ELECTRICALLY-CONDUCTIVE MATERIAL HAVING EXCELLENT WEAR RESISTANCE AND HEAT RESISTANCE

Abstract

An electrically-conductive material containing Ag in an amount of 10 mass % or more and 70 mass % or less, Pd in an amount of 30 mass % or more and 90 mass % or less, Ni in an amount of more than 5 mass % and 45 mass % or less, and inevitable impurities. A ratio of a Ni content (mass %) to a Ag content (mass %) (Ni (mass %)/Ag (mass %)) is 0.1 or more and 5.0 or less, metal structures include a AgPd alloy phase and a PdNi alloy phase, and a volume ratio of the PdNi alloy phase is 18 vol % or more and 80 vol % or less. Ni is added in a high concentration to a AgPd alloy, and the amount of PdNi alloy phases generated as separate phases is controlled to strengthen the entire alloy.

Claims

1. An electrically-conductive material comprising Ag in an amount of 10 mass % or more and 70 mass % or less, Pd in an amount of 30 mass % or more and 90 mass % or less, Ni in an amount of more than 5 mass % and 45 mass % or less, and inevitable impurities, wherein a ratio of a Ni content (mass %) to a Ag content (mass %) (Ni (mass %)/Ag (mass %)) is 0.1 or more and 5.0 or less, and metal structures have a AgPd alloy phase and a PdNi alloy phase, and a volume ratio of the PdNi alloy phase is 18 vol % or more and 80 vol % or less.

2. The electrically-conductive material according to claim 1, wherein the AgPd alloy phase comprises Ag in an amount of 30 mass % or more and 80 mass % or less, Ni in an amount of 0 mass % or more and 1 mass % or less, and Pd and inevitable impurities as a balance, the PdNi alloy phase has Pd in an amount of 40 mass % or more and 90 mass % or less, Ag in an amount of 0 mass % or more and 5 mass % or less, and Ni and inevitable impurities as a balance.

3. The electrically-conductive material according to claim 1, wherein the volume ratio of the PdNi alloy phase is 18 vol % or more and less than 50 vol %, and a thickness of the PdNi alloy phase is in a range of 0.01 m or more and 20 m or less.

4. The electrically-conductive material according to claim 1, wherein the volume ratio of the PdNi alloy phase is 50 vol % or more and 80 vol % or less, and the thickness of the AgPd alloy phase is in the range of 0.01 m or more and 20 m or less.

5. A clad composite material in which the electrically-conductive material defined in claim 1 is cladded to a base material comprising Cu or a Cu alloy.

6. A method for producing the electrically-conductive material defined in claim 1, comprising the step of: producing an alloy material comprising Ag in an amount of 10 mass % or more and 70 mass % or less, Pd in an amount of 30 mass % or more and 90 mass % or less, Ni in an amount of more than 5 mass % and 45 mass % or less, and inevitable impurities, and then plastically processing the alloy material, and the step of plastic processing has a total processing ratio of 80% or more.

7. A DC motor comprising: a rotating shaft; a commutator provided on a periphery of the rotating shaft; and a brush contacting the commutator to supply a current, wherein the brush is formed of a first contact material at least at a contact surface with the commutator, the first contact material is formed of an electrically-conductive material comprising Ag in an amount of 10 mass % or more and 70 mass % or less, Pd in an amount of 30 mass % or more and 90 mass % or less, Ni in an amount of more than 5 mass % and 45 mass % or less, and inevitable impurities, a ratio of a Ni content (mass %) to a Ag content (mass %) (Ni (mass %)/Ag (mass %)) in the electrically-conductive material is 0.1 or more and 5.0 or less, and metal structures of the electrically-conductive material have a AgPd alloy phase and a PdNi alloy phase, and a volume ratio of the PdNi alloy phase is 18 vol % or more and 80 vol % or less.

8. The DC motor according to claim 7, wherein the AgPd alloy phase comprises Ag and Pd as a balance in an amount of 30 mass % or more and 80 mass % or less, Ni in an amount of 0 mass % or more and 1 mass % or less, and inevitable impurities, the PdNi alloy phase comprises Pd and Ni as a balance in an amount of 40 mass % or more and 90 mass % or less, Ag in an amount of 0 mass % or more and 5 mass % or less, and inevitable impurities.

9. The DC motor according to claim 7, wherein the volume ratio of the PdNi alloy phase is 18 vol % or more and less than 50 vol %, and a thickness of the PdNi alloy phase is in a range of 0.01 m or more and 20 m or less.

10. The DC motor according to claim 7, wherein the volume ratio of the PdNi alloy phase is 50 vol % or more and 80 vol % or less, and the thickness of the AgPd alloy phase is in the range of 0.01 m or more and 20 m or less.

11. The DC motor according to claim 7, wherein at least a contact surface of the commutator with the brush is formed of a second contact material, and the second contact material includes a Ag—Ni alloy, a Ag—Cu—Ni alloy or a Ag—Cu—Ni—Zn alloy.

12. The electrically-conductive material according to claim 2, wherein the volume ratio of the PdNi alloy phase is 18 vol % or more and less than 50 vol %, and a thickness of the PdNi alloy phase is in a range of 0.01 m or more and 20 m or less.

13. The electrically-conductive material according to claim 2, wherein the volume ratio of the PdNi alloy phase is 50 vol % or more and 80 vol % or less, and the thickness of the AgPd alloy phase is in the range of 0.01 m or more and 20 m or less.

14. A clad composite material in which the electrically-conductive material defined in claim 2 is cladded to a base material comprising Cu or a Cu alloy.

15. A clad composite material in which the electrically-conductive material defined in claim 3 is cladded to a base material comprising Cu or a Cu alloy.

16. A clad composite material in which the electrically-conductive material defined in claim 4 is cladded to a base material comprising Cu or a Cu alloy.

17. A method for producing the electrically-conductive material defined in claim 2, comprising the step of: producing an alloy material comprising Ag in an amount of 10 mass % or more and 70 mass % or less, Pd in an amount of 30 mass % or more and 90 mass % or less, Ni in an amount of more than 5 mass % and 45 mass % or less, and inevitable impurities, and then plastically processing the alloy material, and the step of plastic processing has a total processing ratio of 80% or more.

18. A method for producing the electrically-conductive material defined in claim 3, comprising the step of: producing an alloy material comprising Ag in an amount of 10 mass % or more and 70 mass % or less, Pd in an amount of 30 mass % or more and 90 mass % or less, Ni in an amount of more than 5 mass % and 45 mass % or less, and inevitable impurities, and then plastically processing the alloy material, and the step of plastic processing has a total processing ratio of 80% or more.

19. A method for producing the electrically-conductive material defined in claim 4, comprising the step of: producing an alloy material comprising Ag in an amount of 10 mass % or more and 70 mass % or less, Pd in an amount of 30 mass % or more and 90 mass % or less, Ni in an amount of more than 5 mass % and 45 mass % or less, and inevitable impurities, and then plastically processing the alloy material, and the step of plastic processing has a total processing ratio of 80% or more.

20. A method for producing the electrically-conductive material defined in claim 5, comprising the step of: producing an alloy material comprising Ag in an amount of 10 mass % or more and 70 mass % or less, Pd in an amount of 30 mass % or more and 90 mass % or less, Ni in an amount of more than 5 mass % and 45 mass % or less, and inevitable impurities, and then plastically processing the alloy material, and the step of plastic processing has a total processing ratio of 80% or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] FIG. 1 is schematic diagram illustrating an example of a structure of a DC motor.

[0058] FIG. 2 illustrates a method for controlling the DC motor.

[0059] FIG. 3 illustrates a contact state of a brush and a commutator in the DC motor, and configurations of members.

[0060] FIG. 4 shows SEM photographs showing metal structures of electrically-conductive materials (AgPdNi alloys) of various compositions which are produced in an embodiment (Examples 1 to 7, Comparative Examples 1, 2 and 5 and Conventional Examples 1 to 4).

[0061] FIG. 5 shows a relationship between a volume ratio and a rigidity modulus of PdNi alloy phases for the AgPdNi alloys produced in the embodiment (Examples 1 to 7 and Comparative Examples 1 to 5).

[0062] FIG. 6 shows a change in hardness when heat treatment is performed over a range of 400° C. to 1000° C. for the AgPdNi alloys produced in the embodiment (Examples 1 to 7).

[0063] FIG. 7 shows a change in hardness when heat treatment is performed over a range of 400° C. to 1000° C. for the AgPdNi alloys and AgPd alloys produced in the embodiment (Comparative Examples 1, 2 and 5 and Conventional Examples 1 to 4).

[0064] FIG. 8 is a schematic diagram of a slide tester for durability tests conducted in the embodiment.

[0065] FIG. 9 shows SEM photographs showing cross-sectional shapes of worn portions after the durability tests conducted for examples and conventional examples in the embodiment.

[0066] FIG. 10 shows SEM photographs showing cross-sectional shapes of worn portions of a AgPd alloy which is a conventional electrically-conductive material.

DESCRIPTION OF EMBODIMENTS

[0067] Hereinafter, an embodiment of the present invention will be described. In the embodiment, AgPdNi alloys of various compositions were produced, the metal structures of the alloys were observed, and material properties were evaluated.

[0068] A plated-shaped alloy ingot was prepared by a high-frequency melting method and a casting method, and rolled with a total processing ratio of 80% or more to produce a test material of AgPdNi alloy (test material size: 200 mm in length, 10 mm in width and 0.3 mm in thickness) Test materials of AgPd alloy and AgPd-based alloy as the conventional art were produced by the same process.

[0069] The metal structures of the produced test materials of AgPdNi alloy and conventional alloys were observed. For observation of the structures, a cross-section parallel to a processing direction was observed by SEM observation. For SEM observation, reflected electron images were photographed at an accelerating voltage of 7 kv and a magnification of 5000 times with JSM-7200F manufactured by JEOL Ltd.

[0070] In parallel to the SEM observation, the compositions of a AgPd alloy phase and a PdNi alloy phase were analyzed by WDS for the AgPdNi alloy test material. From this analysis, it was confirmed that in all the AgPdNi alloy test materials, the composition of the AgPd alloy phase was Ag: 65±3 mass %, Pd: 35±3 mass % and Ni: 0.1 mass % or less, and the composition of the PdNi alloy phase was Pd: 62±3 mass %; Ni: 37±3 mass %; and Ag: 1 mass % or less.

[0071] The SEM photographs taken for the AgPdNi alloy test materials were subjected to image processing, and the volume ratios of PdNi alloy phases in metal structures of the alloys were measured. The image processing was performed by processing the obtained SEM image with image processing software (VK-H1G9 manufactured by KEYENCE CORPORATION). In the image processing, the SEM image was converted into a gray-scaled image, and binarized. In the binarization operation, a density level value of 80 was set to a threshold on the gray-scaled image (the density level values of all pixels range of 0 to 255), portions having a density level value of less than 80 were counted as black (PdNi alloy phases), portions having a density level value of 80 or more were counted as white (AgPd alloy phases), and the area ratios of the alloy phases were calculated. At the same time, the perpendicular ferret diameters of PdNi alloy phases and AgPd alloy phases (ferret diameter in a perpendicular direction in the SEM image) were measured, and average values and maximum thicknesses were obtained. The observation of metal structures and image processing were performed in a total of six observation visual fields selected, and an average value of measured values obtained from the observation and processing was used for evaluation. In the present invention, the volume ratio is approximated by the area ratio. In this way, measurement of the area ratio or the like of PdNi alloy phases in all the six observation visual fields selected enables examination with consideration also given to a width.

[0072] Table 1 below shows the compositions the AgPdNi alloys and the conventional alloys (AgPd alloys and the like) produced in the embodiment. Table 1 shows the volume ratios of PdNi alloy phases in various AgPdNi alloys, and the average thicknesses and the maximum thicknesses of PdNi alloy phases or AgPd alloy phases alloy phases. The alloy phase thickness shown in Table 1 is the thickness of the PdNi alloy phase for AgPdNi alloys having a PdNi alloy phase content of less than 50 vol % (Examples 1 to 3 and Comparative Examples 1 to 4), and the thickness of the AgPd alloy phase for AgPdNi alloys having a PdNi alloy phase content of 50 vol % or more (Examples 4 to 7 and Comparative Example 5).

[0073] However, for the AgPdNi alloy of Comparative Example 6 which had an excessively high Ni content, the test material was so heavily damaged during processing that processing was impossible, and thus the volume ratios of alloy phases and the like were not examined. For the AgPdNi alloy of Comparative Example 7 which had an excessively high Pd content, there were no PdNi alloy phases and AgPd alloy phases, and thus the volume ratios of alloy phases and the like were not examined.

[0074] FIG. 4 shows the results of observation of the metal structures of the AgPdNi alloys produced in the embodiment (Examples 1 to 7 and Comparative Examples 1, 2 and 5 and the conventional alloys (SEM photographs).

TABLE-US-00001 TABLE 1 Volume ratio of PdNi Thickness alloy of alloy Composition (wt %) phases phase (μm).sup.*1 Ag Pd Ni In Ni/Ag (vol %) Average Maximum Example 1 53 40 7 — 0.13 19.6 0.48 3.47 Example 2 46 43 11 — 0.24 28.8 0.52 4.80 Example 3 40 46 14 — 0.35 38.5 0.66 7.10 Example 4 34 48 18 — 0.53 51.3 0.86 10.39 Example 5 27 52 21 — 0.78 59.7 0.53 7.69 Example 6 20 54 26 — 1.30 70.9 0.40 4.71 Example 7 14 57 29 — 2.07 79.6 0.39 3.33 Comparative 62 36 2 — 0.03 4.5 0.39 1.66 Example 1 Comparative 59 37 4 — 0.07 9.6 0.45 2.03 Example 2 Comparative 80 15 5 — 0.06 8.7 0.38 2.13 Example 3 Comparative 73 20 7 — 0.10 10.4 0.41 2.42 Example 4 Comparative 7 61 32 — 4.57 90.9 0.33 1.98 Example 5 Comparative 5 40 55 — 11.00 —*.sup.2 —*.sup.2 —*.sup.2 Example 6 Comparative 3 95 3 — 1.00 —*.sup.3 —*.sup.3 —*.sup.3 Example 7 Conventional 50 50 — — — — — — Example 1 Conventional 69 30 1 — 0.01 — — — Example 2 Conventional 67 30 1 2 0.01 — — — Example 3 Conventional 48 50 1 1 0.02 — — — Example 4 .sup.*1Thickness of PdNi alloy phase for alloys having PdNi alloy phase content of less than 50 vol % Thickness of AgPd alloy phase for alloys having PdNi alloy phase content of 50 vol % or more .sup.*2Measurement was impossible because processing of test material was not possible .sup.*3Alloy phases were not precipitated, and measurement was impossible

[0075] In the SEM photograph of FIG. 4, white or gray contrast phases are AgPd alloy phases. On the other hand, dark gray or black contrast phases are PdNi alloy phases. From FIG. 4, it is apparent that in Example 1 which is a AgPdNi alloy having a Ni content of evidently more than 5%, the ratio of PdNi alloy phases remarkably increases. The PdNi alloy phases become layered in appearance as the Ni content increases. The AgPdNi alloys of Examples 3 to 7 have metal structures with stacked structures of layered AgPd alloy phases and PdNi alloy phases. In the AgPdNi alloys of Comparative Examples 1 and 2 which have a low Ni content (5 mass % or less), PdNi alloy phases are generated, but the amount (volume ratio) of these alloy phases is lower as compared to the above-mentioned examples.

[0076] For conventional alloys, only AgPd alloy phases are observed in the AgPd alloy of Conventional Example 1 as a matter of course. Minute PdNi alloy phases are precipitated in the AgPd-based alloy of Conventional Example 2 which contains a very small amount of Ni. Further, the AgPd-based alloys of Conventional Examples 3 and 4 which contain a small amount of Ni and In have precipitates from these additive elements.

[0077] Next, various electrically-conductive materials produced in the embodiment were subjected to a tensile test and hardness measurement for evaluating strength properties. In the evaluation test for strength properties, a plate-shaped sample (10 mm in width, 20 mm in length and 0.3 mm in thickness) subjected to full annealing (annealing condition: conventional example alloys were held at 700° C. for 1 hour, and Comparative Example and Example alloys were held at 900° C. for 1 hour), and then rolled at 50% was used. In the tensile test, a tensile test was conducted at a tension speed of 10 mm/min with a tensile tester (5966 manufactured by Instron Company), and the maximum stress, the 0.2% yield strength, the longitudinal elastic modulus and lateral elastic modulus were measured with a micro extensometer. The rigidity modulus was calculated from the values of the longitudinal elastic modulus and the lateral elastic modulus. The hardness measurement was performed with a Vickers hardness tester (HMV-G manufactured by Shimadzu Corporation), where the material was held with a test force of 2.942 N for 15 seconds. Table 2 shows the results of measuring the strength properties. FIG. 5 shows a relationship between the volume ratio and the rigidity modulus of PdNi alloy phases in the AgPdNi alloys of Examples 1 to 7 and Comparative Examples 1 to 5, which are obtained from the test results.

TABLE-US-00002 TABLE 2 Volume ratio of Strength properties PdNi 0.2% alloy Maximum Yield Rigidity Hard- Composition (wt %) phases stress strength modulus ness Ag Pd Ni In Ni/Ag (vol %) (mpa) (MPa) (Gpa) (Hv) Example 1 53 40 7 — 0.13 19.6 710.3 665.7 52.0 205 Example 2 46 43 11 — 0.24 28.8 793.4 771.8 51.2 220 Example 3 40 46 14 — 0.35 38.5 846.4 802.7 56.6 245 Example 4 34 48 18 — 0.53 51.3 882.8 818.4 62.1 246 Example 5 27 52 21 — 0.78 59.7 934.9 879.7 61.4 263 Example 6 20 54 26 — 1.30 70.9 1011.5 927.9 63.4 278 Example 7 14 57 29 — 2.07 79.6 1079.2 963.8 66.7 308 Comparative 62 36 2 — 0.03 4.5 606.0 569.4 44.3 178 Example 1 Comparative 59 37 4 — 0.07 9.6 624.6 581.4 42.6 184 Example 2 Comparative 80 15 5 — 0.06 8.7 510.1 476.9 40.8 152 Example 3 — Comparative 73 20 7 — 0.10 10.4 554.3 516.1 45.6 163 Example 4 Comparative 7 61 32 — 4.57 90.9 1108.6 1036.9 76.0 320 Example 5 Comparative 5 40 55 — 11.00 —.sup.*1 —.sup.*1 —.sup.*1 —.sup.*1 —.sup.*1 Example 6 Comparative 3 95 3 — 1.00 —.sup.*1 —.sup.*1 —.sup.*1 —.sup.*1 —.sup.*1 Example 7 Conventional 50 50 — — — — 508.1 482.9 45.0 170 Example 1 Conventional 69 30 1 — 0.01 — 533.2 482.1 43.0 177 Example 2 Conventional 67 30 1 2 0.01 — 619.2 531.9 47.1 154 Example 3 Conventional 48 50 1 1 0.02 — 679.3 643.1 49.4 197 Example 4 .sup.*1Measurement was cancelled because processing of test material was impossible or there were no alloy phases

[0078] The results of conventional examples for the strength properties of the alloys show that the alloy of Conventional Example 2 in which a small amount of Ni is added to the AgPd alloy (Conventional Example 1) and the alloys of Conventional Examples 3 and 4 in which a small amount of In is further added to strengthen precipitation have higher values of maximum stress and yield strength as compared to Conventional Example 1. That is, it can be said that addition of a small amount of Ni (crystal grain refining) and addition of In etc. (precipitation strengthening) improved the strength properties of the AgPd alloy to some degree. However, there is no significant difference in rigidity modulus between the AgPd alloy (Conventional Example 1) and the AgPd-based alloys containing a small amount of additive elements (Conventional Examples 2 to 4), and these alloys each have a rigidity modulus of 50 GPa or less. That is, the method of the conventional art does not allow the rigidity modulus to be sufficiently improved.

[0079] On the other hand, the AgPdNi alloys of examples of the present invention (Examples 1 to 7) exhibit high value not only for the stress property but also for the rigidity modulus. The AgPdNi alloys of examples contain Ni in an amount of more than 5 mass %, and have a PdNi alloy phase volume ratio of 18 vol % or more. As is apparent from FIG. 5, the AgPdNi alloys of the examples have a rigidity modulus of 50 GPa or more, and higher strength properties as compared to the conventional examples. It is considered that the AgPdNi alloys of the examples in which the rigidity modulus is improved are hardly affected by shear stress from sliding, and contribute to improvement of wear resistance.

[0080] However, it is apparent from Table 2 and FIG. 5 that a certain restriction should be placed on the Ni content and the volume ratio of PdNi alloy phases in the AgPdNi alloy. That is, the AgPdNi alloys having a low Ni content (5 mass % or less) (Comparative Examples 1 to 3) have a low volume ratio of PdNi alloy phases and have no rigidity modulus improving effect. In addition, the alloy having a Ni content of 5% or more and Ag and Pd contents outside the specified ranges (Comparative Example 4) has a low volume ratio of PdNi alloy phases and have no rigidity modulus improving effect. On the other hand, the AgPdNi alloy of Comparative Example 5, which has a Ag content of less than 10 mass % and a PdNi alloy phase volume ratio of more than 80 vol %, became unable to plastically deform halfway in processing (at a processing ratio of 50%), resulting in breakage of the material. The alloy of Comparative Example 5 was poor in processability, and did not meet the spirit of the present invention.

[0081] Subsequently, a heat treatment test for evaluation of heat resistance was conducted on various electrically-conductive materials produced in the embodiment (Examples 1 to 7, Comparative Examples 1, 2 and 5 and Conventional Examples 1 to 4). In the heat treatment test, the same sample as that used in the tensile test was held at each of temperatures of 400° C., 500° C., 600° C., 700° C., 800° C., 900° C. and 1000° C. for 30 minutes, and the surface hardness was measured after the sample was held at each of the temperatures. FIGS. 6 and 7 show the results of the heat treatment test. These diagrams show a temperature at which the hardness of each alloy reached equilibrium where the slope of change in hardness was about 0.1.

[0082] From FIG. 7, it can be confirmed that the AgPd alloy and the AgPd-based alloys of Conventional Examples 1 to 3 are recrystallized with the hardness reaching equilibrium through heat treatment at 600° C. to 700° C. Like the alloys of conventional examples, the AgPdNi alloys of Comparative Examples 1 and 2 which have a low Ni content are recrystallized with the hardness reaching equilibrium through treatment at 600° C. to 700° C.

[0083] On the other hand, FIG. 6 shows that in Examples 1 to 7 where the volume ratio of PdNi alloy phases is 18 vol % or more, the hardness reaches equilibrium only through heat treatment at 900° C. to 1000° C. That is, the alloys of examples were each confirmed to have a higher recrystallization temperature as compared to conventional examples and comparative examples. A high crystallization temperature may make metal structures less likely to coarsen and soften even when exposed to friction heat from sliding or heat associated with discharge, resulting in contribution to improvement of wear resistance and heat resistance.

[0084] The test materials of various electrically-conductive materials produced in the embodiment were subjected to a durability test using a slide tester. FIG. 8 shows a configuration of the slide tester used in the embodiment. This slide tester is aimed at reproducing a relationship between a brush and a commutator of a motor in a simulated manner. The reason why the durability test was conducted by use of a tester simulating a motor is that among applications intended by the present invention, use of the electrically-conductive material with a motor may place the electrically-conductive material under a larger electrical load as compared to other applications.

[0085] The tester of FIG. 8 has a mechanism in which a work 1 is a virtual commutator, which is fed with electricity to be rotated. The test is conducted with a flat spring-shaped virtual brush (work 2) pressed against the rotating work 1. In the durability test, a AgNi alloy is used for the virtual commutator (work 1), and the electrically-conductive material produced in the embodiment is used for the virtual brush (work 2). The test conditions are as follows, and both mechanical wear and wear from arc discharge occur. [0086] Load current and voltage: 2.0 A-7.5 V [0087] Rotation speed: 1500 rpm [0088] Weight: 5 gf [0089] Test time: 3 hours [0090] Virtual commutator material: AgNi alloy (Ni: 10 mass %)

[0091] After the durability test, the detached test piece was etched with a Ag etchant to remove a transfer layer from the commutator material. The surface of the test piece was observed with a laser microscope, the depths of abraded portions were measured by a focus depth method, and the depth of the deepest abraded portion (maximum wear depth) and abraded cross-section areas (wear amount) were measured.

[0092] Table 3 shows the results of the durability test conducted in the embodiment. FIG. 9 shows SEM photographs in which the cross-sectional shapes of worn portions are compared between the alloys of Conventional Example 1 and Example 4 after the durability test.

TABLE-US-00003 TABLE 3 Volume ratio of PdNi alloy Wear Wear Composition phases depth amount Ag Pd Ni In Ni/Ag (vol %) (μm) (μm.sup.2) Example 1 53 40 7 — 0.13 19.6 4.44 829 Example 2 46 43 11 — 0.24 28.8 3.84 689 Example 3 40 46 14 — 0.35 38.5 3.05 515 Example 4 34 48 18 — 0.53 51.3 2.72 556 Example 5 27 52 21 — 0.78 59.7 4.40 716 Example 6 20 54 26 — 1.30 70.9 3.96 693 Example 7 14 57 29 — 2.07 79.6 3.67 730 Comparative 62 36 2 — 0.03 4.5 7.21 2519 Example 1 Comparative 59 37 4 — 0.07 9.6 6.36 1896 Example 2 — Comparative 80 15 5 — 0.06 8.7 7.87 2714 Example 3 Comparative 73 20 7 — 0.10 10.4 7.52 2633 Example 4 Comparative 7 61 32 — 4.57 90.9 3.71 700 Example 5 Comparative 5 40 55 — 11.00 —.sup.*1 —.sup.*1 —.sup.*1 Example 6 — —.sup.*1 —.sup.*1 —.sup.*1 Comparative 3 95 3 — 1.00 —.sup.*1 —.sup.*1 —.sup.*1 Example 7 Conventional 50 50 — — — — 5.94 1733 Example 1 Conventional 69 30 1 — 0.01 — 8.01 2755 Example 2 — Conventional 67 30 1 2 0.01 — 6.01 1781 Example 3 — Conventional 48 50 1 1 0.02 — 5.02 1054 Example 4 .sup.*1Measurement was cancelled because processing of test material was impossible or there were no alloy phases

[0093] From Table 3, it was confirmed that when the AgPdNi alloy has the added amount of Ni of more than 5 mass % and a PdNi alloy phase volume ratio of 18 vol % or more while having appropriate Ag and Pd contents, it is possible to obtain an electrically-conductive material having a lower wear amount and wear depth as compared to the conventional art. The wear depth and the wear amount tend to decrease as the volume ratio of PdNi alloy phases increases. For evaluation of wear resistance, the wear amount and the wear depth should be comprehensively examined, and alloys excellent in balance between the wear amount and the wear depth and particularly excellent in wear resistance are those of Examples 3 and 4. These results indicate that with regard to wear resistance, the volume ratio of PdNi alloy phases is particularly preferably about 35% or more and 55% or less.

[0094] In Comparative Example 5 where the ratio of PdNi alloy phases was more than 80 vol %, the wear amount was lower as compared to conventional examples, but there was a high inclination for abrasive wear in which the counterpart (AgNi alloy: commutator) was scraped. Thus, when the ratio of PdNi alloy phases is excessively high, the contact as a whole lacks balance in wear.

[0095] From FIG. 9, it is apparent that a cross-section of the AgPd alloy of Conventional Example 1 has an altered layer affected by sliding stress is present within a range of about 10 μm from the surface layer in a mechanically abraded portion. On the other hand, it can be confirmed that in the AgPdNi alloy of Example 6, the thickness of the altered phase is limited within a range of about 3 μm from the surface layer. The result of the comparison shows that the AgPdNi alloy of the example is less likely to plastically deform even when placed under actual shear stress from sliding. Further, for the arc discharge generation portion, the AgPd alloy of Conventional Example 1 is intensely melted, so that surface structures can be confirmed to be thermally affected, while the AgPdNi alloy of Example 6 is melted over a narrow range, and is considered to have resistance to arc discharge.

INDUSTRIAL APPLICABILITY

[0096] As described above, the present inventive electrically-conductive material has higher durability as compared to conventional AgPd alloys and AgPd alloys containing a very small amount of elements. The present invention is useful for electrodes and contact materials to be used for slide switches and variable resistors, in addition to brushes of DC motors, slip rings and the like.

[0097] In particular, when the present inventive electrically-conductive material is applied to brushes of micro DC motors, the present invention is useful for motors having a stall current of 1.0 A or more. When the stall current is 1.0 A or more, arc discharge is generated between contacts, and therefore the AgPd alloy described above as a prior art is heavily worn, resulting in reduction of the life of the brush. The present inventive electrically-conductive material has high resistance to not only mechanical wear but also arc discharge, and therefore can be hoped to extend the life of the motor as compared to conventional AgPd alloys. Thus, when the electrically-conductive material is used as a constituent material of a brush of a motor having stall current of 1.0 A or more, extension of the life of the motor can be expected.