A Cold Spraying Preparation Process for CuCr-based Contact Coatings

Abstract

This application relates to a cold spraying process, specifically for preparing CuCr-based contact tips. By preheating the powder raw materials, the spraying speed is relatively reduced, the impact on the copper substrate is reduced, its thermal stress and thermal deformation are reduced, and the density of the coating can be ensured without causing an increase in resistance. Adding Ti to the CuCr alloy coating can reduce its welding force, and lanthanum oxide plays a role in dispersion strengthening in the matrix to increase the hardness. Moreover, due to its dispersion distribution, the breakdown points increase, the arc energy per unit area decreases, and the life of the contact tip is significantly improved.

Description

Technical Field

[0001] The present application relates to a cold spraying process, specifically for preparing CuCr-based contact heads. Background Art

[0002] Electrical contacts, also known as contacts or joints, are key components in high- and low-voltage electrical appliances, responsible for connecting and disconnecting currents. They directly affect the reliability and service life of switches and electrical appliances. Therefore, contacts are called the "heart" of electrical appliances. The situation of electrical contacts during actual use is very complex. In addition to mechanical forces and friction, there are also Joule heat, arc burning, and material transfer due to current polarity, etc., all of which will affect the material. This requires the contact head material to have low resistivity and vapor pressure, high thermal conductivity, melting point, boiling point, heat of fusion and heat of sublimation, good thermal stability, large heat capacity, and high electron work function to ensure high arc ignition voltage and low current; stable chemical properties; low and stable contact resistance, good anti-welding property, and good arc erosion resistance.

[0003] Cu-Cr alloys currently dominate the field of vacuum contact materials at home and abroad. Among them, CuCr alloys have become the first choice for contact materials in medium- and high-voltage circuits and small- and medium-sized vacuum switches due to their excellent comprehensive properties. Copper and chromium are immiscible, which easily causes composition segregation and poses great difficulties in the preparation of alloys. Using traditional processes to prepare such alloys, chromium segregation is serious and the structure is coarse. The presence of large-sized Cr phases will increase the resistivity of the material, making it difficult to obtain ideal CuCr alloy contact materials. Cold spraying is to use high-pressure gas to carry powder particles into a high-speed gas flow, generate a supersonic gas-solid two-phase flow through a Laval tube, and the powder particles are accelerated by a supersonic nozzle and collide with the substrate at an extremely high speed in a solid state, and deposit on the surface of the substrate to form a coating through strong plastic deformation. The spraying heating temperature is much lower than its melting point, and there are basically no phenomena such as oxidation, burning loss, and grain growth of the particles; the thermal influence of the coating on the substrate is small, reducing the thermal stress between the coating and the substrate.

[0004] In the present application, a cold spraying process is used to prepare CuCr alloy contact heads, and CuCr contacts with excellent comprehensive properties are obtained by adjusting process parameters and specific components. Summary of the Invention

[0005] A method for preparing a CuCr contact head coating is prepared by using cold spraying technology.

[0006] Using multi-purpose 110 copper with a mass purity of 99.9% as the base material, first sandblast and clean the copper base material. Set the inlet pressure of the sandblasting treatment to 0.7 MPa. After completion, put it into an ethanol solvent and ultrasonically treat it at 60 kHz for 25 min, and then dry it at 60 °C for 4 h.

[0007] Ball mill copper powder with a mass fraction of 85 - 90%, chromium powder with a mass fraction of 5 - 10%, Ti powder with a mass fraction of 3 - 8% and lanthanum oxide powder with a mass fraction of 1 - 2%. The ball-to-material ratio is 8:1. Add absolute ethanol as a dispersant. The ball mill rotation speed is 80 - 100 r / min, and the ball milling time is 8 - 10 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns is obtained.

[0008] Spray the raw material powder on the copper substrate using a cold spraying device. The process parameters of the cold spraying device are: the cold spraying distance is 20 - 25 mm, the spraying pressure is 5 - 7 MPa, the spray gun moving speed is 20 - 25 mm / s, the spraying powder is preheated to 400 - 500 °C, and nitrogen or argon with a purity of 99.99% is used for cold spraying. Finally, a CuCr-based coating is obtained on the copper substrate.

[0009] This application uses cold spraying technology. By preheating the powder raw materials, the spraying speed is relatively reduced, the impact on the copper substrate is reduced, its thermal stress and thermal deformation are reduced, and the density of the coating can be guaranteed without causing an increase in resistance. Adding Ti to the CuCr alloy coating can reduce its welding force. Lanthanum oxide plays a role in dispersion strengthening in the matrix, improving the hardness. And due to its dispersion distribution, the breakdown point increases, the arc energy per unit area decreases, and the life of the contact is significantly improved. Specific embodiments

[0010] Example 1:

[0011] Use multi-purpose 110 copper with a mass purity of 99.9% as the substrate. First, sandblast and clean the copper substrate. Set the inlet pressure of the sandblasting treatment to 0.7 MPa. After completion, put it into an ethanol solvent and ultrasonically treat it at 60 kHz for 25 min, and then dry it at 60 °C for 4 h.

[0012] Ball mill copper powder with a mass fraction of 85%, chromium powder with a mass fraction of 10%, Ti powder with a mass fraction of 3% and lanthanum oxide powder with a mass fraction of 2%. The ball-to-material ratio is 8:1. Add absolute ethanol as a dispersant. The ball mill rotation speed is 100 r / min, and the ball milling time is 8 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns is obtained.

[0013] Spray the raw material powder on the copper substrate using a cold spraying device. The process parameters of the cold spraying device are: the cold spraying distance is 25 mm, the spraying pressure is 7 MPa, the spray gun moving speed is 25 mm / s, the spraying powder is preheated to 400 °C, and nitrogen with a purity of 99.99% is used for cold spraying. Finally, a CuCr-based coating is obtained on the copper substrate.

[0014] Perform performance tests on the obtained samples:

[0015] The hardness test was carried out on an L102MVD Vickers hardness tester. The included angle of the diamond indenter facet was 135°, the applied pressure was 50 N, the holding time was 10 s, and the test temperature was room temperature.

[0016] The conductivity was measured using a sigmacope SMP10 conductivity tester. The test probe was ES40, the measurement frequency was 20 KHz, and the measurement temperature was room temperature. At least 5 measurement points at different positions of the sample were selected for measurement, and the average value was taken as the conductivity of the sample. The unit is the relative conductivity %IACS with the international annealed copper standard conductivity as 100%.

[0017] The fusion welding force test and the contact loss test were carried out using a JF04C contact material tester. The test current was 15 A, the voltage was 18 V, the test interval was 500 ms, the contact spacing was 1 mm, and 10,000 dotting tests were carried out. Record the magnitude of the fusion welding force each time and calculate the average value. Use an electronic balance with a precision of 0.01 mg to measure the mass of the sample before and after the electrical contact performance test respectively. The fusion welding force of the contact material refers to the magnitude of the force required to separate two contacts after they are fused. The fusion welding force is an important parameter in the study of contact materials and can be used to measure the anti-fusion welding performance of electrical contact materials. The evaluation of the anti-fusion welding performance of contact materials is judged according to the magnitude of the fusion welding force value. The smaller the force value, the better the anti-fusion welding performance.

[0018] For the arc energy test, the sample was used as the cathode and a tungsten rod was used as the anode. The tip was a 2-mm cylinder, placed in a closed environment, and argon gas at 1 standard atmosphere was introduced. The DC was adjusted to make the voltage across the load between the anode and the cathode stable at 9 kV. During the test, the cathode sample slowly moved towards the tip of the tungsten rod at a speed of 0.2 mm / min until arc discharge occurred and then stopped. The magnitude of the arc energy can be obtained through the arc burning time and the breakdown current. Arc energy is one of the important parameters of the arc. Generally speaking, the greater the arc energy, the more severely the surface of the electrical contact material is ablated.

[0019] Example 2:

[0020] Using multi-purpose 110 copper with a mass purity of 99.9% as the base material, first, the copper base material was sandblasted and cleaned. The intake pressure of the sandblasting treatment was set at 0.7 MPa. After completion, it was placed in an ethanol solvent and ultrasonically treated at 60 kHz for 25 min, and then dried at 60 °C for 4 h.

[0021] Copper powder with a mass fraction of 98%, chromium powder with a mass fraction of 5%, Ti powder with a mass fraction of 6%, and lanthanum oxide powder with a mass fraction of 1% were ball-milled. The ball-to-material ratio was 8:1. Anhydrous ethanol was added as a dispersant. The ball-milling speed was 90 r / min, and the ball-milling time was 8 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns was obtained.

[0022] The raw material powder was sprayed on the copper substrate using a cold spray device. The process parameters of the cold spray device were as follows: the cold spray distance was 20 mm, the spraying pressure was 5 MPa, the spray gun moving speed was 20 mm / s, the sprayed powder was preheated to 500 °C, and nitrogen with a purity of 99.99% was used for cold spraying. Finally, a CuCr-based coating was obtained on the copper substrate.

[0023] Subsequently, the test was carried out with reference to Example 1.

[0024] Comparative Example 1:

[0025] Using multi-purpose 110 copper with a mass purity of 99.9% as the substrate, the copper substrate was first sandblasted and cleaned. The inlet pressure of the sandblasting treatment was set to 0.7 MPa. After completion, it was placed in an ethanol solvent and ultrasonically treated at 60 kHz for 25 min, and then dried at 60 °C for 4 h.

[0026] Copper powder with a mass fraction of 85%, chromium powder with a mass fraction of 10%, and Ti powder with a mass fraction of 5% were ball milled with a ball-to-material ratio of 8:1. Anhydrous ethanol was added as a dispersant, the ball milling speed was 100 r / min, and the ball milling time was 8 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns was obtained.

[0027] The raw material powder was sprayed on the copper substrate using a cold spray device. The process parameters of the cold spray device were as follows: the cold spray distance was 25 mm, the spraying pressure was 7 MPa, the spray gun moving speed was 25 mm / s, the sprayed powder was preheated to 400 °C, and nitrogen with a purity of 99.99% was used for cold spraying. Finally, a CuCr-based coating was obtained on the copper substrate.

[0028] Subsequently, the test was carried out with reference to Example 1.

[0029] Comparative Example 2:

[0030] Using multi-purpose 110 copper with a mass purity of 99.9% as the substrate, the copper substrate was first sandblasted and cleaned. The inlet pressure of the sandblasting treatment was set to 0.7 MPa. After completion, it was placed in an ethanol solvent and ultrasonically treated at 60 kHz for 25 min, and then dried at 60 °C for 4 h.

[0031] Copper powder with a mass fraction of 87%, chromium powder with a mass fraction of 10%, Ti powder with a mass fraction of 1%, and lanthanum oxide powder with a mass fraction of 2% were ball milled with a ball-to-material ratio of 8:1. Anhydrous ethanol was added as a dispersant, the ball milling speed was 100 r / min, and the ball milling time was 8 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns was obtained.

[0032] The raw material powder is sprayed on the copper substrate using a cold spraying device. The process parameters of the cold spraying device are as follows: the cold spraying distance is 25 mm, the spraying pressure is 7 MPa, the moving speed of the spray gun is 25 mm / s, the spraying powder is preheated to 400 °C, and nitrogen with a purity of 99.99% is used for cold spraying. Finally, a CuCr-based coating is obtained on the copper substrate.

[0033] Subsequently, the test is carried out with reference to Example 1.

[0034] Comparative Example 3:

[0035] Using multi-purpose 110 copper with a mass purity of 99.9% as the substrate, the copper substrate is first sandblasted and cleaned. The inlet pressure of the sandblasting treatment is set to 0.7 MPa. After completion, it is placed in an ethanol solvent and ultrasonically treated at 60 kHz for 25 min, and then dried at 60 °C for 4 h.

[0036] Copper powder with a mass fraction of 85%, chromium powder with a mass fraction of 5%, Ti powder with a mass fraction of 8%, and lanthanum oxide powder with a mass fraction of 2% are ball-milled with a ball-to-material ratio of 8:1. Anhydrous ethanol is added as a dispersant, the ball-milling speed is 100 r / min, and the ball-milling time is 8 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns is obtained.

[0037] The raw material powder is sprayed on the copper substrate using a cold spraying device. The process parameters of the cold spraying device are as follows: the cold spraying distance is 25 mm, the spraying pressure is 7 MPa, the moving speed of the spray gun is 25 mm / s, the spraying powder is preheated to 400 °C, and nitrogen with a purity of 99.99% is used for cold spraying. Finally, a CuCr-based coating is obtained on the copper substrate.

[0038] Subsequently, the test is carried out with reference to Example 1.

[0039] Comparative Example 4:

[0040] Using multi-purpose 110 copper with a mass purity of 99.9% as the substrate, the copper substrate is first sandblasted and cleaned. The inlet pressure of the sandblasting treatment is set to 0.7 MPa. After completion, it is placed in an ethanol solvent and ultrasonically treated at 60 kHz for 25 min, and then dried at 60 °C for 4 h.

[0041] Copper powder with a mass fraction of 85%, chromium powder with a mass fraction of 10%, Ti powder with a mass fraction of 3%, and lanthanum oxide powder with a mass fraction of 2% are ball-milled with a ball-to-material ratio of 8:1. Anhydrous ethanol is added as a dispersant, the ball-milling speed is 100 r / min, and the ball-milling time is 8 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns is obtained.

[0042] The raw material powder is sprayed on the copper substrate using a cold spraying device. The process parameters of the cold spraying device are as follows: the cold spraying distance is 25 mm, the spraying pressure is 7 MPa, the moving speed of the spray gun is 25 mm / s, the spraying powder is preheated to 300 °C, and nitrogen with a purity of 99.99% is used for cold spraying. Finally, a CuCr-based coating is obtained on the copper substrate.

[0043] Subsequently, the test is carried out with reference to Example 1.

[0044] Comparative Example 5:

[0045] Using multi-purpose 110 copper with a mass purity of 99.9% as the substrate, the copper substrate is first sandblasted and cleaned. The inlet pressure of the sandblasting treatment is set to 0.7 MPa. After completion, it is placed in an ethanol solvent and ultrasonically treated at 60 kHz for 25 min, and then dried at 60 °C for 4 h.

[0046] Copper powder with a mass fraction of 85%, chromium powder with a mass fraction of 10%, Ti powder with a mass fraction of 3%, and lanthanum oxide powder with a mass fraction of 2% are ball-milled. The ball-to-material ratio is 8:1. Anhydrous ethanol is added as a dispersant. The ball-milling speed is 100 r / min, and the ball-milling time is 8 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns is obtained.

[0047] The raw material powder is sprayed on the copper substrate using a cold spraying device. The process parameters of the cold spraying device are as follows: the cold spraying distance is 25 mm, the spraying pressure is 7 MPa, the moving speed of the spray gun is 25 mm / s, the spraying powder is preheated to 600 °C, and nitrogen with a purity of 99.99% is used for cold spraying. Finally, a CuCr-based coating is obtained on the copper substrate.

[0048] Subsequently, the test is carried out with reference to Example 1.

[0049] Comparative Example 6:

[0050] Using multi-purpose 110 copper with a mass purity of 99.9% as the substrate, the copper substrate is first sandblasted and cleaned. The inlet pressure of the sandblasting treatment is set to 0.7 MPa. After completion, it is placed in an ethanol solvent and ultrasonically treated at 60 kHz for 25 min, and then dried at 60 °C for 4 h.

[0051] Copper powder with a mass fraction of 85%, chromium powder with a mass fraction of 10%, Ti powder with a mass fraction of 3%, and lanthanum oxide powder with a mass fraction of 2% are ball-milled. The ball-to-material ratio is 8:1. Anhydrous ethanol is added as a dispersant. The ball-milling speed is 100 r / min, and the ball-milling time is 8 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns is obtained.

[0052] The raw material powder is sprayed on the copper substrate using a cold spray equipment. The process parameters of the cold spray equipment are as follows: the cold spray distance is 25 mm, the spraying pressure is 4 MPa, the moving speed of the spray gun is 25 mm / s, the spraying powder is preheated to 400 °C, and nitrogen with a purity of 99.99% is used for cold spraying. Finally, a CuCr-based coating is obtained on the copper substrate.

[0053] Subsequently, the tests are carried out with reference to Example 1.

[0054] Comparative Example 7:

[0055] Using multi-purpose 110 copper with a mass purity of 99.9% as the substrate, the copper substrate is first sandblasted and cleaned. The inlet pressure of the sandblasting treatment is set to 0.7 MPa. After completion, it is placed in an ethanol solvent and ultrasonically treated at 60 kHz for 25 min, and then dried at 60 °C for 4 h.

[0056] Copper powder with a mass fraction of 85%, chromium powder with a mass fraction of 10%, Ti powder with a mass fraction of 3%, and lanthanum oxide powder with a mass fraction of 2% are ball-milled. The ball-to-material ratio is 8:1. Anhydrous ethanol is added as a dispersant. The ball-milling speed is 100 r / min, and the ball-milling time is 8 h. After drying and screening, raw material powder with a particle size of 30 - 50 microns is obtained.

[0057] The raw material powder is sprayed on the copper substrate using a cold spray equipment. The process parameters of the cold spray equipment are as follows: the cold spray distance is 25 mm, the spraying pressure is 8 MPa, the moving speed of the spray gun is 25 mm / s, the spraying powder is preheated to 400 °C, and nitrogen with a purity of 99.99% is used for cold spraying. Finally, a CuCr-based coating is obtained on the copper substrate.

[0058] Subsequently, the tests are carried out with reference to Example 1.

[0059] Table 1 Test Results

[0060]

[0061]

[0062] In Comparative Example 1, lanthanum oxide powder was not added, resulting in a decrease in the final hardness and an increase in the arc energy. In Comparative Example 2, the addition of a lower Ti content did not effectively reduce the welding force. In Comparative Example 3, the Ti was excessive, resulting in deterioration of the final electrical conductivity. In Comparative Examples 4 - 7, the spraying parameters were adjusted. The spraying process will affect the microstructure and morphology of the final coating. If the coating voids, cracks, and voids increase significantly, the uniformity of the coating microstructure will deteriorate, which will affect the final comprehensive performance. Excessive spraying energy input will also lead to deterioration of the substrate and even the generation of voids in the coating.

Claims

1. A cold spraying preparation process for a CuCr-based contact coating, characterized in that: First, the copper substrate was sandblasted and cleaned in water and ethanol and ultrasonically treated at 60kHz for 25min; Ball milling 85-90% copper powder, 5-10% chromium powder, 3-8% Ti powder and 1-2% lanthanum oxide powder at a ball milling speed of 80-100 r / min for 8-10 h, drying and sieving to obtain a raw material powder with a particle size of 30-50 μm; The raw material powder is sprayed on the copper substrate by cold spraying equipment. The process parameters of the cold spraying equipment are as follows: the cold spraying distance is 20-25 mm, the spraying pressure is 5-7 MPa, the spray gun moving speed is 20-25 mm / s, the spraying powder is preheated to 400-500° C., and the purity of nitrogen or argon used for cold spraying is 99.99%; Multipurpose 110 copper with a purity of 99.9% is used as the base material.

2. The preparation process according to claim 1, characterized in that: The air inlet pressure for sandblasting is 0.7MPa.

3. The preparation process according to claim 1, characterized in that: After cleaning, dry at 60°C for 4 h.

4. The preparation process according to claim 1, characterized in that: The ball-to-material ratio in ball milling is 8:

1.

5. The preparation process according to claim 1, characterized in that: Anhydrous ethanol was added as a dispersant during the ball milling process.

6. A contact manufactured by the manufacturing process as claimed in any one of claims 1 to 5.

7. The contact according to claim 6, characterized in that Multipurpose 110 copper with a purity of 99.9% is used as the base material.

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