Yttria-reinforced dual-scale copper-graphite composite and preparation method and use thereof

Abstract

A method of making a yttria-reinforced copper-graphite composite by mixing a first CuO powder having an average size of 40-60 nanometres with a second CuO powder having an average size of 8-12 microns

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of metal matrix composites, in particular to an yttria-reinforced dual-scale copper-graphite composite and a preparation method and use thereof. BACKGROUND

[0002] Copper-graphite composites have excellent electrical and thermal conductivity, as well as desirable lubricating properties and arc ablation resistance. Therefore, these composites are widely used in various fields such as friction materials, self-lubricating bearings, and electrical contact materials (including pantographic slipper for high-speed trains, conductive rings in aerospace, or brushes for generators).

[0003] The matrix of traditional copper-graphite composites is coarse copper grains. Under harsh environments such as high temperature and high load, the copper grains are prone to coarsening, resulting in poor high-temperature softening resistance of the composites, thereby seriously affecting stability and service life. In addition, copper and graphite have low mutual solubility, poor wettability, and a mechanically interlocked interface, making the graphite easy to fall off and peel off from the copper matrix during use of the material, which causes certain difficulties in the preparation of high-performance and high-stable materials. SUMMARY

[0004] An objective of the present disclosure is to provide an yttria-reinforced dual-scale copper-graphite composite and a preparation method and use thereof. In the present disclosure, the yttria-reinforced dual-scale copper-graphite composite has a high density, high-temperature softening resistance, and desirable electrical conductivity, which can effectively improve mechanical properties and a high-temperature stability of the copper-graphite composite, thereby prolonging a service life of the copper-graphite composite under high-temperature and high-load conditions.

[0005] To achieve the above objective of the present disclosure, the present disclosure provides the following technical solutions.

[0006] The present disclosure provides a preparation method of an yttria-reinforced dual-scale copper-graphite composite, including the following steps:

[0007] mixing a CuO powder with an Y2O3 powder to obtain a precursor powder; where the CuO powder includes a nano CuO powder and a micron CuO powder; the nano-CuO powder has an 08 09 23 average particle size of 40 run to 60 nm; and the micron CuO powder has an average particle size of 8 pm to 12 pm;

[0008] conducting primary reduction on the precursor powder in a reducing atmosphere to obtain a primary composite powder;

[0009] conducting ball milling on the primary composite powder to obtain a fine primary composite powder;

[0010] conducting deep reduction on the fine primary composite powder in a reducing atmosphere to obtain a secondary composite powder; wherein the deep reduction is conducted at 350°C to 450°C for 120 min to 210 min;

[0011] mixing the secondary composite powder with a modified graphite powder to obtain a Cu-YzCh-graphite composite powder; where the modified graphite powder includes a graphite powder matrix, and a nickel coating and a copper coating that are sequentially coated on a surface of the graphite powder matrix; and

[0012] conducting hot-pressed sintering on the Cu-Y2O3-graphite composite powder to obtain the yttria-reinforced dual-scale copper-graphite composite.

[0013] Preferably, the nano CuO powder and the micro CuO powder have a mass ratio of (3-4.5):1.

[0014] Preferably, the Y2O3 powder has an average particle size of 40 nm to 60 nm; and the precursor powder has 0.6 wt.% to 4 wt.% of the Y2O3 powder.

[0015] Preferably, the primary reduction is conducted at 100°C to 150°C for 120 min to 180 min.

[0016] The deep reduction is conducted at 350°C to 450°C for 120 min to 210 min.

[0017] Preferably, in the modified graphite powder, the nickel coating has a thickness of 200 nm to 300 nm, and the copper coating has a thickness of 130 nm to 170 nm.

[0018] Preferably, the modified graphite powder and the Y2O3 powder have a mass ratio of (1-8):(0.6-4).

[0019] Preferably, the hot-pressed sintering is conducted at 750°C to 950°C and 25 MPa to 50 MPa for 10 min to 25 min.

[0020] There is also disclosed an yttria-reinforced dual-scale copper-graphite composite prepared by the preparation method, including yttria, a dual-scale copper matrix, and a graphite powder; where the dual-scale copper matrix includes nano copper and micron copper; there is a transition layer composed of Ni, O, and Cu at an interface between the dual-scale copper matrix and the graphite powder; and the yttria and the nano copper are coated on a surface of the micron copper.

[0021] There is also disclosed the use of the yttria-reinforced dual-scale copper-graphite composite in a friction material, a self-lubricating bearing, or an electrical contact material.

[0022] The present disclosure provides a preparation method of an yttria-reinforced dual-scale 08 09 23 copper-graphite composite. In the present disclosure, the nano CuO powder, having an average particle size of 40 nm to 60 nm, and the micron CuO powder, having an average particle size of 8 pm to 12 pm„ are used as CuO raw material powders, and a copper matrix composed of two crystal grains with obvious size differences is obtained through ball milling, two reductions and hot-pressed sintering, which significantly improves mechanical properties of the material. Adding the Y2O3 powder can inhibit the growth of grain size caused by high temperature and the subsequent reduction of mechanical properties during the preparation and use; by mixing the CuO powder with the Y2O3 powder, the Y2O3 powder is fully dispersed, and the nano-sized copper grains are isolated as much as possible, thus significantly increasing a softening temperature of the material. The modified graphite powder is used as a raw material. In the air, the copper coating of the modified graphite powder is transformed into a CU2O layer, and the migration of Ni, O, Cu and other elements at a graphite / Cu interface is controlled by hot-pressed sintering, forming an interfacial transition layer that nearly fully covers the graphite. Accordingly, an interface structure of the composite can be improved, so as to enhance a density, mechanical properties, and a stability of the composite.

[0023] In the present disclosure, the preparation method still belongs to the traditional powder metallurgy, which does not greatly change a manufacturing process of the traditional copper-graphite composites. Therefore, the preparation method can easily realize integration with the original equipment and technology, and the prepared composite has obviously improved performances. The results of examples show that the yttria-reinforced dual-scale copper-graphite composite has a density of not less than 98%, a hardness of 90 HV to 160 HV, a softening temperature of 650°C to 900°C, an electrical conductivity of 33 IACS% to 55 IACS%, and a coefficient of friction at 0.09 to 0.20. The yttria-reinforced dual-scale copper-graphite composite has a high density, high-temperature softening resistance, and desirable electrical conductivity, which can effectively improve mechanical properties and a high-temperature stability of the copper-graphite composite, thereby prolonging a service life of the copper-graphite composite under high-temperature and high-load conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows scanning electron microscopy (SEM) images of a combination effect of composites prepared in Example 2 and Comparative Examples 1 to 2; and

[0025] FIG. 1 shows an electron back-scattered diffraction (EBSD) pattern of a dual-scale structure of the yttria-reinforced dual-scale copper-graphite composite prepared in Example 2. 08 09 23 DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The present disclosure provides a preparation method of an yttria-reinforced dual-scale copper-graphite composite, including the following steps:

[0027] mixing a CuO powder with an Y2O3 powder to obtain a precursor powder; where the CuO powder includes a nano CuO powder and a micron CuO powder; the nano-CuO powder has an average particle size of 40 nm to 60 nm; and the micron CuO powder has an average particle size of 8 pm to 12 pm;

[0028] conducting primary reduction on the precursor powder in a reducing atmosphere to obtain a primary composite powder;

[0029] conducting ball milling on the primary composite powder to obtain a fine primary composite powder;

[0030] conducting deep reduction on the fine primary composite powder in a reducing atmosphere to obtain a secondary composite powder; wherein the deep reduction is conducted at 350°C to 450°C for 120 min to 210 min;

[0031] mixing the secondary composite powder with a modified graphite powder to obtain a Cu-YjOa-graphite composite powder; where the modified graphite powder includes a graphite powder matrix, and a nickel coating and a copper coating that are sequentially coated on a surface of the graphite powder matrix; and

[0032] conducting hot-pressed sintering on the Cu-Y2O3-graphite composite powder to obtain the yttria-reinforced dual-scale copper-graphite composite.

[0033] In the present disclosure, a CuO powder is mixed with an Y2O3 powder to obtain a precursor powder. The CuO powder includes a nano CuO powder and a micron CuO powder. The nano CuO powder has an average particle size of 40 nm to 60 nm, more preferably 50 nm; the micron CuO powder has an average particle size of 8 pm to 12 pm, more preferably 10 pm. The nano CuO powder and the micron CuO powder have a mass ratio of preferably (3-4.5):1, specifically preferably 4.5:1, 4:1, 3.5:1, or 3:1.

[0034] In the present disclosure, the Y2O3 powder has an average particle size of preferably 40 nm to 60 nm, more preferably 50 nm; and the precursor powder has preferably 0.6 wt.% to 4 wt.%, more preferably 2.4 wt.% to 3.5 wt.% of the Y2O3 powder. The yttria can prevent the growth of the nano copper, and can also improve the hardness, high-temperature softening resistance, and friction and wear properties of the material.

[0035] In the present disclosure, the CuO powder and the Y2O3 powder are mixed by preferably ball milling. The mixing by ball milling is conducted through preferably wet milling; a mixing medium of the ball milling is preferably alcohol. The mixing by ball milling is conducted preferably in a planetary ball mill; the mixing by ball mill mixing is conducted at preferably 100 08 09 23 r / min to 200 r / min, more preferably 150 r / min at a ball-to-material ratio of preferably (8-15):1, more preferably (9-12):1 for preferably 2 h; during the mixing by ball milling, preferably the ball milling is stopped for 15 min every 15 min of ball milling, and then continued by reverse rotation. The mixing by ball milling can further improve a dispersion degree of the Y2O3 powder, isolate the nano-sized copper grains, and significantly increase a softening temperature of the material. Preferably, after the mixing, an obtained powder is dried to obtain the precursor powder. The drying is preferably vacuum drying at preferably 80°C for preferably 1 h. The precursor powder has a particle size of preferably 80 mesh.

[0036] In the present disclosure, a binder is preferably added during the mixing by ball milling. The binder is preferably stearic acid. The binder in the precursor powder has a content of preferably 1 wt.%. Adding the binder facilitates powder molding and facilitates subsequent hot-pressed sintering.

[0037] In the present disclosure, primary reduction is conducted on the precursor powder in a reducing atmosphere to obtain a primary composite powder. The primary reduction is conducted preferably in a tubular furnace. The reducing atmosphere is preferably a hydrogen atmosphere; the hydrogen atmosphere is provided with a hydrogen flow rate of preferably 200 mL / min. A method for providing the reducing atmosphere includes preferably: introducing argon gas at 200 mL / min, heating to a primary reduction temperature at 5°C / min, and holding the temperature for 30 min; after the temperature in a temperature zone of the furnace basically tends to be stable, hydrogen gas is introduced at 200 mL / min to conduct the primary reduction.

[0038] In the present disclosure, the primary reduction is conducted at preferably 100°C to 150°C, more preferably 120°C to 130°C for preferably 120 min to 180 min, more preferably 150 min.

[0039] In the present disclosure, preferably after the primary reduction, the hydrogen gas supply is turned off and switched to argon gas at 200 mL / min, followed by cooling to a room temperature with the furnace to obtain the primary composite powder. The primary composite powder includes the Y2O3 powder, the Cu powder, and the CuO powder.

[0040] In the present disclosure, ball milling is conducted on the primary composite powder to obtain a fine primary composite powder. The ball milling is conducted through preferably wet milling; a mixing medium of the ball milling is preferably alcohol. The ball milling is conducted preferably in an argon atmosphere. The ball milling is conducted preferably in a planetary ball mill; and the ball milling is preferably high-energy ball milling. The ball milling is conducted at preferably 200 r / min to 300 r / min, more preferably 250 r / min at a ball-to-material ratio of preferably (8-15):1, more preferably (9-12):1 for preferably 7 h to 8 h, more preferably 7.5 h; during the ball milling, preferably the ball milling is stopped for 15 min every 15 min of ball milling, and then continued by reverse rotation. A powder size of the primary composite powder 08 09 23 can be reduced by the ball milling to prepare for deep reduction. Preferably, after the ball milling, an obtained powder is dried to obtain a fine primary composite powder. The drying is preferably vacuum drying at preferably 80°C for preferably 1 h. The fine primary composite powder has a particle size of preferably 80 mesh.

[0041] In the present disclosure, deep reduction is conducted on the fine primary composite powder in a reducing atmosphere to obtain a secondary composite powder. The deep reduction is conducted preferably in a tubular furnace. The reducing atmosphere is preferably a hydrogen atmosphere; the hydrogen atmosphere is provided with a hydrogen flow rate of preferably 500 mL / min. A method for providing the reducing atmosphere includes preferably: introducing argon gas at 200 mL / min, heating to a deep reduction temperature at 5°C / min, and holding the temperature for 30 min; after the temperature in a temperature zone of the furnace basically tends to be stable, hydrogen gas is introduced at 500 mL / min to conduct the deep reduction.

[0042] In the present disclosure, the deep reduction is conducted at 350°C to 450°C, more preferably 400°C for 120 min to 210 min, more preferably 150 min to 180 min. Through temperature, time, and hydrogen flow, it is beneficial to promote the complete reduction of powder.

[0043] In the present disclosure, preferably after the deep reduction, the hydrogen gas supply is turned off and switched to argon gas at 200 mL / min, followed by cooling to a room temperature with the furnace to obtain the secondary composite powder. The secondary composite powder includes the Y2O3 and the Cu.

[0044] In the present disclosure, the secondary composite powder is mixed with a modified graphite powder to obtain a CuASCh-graphite composite powder. The modified graphite powder includes a graphite powder matrix, and a nickel coating and a copper coating that are sequentially coated on a surface of the graphite powder matrix. In the modified graphite powder, the nickel coating has a thickness of preferably 200 nm to 300 nm, more preferably 220 nm to 250 nm, and the copper coating has a thickness of preferably 130 nm to 170 nm, more preferably 140 nm to 150 nm. Limiting the thicknesses of the nickel coating and the copper coating to the above range can ensure that the copper coating is transformed into a CU2O layer during the subsequent high-temperature heat preservation, and the plating layer does not fall off due to the excessive formation of the oxide layer.

[0045] In the present disclosure, the modified graphite powder and the Y2O3 powder have a mass ratio of preferably (1-8):(0.6-4), more preferably (3-6):(1-2).

[0046] In the present disclosure, before the modified graphite powder is mixed with the secondary composite powder, high-temperature heat preservation is preferably conducted; the high-temperature heat preservation is conducted in preferably an air atmosphere at preferably 450°C to 650°C, more preferably 580°C to 600°C for preferably 0.5 h to 2 h, more preferably 1 h. The high- 08 09 23 temperature heat preservation is conducted preferably by stirring at preferably 10 r / min. The stirring ensures that the modified graphite powder is fully in contact with the air, and cuprous oxide is generated on the surface of the graphite powder, which is beneficial to the combination with the copper matrix.

[0047] In the present disclosure, preferably, the modified graphite powder that has been subjected to high-temperature heat preservation is cooled to a room temperature, and then mixed with the secondary composite powder.

[0048] In the present disclosure, the secondary composite powder and the modified graphite powder are mixed preferably in a V-type mixer at a ball-to-material ratio of preferably (1-5):1, more preferably (2-4):1 at preferably 10 r / min to 30 r / min, more preferably 15 r / min to 25 r / min for preferably 10 h to 36 h, more preferably 15 h to 24 h. The Cu-YiOs-graphite composite powder has a particle size of preferably 9 pm to 12 pm.

[0049] In the present disclosure, hot-pressed sintering is conducted on the CU-Y2O3-graphite composite powder to obtain the yttria-reinforced dual-scale copper-graphite composite. The hot-pressed sintering is conducted preferably in a mold; and the mold is preferably a graphite cylinder mold.

[0050] In the present disclosure, the hot-pressed sintering is conducted at preferably 750°C to 950°C, more preferably 800°C to 900°C and preferably 25 MPa to 50 MPa, more preferably 30 MPa for preferably 10 min to 25 min, more preferably 15 min to 20 min. A heating rate from a room temperature to a temperature of the hot-pressed sintering is preferably 10°C / min to 40°C / min, more preferably 20°C / min to 30°C / min.

[0051] In the present disclosure, preferably, after the hot-pressed sintering, the yttria-reinforced dual-scale copper-graphite composite is obtained by cooling with the furnace.

[0052] The present disclosure further provides an yttria-reinforced dual-scale copper-graphite composite prepared by the preparation method, including yttria, a dual-scale copper matrix, and a graphite powder; where the dual-scale copper matrix includes nano copper and micron copper; there is a transition layer composed of Ni, O, and Cu at an interface between the dual-scale copper matrix and the graphite powder; and the yttria and the nano copper are coated on a surface of the micron copper. The nano copper has an average particle size of preferably 40 nm to 60 nm, more preferably 50 nm; the micron copper has an average particle size of preferably 8 pm to 12 pm, more preferably 10 pm. The yttria has a particle size of preferably 40 nm to 60 nm, more preferably 50 nm. The graphite powder has a particle size of preferably 25 pm to 35 pm, more preferably 30 pm.

[0053] In the present disclosure, the yttria-reinforced dual-scale copper-graphite composite includes: 1 vol% to 6 vol% of the yttria, 5 vol% to 20 vol% of the graphite, and Cu and impurities 08 09 23 as a balance. The impurities include preferably Ni, Cr, P, Mn, Ag, Co, Mo, As, Sb, Al, Hf, Zr, Ti, Ta, Sn, Zn, and Sr; and the impurities have a total content of preferably 0.01 wt% to 0.4 wt%.

[0054] In the present disclosure, the yttria-reinforced dual-scale copper-graphite composite has a density of preferably not less than 98%, more preferably 99.2%, a hardness of preferably 90 HV to 160 HV, more preferably 149 HV, a softening temperature of preferably 650°C to 900°C, more preferably 850°C, an electrical conductivity of preferably 33 IACS% to 55 IACS%, more preferably 46 IACS%, and a coefficient of friction at preferably 0.09 to 0.20, more preferably 0.125.

[0055] The present disclosure further provides use of the yttria-reinforced dual-scale copper-graphite composite in a friction material, a self-lubricating bearing, or an electrical contact material. The electrical contact material includes preferably a pantographic slipper for a high-speed train, a conductive ring in aerospace, or a brush for a generator.

[0056] The technical solutions of the present disclosure will be described below clearly and completely in conjunction with the examples of the present disclosure. Apparently, the described examples are only a part of, not all of, the examples of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

[0057] Example 1

[0058] (1) Preparation of a precursor powder: 50 g of a CuO powder, 1.2 g of an Y2O3 powder, and 0.5 g of stearic acid were mixed, placed in a planetary ball mill for ball milling at 100 r / min, with a ball-to-material ratio of 9:1 using 5 g to 8 g of alcohol for 2 h, where the ball milling was stopped for 15 min every 15 min of working, and then continued with reverse rotation; after the ball milling, a powder was washed out in a ball mill tank with alcohol, and dried in a vacuum drying oven at 80°C for 1 h, and a dried powder was sieved by an 80-mesh sieve to obtain the precursor powder; where the CuO powder included a nano CuO powder and a micron CuO powder; the nano CuO powder had an average particle size of 50 nm; the micron CuO powder had an average particle size of 10 urn; the nano CuO powder and the micron CuO powder had a mass ratio of 3:1; the Y2O3 powder had an average particle size of 50 nm; the Y2O3 powder had a content in the precursor powder of 2.4 wt.%; and the stearic acid had a content in the precursor powder of 1 wt.%.

[0059] (2) Primary reduction: the precursor powder was added into a tubular furnace, argon gas was introduced at a flow rate of 0.2 L / min for sealing protection, and heated at 5°C / min to a reduction temperature of 120°C and the temperature held was for 30 min; after the temperature in a temperature zone of the furnace basically tended to be stable, H2 was introduced at a flow rate of 0.2 L / min and the temperature was held for 120 min; after the primary reduction was completed, 08 09 23 a H2 gas path was turned off, the argon gas was introduced at a flow rate of 0.2 L / min, and the furnace was cooled to a room temperature to obtain a primary composite powder composed of the Y2O3 powder, a Cu powder, and an unreduced CuO powder.

[0060] (3) Ball milling-based mixing: the primary composite powder was placed in a planetary ball mill for high-energy ball milling at 200 r / min, with a ball-to-material ratio of 9:1 using 5 g to 8 g of alcohol for 7 h, where the high-energy ball milling was stopped for 15 min every 15 min of working, and then continued with reverse rotation; after the high-energy ball milling, a powder was washed out in the ball mill tank with alcohol, and dried in a vacuum drying oven at 80°C for 1 h, and a dried powder was sieved by an 80-mesh sieve to obtain a fine primary composite powder.

[0061] (4) Deep reduction: the fine primary composite powder was added into the tubular furnace, the argon gas was introduced at a flow rate of 0.2 L / min for sealing protection, and heated at 5°C / min to a deep reduction temperature of 400°C and the temperature was held for 30 min; after the temperature in the temperature zone of the furnace basically tended to be stable, H2 was introduced at a flow rate of 0.5 L / min and the temperature was held for 120 min; after the deep reduction was completed, the H2 gas path was turned off, the argon gas was introduced at a flow rate of 0.2 L / min, and the furnace was cooled to a room temperature to obtain a secondary composite powder.

[0062] (5) Secondary mixing: a modified graphite powder was heated at 580°C for 1 h, and subjected to mechanical stirring at 10 r / min; the secondary composite powder was mixed with the modified graphite powder after high-temperature insulation through a V-type mixer in a ball-to-material ratio of 1:1 at 10 r / min for 10 h, and then sieved by an 80-mesh sieve to obtain a Cu-Y2O3-graphite composite powder; where the modified graphite powder was composed of a graphite powder matrix, and a nickel coating and a copper coating that were successively coated on a surface of the graphite powder matrix; the nickel coating had a thickness of 200 nm; and the copper coating had a thickness of 130 nm.

[0063] (6) Hot-pressed sintering: 10 g of the Cu-Y2O3-graphite composite powder was put into a high-strength graphite cylindrical mold with an inner diameter of 20 mm, an outer diameter of 45 mm, and a height of 70 mm, and the mold was put into a hot-pressed sintering furnace for sintering; the sintering was conducted for 10 min at a sintering temperature of 800°C obtained by heating at 40°C / min, and the powder was cooled with the furnace, where the sintering was conducted under an initial pressure of 5 MPa and a pressure of 30 MPa at the beginning of heat preservation, and the pressure was released directly after the end of heat preservation; when the temperature dropped below 100°C, a vacuum valve was closed to release the gas until the pressures inside and outside the furnace were consistent, a furnace door was opened, the graphite mold was taken out to collect the sample, to obtain an yttria-reinforced dual-scale copper-graphite composite. 08 09 23

[0064] Example 2

[0065] (1) Preparation of a precursor powder: 50 g of a CuO powder, 1.2 g of an Y2O3 powder, and 0.5 g of stearic acid were mixed, placed in a planetary ball mill for ball milling at 150 r / min, with a ball-to-material ratio of 11:1 using 5 g to 8 g of alcohol for 2 h, where the ball milling was stopped for 15 min every 15 min of working, and then continued with reverse rotation; after the ball milling, a powder was washed out in a ball mill tank with alcohol, and dried in a vacuum drying oven at 80°C for 1 h, and a dried powder was sieved by an 80-mesh sieve to obtain the precursor powder; where the CuO powder included a nano CuO powder and a micron CuO powder; the nano CuO powder had an average particle size of 50 nm; the micron CuO powder had an average particle size of 10 pm; the nano CuO powder and the micron CuO powder had a mass ratio of 3.5:1; the Y2O3 powder had an average particle size of 50 nm; the Y2O3 powder had a content in the precursor powder of 2.4 wt.%; and the stearic acid had a content in the precursor powder of 1 wt.%.

[0066] (2) Primary reduction: the precursor powder was added into a tubular furnace, argon gas was introduced at a flow rate of 0.2 L / min for sealing protection, and heated at 5°C / min to a reduction temperature of 120°C and the temperature held was for 30 min; after the temperature in a temperature zone of the furnace basically tended to be stable, H2 was introduced at a flow rate of 0.2 L / min and the temperature was held for 150 min; after the primary reduction was completed, a H2 gas path was turned off, the argon gas was introduced at a flow rate of 0.2 L / min, and the furnace was cooled to a room temperature to obtain a primary composite powder composed of the Y2O3 powder, a Cu powder, and an unreduced CuO powder.

[0067] (3) Ball milling-based mixing: the primary composite powder was placed in a planetary ball mill for high-energy ball milling at 250 r / min, with a ball-to-material ratio of 11:1 using 5 g to 8 g of alcohol for 7.5 h, where the high-energy ball milling was stopped for 15 min every 15 min of working, and then continued with reverse rotation; after the high-energy ball milling, a powder was washed out in the ball mill tank with alcohol, and dried in a vacuum drying oven at 80°C for 1 h, and a dried powder was sieved by an 80-mesh sieve to obtain a fine primary composite powder.

[0068] (4) Deep reduction: the fine primary composite powder was added into the tubular furnace, the argon gas was introduced at a flow rate of 0.2 L / min for sealing protection, and heated at 5°C / min to a deep reduction temperature of 400°C and the temperature was held for 30 min; after the temperature in the temperature zone of the furnace basically tended to be stable, H2 was introduced at a flow rate of 0.5 L / min and the temperature was held for 150 min; after the deep reduction was completed, the H2 gas path was turned off, the argon gas was introduced at a flow rate of 0.2 L / min, and the furnace was cooled to a room temperature to obtain a secondary 08 09 23 composite powder.

[0069] (5) Secondary mixing: a modified graphite powder was heated at 580°C for 1 h, and subjected to mechanical stirring at 10 r / min; the secondary composite powder was mixed with the modified graphite powder after high-temperature insulation through a V-type mixer in a ball-to-material ratio of 2:1 at 15 r / min for 15 h, and then sieved by an 80-mesh sieve to obtain a Cu-YsCh-graphite composite powder; where the modified graphite powder was composed of a graphite powder matrix, and a nickel coating and a copper coating that were successively coated on a surface of the graphite powder matrix; the nickel coating had a thickness of 220 nm; and the copper coating had a thickness of 140 nm.

[0070] (6) Hot-pressed sintering: 10 g of the Cu-YjOs-graphite composite powder was put into a high-strength graphite cylindrical mold with an inner diameter of 20 mm, an outer diameter of 45 mm, and a height of 70 mm, and the mold was put into a hot-pressed sintering furnace for sintering; the sintering was conducted for 15min at a sintering temperature of 850°C obtained by heating at 30°C / min, and the powder was cooled with the furnace, where the sintering was conducted under an initial pressure of 5 MPa and a pressure of 30 MPa at the beginning of heat preservation, and the pressure was released directly after the end of heat preservation; when the temperature dropped below 100°C, a vacuum valve was closed to release the gas until the pressures inside and outside the furnace were consistent, a furnace door was opened, the graphite mold was taken out to collect the sample, to obtain an yttria-reinforced dual-scale copper-graphite composite.

[0071] Example 3

[0072] (1) Preparation of a precursor powder: 50 g of a CuO powder, 1.2 g of an Y2O3 powder, and 0.5 g of stearic acid were mixed, placed in a planetary ball mill for ball milling at 200 r / min, with a ball-to-material ratio of 12:1 using 5 g to 8 g of alcohol for 2 h, where the ball milling was stopped for 15 min every 15 min of working, and then continued with reverse rotation; after the ball milling, a powder was washed out in a ball mill tank with alcohol, and dried in a vacuum drying oven at 80°C for 1 h, and a dried powder was sieved by an 80-mesh sieve to obtain the precursor powder; where the CuO powder included a nano CuO powder and a micron CuO powder; the nano CuO powder had an average particle size of 50 nm; the micron CuO powder had an average particle size of 10 pm; the nano CuO powder and the micron CuO powder had a mass ratio of 4:1; the Y2O3 powder had an average particle size of 50 nm; the Y2O3 powder had a content in the precursor powder of 2.4 wt.%; and the stearic acid had a content in the precursor powder of 1 wt.%.

[0073] (2) Primary reduction: the precursor powder was added into a tubular furnace, argon gas was introduced at a flow rate of 0.2 L / min for sealing protection, and heated at 5°C / min to a reduction temperature of 120°C and the temperature held was for 30 min; after the temperature in 08 09 23 a temperature zone of the furnace basically tended to be stable, H2 was introduced at a flow rate of 0.2 L / min and the temperature was held for 180 min; after the primary reduction was completed, a H2 gas path was turned off, the argon gas was introduced at a flow rate of 0.2 L / min, and the furnace was cooled to a room temperature to obtain a primary composite powder composed of the Y2O3 powder, a Cu powder, and an unreduced CuO powder.

[0074] (3) Ball milling-based mixing: the primary composite powder was placed in a planetary ball mill for high-energy ball milling at 300 r / min, with a ball-to-material ratio of 12:1 using 5 g to 8 g of alcohol for 8 h, where the high-energy ball milling was stopped for 15 min every 15 min of working, and then continued with reverse rotation; after the high-energy ball milling, a powder was washed out in the ball mill tank with alcohol, and dried in a vacuum drying oven at 80°C for 1 h, and a dried powder was sieved by an 80-mesh sieve to obtain a fine primary composite powder.

[0075] (4) Deep reduction: the fine primary composite powder was added into the tubular furnace, the argon gas was introduced at a flow rate of 0.2 L / min for sealing protection, and heated at 5°C / min to a deep reduction temperature of 400°C and the temperature was held for 30 min; after the temperature in the temperature zone of the furnace basically tended to be stable, H2 was introduced at a flow rate of 0.5 L / min and the temperature was held for 180 min; after the deep reduction was completed, the H2 gas path was turned off, the argon gas was introduced at a flow rate of 0.2 L / min, and the furnace was cooled to a room temperature to obtain a secondary composite powder.

[0076] (5) Secondary mixing: a modified graphite powder was heated at 580°C for 1 h, and subjected to mechanical stirring at 10 r / min; the secondary composite powder was mixed with the modified graphite powder after high-temperature insulation through a V-type mixer in a ball-to-material ratio of 3:1 at 20 r / min for 20 h, and then sieved by an 80-mesh sieve to obtain a Cu-Y2O3-graphite composite powder; where the modified graphite powder was composed of a graphite powder matrix, and a nickel coating and a copper coating that were successively coated on a surface of the graphite powder matrix; the nickel coating had a thickness of 250 nm; and the copper coating had a thickness of 150 nm.

[0077] (6) Hot-pressed sintering: 10 g of the Cu-Y2O3-graphite composite powder was put into a high-strength graphite cylindrical mold with an inner diameter of 20 mm, an outer diameter of 45 mm, and a height of 70 mm, and the mold was put into a hot-pressed sintering furnace for sintering; the sintering was conducted for 20min at a sintering temperature of 900°C obtained by heating at 20°C / min, and the powder was cooled with the furnace, where the sintering was conducted under an initial pressure of 5 MPa and a pressure of 30 MPa at the beginning of heat preservation, and the pressure was released directly after the end of heat preservation; when the temperature dropped below 100°C, a vacuum valve was closed to release the gas until the pressures inside and outside 08 09 23 the furnace were consistent, a furnace door was opened, the graphite mold was taken out to collect the sample, to obtain an yttria-reinforced dual-scale copper-graphite composite.

[0078] Example 4

[0079] (1) Preparation of a precursor powder: 50 g of a CuO powder, 1.2 g of an Y2O3 powder, and 0.5 g of stearic acid were mixed, placed in a planetary ball mill for ball milling at 200 r / min, with a ball-to-material ratio of 12:1 using 5 g to 8 g of alcohol for 2 h, where the ball milling was stopped for 15 min every 15 min of working, and then continued with reverse rotation; after the ball milling, a powder was washed out in a ball mill tank with alcohol, and dried in a vacuum drying oven at 80°C for 1 h, and a dried powder was sieved by an 80-mesh sieve to obtain the precursor powder; where the CuO powder included a nano CuO powder and a micron CuO powder; the nano CuO powder had an average particle size of 50 nm; the micron CuO powder had an average particle size of 10 pm; the nano CuO powder and the micron CuO powder had a mass ratio of 4.5:1; the Y2O3 powder had an average particle size of 50 nm; the Y2O3 powder had a content in the precursor powder of 2.4 wt.%; and the stearic acid had a content in the precursor powder of 1 wt.%.

[0080] (2) Primary reduction: the precursor powder was added into a tubular furnace, argon gas was introduced at a flow rate of 0.2 L / min for sealing protection, and heated at 5°C / min to a reduction temperature of 120°C and the temperature held was for 30 min; after the temperature in a temperature zone of the furnace basically tended to be stable, H2 was introduced at a flow rate of 0.2 L / min and the temperature was held for 180 min; after the primary reduction was completed, a H2 gas path was turned off, the argon gas was introduced at a flow rate of 0.2 L / min, and the furnace was cooled to a room temperature to obtain a primary composite powder composed of the Y2O3 powder, a Cu powder, and an unreduced CuO powder.

[0081] (3) Ball milling-based mixing: the primary composite powder was placed in a planetary ball mill for high-energy ball milling at 300 r / min, with a ball-to-material ratio of 12:1 using 5 g to 8 g of alcohol for 8 h, where the high-energy ball milling was stopped for 15 min every 15 min of working, and then continued with reverse rotation; after the high-energy ball milling, a powder was washed out in the ball mill tank with alcohol, and dried in a vacuum drying oven at 80°C for 1 h, and a dried powder was sieved by an 80-mesh sieve to obtain a fine primary composite powder.

[0082] (4) Deep reduction: the fine primary composite powder was added into the tubular furnace, the argon gas was introduced at a flow rate of 0.2 L / min for sealing protection, and heated at 5°C / min to a deep reduction temperature of 400°C and the temperature was held for 30 min; after the temperature in the temperature zone of the furnace basically tended to be stable, H2 was introduced at a flow rate of 0.5 L / min and the temperature was held for 180 min; after the deep reduction was completed, the H2 gas path was turned off, the argon gas was introduced at a flow 08 09 23 rate of 0.2 L / min, and the furnace was cooled to a room temperature to obtain a secondary composite powder.

[0083] (5) Secondary mixing: a modified graphite powder was heated at 580°C for 1 h, and subjected to mechanical stirring at 10 r / min; the secondary composite powder was mixed with the modified graphite powder after high-temperature insulation through a V-type mixer in a ball-to-material ratio of 4:1 at 25 r / min for 24 h, and then sieved by an 80-mesh sieve to obtain a Cu-Y2O3-graphite composite powder; where the modified graphite powder was composed of a graphite powder matrix, and a nickel coating and a copper coating that were successively coated on a surface of the graphite powder matrix; the nickel coating had a thickness of 300 nm; and the copper coating had a thickness of 170 nm.

[0084] (6) Hot-pressed sintering: 10 g of the Cu-YjCh-graphite composite powder was put into a high-strength graphite cylindrical mold with an inner diameter of 20 mm, an outer diameter of 45 mm, and a height of 70 mm, and the mold was put into a hot-pressed sintering furnace for sintering; the sintering was conducted for 20min at a sintering temperature of 900°C obtained by heating at 25°C / min, and the powder was cooled with the furnace, where the sintering was conducted under an initial pressure of 5 MPa and a pressure of 30 MPa at the beginning of heat preservation, and the pressure was released directly after the end of heat preservation; when the temperature dropped below 100°C, a vacuum valve was closed to release the gas until the pressures inside and outside the furnace were consistent, a furnace door was opened, the graphite mold was taken out to collect the sample, to obtain an yttria-reinforced dual-scale copper-graphite composite.

[0085] Comparative Example 1

[0086] A preparation method of this comparative example was basically the same as that of Example 2, except that: the CuO powder is adjusted to a CuO powder with an average particle size of 10 pm.

[0087] Comparative Example 2

[0088] A preparation method of this comparative example was basically the same as that of Example 2, except that: the CuO powder is adjusted to a CuO powder with an average particle size of 50 nm.

[0089] Test Example

[0090] The electrical conductivity, mechanical properties, and frictional properties of the composites of Examples 1 to 4 and Comparative Examples 1 to 2 were tested, and the results were shown in Table 1. The density was tested by the Archimedes drainage method, and the conductivity test method referred to GB / T 32791-2016 "Electromagnetic (Eddy-Current) examination method for electrical conductivity of copper and copper alloys".

[0091] Table 1 Performance test results of composites

[0092] Group Compactness (%) Hardness (HV) Softening temperature (°C) Electrical conductivity (IACS%) Coefficient of friction Example 1 98.6 116 800 48 0.172 Example 2 98.9 124 850 46 0.153 Example 3 99.2 146 900 50 0.135 Example 4 99.5 155 900 51 0.125 Comparative Example 1 96.9 131 700 21 0.271 Comparative Example 2 97.6 151 750 44 0.212

[0093] It was seen from Table 1 that in the present disclosure, the dual-scale copper (as shown in FIG. 2) could improve the strength, high-temperature softening resistance, and friction properties of the composite. 08 09 23

[0094] FIG. 1 showed SEM images of a combination effect of composites prepared in Example 2 and Comparative Examples 1 to 2. It was seen from FIG. 1 that by regulating the migration of Ni, O, Cu and other elements at the graphite / Cu interface, a nearly fully-covered interface transition layer was formed.

[0095] FIG. 2 showed an electron back-scattered diffraction (EBSD) pattern of a dual-scale structure of the yttria-reinforced dual-scale copper-graphite composite prepared in Example 2. It was seen from FIG. 2 that a composite with a dual-scale structure could be prepared by the method of the present disclosure.

[0096] In the present disclosure, the yttria-reinforced dual-scale copper-graphite composite has desirable electrical conductivity, hardness, high-temperature softening resistance, and friction and wear performance, which can be applied to pantographic slipper materials, electrode brush materials, electrical contact materials, conductive materials, or friction materials.

[0097] The above descriptions are merely preferred implementations of the present disclosure. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present disclosure, but such improvements and modifications should be deemed as falling within the protection scope of the present disclosure.

Claims

08 09 231. A preparation method of an yttria-reinforced dual-scale copper-graphite composite, comprising the following steps:mixing a CuO powder with an Y2O3 powder to obtain a precursor powder; wherein the CuO powder comprises a nano CuO powder and a micron CuO powder; the nano-CuO powder has an average particle size of 40 nm to 60 nm; and the micron CuO powder has an average particle size of 8 pm to 12 pm;conducting primary reduction on the precursor powder in a reducing atmosphere to obtain a primary composite powder;conducting ball milling on the primary composite powder to obtain a fine primary composite powder;conducting deep reduction on the fine primary composite powder in a reducing atmosphere to obtain a secondary composite powder; wherein the deep reduction is conducted at 35O°C to 450°C for 120 min to 210 min;mixing the secondary composite powder with a modified graphite powder to obtain a Cu-YjCh-graphite composite powder; wherein the modified graphite powder comprises a graphite powder matrix, and a nickel coating and a copper coating that are sequentially coated on a surface of the graphite powder matrix; andconducting hot-pressed sintering on the Cu-Y2O3-graphite composite powder to obtain the yttria-reinforced dual-scale copper-graphite composite.

2. The preparation method according to claim 1, wherein the nano CuO powder and the micro CuO powder have a mass ratio of (3-4.5):1.

3. The preparation method according to claim 1, wherein the Y2O3 powder has an average particle size of 40 nm to 60 nm; and the precursor powder has 0.6 wt.% to 4 wt.% of the Y2O3 powder.

4. The preparation method according to claim 1, wherein the primary reduction is conducted at 100°C to 150°C for 120 min to 180 min.

5. The preparation method according to claim 1, wherein in the modified graphite powder, the nickel coating has a thickness of 200 nm to 300 nm, and the copper coating has a thickness of 130nm to 170 nm.

6. The preparation method according to claim 1, wherein the modified graphite powder and the Y2O3 powder have a mass ratio of (1-8):(0.6-4).

7. The preparation method according to claim 1, wherein the hot-pressed sintering is conducted at 750°C to 950°C and 25 MPa to 50 MPa for 10 min to 25 min.08 09 23

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