary crystalline -copper greatly grew and formed an inhomogeneous metal structure with the eutectoid structure, and a precipitated compound (copper sulfide) was large and sparsely dispersed. Thus, it is clear that a dramatic effect for homogenizing the metal structure can be obtained by adding almost equal amounts of Fe and Ni to a lead-free bronze of the present invention.

[0046] The tensile strength (MPa) and the braking elongation (%) were measured in accordance with JIS Z2241, and the Brinell hardness was measured in accordance with a provision of JIS Z2243, and they are presented in Table 2. The crystal grain size was measured by a cutting method, and typical values are shown in Table 2.

TABLE-US-00002 TABLE 2 Tensile Braking Brinell Crystal Strength Elongation Hardness Grain Size No. (N/mm.sup.2) (%) (HB) (m) 1 301 2 128 28 2 254 1 107 80 3 272 2 124 35 4 134 40 5 316 2 148 18 6 277 1 150 70 7 116 80 8 280 3 110 55 9 264 6 103 85 10 285 4 100 90 11 274 4 98 130 Comparative Material 1 234 3 107 180 Comparative Material 2 300 17 96 310 Comparative Material 3 262 4 96 330 Comparative Material 4 300 4 100 220 Comparative Material 5 264 3 106 140 Comparative Material 6 255 4 91 280 Comparative Material 7 306 3 113 130 Comparative Material 8 274 5 110 110 Comparative Material 9 295 28 90 160

[0047] In results of the mechanical property tests and the grain size measurement presented in Table 2, all of the bronze alloys containing more than 2.0 mass % of Fe according to the present invention have Brinell hardness of higher than 120, indicating that a hardness higher than that of a comparative material containing almost the same amount of Sn can be obtained. Incidentally, in No. 2 and No. 8 to 11 containing 2.0 mass % or less of Fe, the Brinell hardness did not exceed 110. Also, as shown in FIG. 2 and FIG. 3, the primary crystal of the -copper became fine when the Fe content was more than 1.5 mass %, thus the grain size was smaller than that of the comparative material by one digit. In No. 5 containing about 3.5 mass % of Fe and Ni, a grain size was not more than one-tenth that of a bronze alloy not according to the present invention (Comparative Material 1). Also, it can be seen that the Ni content and the Bi content also affect the grain size.

[0048] Furthermore, some of the sample materials (No. 5, No. 9 (Examples), and Comparative Materials 1, 7, 8 and 9 among the bronze alloys in Table 1) were casted into a cylindrical mold of 60150 mm, then machined into a ring test piece R of 25.52020 mm, and subjected to a ring/disk-type plane sliding test using a tester T shown in FIG. 1 (FIG. 1). In the plane sliding test, a 10 W class diesel engine oil heated to 60 C. was used as a lubricating oil lu. As a friction material disk D, SCM420 steel having a hardness adjusted to HRC58 by carburizing and quenching was used. Incidentally, symbol M represents a torque meter, and symbol d represents a drain oil (FIG. 1). For these test pieces R, a seizure limit PV value (N/mm.sup.2.Math.m/min) and a specific wear amount (mm/(N/cm.sup.2.Math.m/min.Math.hr)) were measured. The limit PV value was measured by a process that the test piece R was pressed against the disc D rotating around a rotation axis S at a constant speed of 10 msec, the test piece R was left under running-in operation at 1.25 MPa for 10 minutes, then a load L was continuously increased with a gradient of 0.4 MPa/min, and it was judged that there was seizure when rotation abnormality or abnormal noise occurred, or the test piece temperature reached 120 C. or higher, or a friction coefficient reached 0.2. The specific wear amount was measured by a process that the test piece R was pressed against the disc D rotating around the rotation axis S at a constant speed of 5 or 10 msec, the test piece R was left under running-in operation at 2.5 MPa for 10 minutes, then subjected to a friction test at a constant pressure of 6.4 MPa for 8 hours, and the specific wear amount was calculated from a dimensional change between before and after the test. These results are presented in Tables 3 and 4.

TABLE-US-00003 TABLE 3 Seizure Limit PV Value Specific Wear Rate No. N/mm.sup.2 .Math. m/min mm/(N/cm.sup.2 .Math. m/min-hr) 5 6191 1.3 10.sup.8 9 6092 2.5 10.sup.8 Comparative Material 1 4900 6.4 10.sup.8 Comparative Material 7 5566 5.1 10.sup.8 Comparative Material 8 5834 2.9 10.sup.8 Comparative Material 9 5389 3.2 10.sup.8

TABLE-US-00004 TABLE 4 Seizure Limit PV Value Specific Wear Rate No. N/mm.sup.2 .Math. m/min mm/(N/cm.sup.2 .Math. m/min-hr) 5 5912 4.8 10.sup.9 9 6395 1.5 10.sup.9 Comparative Material 1 2121 1.8 10.sup.7 Comparative Material 7 5047 5.6 10.sup.9 Comparative Material 8 6414 4.0 10.sup.9 Comparative Material 9 6452 3.0 10.sup.9

[0049] In results of the plane sliding test at a friction velocity of 5 msec presented in Table 3, the bronze alloys No. 5 and 9 according to the present invention exhibited seizure limit PV values exceeding 6000, which were higher than those of the lead-free bronze alloy-based Comparative Materials 1 and 7 and the lead-bronze-based Comparative Materials 8 and 9, indicating that the specific wear amount of the bronze alloys No. 5 and 9 were also low. Also in results of the plane sliding test at a friction velocity of 10 msec presented in Table 4, the bronze alloys No. 5 and 9 exhibited seizure limit PV values and specific wear amounts equivalent to those of the lead-bronze-based Comparative Materials 8 and 9, and particularly in No. 9 having Fe and Ni contents limited to 1.5 mass % or lower, the specific wear amount was lower than that of the lead-bronze-based Comparative Materials 8 and 9. It is considered that this is because preferable initial conformability was obtained even at a high friction velocity by suppressing increase in the hardness of the bronze alloy.

[0050] FIG. 4 shows an example of seizure resistance test data of the bronze alloy No. 5 according to the present invention at a friction velocity of 10 msec. The horizontal axis represents time (m). The vertical axis represents a frictional coefficient (), a load (N), and a temperature ( C.), and each of them corresponds to a frictional coefficient data (symbol A), a load data (symbol B), and a test piece temperature data (symbol C) respectively in the graph. A graph with a wide fluctuation range represents a change in the frictional coefficient associated with increase of the load. The seizure limit PV value is calculated from a load at which the friction coefficient steeply rises. The difference in the seizure limit PV value is due to a difference in a test piece-pressing load. Because of the high-speed sliding with a friction velocity of 10 msec, as soon as an oil film on the friction surface is ruptured, seizure occurs. Thus, the reason why there is a difference of the bronze alloys No. 5 and 9 according to the present invention from the lead-free bronze alloy-based Comparative Materials 1 and 7 in Table 3 may be because deposition of transferred substance was suppressed by crystallization of the FeNi-based intermetallic compound and change of a microstructure in the eutectoid structure, and retention of the lubricating oil was improved.

Each Additive Element and Hardness

[0051] In the bronze alloy according to the present invention, elements which greatly affect the hardness of the alloy are Sn, Fe, and Ni. FIG. 5 presents the hardness of the specimens organized in terms of amounts of the additive elements. The horizontal axis represents an addition amount (mass %), and the vertical axis represents a Brinell hardness (HB). A gradient of an approximate straight line of Fe is twice as large as inclinations of approximate straight lines of Sn and Ni, and thus even a small amount of Fe has a high effect of increasing the hardness. It is considered that this is because Sn and Ni dissolve in the Cu matrix to strengthen solid solution, whereas Fe binds to Ni to form a fine intermetallic compound particle, which precipitates homogeneously in the metal structure to cause a dispersion strengthening.

[0052] In Table 2, No. 1 to No. 8 according to the present invention also exhibit effects of improving the hardnesses compared to that of Comparative Material 1, and of refining the crystal grains. Additionally, Comparative Material 1 is inferior in both the hardness and the crystal grain size to No. 1. Furthermore, in No. 6 containing 6.16 mass % of Fe and 5.96 mass % of Ni, and No. 2 containing 1.48 mass % of Fe and 1.60 mass % of Ni, braking elongation is decreased. From these facts, the Ni content is preferably 1.5 to 5.0 mass %, and the Fe content is preferably 1.5 to 5.5 mass %. Also, ratios of Fe and Ni are important, and the Fe/Ni ratio is preferably in a range of 0.7 to 1.5. In this range, the primary crystalline austenite produced by peritectic-eutectic reaction of Fe binds to Ni to form a fine intermetallic compound, which uniformly precipitates in the metal structure, and thereby generation of hard spots is suppressed.

[0053] FIG. 6 shows sliding surface states of the bronze alloys of Comparative Material 1 (FIG. 6a, left side) and Example 5 (FIG. 6b, right side) after a wear test. The alloy according to the present invention has a high adhesive wear resistance because of high hardness, and has no transferred substance on the sliding surface. Also, the FeNi-based intermetallic compound precipitating uniformly in the metal structure is considered to hinder deposition of the transferred substance and improve the adhesive wear resistance. On the other hand, deposition of the stripe-like transferred substance is confirmed on the sliding surface of Comparative Material 1 having a low hardness. Since the transferred substance is brittle and grows into microcracks when receiving a strong frictional force, the inventive alloy on which the transferred substance hardly deposits was confirmed to be excellent in microcrack resistance.

Identification of Precipitate in Metal Structure

[0054] FIG. 7 shows electron micrographs of identified substances precipitated in the bronze alloy of Example 5. FIG. 7a shows an analytical field, FIG. 7b shows an identified copper, FIG. 7c shows an identified sulfur, FIG. 7d shows an identified nickel, and FIG. 7e shows an identified iron. In the left analytical field, the precipitates indicated by arrows correspond to the sulfur signals in the right figure, shapes of copper and iron stand out lightly against background, and therefore the precipitates are determined to be sulfide complexes. Many spherical precipitates other than sulfides are also observed. These precipitates other than sulfides are found only in the bronze alloy according to the present invention, in which shapes of nickel and iron stand out lightly against background, indicating that these precipitates are FeNi-based intermetallic compounds. As described above, by practicing the present invention, fine FeNi-based intermetallic compounds other than sulfides precipitate and the intermetallic compounds generated in the metal structure complicate the microstructure of the metal structure synergistically with the CuSnNi-based precipitates in the eutectoid structure. The difference in precipitates generated in this metal structure is considered to be the reason why the bronze alloy of the present invention has a high seizure limit PV value, and excellent adhesive wear resistance and microcrack resistance.

[0055] As described above, the present invention can provide a copper alloy-based sliding member which has an excellent seizure resistance equal to or higher than that of a lead-bronze-based alloy while being a bronze alloy having a lead-free composition and is furthermore excellent in mechanical strength and microcrack resistance.

BRIEF DESCRIPTION OF DRAWINGS

[0056] FIG. 1 shows a schematic drawing of a tester used for a ring/disk-type plane sliding test.

[0057] FIG. 2 shows a microphotograph of a metal structure in Example 5.

[0058] FIG. 3 shows a microphotograph of a metal structure in Comparative Material 1.

[0059] FIG. 4 shows an example of seizure resistance test data of a bronze alloy according to the present invention.

[0060] FIG. 5 shows a graph in which hardness of specimens are organized in terms of amounts of the additive elements.

[0061] FIG. 6 shows photographs of sliding surface states of bronze alloys in Comparative Material 1 and Example 5 after a wear test.

[0062] FIG. 7 shows electron micrographs of identified substances precipitated in the bronze alloy in Example 5.

REFERENCE NUMERALS

[0063] T Tester [0064] L Load [0065] Lu Lubricating oil [0066] M Torque meter [0067] R Test piece [0068] D Disk [0069] d Oil drain port [0070] S Rotation axis