Preparation method of nickel-silver-tungsten composite electric contact material, electric contact material and electric contact

Abstract

This invention provides a method for preparing nickel-silver-tungsten composite electrical contact materials, the electrical contact materials themselves, and electrical contacts. The method involves chemically plating silver and nickel metal nanoparticles onto the surface of tungsten powder in a layered manner, resulting in tungsten powder with a tightly packed core-shell structure of silver-nickel bimetallic layers. Then, different mass fractions of the core-shell tungsten powder and silver powder are uniformly mixed using solution ball milling. Finally, the mixed powder is crystallized and solidified using electro-spark plasma sintering technology to obtain a series of nickel-silver-tungsten composite electrical contact materials. The nickel-silver-tungsten composite electrical contact materials provided by this invention exhibit good compressive strength, excellent ductility, and superior resistance to arc erosion.

Description

Technical Field

[0001] This invention belongs to the field of low-voltage electrical contact technology, and in particular relates to a method for preparing a nickel-silver-tungsten composite electrical contact material, the electrical contact material, and the electrical contact. Background Technology

[0002] Electrical contact materials are widely used in electronic and electrical systems, such as power relays, electrical switches, circuit breakers, and fixed electrical connectors. They play a fundamental role in controlling the current flow and load carrying in circuits, and are crucial for ensuring the efficiency and reliability of electrical equipment and electronic products. As the heart of electrical contacts, these materials must possess high electrical and thermal conductivity, good resistance to arc erosion, excellent processing performance, and good mechanical properties. To meet these performance requirements, electrical contact materials are typically composite materials consisting of a metal matrix (Ag or Cu) reinforced with one or more reinforcing materials. The metal provides electrical and thermal conductivity, while the reinforcing materials provide strength, hardness, and resistance to arc erosion. Compared to copper-based composite materials mainly used in high-voltage electrical contacts, silver-based composite electrical contact materials exhibit higher electrical and thermal conductivity at the same metal mass fraction, benefiting from the inherent properties of silver. Therefore, they are more advantageous in medium- and low-voltage electrical applications, especially in emerging microelectronic devices and integrated circuits. To date, numerous silver-based contact materials have been developed, primarily using ceramics (CdO, SnO2, CuO, Ti3SiC2, Ti3AlC2) and metals (W, Ni, Cu, Ti) as reinforcing materials. While ceramics possess high strength, high modulus, and high melting point, their lack of readily excitable free electrons and efficient dislocation movement results in less than ideal conductivity and toughness in composite materials. Metals, due to the presence of metallic bonds, typically exhibit high conductivity and superior fracture toughness. Tungsten, as one of the metals with excellent resistance to arc erosion, plays a crucial role in enhancing the hardness, strength, and service life of silver-based composite contact materials.

[0003] The mechanical and structural properties of silver-based composite electrical contact materials mainly depend on the structural characteristics of the composite material and the uniformity of the reinforcement dispersion. To address the drawbacks of W-Ag composites caused by significant differences in physical properties and incompatibility (such as difficulty in ensuring structural uniformity and the formation of poorly conductive tungsten oxides during arc erosion), many improvement strategies have been proposed. The relevant technologies retrieved here mainly fall into three categories: First, structural modification, which improves the structure of the initial W powder through chemical reactions or related processes, such as the common core-shell structure, utilizing the special structural characteristics of the powder to promote the structural uniformity of the sintered material; second, component modification, which mainly introduces other elements into the composite system during powder preparation or sintering, commonly including elemental silver, copper, nickel, and ceramic phase materials such as tungsten carbide, using dopants as lubricants or metal binders to enhance the indirect wettability of the tungsten and silver phases, thereby improving the overall comprehensive performance of the material; third, modifying the material's thermal processing technology, with common thermal processing technologies for silver-tungsten composite contact materials being hot pressing sintering and metal infiltration technology. To ensure the structural compactness of silver-tungsten composite materials, hot pressing sintering technology typically requires high pressure and processing temperatures below the melting point of silver (960°C). Metal infiltration technology, on the other hand, requires a step-by-step process: first, tungsten powder is sintered into a tungsten framework under high temperature and pressure, and then liquid silver is infiltrated into the voids of the tungsten framework to obtain a bulk material.

[0004] Although the above three related technologies can improve the defects of poor two-phase wettability and non-uniform structure of silver-tungsten composite contact materials to a certain extent, the inventors found that the above related technologies have at least the following technical problems: (1) Structure and component modification is beneficial to improve the structural advantages of single-phase powder particles, but the uniformity of two-phase powder mixing needs to be further improved; (2) Hot pressing sintering technology often needs to be carried out at high temperature and high pressure for several hours, and the preparation process of metal melting and infiltration technology is relatively complicated and the preparation cost is high. It is difficult to ensure that the electrical conductivity of composite materials is at a relatively high level.

[0005] Therefore, developing high-performance new silver-based composite materials for the electrical field and corresponding preparation processes is of great significance for conserving precious metal resources, improving the properties of contact materials such as conductivity, strength and resistance to arc erosion, and enhancing product quality stability. Summary of the Invention

[0006] The first objective of this invention is to provide a method for preparing a nickel-silver-tungsten composite electrical contact material, in order to at least partially solve the aforementioned technical problems.

[0007] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution:

[0008] A method for preparing a nickel-silver-tungsten composite electrical contact material includes the following steps:

[0009] S1. Chemical plating is performed under mild conditions in an aqueous solution system:

[0010] A layer of silver nanoparticles is coated on the surface of tungsten powder to obtain tungsten powder with a single layer of metallic silver coating;

[0011] A layer of nickel nanoparticles was coated onto the surface of the obtained silver-coated tungsten powder to obtain silver-nickel bimetallic coated tungsten powder.

[0012] S2. Using solution ball milling, tungsten powder coated with a silver-nickel bimetallic layer is mixed with silver powder using anhydrous ethanol as a dispersant to obtain a composite powder.

[0013] S3. The composite powder is sintered and solidified under high temperature, high pressure and vacuum conditions using electric spark plasma sintering to obtain nickel-silver-tungsten composite electrical contact material.

[0014] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0015] As a preferred technical solution of the present invention: before step S1, tungsten powder is sensitized by hydrochloric acid and stannous chloride dihydrate aqueous solution.

[0016] As a preferred technical solution of the present invention: In step S1, silver nitrate is used as the silver source, ammonia water as the complexing agent, polyvinylpyrrolidone as the dispersant, sodium hydroxide aqueous solution as the pH adjuster, and glucose as the reducing agent to deposit a layer of silver nanoparticles on the surface of tungsten powder to obtain a single layer of metallic silver coated tungsten powder.

[0017] As a preferred embodiment of the present invention: the amount of silver nitrate is 0.85-1.7g, the amount of ammonia water is 2-4mL, the amount of polyvinylpyrrolidone is 0.1-0.2g, the amount of glucose is 0.35-0.7g, the mass of tungsten powder is 2-10g, and the pH value of the solution is between 11 and 11.5.

[0018] The reaction water bath temperature was 40℃, and the magnetic stirring speed was 500 rpm.

[0019] As a preferred technical solution of the present invention: In step S1, nickel sulfate hexahydrate is used as the nickel source, sodium pyrophosphate as the complexing agent, ammonia as the pH adjuster, and dimethylamine borane as the reducing agent. A layer of nickel nanoparticles is then plated on the surface of the tungsten powder coated with a single layer of metallic silver to obtain tungsten powder coated with a silver-nickel bimetallic layer.

[0020] As a preferred embodiment of the present invention: the amount of nickel sulfate hexahydrate is 5-6g, the amount of sodium pyrophosphate is 10-12.5g, the amount of ammonia water is 8-10mL, the amount of dimethylaminoborane is 0.3-0.4g, and the mass of tungsten powder coated with a single layer of metallic silver is 10.5-21.0g.

[0021] The reaction water bath temperature was 25℃, and the magnetic stirring speed was 600 rpm.

[0022] As a preferred technical solution of the present invention: in step S1

[0023] After the reaction is complete, the tungsten powder coated with a single layer of metallic silver needs to be filtered, washed with water and dried under vacuum.

[0024] After the reaction is complete, the silver-nickel bimetallic coated tungsten powder needs to be filtered, washed with water and dried under vacuum.

[0025] As a preferred technical solution of the present invention: in step S1, the vacuum drying temperature is 40°C and the time is 8 hours.

[0026] As a preferred technical solution of the present invention: in step S2

[0027] The ratio of the total mass of tungsten powder and silver powder coated with a silver-nickel bimetallic layer to the mass of the ball milling media is 1:10;

[0028] The ratio of the total mass of tungsten powder and silver powder coated with a silver-nickel bimetallic layer to the mass of anhydrous ethanol is 1:4;

[0029] The ball mill rotated at 250 rpm for 40 minutes.

[0030] As a preferred technical solution of the present invention: In step S2, after ball milling, the mixture is filtered, washed three times with 95% ethanol, and vacuum dried at 40°C for 12 hours.

[0031] As a preferred technical solution of the present invention: in step S3, a graphite mold with an inner diameter of 15mm is used; the processing temperature is 700-800℃, the applied pressure is 40MPa, and the heat preservation time is 10 minutes.

[0032] The second objective of this invention is to provide a nickel-silver-tungsten composite electrical contact material prepared by the preparation method described above.

[0033] Another objective of this invention is to provide electrical contacts prepared from the nickel-silver-tungsten composite electrical contact material as described above.

[0034] This invention provides a method for preparing a nickel-silver-tungsten composite electrical contact material, the electrical contact material itself, and an electrical contact. The method involves chemically plating silver and nickel metal nanoparticles onto the surface of tungsten powder through a layered coating process, resulting in tungsten powder with a tightly encapsulated core-shell structure of silver-nickel bimetallic layers. Then, different mass fractions of the core-shell tungsten powder and silver powder are uniformly mixed using solution ball milling. Finally, the mixed powder is crystallized and solidified using electro-spark plasma sintering technology to obtain a series of nickel-silver-tungsten composite electrical contact materials. The nickel-silver-tungsten composite electrical contact materials provided by this invention exhibit good compressive strength, excellent ductility, and superior resistance to arc erosion. Utilizing the high work function of elemental nickel, electrons are preferentially emitted during arc erosion, protecting the encapsulated tungsten framework from oxidation by the arc and the resulting oxidation of tungsten oxides under the influence of oxygen in the air, which reduces the material's conductivity and increases temperature rise. Furthermore, the outer nickel metal acts as a metal binder during sintering, reducing the internal microporosity of the nickel-silver-tungsten composite electrical contact material and improving its structural uniformity and mechanical strength. Attached Figure Description

[0035] Figure 1 Field emission scanning electron microscope (FESEM) images of tungsten powder coated with metal nanoparticles, from top to bottom: W@Ag, W@Ag@Cu, and W@Ag@Ni particles.

[0036] Figure 2 XRD patterns of tungsten powder coated with the prepared bimetallic nanoparticles (W@Ag@Cu and W@Ag@Ni).

[0037] Figure 3 The image shows the XRD pattern of the prepared silver-tungsten composite contact material, where (b) is an enlarged view of the area within the black dashed box in (a).

[0038] Figure 4 The value is the Vickers hardness of the prepared silver-tungsten composite contact material.

[0039] Figure 5 The stress-strain curves for the compression test of the prepared silver-tungsten composite contact material are shown.

[0040] Figure 6 The diagram shows the arc erosion resistance of the prepared silver-tungsten composite contact material. Detailed Implementation

[0041] A method for preparing a silver-tungsten composite contact material includes the following steps:

[0042] 1) In an aqueous solution, polyvinylpyrrolidone, silver nitrate, and ammonia (AR) were dissolved in deionized water. Then, under water bath heating conditions, the silver ammonia solution was slowly added to an aqueous solution of glucose containing tungsten powder while stirring. The reaction was carried out for about 30 minutes. After standing for a period of time, the mixture was vacuum filtered, washed, and vacuum dried to obtain tungsten powder (W@Ag) coated with a single layer of silver nanoparticles. This is used as a control experiment in the following text and is also the basis for the synthesis of silver-nickel bimetallic coated tungsten powder.

[0043] 2) In an aqueous solution, 2,2'-bipyridine, disodium ethylenediaminetetraacetate dihydrate, potassium sodium tartrate tetrahydrate, copper sulfate pentahydrate, and flake sodium hydroxide were added to deionized water, respectively. Then, the product W@Ag powder from step 1 was added. Standard formaldehyde aqueous solution was slowly added while heating in a water bath and stirring. The reaction was carried out for about 40 minutes. After standing for a period of time, the mixture was vacuum filtered, washed, and vacuum dried to obtain tungsten powder (W@Ag@Cu) with double-layer coating of nano-copper and silver particles. This is used as a control experiment below.

[0044] 3) In an aqueous solution, sodium pyrophosphate, nickel sulfate hexahydrate and ammonia were dissolved in deionized water, and then the product W@Ag powder from step 1 was added. Dimethylaminoborane was added while heating in a water bath and stirring. The reaction was carried out for about 60 minutes. After standing for a period of time, the mixture was vacuum filtered, washed and vacuum dried to obtain tungsten powder (W@Ag@Ni) coated with nano-nickel and silver particles.

[0045] 4) Weigh the tungsten powder coated with metal nanoparticles obtained by the chemical plating method in steps 1, 2 and 3 above and silver powder in a certain proportion, add them to a stainless steel ball mill jar, add balls and anhydrous ethanol, and ball mill. After the process is completed, let it stand for a period of time, then vacuum filter, wash and vacuum dry to obtain a uniformly mixed composite powder of silver and tungsten powder coated with metal nanoparticles.

[0046] 5) The uniformly mixed silver and tungsten powder composite powder coated with metal nanoparticles obtained in step 4 is placed in a graphite mold and sintered using an electric spark plasma sintering method to obtain a series of silver-tungsten composite contact materials (W@Ag / Ag-MC-ECMs, W@Ag@Cu / Ag-MC-ECMs, W@Ag@Ni / Ag-MC-ECMs).

[0047] In step 1: the amount of deionized water in the silver ammonia solution is 200-400 mL, the amount of silver nitrate is 0.85-1.7 g, the amount of polyvinylpyrrolidone is 0.1-0.2 g, and the amount of ammonia water is 2-4 mL; the mass of tungsten powder added to the glucose solution is 2-10 g; the amount of deionized water in the glucose solution is 300-600 mL, the amount of glucose is 0.35-0.7 g, and the pH value of the solution is between 11 and 11.5; the silver ammonia solution is slowly added over a period of 2-10 minutes; the specific reaction conditions are: water bath temperature of 40℃, magnetic stirring speed of 500 rpm; the filter residue is washed three times with deionized water during vacuum filtration; and the vacuum drying temperature is 40℃ for 8 hours.

[0048] In step 2: the amount of deionized water used in the solution is 500-1000 mL, the amount of 2,2'-bipyridine is 4-8 mg, the amount of disodium ethylenediaminetetraacetate dihydrate is 5-11 g, the amount of potassium sodium tartrate tetrahydrate is 1-5 g, the amount of copper sulfate pentahydrate is 4-8 g, and the amount of sodium hydroxide is 2-5 g, and the pH value of the solution is between 12 and 13; the mass of W@Ag powder added to the solution is 5-12 g; the amount of formaldehyde standard solution is 2-7 mL; the specific reaction conditions are: water bath temperature is 40℃, magnetic stirring speed is 500 rpm; the filter residue is washed 3 times with deionized water in the vacuum filtration stage; the vacuum drying temperature is 40℃, and the drying time is 8 h.

[0049] In step 3: the amount of deionized water in the nickel pyrophosphate ion complex solution is 200-250 mL, the amount of sodium pyrophosphate is 10-12.5 g, the amount of nickel sulfate hexahydrate is 5-6 g, and the amount of ammonia is 8-10 mL; the mass of W@Ag powder added to the nickel pyrophosphate ion complex solution is 10-12 g; the amount of dimethylaminoborane is 0.3-0.4 g; the specific reaction conditions are: water bath temperature is 25℃, magnetic stirring speed is 600 rpm; the filter residue is washed 3 times with deionized water in the vacuum filtration stage; the vacuum drying temperature is 40℃, and the drying time is 8 h.

[0050] In step 4: the amount of tungsten powder coated with the metal nanoparticle layer is 24-32g, and the amount of silver powder is 3-11g; in ball milling, the powder mass: ball mass = 1:10, and the powder mass: anhydrous ethanol mass = 1:4; the ball milling speed is 250rpm, and the time is 40 minutes; in the vacuum filtration stage, the filter residue is washed 3 times with 95% ethanol; the vacuum drying temperature is 40℃, and the drying time is 8h.

[0051] In step 5: the inner diameter of the graphite mold is 15mm; the processing temperature is 700-800℃; the applied pressure is 40MPa; and the holding time is 10 minutes.

[0052] The present invention will now be described in further detail with reference to specific embodiments.

[0053] Example 1

[0054] In an aqueous solution system, 0.1 g (0.2 g / L) of polyvinylpyrrolidone (K60), 0.85 g (1.7 g / L) of silver nitrate, and 2 mL (4 mL / L) of ammonia were added sequentially to a beaker containing 200 mL of deionized water to prepare a silver ammonia solution. 0.35 g (0.7 g / L) of glucose was added to a round-bottom flask containing 300 mL of deionized water, followed by 10 g of tungsten powder. The mixture was then sonicated for 10 minutes. The 200 mL silver ammonia solution was then slowly added over 5 minutes in a 40°C water bath at 500 rpm. After reacting for approximately 30 minutes, the mixture was allowed to stand for a period of time, followed by vacuum filtration, washing, and vacuum drying to obtain tungsten powder (W@Ag) coated with a layer of nano-silver particles.

[0055] Field emission scanning electron microscopy was used to test the tungsten powder (W@Ag) coated with the obtained silver nanoparticle layer. The results are as follows: Figure 1 As shown in a and b, the surface of the tungsten particles is uniformly coated with a layer of spherical silver particles with a size of 20-50 nm.

[0056] Example 2

[0057] In an aqueous solution system, 4 mg (8 mg / L) of 2,2'-bipyridine, 5.5 g (11 g / L) of disodium ethylenediaminetetraacetate dihydrate, 1.25 g (2.5 g / L) of potassium sodium tartrate tetrahydrate, 4 g (8 g / L) of copper sulfate pentahydrate, and 4 g (8 g / L) of flake sodium hydroxide were added sequentially to a beaker containing 500 mL of deionized water. 10.5 g of W@Ag powder was then added, followed by ultrasonic treatment for 10 minutes. Then, 5 mL (10 mL / L) of formaldehyde standard solution was added under 40°C water bath conditions at 500 rpm. After reacting for 40 minutes, the mixture was allowed to stand for a period of time, followed by vacuum filtration, washing, and vacuum drying to obtain tungsten powder (W@Ag@Cu) coated with silver and copper nanoparticles.

[0058] Field emission scanning electron microscopy was performed on the tungsten powder (W@Ag@Cu) coated with the obtained silver and copper nanoparticle layers. The results are as follows: Figure 1 As shown in c and d, the surface of the W@Ag particles is covered by a layer of tetrahedral scale-like copper particles.

[0059] Meanwhile, XRD tests were performed on the tungsten powder (W@Ag@Cu) coated with the obtained silver and copper nanoparticle layers, and the results are as follows. Figure 2 As shown, only the characteristic peaks of tungsten, silver, and copper are displayed, with no other impurities.

[0060] Example 3

[0061] In an aqueous solution system, 10g of sodium pyrophosphate (50g / L), 5g of nickel sulfate hexahydrate (25g / L), and 8.5mL of ammonia (42.5mL / L) were added sequentially to a beaker containing 200mL of deionized water. Then, 10.5g of W@Ag powder was added and sonicated for 10 minutes. Next, 0.3g of dimethylaminoborane (1.5g / L) was added under the condition of 25℃ water bath and 600rpm. After reacting for 60 minutes, the mixture was allowed to stand for a period of time, and then vacuum filtered, washed, and vacuum dried to obtain tungsten powder (W@Ag@Ni) coated with nano-silver and nickel particles.

[0062] Field emission scanning electron microscopy was performed on the tungsten powder (W@Ag@Ni) coated with the obtained silver and nickel nanoparticle layers. The results are as follows: Figure 1 As shown in e and f, the surface of the W@Ag particles is coated with a layer of spherical nickel particles.

[0063] Meanwhile, XRD tests were performed on the tungsten powder (W@Ag@Ni) coated with the obtained silver and nickel nanoparticle layers, and the results are as follows. Figure 2 As shown, only the characteristic peaks of tungsten, silver, and nickel are displayed, with no other impurities.

[0064] Example 4

[0065] W@Ag@Ni powder and Ag powder were fed into a solution ball mill at a silver powder mass ratio of 30 wt.%, with W@Ag@Ni and Ag powders weighing 24.5 g and 10.5 g respectively. The powder-to-steel-ball mass ratio was 1:10, and the powder-to-anhydrous ethanol mass ratio was 1:4. After ball milling at 250 rpm for 40 minutes, the mixture was allowed to stand for a period of time, then filtered, washed, and vacuum dried to obtain a homogeneous W@Ag@Ni / Ag composite powder. 30 g of the composite powder was then poured into a graphite mold with an inner diameter of 15 mm and sintered in a vacuum atmosphere at 750℃ and 40 MPa with a heating rate of 100℃ / min for 10 minutes using electrical discharge plasma sintering technology. The resulting product was then cooled to room temperature in the furnace to obtain W@Ag@Ni / Ag-MC-ECMs. Replacing W@Ag@Ni powder with W@Ag or W@Ag@Cu powder can prepare W@Ag / Ag-MC-ECMs and W@Ag@Cu / Ag-MC-ECMs.

[0066] The XRD test results of the obtained W@Ag@Ni / Ag-MC-ECMs, W@Ag / Ag-MC-ECMs and W@Ag@Cu / Ag-MC-ECMs are as follows: Figure 3As shown, W@Ag@Ni / Ag-MC-ECMs contain only characteristic peaks of tungsten, silver, and nickel, with no other impurities. W@Ag / Ag-MC-ECMs contain only W and Ag characteristics; due to the dissolution of the Cu-Ag eutectic phase at 750℃ to form a solid solution, the characteristic peaks of silver at 38.2° (111) and 44.2° (200) in the XRD pattern of W@Ag@Cu / Ag-MC-ECMs shift to higher angles.

[0067] Example 5

[0068] By varying the mass percentage of the powder, a series of silver-tungsten composite contact materials can be prepared. The mechanical properties of these materials were investigated. The silver-tungsten composite contact materials were cut into 10×10×5mm cuboids using wire cutting, then resin-mounted at 156℃. After being successively polished with 600-grit, 1000-grit, and 2000-grit sandpaper, they were polished using diamond polishing paste on a polishing machine. The Vickers hardness of the material was tested after applying a 500g load for 15 seconds.

[0069] from Figure 4 It is known that when the silver content is 30 wt.%, the Vickers hardness of W@Ag / Ag-MC-ECMs, W@Ag@Cu / Ag-MC-ECMs, and W@Ag@Ni / Ag-MC-ECMs are 160 HV, 188 HV, and 130 HV, respectively. Compared with W@Ag / Ag-MC-ECMs, W@Ag@Cu / Ag-MC-ECMs exhibits a higher Vickers hardness, mainly due to the formation of a uniform Cu-Ag solid solution. This is because the Cu-Ag solid solution not only acts as an intergranular lubricant, enhancing the uniformity of the composite structure, but also generates lattice mismatches, causing a hardening transformation between grains and inhibiting dislocation and slip deformation. However, W@Ag@Ni / Ag-MC-ECMs did not exhibit the same reinforcing effect as W@Ag@Cu / Ag-MC-ECMs. This can be explained by a grain coarsening mechanism. Because there are no effective interfacial bonds and strengthening effects, the introduction of the bimetallic layer increases the particle size of W@Ag@Ni particles with a dual core-shell structure, reduces the density of grain boundaries inside the composite material, and thus reduces the hardness strengthening effect of the material.

[0070] A cylinder with a diameter of 5 × 10 mm was subjected to a compression test at a compression rate of 0.01 mm / min using an electronic universal testing machine. Figure 5The results show that when the silver content is 30 wt.%, the compressive strength and fracture deformation rate of W@Ag / Ag-MC-ECMs, W@Ag@Cu / Ag-MC-ECMs, and W@Ag@Ni / Ag-MC-ECMs are 303 MPa, 590 MPa, and 598 MPa, and 8.3%, 23.4%, and 22.1%, respectively. For W@Ag@Cu / Ag-MC-ECMs, the solid solution effect indicates that the lattice mismatch between the copper solute and the silver matrix leads to lattice deformation; the interaction with the surrounding elastic stress field generates stress that hinders dislocation movement, significantly increasing the yield stress of the composite material. When Ni is uniformly distributed and acts as a metallic binder, it improves the interfacial bonding, reduces the porosity inside the bulk composite material, and significantly inhibits the propagation of internal microcracks and micropores caused by load-induced microcracks, resulting in a comprehensive improvement in the strength and toughness of W@Ag@Ni / Ag-MC-ECMs.

[0071] Example 6

[0072] The arc erosion resistance of the silver-tungsten composite contact material prepared above was investigated. Rivet-shaped composite silver-tungsten contact materials were obtained by turning and welded onto a copper sheet. Using a JF04D electrical contact testing system, under AC power conditions of 250V, 25A, ON 1s, OFF 1s, with copper as the moving contact (anode) and the silver-tungsten composite contact material as the stationary contact (cathode), with a 2mm distance between the two contacts, an arc erosion resistance test was conducted in air.

[0073] from Figure 6The results show that the mass loss of W@Ag@Ni / Ag-MC-ECMs is reduced by two orders of magnitude compared to W@Ag@Cu / Ag-MC-ECMs and W@Ag / Ag-MC-ECMs, and its service life can reach approximately 1900 cycles. After 833 effective arc erosion cycles, the mass loss of W@Ag / Ag-MC-ECMs is 0.045g; after 1924 effective arc erosion cycles, the mass loss of W@Ag@Cu / Ag-MC-ECMs is 0.031g; and after 1883 effective arc erosion cycles, the mass loss of W@Ag@Ni / Ag-MC-ECMs is 0.0038g. The lowest mass loss and increased effective service life of W@Ag@Ni / Ag-MC-ECMs are attributed to the introduction of metallic nickel. According to the Richardson-Dushman equation, because Ni (5.15 eV) has a higher work function than silver (4.26 eV) and tungsten (4.55 eV), the emission current density decreases during the arc initiation stage, leading to a reduction in arc energy and mitigating the degree of arc erosion of the electrical contacts. Furthermore, during arc erosion, in addition to increasing the viscosity of the molten silver pool, the precipitation and dissolution of high-melting-point (1455℃) Ni also facilitates arc dispersion, resulting in a relatively smooth corrosion surface of W@Ag@Ni / Ag-MC-ECMs without large pits, reducing material transfer and spatter from the cathode to the anode.

[0074] Meanwhile, based on the mass loss characteristics of the cathode and anode, it can be determined that the arc erosion material transfer direction of the silver-tungsten composite contact material prepared by the present invention is from the cathode to the anode.

[0075] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-silver-tungsten composite electrical contact material, characterized in that: The method includes the following steps: S1. Chemical plating is performed under mild conditions in an aqueous solution system: A layer of silver nanoparticles is coated on the surface of tungsten powder to obtain tungsten powder with a single layer of metallic silver coating; A layer of nickel nanoparticles was coated onto the surface of the obtained silver-coated tungsten powder to obtain silver-nickel bimetallic coated tungsten powder. S2. Using solution ball milling, tungsten powder coated with a silver-nickel bimetallic layer is mixed with silver powder using anhydrous ethanol as a dispersant to obtain a composite powder. S3. The composite powder is sintered and solidified under high temperature, high pressure and vacuum conditions by using electric spark plasma sintering to obtain nickel-silver-tungsten composite electrical contact material. In step S1, silver nitrate is used as the silver source, ammonia water as the complexing agent, polyvinylpyrrolidone as the dispersant, sodium hydroxide aqueous solution as the pH adjuster, and glucose as the reducing agent to deposit a layer of silver nanoparticles on the surface of tungsten powder to obtain a single layer of metallic silver coated tungsten powder. The amount of silver nitrate used is 0.85-1.7 g, the amount of ammonia water is 2-4 mL, the amount of polyvinylpyrrolidone is 0.1-0.2 g, the amount of glucose is 0.35-0.7 g, the mass of tungsten powder is 2-10 g, and the pH value of the solution is between 11 and 11.

5. The reaction water bath temperature was 40℃, and the magnetic stirring speed was 500 rpm; In step S1, nickel sulfate hexahydrate is used as the nickel source, sodium pyrophosphate as the complexing agent, ammonia as the pH adjuster, and dimethylamine borane as the reducing agent. A layer of nickel nanoparticles is then deposited on the surface of tungsten powder coated with a single layer of metallic silver to obtain tungsten powder coated with a silver-nickel bimetallic layer. The amount of nickel sulfate hexahydrate used is 5-6 g, the amount of sodium pyrophosphate used is 10-12.5 g, the amount of ammonia water used is 8-10 mL, the amount of dimethylaminoborane used is 0.3-0.4 g, and the mass of tungsten powder coated with a single layer of metallic silver is 10.5-21.0 g. The reaction was carried out at a water bath temperature of 25°C and a magnetic stirring speed of 600 rpm. In step S3, a graphite mold with an inner diameter of 15 mm is used; the processing temperature is 700-800℃; the applied pressure is 40 MPa; and the holding time is 10 minutes.

2. The preparation method according to claim 1, characterized in that: Before step S1, tungsten powder is sensitized using hydrochloric acid and an aqueous solution of stannous chloride dihydrate.

3. The preparation method according to claim 1, characterized in that: In step S2, The ratio of the total mass of tungsten powder and silver powder coated with a silver-nickel bimetallic layer to the mass of the ball milling media is 1:10; The ratio of the total mass of tungsten powder and silver powder coated with a silver-nickel bimetallic layer to the mass of anhydrous ethanol is 1:4; The ball mill was operated at 250 rpm for 40 minutes.

4. A nickel-silver-tungsten composite electrical contact material, characterized in that: The nickel-silver-tungsten composite electrical contact material is prepared by the preparation method described in any one of claims 1-3.

5. An electrical contact, characterized in that: The electrical contact is prepared from the nickel-silver-tungsten composite electrical contact material as described in claim 4.

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