Copper-based powder metallurgical friction material containing nitrides and method for its production

Abstract

This invention discloses a nitride-containing copper-based powder metallurgy friction material and its preparation method, comprising composite copper powder, iron powder, tin powder, flake graphite, hexagonal boron nitride powder, aluminum nitride powder, and ferrochrome powder. The composite copper powder is obtained by ball milling copper powder and reinforcing particle powder at a mass ratio of 100:1-3 in a planetary high-energy ball mill. The reinforcing particle powder is a high-entropy alloy powder or oxide powder. Compared with the prior art, the friction material of this invention has a stable coefficient of friction, wear resistance, and working stability during braking, while also possessing high hardness, high strength, and good heat dissipation, making it more suitable for manufacturing high-speed train brake pads.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy friction materials, specifically relating to a nitride-containing copper-based powder metallurgy friction material and its preparation method, especially a material for manufacturing high-speed train brake pads.

[0002] This invention belongs to the strategic emerging industries catalogue, specifically to the new materials industry, under the key direction of the high-performance composite materials industry, specifically to other high-performance composite materials and green composite materials for rail transit. Background Technology

[0003] Among various friction materials, copper-based powder metallurgy friction materials stand out due to their excellent mechanical properties, thermal conductivity, and wear resistance, making them the most reliable and widely used brake pad material for high-speed trains. Copper-based powder metallurgy friction materials can fully utilize the advantages of the copper matrix, friction components, and lubrication components, as well as their synergistic effects. Furthermore, they are directly produced using powder metallurgy technology, enabling the widespread use of copper-based powder metallurgy brake pads in high-speed train braking systems at speeds up to 350 km / h. The copper matrix dominates the overall properties of the material, including strength, toughness, and thermal conductivity. The friction-enhancing phase plays a role in increasing friction; it possesses high hardness and strength, increasing the coefficient of friction while preventing the matrix from detaching during braking. The lubrication phase provides lubrication, stabilizing the coefficient of friction, improving the working stability and wear resistance of the friction material, and also helping to reduce wear on the mating materials and ensure smooth operation of the friction pair. With the continuous increase in the operating speed of high-speed trains, the heat generated by friction braking is increasing, with the instantaneous temperature of the friction surface reaching over 900℃, placing higher demands on the high-temperature stability and high-temperature oxidation resistance of the friction materials. As a core component of the high-speed train braking system, the performance of the friction materials used in brake pads directly affects the train's speed and the safety and stability of the braking process. Currently used copper-based friction materials are prone to problems such as unstable friction coefficients and high wear under these service conditions, necessitating the development of new friction materials to overcome the shortcomings of existing materials.

[0004] There have been some reports on related patents regarding copper-based powder metallurgy friction materials. For example, Chinese patent CN115612947A discloses a powder metallurgy friction block and its preparation method. The friction body comprises the following components by mass fraction: 45-60% atomized copper powder, 2-4% Sn, 2-4% Ni, 5-15% copper-clad iron powder, 4-10% high-carbon Cr-Fe powder, 1-3% short carbon fiber, 3-5% TiB2, 7-9% NbC, 4.5-9% artificial graphite, 0.5-1% natural graphite, and 1-5% MoS2. However, the friction block described above has a relatively low average coefficient of friction of 0.369-0.378 at a braking speed of 350 km / h. Chinese patent CN114210966A discloses a copper-based powder metallurgy friction material with a high stable coefficient of friction. The composition consists of 48-52% electrolytic copper powder, 18-24% reduced iron powder, 12-16% graphite, 3-6% ferrochrome alloy, 2-4% aluminum oxide, 2-4% molybdenum powder, 2-5% precipitated barium sulfate, and 3-6% polyvinyl alcohol powder. Although it can stabilize the coefficient of friction, the organic matter volatilized during sintering due to the presence of polyvinyl alcohol powder in the composition is not environmentally friendly. Chinese patent CN110923498A discloses a copper-based powder metallurgy friction material containing a composite ceramic friction component of metal carbides and metal oxides, and its preparation method. This method improves the friction coefficient of the copper-based friction material by adding a composite ceramic of metal carbides and metal oxides as a friction component. However, this method uses pure copper powder as the matrix, resulting in poor mechanical properties of the friction material at high temperatures. This is because pure copper has low mechanical strength and is prone to softening at high temperatures, failing to meet current application requirements. Furthermore, the traditional ceramic reinforcing phase has a large difference in thermal expansion coefficients with the pure copper matrix, leading to poor wettability between the ceramic reinforcing phase and the pure copper matrix, which easily generates defects at the interface, affecting the performance of the composite material. Therefore, ensuring excellent tribological properties while simultaneously improving the matrix strength and maintaining high bonding strength between the matrix and other components to meet high-speed, heavy-load conditions is a common goal pursued by researchers. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a nitride-containing copper-based powder metallurgy friction material and its preparation method, which can improve the strength of the copper matrix, enhance the stability of the friction coefficient of the friction material, and reduce wear.

[0006] The object of this invention is achieved in the following manner:

[0007] A copper-based powder metallurgy friction material containing nitrides comprises the following raw materials in weight percentages: 56-65% composite copper powder, 12-16% iron powder, 1-4% tin powder, 9% flake graphite, 1-3% hexagonal boron nitride powder, 3-9% aluminum nitride powder, and 3-9% ferrochrome powder, wherein the total amount of aluminum nitride powder and ferrochrome powder is not higher than 12%; the composite copper powder is obtained by ball milling copper powder and reinforcing particle powder at a mass ratio of 100:1-3 in a planetary high-energy ball mill, wherein the reinforcing particle powder is high-entropy alloy powder or oxide powder.

[0008] The high-entropy alloy powder has a particle size of 400 mesh and is one of FeCoNiCrAl, FeCoNiCrAlCu, and FeCoNiCrTi.

[0009] The oxide powder has a particle size of 100-200 nm and is one of Al2O3, SiO2, and ZrO2.

[0010] The ball mill rotates at 200-350 r / min, the weight ratio of steel balls to powder in the ball mill is 5:1, and the milling time is 2-4 h.

[0011] The copper powder is 200-mesh electrolytic copper powder, the iron powder is 200-mesh reduced iron powder, the ferrochrome alloy powder and tin powder are both 100-mesh, the flake graphite is 80-mesh, the hexagonal boron nitride powder is 200-mesh, and the aluminum nitride powder is 400-mesh.

[0012] A method for preparing nitride-containing copper-based powder metallurgy friction materials includes the following steps:

[0013] (1) Preparation of composite copper powder: Copper powder and reinforcing particle powder are ball-milled in a planetary high-energy ball mill at a mass ratio of 100:1-3. The rotation speed of the ball mill is 200-350 r / min, the weight ratio of steel balls to powder in the ball mill is 5:1, and the ball milling time is 2-4 h.

[0014] (2) Mixing: The composite copper powder, iron powder, tin powder, aluminum nitride powder and ferrochrome powder obtained in step (1) are put into a V-type mixer and mixed for 2-4 hours. Flake graphite and hexagonal boron nitride powder are added 10-20 minutes before the end of mixing.

[0015] (3) Cold pressing: The powder mixed in step (2) is placed into a cold pressing mold and cold pressed using a vertical hydraulic press. The pressure is 400-600 MPa and the holding time is 40-60 s.

[0016] (4) Sintering: After cold pressing, the sample is placed in a high-temperature high-vacuum hot pressing sintering furnace for sintering. The sintering temperature is 900-1000℃ and the sample is kept in a vacuum or argon atmosphere for 2-3 hours.

[0017] In step (2), the rotation speed of the V-type mixer is 10-20 r / min.

[0018] In step (3), the descent rate of the vertical hydraulic press during operation is 10-15 mm / min.

[0019] The temperature curve for the sintering process in step (4) is set as follows: 10-20 min from room temperature to 200℃, hold for 5-10 min; 40-60 min from 200℃ to 800℃, hold for 10-20 min; 10-30 min from 800℃ to 900-1000℃, hold the sample for 2-3 h, then water cool to below 100℃, and cool to room temperature with the furnace.

[0020] Compared with existing technologies, the friction material described in this invention has a stable coefficient of friction, wear resistance and working stability during braking, and also has the characteristics of high hardness, high strength and good heat dissipation, making it more suitable for manufacturing high-speed train brake pads. Attached Figure Description

[0021] Figure 1 This is a comparison chart of the average friction coefficients of the friction materials in the examples and comparative examples.

[0022] Figure 2 This is a comparison chart of the wear amount of the friction materials in the examples and comparative examples.

[0023] Figure 3 This is a microstructure diagram of the copper-based powder metallurgy friction material sample prepared in Example 1. Detailed Implementation

[0024] A nitride-containing copper-based powder metallurgy friction material comprises the following raw materials in the indicated mass percentages: 56-65% composite copper powder, 12-16% iron powder, 1-4% tin powder, 9% flake graphite, 1-3% hexagonal boron nitride powder, 3-12% aluminum nitride powder, and 3-12% ferrochrome powder, wherein the total amount of aluminum nitride powder and ferrochrome powder is not higher than 12%. The composite copper powder is obtained by ball milling copper powder and reinforcing particle powder at a mass ratio of 100:1-3 in a planetary high-energy ball mill. The reinforcing particle powder is a high-entropy alloy powder or oxide powder. The preferred preparation process for the composite copper powder involves a ball mill speed of 200-350 r / min, a steel ball to powder weight ratio of 5:1, and a milling time of 2-4 h.

[0025] In a further preferred embodiment, the high-entropy alloy powder has a particle size of 400 mesh and is selected from FeCoNiCrAl, FeCoNiCrAlCu, and FeCoNiCrTi; the oxide powder has a particle size of 100-200 nm and is selected from Al2O3, SiO2, and ZrO2.

[0026] The preferred formulations for the above-mentioned raw materials are as follows: copper powder is 200-mesh electrolytic copper powder, iron powder is 200-mesh reduced iron powder, ferrochrome alloy powder and tin powder are both 100-mesh, flake graphite is 80-mesh, hexagonal boron nitride powder is 200-mesh, and aluminum nitride powder is 400-mesh.

[0027] High-entropy alloys possess superior properties such as high strength, excellent wear resistance, high work hardening, resistance to high-temperature softening, resistance to high-temperature oxidation, and corrosion resistance. Furthermore, compared to ceramic reinforcements, high-entropy alloys exhibit better interfacial bonding and superior compatibility with the copper matrix in physical metallurgy. Therefore, high-entropy alloys are an ideal matrix reinforcement material for copper-based friction materials. Using high-entropy alloy powder to reinforce the copper matrix can improve the strength, hardness, and high-temperature softening resistance of the Cu matrix, preventing softening of the Cu matrix at high temperatures, improving the stability of the friction coefficient of the friction material, and reducing wear.

[0028] The hexagonal boron nitride used in this invention is a white powder with a hexagonal crystal structure. It has a similar lamellar structure to graphite, a commonly used lubricant. Within the same layer, hBN atoms are connected by covalent bonds, and the layers are bonded together by van der Waals forces. When hBN is subjected to shear force, the layers bonded by van der Waals forces are relatively fragile and prone to slippage, further forming an hBN lubricating film, which can reduce the wear of friction materials. hBN possesses excellent high-temperature resistance and corrosion resistance, and compared to graphite, it has higher thermal stability, maintaining excellent lubricity even at temperatures up to 900℃. Adding hBN as a lubricating phase can reduce the amount of wear at high temperatures and stabilize the coefficient of friction. hBN exhibits good stability at high temperatures, remaining stable even during high-speed braking, providing excellent lubricity and keeping the coefficient of friction relatively stable during high-speed braking. The combined use of flake graphite and hBN ensures the stability of the material under both low and high speed conditions.

[0029] Aluminum nitride (AlN) not only possesses high hardness but also exhibits significantly higher thermal conductivity than commonly used friction components, approaching that of pure copper. AlN also boasts advantages such as low density, low coefficient of thermal expansion, and high high-temperature strength, making it an ideal material for reinforcing copper-based powder metallurgy friction materials. The addition of AlN enhances the material's strength and hardness, allowing it to maintain a high coefficient of friction even at high temperatures. Furthermore, the high thermal conductivity of AlN effectively dissipates heat generated during high-speed friction, reducing its impact on the friction material and minimizing wear.

[0030] The formulation of copper-based powder metallurgy friction materials does not contain environmentally harmful metals such as zinc and lead, nor does it contain organic materials, thus meeting environmental protection requirements.

[0031] A method for preparing a nitride-containing copper-based powder metallurgy friction material includes the following steps:

[0032] (1) Preparation of composite copper powder: Copper powder and reinforcing particle powder are ball-milled in a planetary high-energy ball mill at a mass ratio of 100:1-3. The rotation speed of the ball mill is 200-350 r / min, the weight ratio of steel balls to powder in the ball mill is 5:1, and the ball milling time is 2-4 h. High-entropy alloy powder or nano-oxide particles are used as the reinforcing phase of the electrolytic copper matrix. The high-hardness and high-wear-resistance reinforcing particles are dispersed in the copper matrix by mechanical ball milling, which plays a dispersion strengthening role, thereby improving the strength, hardness and high-temperature softening resistance of the copper matrix, avoiding the softening of the copper matrix at high temperature, improving the stability of the friction coefficient of the friction material and reducing the amount of wear.

[0033] (2) Mixing: The composite copper powder, iron powder, tin powder, aluminum nitride powder and ferrochrome powder obtained in step (1) are put into a V-type mixer and mixed for 2-4 hours. Flake graphite and hexagonal boron nitride powder are added 10-20 minutes before the end of mixing. The optimal speed of the V-type mixer is 10-20 r / min.

[0034] (3) Cold pressing: The powder mixed in step (2) is placed into a cold pressing mold and cold pressed using a vertical hydraulic press. The pressure is 400-600 MPa and the holding time is 40-60s. The optimal descent rate of the vertical hydraulic press is 10-15 mm / min.

[0035] (4) Sintering: After cold pressing, the sample is placed in a high-temperature high-vacuum hot pressing sintering furnace for sintering. The sintering temperature is 900-1000℃, and the sample is held in a vacuum or argon atmosphere for 2-3 hours. The optimal temperature curve for the sintering process is set as follows: 10-20 min from room temperature to 200℃, hold for 5-10 min; 40-60 min from 200℃ to 800℃, hold for 10-20 min; 10-30 min from 800℃ to 900-1000℃; the sample is held for 2-3 hours, then water-cooled to below 100℃, and then cooled to room temperature with the furnace.

[0036] This invention employs unique material ratios, pressing parameters, and sintering parameters to prepare powder metallurgy friction materials that meet the application requirements through powder metallurgy technology. The preparation process is simple, the performance is reliable, and it is suitable for industrial production.

[0037] Example 1

[0038] A copper-based powder metallurgy friction material containing nitrides comprises the following raw materials in the following mass percentages: 59% composite copper powder, 15% iron powder, 4% tin powder, 9% flake graphite, 1% hexagonal boron nitride powder, 3% aluminum nitride powder, and 9% ferrochrome powder; wherein the copper powder is 200-mesh electrolytic copper powder, the iron powder is 200-mesh reduced iron powder, the high-purity ferrochrome alloy powder and tin powder are both 100-mesh, the flake graphite is 80-mesh, the hexagonal boron nitride powder is 200-mesh, and the aluminum nitride powder is 400-mesh; the composite copper powder is obtained by ball milling copper powder and high-entropy alloy powder FeCoNiCrAl at a mass ratio of 100:1 in a planetary high-energy ball mill.

[0039] A method for preparing a nitride-containing copper-based powder metallurgy friction material includes the following steps:

[0040] First, composite copper powder was prepared: electrolytic copper powder and high-entropy alloy powder FeCoNiCrAl were ball-milled in a planetary high-energy ball mill at a mass ratio of 100:1. The ball mill speed was 200 r / min, the weight ratio of steel balls to powder in the ball mill was 5:1, and the ball milling time was 2 hours. Then, the prepared composite copper powder was mixed with iron powder, tin powder, aluminum nitride powder, and ferrochrome powder in a V-type mixer for 2 hours. Flake graphite and hexagonal boron nitride powder were added 10 minutes before the end of mixing. The mixed powder was then placed in a mold and cold-pressed at 600 MPa to form a blank. Finally, the cold-pressed blank was placed in a high-temperature, high-vacuum hot-pressing sintering furnace, evacuated, and purged with argon gas. It was sintered at 950℃ and held for 3 hours, then water-cooled to below 100℃ and cooled to room temperature in the furnace. The sintered friction material was then removed.

[0041] The density of the sintered friction material was tested and found to be 5.21 g / cm³. 3 The hardness is 25.91 HB. Braking tests were conducted using a Xi'an Shuntong MM3000 friction and wear testing machine at braking speeds of 150 km / h, 200 km / h, 250 km / h, 300 km / h, and 350 km / h. The measured friction coefficients were 0.419, 0.405, 0.403, 0.398, and 0.393, respectively, and the wear amounts were 18.1 mg, 32.5 mg, 47.7 mg, 82.2 mg, and 147.7 mg, respectively.

[0042] Example 2

[0043] A copper-based powder metallurgy friction material containing nitrides comprises the following raw materials in weight percentages: 56% composite copper powder, 16% iron powder, 4% tin powder, 9% flake graphite, 3% hexagonal boron nitride powder, 5% aluminum nitride powder, and 7% ferrochrome powder. In the composite copper powder, the mass ratio of copper powder to high-entropy alloy powder FeCoNiCrAl is 100:3, and the ball milling time is 4 h. The mixture is mixed in a V-type mixer for 3 h, with flake graphite and hexagonal boron nitride powder added 15 min before the end of mixing; the cold pressing pressure is 500 MPa. The remaining preparation methods are as described in Example 1.

[0044] The density of the sintered friction material is 5.17 g / cm³. 3 The hardness is 27.15HB. Braking tests were conducted using a Xi'an Shuntong MM3000 friction and wear testing machine at braking speeds of 150km / h, 200km / h, 250km / h, 300km / h, and 350km / h. The measured friction coefficients were 0.423, 0.421, 0.409, 0.392, and 0.388, respectively, and the wear amounts were 16.3 mg, 26.6 mg, 50.9 mg, 79.4 mg, and 140.1 mg, respectively.

[0045] Example 3

[0046] A nitride-containing copper-based powder metallurgy friction material comprises the following raw materials in the indicated mass percentages: 65% composite copper powder, 12% iron powder, 1% tin powder, 9% flake graphite, 2% hexagonal boron nitride powder, 8% aluminum nitride powder, and 3% ferrochrome powder. The mass ratio of copper powder to high-entropy alloy powder (FeCoNiCrAlCu) in the composite copper powder is 100:2. The ball mill speed is 300 r / min, and the ball milling time is 3 h. The mixture is mixed in a V-type mixer for 4 h, with flake graphite and hexagonal boron nitride powder added 20 min before the end of mixing. Sintering is performed at 980℃ and held for 2 h. Other process conditions are the same as in Example 1.

[0047] The density of the sintered friction material is 5.19 g / cm³. 3 The hardness is 29.83 HB. Braking tests were conducted using a Xi'an Shuntong MM3000 friction and wear testing machine at braking speeds of 150 km / h, 200 km / h, 250 km / h, 300 km / h, and 350 km / h. The measured friction coefficients were 0.412, 0.409, 0.392, 0.394, and 0.383, respectively, and the wear amounts were 19.8 mg, 25.7 mg, 29 mg, 69.7 mg, and 118.4 mg, respectively.

[0048] Example 4

[0049] A nitride-containing copper-based powder metallurgy friction material comprises the following raw materials in the indicated mass percentages: 58% composite copper powder, 15% iron powder, 3% tin powder, 9% flake graphite, 3% hexagonal boron nitride powder, 9% aluminum nitride powder, and 3% ferrochrome powder. The mass ratio of copper powder to high-entropy alloy powder (FeCoNiCrTi) in the composite copper powder is 100:2. The ball mill speed is 250 rpm, the ball milling time is 4 h, the mixture is mixed in a V-type mixer for 4 h, cold-pressed at 400 MPa, sintered at 1000℃ and held for 3 h. Other process conditions are the same as in Example 1.

[0050] The density of the sintered friction material is 5.22 g / cm³. 3 The hardness is 30.47HB. Braking tests were conducted using a Xi'an Shuntong MM3000 friction and wear testing machine at braking speeds of 150km / h, 200km / h, 250km / h, 300km / h, and 350km / h. The measured friction coefficients were 0.428, 0.421, 0.419, 0.411, and 0.402, respectively, and the wear amounts were 21.1 mg, 23.1 mg, 34.6 mg, 57 mg, and 91.1 mg, respectively.

[0051] Example 5

[0052] A nitride-containing copper-based powder metallurgy friction material comprises the following raw materials in the indicated mass percentages: 60% composite copper powder, 15% iron powder, 2% tin powder, 9% flake graphite, 2% hexagonal boron nitride powder, 6% aluminum nitride powder, and 6% ferrochrome powder. The mass ratio of copper powder to 200-mesh Al₂O₃ powder in the composite copper powder is 100:2. The ball mill speed is 350 rpm, mixing is performed in a V-type mixer for 4 hours, cold pressing is applied at 450 MPa, and sintering is carried out at 900°C with a holding time of 2 hours. Other process conditions are the same as in Example 1.

[0053] The density of the sintered friction material is 4.75 g / cm³. 3 The hardness is 30.83HB. Braking tests were conducted using a Xi'an Shuntong MM3000 friction and wear testing machine at braking speeds of 150km / h, 200km / h, 250km / h, 300km / h, and 350km / h. The measured friction coefficients were 0.424, 0.402, 0.397, 0.382, and 0.374, respectively, and the wear amounts were 23.2 mg, 25.9 mg, 31.6 mg, 44 mg, and 88.9 mg, respectively.

[0054] Comparative Example 1

[0055] The difference from Example 4 is that the composite copper powder is replaced with an equal amount of electrolytic copper powder.

[0056] The density of the sintered friction material is 5.19 g / cm³.3 The hardness is 25.17 HB. Braking tests were conducted using a Xi'an Shuntong MM3000 friction and wear testing machine at braking speeds of 150 km / h, 200 km / h, 250 km / h, 300 km / h, and 350 km / h. The measured friction coefficients were 0.378, 0.356, 0.335, 0.317, and 0.309, respectively, and the wear amounts were 23.1 mg, 35.6 mg, 47.1 mg, 114.6 mg, and 219.1 mg, respectively.

[0057] Compared to Example 4, replacing the composite copper powder with an equal amount of electrolytic copper powder resulted in a decrease in the density and hardness of the friction material. Within the braking speed range of 150 km / h to 350 km / h, the material exhibited a lower coefficient of friction and higher wear, with the coefficient of friction decreasing significantly with increasing braking speed, indicating poor stability. This is primarily due to the excellent interfacial bonding and compatibility between the high-entropy alloy powder FeCoNiCrTi and the electrolytic copper matrix. Adding the high-entropy alloy powder FeCoNiCrTi to the electrolytic copper powder via mechanical ball milling forms the composite copper powder, improving the strength, hardness, and high-temperature softening resistance of the copper matrix. Compared to electrolytic copper powder, the composite copper powder possesses higher hardness, wear resistance, and high-temperature softening resistance. Using it as the matrix for friction materials can improve the coefficient of friction, reduce wear rate, and exhibit better stability of the coefficient of friction. Furthermore, the microstructure of the electrolytic copper powder changes after mechanical ball milling, breaking down the dendritic morphology and increasing the material's compression density during the forming process.

[0058] Comparative Example 2

[0059] The difference from Example 3 is that the electrolytic copper powder (63%) and high-entropy alloy powder (FeCoNiCrAlCu) (2%) are not made into composite copper powder, but are directly mixed with other raw materials.

[0060] The density of the sintered friction material is 5.02 g / cm³. 3 The hardness is 27.83 HB. Braking tests were conducted using a Xi'an Shuntong MM3000 friction and wear testing machine at braking speeds of 150 km / h, 200 km / h, 250 km / h, 300 km / h, and 350 km / h. The measured friction coefficients were 0.391, 0.379, 0.352, 0.334, and 0.313, respectively, and the wear amounts were 27.8 mg, 45.7 mg, 69.2 mg, 138.7 mg, and 308.4 mg, respectively.

[0061] Compared to Example 3, when high-entropy alloy powder FeCoNiCrAlCu is directly mixed with other raw materials, the high-entropy alloy powder FeCoNiCrAlCu essentially exists as a friction component and fails to enhance the electrolytic copper matrix. Compared to composite copper powder, electrolytic copper powder has poorer mechanical properties and resistance to high-temperature softening as a matrix, resulting in decreased hardness, lower friction coefficient, and increased wear in the friction material.

[0062] All the above embodiments and comparative examples were tested on a Xi'an Shuntong MM3000 friction and wear testing machine. After the material was sintered, it was cut using a DK7720 CNC wire EDM machine. The cut material was 20mm × 10mm in size, and three pieces were cut from each material. The friction and wear test was conducted on the MM3000 friction and wear testing machine with real-time temperature measurement using thermocouples. The test included five different braking speeds: 150 km / h, 200 km / h, 250 km / h, 300 km / h, and 350 km / h. Ten friction and wear tests were conducted at each braking speed, and the average value of the data was taken. After each braking test, the sample was air-cooled down until the temperature was below 60 ℃. The friction material was then removed, and the wear rate was measured and calculated using a high-precision electronic balance with an accuracy of 0.001 g. The friction material was then reassembled in the friction and wear testing machine, and another set of braking speeds was selected in an increasing order. The above test steps were repeated to obtain the friction coefficient and wear rate at different speeds. This process was repeated until the friction coefficient and wear amount of the friction material at five braking speeds were tested. The hardness of the material was tested using a 320HBS-3000 Brinell hardness tester with an indenter diameter of 10 mm, a load of 500 N, and a holding time of 30 s. The indentation diameter was taken to calculate the hardness value. Each sample was tested 5 times, and the hardness was taken as the average value. The density of the sintered material was measured using the Archimedes displacement method.

[0063] The average coefficients of friction and wear amounts of the friction materials prepared in Examples 1-5 and Comparative Examples 1-2 are as follows: Figure 1 and 2 As shown in the figure, compared with Comparative Examples 1 and 2, Examples 1-5 simultaneously possess a higher coefficient of friction, a lower wear rate, and a more stable coefficient of friction, exhibiting excellent overall tribological performance.

[0064] Figure 3 This is a microstructure diagram of the copper-based powder metallurgy friction material sample prepared in Example 1. Figure 3 As can be seen, the matrix has a good bonding effect with the friction and lubrication components, and the distribution is relatively uniform. The stable structure ensures its excellent performance.

[0065] The above embodiments and comparative examples illustrate the basic principles and features of the present invention. However, the above descriptions are merely preferred embodiments of the present invention and are not limited to these embodiments. Those skilled in the art, inspired by this patent, can make many modifications and improvements without departing from the spirit and scope of the claims, and all of these fall within the protection scope of the present invention.

Claims

1. A copper-based powder metallurgy friction material containing nitrides, characterized in that: The raw materials include the following percentages by mass: 56-65% composite copper powder, 12-16% iron powder, 1-4% tin powder, 9% flake graphite, 1-3% hexagonal boron nitride powder, 3-9% aluminum nitride powder, and 3-9% ferrochrome powder, with the total amount of aluminum nitride powder and ferrochrome powder not exceeding 12%. The composite copper powder is obtained by ball milling copper powder and reinforcing particle powder at a mass ratio of 100:1-3 in a planetary high-energy ball mill. The reinforcing particle powder is a high-entropy alloy powder with a particle size of 400 mesh, and is one of FeCoNiCrAl, FeCoNiCrAlCu, and FeCoNiCrTi. The ball mill speed is 200-350 r / min, the weight ratio of steel balls to powder in the ball mill is 5:1, and the ball milling time is 2-4 h.

2. The nitride-containing copper-based powder metallurgy friction material according to claim 1, characterized in that: The copper powder is 200-mesh electrolytic copper powder, the iron powder is 200-mesh reduced iron powder, the ferrochrome alloy powder and tin powder are both 100-mesh, the flake graphite is 80-mesh, the hexagonal boron nitride powder is 200-mesh, and the aluminum nitride powder is 400-mesh.

3. The method for preparing the nitride-containing copper-based powder metallurgy friction material according to any one of claims 1-2, characterized in that: Includes the following steps: (1) Preparation of composite copper powder: Copper powder and reinforcing particle powder are ball-milled in a planetary high-energy ball mill at a mass ratio of 100:1-3. The rotation speed of the ball mill is 200-350 r / min, the weight ratio of steel balls to powder in the ball mill is 5:1, and the ball milling time is 2-4 h. (2) Mixing: The composite copper powder, iron powder, tin powder, aluminum nitride powder and ferrochrome powder obtained in step (1) are put into a V-type mixer and mixed for 2-4 hours. Flake graphite and hexagonal boron nitride powder are added 10-20 minutes before the end of mixing. (3) Cold pressing: The powder mixed in step (2) is placed into a cold pressing mold and cold pressed using a vertical hydraulic press. The pressure is 400-600 MPa and the holding time is 40-60 s. (4) Sintering: After cold pressing, the sample is placed in a high-temperature high-vacuum hot pressing sintering furnace for sintering. The sintering temperature is 900-1000℃ and the sample is kept in a vacuum or argon atmosphere for 2-3 hours.

4. The method for preparing the nitride-containing copper-based powder metallurgy friction material according to claim 3, characterized in that: In step (2), the rotation speed of the V-type mixer is 10-20 r / min.

5. The method for preparing the nitride-containing copper-based powder metallurgy friction material according to claim 3, characterized in that: In step (3), the descent rate of the vertical hydraulic press during operation is 10-15 mm / min.

6. The method for preparing the nitride-containing copper-based powder metallurgy friction material according to claim 3, characterized in that: The temperature curve for the sintering process in step (4) is set as follows: 10-20 min from room temperature to 200℃, hold for 5-10 min; 40-60 min from 200℃ to 800℃, hold for 10-20 min; 10-30 min from 800℃ to 900-1000℃, hold the sample for 2-3 h, then water cool to below 100℃, and cool to room temperature with the furnace.

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