A tungsten carbide silver contact material and its preparation method

Abstract

This application discloses a tungsten carbide silver contact material and its preparation method. The preparation method includes the following steps: adding silver nitrate solution to sodium tungstate solution, stirring at a constant temperature, and allowing to stand for aging to obtain Ag2WO4· n The H2O colloidal precipitate was filtered, washed, dispersed, dissolved, and ultrasonically vibrated to obtain Ag2WO4· n H2O sol; WC powder added to Ag2WO4· n In H2O sol, a first ball milling is performed to obtain a two-phase mixed slurry. Silver powder and dispersant are added to the two-phase mixed slurry, and a second ball milling is performed to obtain a three-phase mixed slurry. Granulation and vacuum drying are then performed to obtain a composite feedstock. The composite feedstock is pressed to obtain a green body. The green body is placed in a sintering furnace for three-stage temperature gradient sintering to obtain tungsten carbide silver contact material. This tungsten carbide silver contact material is composed of the following percentage mass components: WC 35%-80%, Ag 15%-60%, Ag4WO3. x With a concentration of 1%–5%, tungsten carbide silver contact materials possess high density, high hardness, high conductivity, and good resistance to welding.

Description

Technical Field

[0001] This invention belongs to the technical field of alloy materials, and particularly relates to a tungsten carbide silver contact material and its preparation method. Background Technology

[0002] As the core component of electrical switches such as circuit breakers and contactors, the performance of electrical contacts directly determines the reliability and lifespan of switching equipment. Tungsten carbide silver (WC-Ag) material, due to its combination of tungsten carbide's high melting point and strong resistance to arc erosion with silver's excellent electrical and thermal conductivity, has become an ideal choice for medium and high voltage electrical contacts.

[0003] Currently, the main preparation processes for tungsten carbide silver electrical contact materials are melt infiltration and sintering. However, both methods have significant drawbacks. Melt infiltration requires liquid silver to be infiltrated into the WC preform above the melting point of Ag. Due to the poor wettability of Ag to WC, uneven penetration after Ag melting leads to component segregation, resulting in uneven metallographic structure, poor compositional stability, and increased resistivity of the contact material. In severe cases, it can also affect the service life of the electrical contact material. Although the traditional sintering method is simple, uneven mechanical powder mixing and the tendency of ultrafine WC powder to agglomerate during mixing result in insufficient dispersion, leading to component segregation inside the sintered body. This, in turn, causes cracking defects. Furthermore, the compacted sintered material has insufficient density, high grain boundary resistance, and poor resistance to fusion welding. Although nanotechnology has been attempted for AgMeO-type contacts in recent years, the nano-tungsten carbide silver system still faces the following challenges: 1) WC nanoparticles are prone to cold welding and agglomeration during high-energy ball milling, deteriorating dispersibility; 2) Nanoparticles have high surface energy, making them prone to growth during sintering, and porosity is difficult to eliminate when the pressure is insufficient; 3) Adding sintering aids can block conductive pathways, increasing resistivity. Existing processes, such as spray pyrolysis, can prepare nano-tungsten carbide silver powder, but the process is complex, has low production capacity, and leaves residual carbon impurities; while chemical silver plating generates cyanide-containing wastewater, violating environmental protection trends. Therefore, developing a simple, environmentally friendly, and efficient technology that can simultaneously achieve nanoscale WC dispersion, high densification, and low resistivity in the preparation of tungsten carbide silver contacts has become a bottleneck that the industry urgently needs to overcome. Summary of the Invention

[0004] The purpose of this invention is to solve at least one problem in the prior art and to propose a tungsten carbide silver contact material and its preparation method.

[0005] To achieve the above objectives, this invention proposes a method for preparing tungsten carbide silver contact material, comprising the following steps:

[0006] Silver nitrate solution was added to sodium tungstate solution, stirred at a constant temperature, and allowed to stand for aging to obtain Ag₂WO₄· n The H2O colloidal precipitate was filtered and washed, then the washed precipitate was dispersed in distilled water and ultrasonically vibrated to obtain Ag2WO4· n H2O sol;

[0007] Add WC powder to Ag2WO4· n In H2O sol, a first ball milling is performed to obtain a two-phase mixed slurry. Silver powder and dispersant are added to the two-phase mixed slurry, and a second ball milling is performed to obtain a three-phase mixed slurry. Granulation and vacuum drying are then performed to obtain a composite feed.

[0008] The composite feed is pressed to obtain a green body;

[0009] The green blanks are placed in a sintering furnace and subjected to the following three-stage sintering process under a reducing atmosphere: first, sintering at 400℃-550℃ to remove Ag2WO4· n The crystallization water of H2O yields a mixture of nano-Ag2WO4 and Ag / WC particles; sintering at 700℃-750℃ allows the nano-Ag2WO4 to undergo a solid-phase diffusion reaction with the WC particles, generating non-stoichiometric functional Ag4WO4 on the WC surface in situ. x Interface, Ag4WO x In the formula, x = 0.8-1.2; finally, it is heated to 900℃-950℃ for sintering, and then cooled to room temperature in the furnace, allowing Ag particles to undergo grain boundary diffusion and surface diffusion for particle rearrangement to achieve efficient densification, Ag4WO x The interface phase combines with the Ag interface to obtain tungsten carbide silver contact material.

[0010] As an optional implementation, the preparation method further includes the following steps: finishing or precision processing the tungsten carbide silver contact material to achieve the required dimensions and surface finish.

[0011] As an optional implementation, the concentration of the silver nitrate solution is 0.1 mol / L-0.5 mol / L, the concentration of the sodium tungstate solution is 0.01 mol / L-0.25 mol / L, and the constant temperature stirring conditions are as follows: temperature is 40℃-60℃, stirring time is 1h-3h; the dispersant is anhydrous ethanol or acetone.

[0012] As an optional implementation, the filtration and washing process is carried out until the filtrate is neutral. During the filtration and washing process, the pH value of the filtrate is adjusted to maintain at 6.5-7.5 by adding dilute HNO3 or NH3·H2O dropwise. The settling and aging time is 10-15 hours.

[0013] As an optional implementation, the conditions for the first ball milling are as follows: rotation speed of 100 rpm-200 rpm and ball milling time of 2 h-5 h; the conditions for the second ball milling are as follows: rotation speed of 200 rpm-300 rpm and ball milling time of 1 h-2 h; the granulation process is carried out in a spray dryer, and the conditions for vacuum drying are as follows: vacuum degree ≤10 Pa, temperature of 80℃-120℃, and drying time of 4 h-12 h.

[0014] As an optional implementation, the WC powder has a particle size of 1μm-20μm, the silver powder has a particle size of 50μm-100μm, and the composite feed has a particle size of 50μm-150μm.

[0015] As an optional implementation, the pressing is carried out by bidirectional pressing, and the pressing conditions are as follows: pressure is 200MPa-400MPa, and holding time is 10s-30s.

[0016] As an optional implementation, the reducing atmosphere is hydrogen or ammonia decomposition hydrogen with a dew point ≤ -20℃. The sintering conditions for the three-stage gradient heating sintering treatment are as follows: heating to 400℃-550℃ at a heating rate of 1℃ / min-5℃ / min, sintering for 5min-15min; heating to 700℃-750℃ at a heating rate of 0.5℃ / min-3℃ / min, sintering for 1h-2h; heating to 900℃-950℃ at a heating rate of 5℃ / min-10℃ / min, sintering for 2h-3h.

[0017] This invention also proposes a tungsten carbide silver contact material prepared according to the above preparation method, which is composed of the following percentage by mass: WC 35%-80%, Ag 15%-60%, Ag4WOx 1%-5%, wherein Ag4WOx... x In the equation x = 0.8 - 1.2, Ag4WO x It is generated by the in-situ interfacial reaction between the active component released from the thermal decomposition of Ag2WO4 and WC. Among them, Ag4WO xThe x-value is synergistically regulated by the activity of the precursor Ag₂WO₄ decomposition, the sufficiency of the interfacial reaction, and the stabilization process during final sintering. The decomposition of the precursor Ag₂WO₄ provides an active intermediate tungsten-oxygen composite compound, the degree of which reacts with the solid-phase carbon on the surface of WC particles determines the initial x-value. The subsequent sintering temperature and holding time ultimately determine the x-value by regulating atomic diffusion. When the x-value is below 0.8, it indicates excessive oxygen loss in the interfacial phase and an excessively high oxygen vacancy concentration in the lattice, resulting in excessive metallicity of the phase at room temperature. Although the intrinsic conductivity is improved, the lattice is difficult to undergo effective structural fluctuations at the high temperature of the electric arc due to the limited space for vacancy migration, significantly weakening the thermal conductivity switching ability and reducing the resistance to arc erosion. When the x value is higher than 1.2, it indicates that the interface reaction is insufficient and the interface phase is close to the insulating WO3-type structure. This not only seriously hinders the interface conductivity and greatly reduces the overall conductivity of the material, but also causes a more serious mismatch between its thermal expansion coefficient and the Ag matrix. It is prone to microcracks during thermal cycling, which become the origin of arc erosion and accelerate contact failure.

[0018] As an optional implementation, the WC phase size of the tungsten carbide silver contact material is 50nm-500nm.

[0019] Introduction to the preparation mechanism of tungsten carbide silver contact materials: During sintering, the active components released by the thermal decomposition of the Ag2WO4 precursor undergo an in-situ interfacial reaction with WC, generating Ag4WO4 with non-stoichiometric properties on the WC surface. x The transition layer possesses excellent conductivity at room temperature, completely preventing damage to the silver-based conductive network from heterogeneous elements. Furthermore, it reversibly transforms into a high-thermal-conductivity state under high-temperature arc impact, significantly enhancing the arc erosion resistance of the electrical contact material. During the preparation of the composite feedstock, the Ag2WO4 precursor is pre-anchored to the surface of WC particles using sol-gel coating technology. Spray granulation directly transforms the mixed slurry into uniformly composed, highly fluid spherical composite feedstock, completely eliminating nano-WC agglomeration and greatly improving the uniformity and density of the pressed preform. This ensures the precision and stability of nano-WC scale dispersion from the source, solving the core bottlenecks of component segregation and weak interfacial bonding that are difficult to avoid with traditional mechanical mixing. A continuous three-stage gradient heating atmosphere sintering process is employed, simultaneously completing precursor decomposition, interfacial reaction induction, and matrix densification in a single heat treatment. Through an in-situ reaction self-assembly mechanism, a WC-intelligent interface layer (i.e., Ag4WO4) is formed. x (Transition layer) - A multi-level reinforcement structure of Ag.

[0020] The beneficial effects of this invention are:

[0021] 1. This invention obtains Ag2WO4 precursor by sol-gel method, ball mills WC-Ag-Ag2WO4 mixed raw material, uses bidirectional molding, and combines in-situ reaction-induced self-assembly sintering process to prepare tungsten carbide silver contact material with high density, high hardness, high conductivity and good anti-welding properties.

[0022] 2. The preparation method of this invention only requires conventional ball milling, spray drying, pressing and sintering equipment, without the need for repressing and re-sintering or a dedicated nano production line, which greatly reduces equipment investment and energy consumption costs.

[0023] 3. The present invention produces no wastewater or waste gas during the preparation of tungsten carbide silver contact materials, avoiding the environmental hazards of chemical or melt infiltration methods. It has a wide range of composition systems and strong process adaptability, and can flexibly prepare a series of contact products from high conductivity to high wear resistance on the same production line, providing a reliable path for the green, low-cost and large-scale manufacturing of high-performance contacts.

[0024] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. Attached Figure Description

[0025] Figure 1 This is an OM morphology diagram of the nano-tungsten carbide silver contact material of Embodiment 1 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0027] Example 1

[0028] See Figure 1 This embodiment provides a tungsten carbide silver contact material, which is composed of the following percentage by mass: WC 70%, Ag 28%, Ag4WO3 x 2%, Ag4WO x In the tungsten carbide silver contact material, x = 0.8-1.2, the size of the WC phase is 100 nm.

[0029] In this embodiment, the preparation method of the tungsten carbide silver contact material specifically includes the following steps:

[0030] S01. A 0.25 mol / L sodium tungstate solution was placed in a glass reactor. Under constant temperature (60°C) and stirring conditions, a 0.5 mol / L silver nitrate solution was slowly added dropwise to the sodium tungstate solution using a dropping funnel. After the addition was complete, stirring was continued at the constant temperature for 2 hours, followed by aging for 13 hours to obtain Ag₂WO₄·n The H2O colloidal precipitate was filtered and washed until the filtrate was neutral. The washed precipitate was then dispersed in distilled water and ultrasonically vibrated to obtain Ag2WO4 with a solid content of 20%. n H2O sol;

[0031] S02. Weigh 700g of WC powder with an average particle size of 15μm and 280g of Ag powder with an average particle size of 50μm, and mix the WC powder and Ag2WO4· according to the ratio. n The H2O sol was loaded into a planetary ball mill jar, and the milling speed was set to 200 rpm for 4 hours for the first milling, so that Ag2WO4· n H2O sol fully encapsulates WC to obtain a two-phase mixed slurry. Ag powder and anhydrous ethanol are then added, and a second ball milling is performed at a speed of 300 rpm and a time of 2 hours to obtain a uniform three-phase mixed slurry. The three-phase mixed slurry is then transferred to a spray dryer for spray granulation to obtain spherical composite feed with an average particle size of 50 μm. The feed is then vacuum dried at a vacuum degree of 9 Pa and a temperature of 80 °C for 4 hours.

[0032] S03. The vacuum-dried composite feed is subjected to biaxial pressing at a pressure of 300MPa and a holding time of 15s to obtain a green body.

[0033] S04. Place the green billet in a sintering furnace and perform the following three-stage sintering treatment under an atmosphere of ammonia decomposition hydrogen with a dew point of -26℃: first, heat to 500℃ at a heating rate of 3℃ / min and hold for 5min to remove Ag2WO4· n The crystallization water of H2O yields a mixture of nano-Ag2WO4 and Ag / WC particles; this mixture is then heated to 700℃ at a heating rate of 3℃ / min and held for 1.5h, allowing the nano-Ag2WO4 to undergo a solid-phase diffusion reaction with the WC particles, resulting in the in-situ generation of non-stoichiometric functional Ag4WO4 on the WC surface. x Interface, Ag4WO x x = 0.8-1.2; finally, heat to 930℃ at a heating rate of 5℃ / min, hold for 2.5h, and cool to room temperature with the furnace. This allows Ag particles to undergo grain boundary diffusion and surface diffusion for particle rearrangement, achieving efficient densification, Ag4WO3. x The interface phase combines with the Ag interface to obtain tungsten carbide silver contact blank material;

[0034] S05. The tungsten carbide silver contact blank material will be precision machined according to the dimensional accuracy requirements of the contact product to obtain the tungsten carbide silver contact material with the required dimensional accuracy.

[0035] Example 2

[0036] This embodiment provides a tungsten carbide silver contact material, which is composed of the following percentage by mass: WC 60%, Ag 38.5%, Ag4WO3 x 1.5%, Ag4WO x In the figure, x = 0.8-1.2, the size of the WC phase in the tungsten carbide silver contact material is 200 nm.

[0037] In this embodiment, the preparation method of the tungsten carbide silver contact material specifically includes the following steps:

[0038] S01. A 0.1 mol / L sodium tungstate solution was placed in a glass reactor. Under constant temperature (50°C) and stirring conditions, a 0.25 mol / L silver nitrate solution was slowly added dropwise to the sodium tungstate solution using a dropping funnel. After the addition was complete, stirring was continued at the constant temperature for 3 hours, followed by aging for 10 hours to obtain Ag₂WO₄· n The H2O colloidal precipitate was filtered and washed until the filtrate was neutral. The washed precipitate was then dispersed in distilled water and ultrasonically vibrated to obtain Ag2WO4· n H2O sol;

[0039] S02. Weigh 600g of WC powder with an average particle size of 20μm and 385g of Ag powder with an average particle size of 75μm, and mix the WC powder and Ag2WO4· according to the ratio. n The H2O sol was loaded into a planetary ball mill jar, and the milling speed was set to 150 rpm for 5 hours for the first milling, so that Ag2WO4· n H2O sol fully encapsulates WC to obtain a two-phase mixed slurry. Ag powder and anhydrous ethanol are then added, and a second ball milling is performed at a speed of 250 rpm and a time of 1.5 h to obtain a uniform three-phase mixed slurry. The three-phase mixed slurry is then transferred to a spray dryer for spray granulation to obtain spherical composite feed with an average particle size of 85 μm. The feed is then vacuum dried at a vacuum degree of 8 Pa and a temperature of 100 °C for 6 h.

[0040] S03. The vacuum-dried composite feed is subjected to biaxial pressing at a pressure of 400MPa and a holding time of 10s to obtain a green body.

[0041] S04. Place the green billet in a sintering furnace and perform the following three-stage sintering treatment under a hydrogen atmosphere with a dew point of -25℃: first, heat to 400℃ at a heating rate of 1℃ / min and hold for 15 min to remove Ag2WO4· nThe crystallization water of H2O yields a mixture of nano-Ag2WO4 and Ag / WC particles; this mixture is then heated to 720℃ at a heating rate of 2℃ / min and held for 2 hours, allowing the nano-Ag2WO4 to undergo a solid-phase diffusion reaction with the WC particles, resulting in the in-situ generation of non-stoichiometric functional Ag4WO4 on the WC surface. x Interface, Ag4WO x x = 0.8-1.2; finally, heat to 950℃ at a heating rate of 7℃ / min, hold for 2 hours, and cool to room temperature with the furnace. This allows Ag particles to undergo grain boundary diffusion and surface diffusion for particle rearrangement, achieving efficient densification, Ag4WO3. x The interface phase combines with the Ag interface to obtain tungsten carbide silver contact blank material;

[0042] S05. The tungsten carbide silver contact blank material will be precision machined according to the dimensional accuracy requirements of the contact product to obtain the tungsten carbide silver contact material with the required dimensional accuracy.

[0043] Example 3

[0044] This embodiment provides a tungsten carbide silver contact material, which is composed of the following percentage by mass: WC 80%, Ag 17.5%, Ag4WO3 x 2.5%, Ag4WO x In the tungsten carbide silver contact material, x = 0.8-1.2, the size of the WC phase is 50 nm.

[0045] In this embodiment, the preparation method of the tungsten carbide silver contact material specifically includes the following steps:

[0046] S01. A 0.05 mol / L sodium tungstate solution was placed in a glass reactor. Under constant temperature (40°C) and stirring conditions, a 0.1 mol / L silver nitrate solution was slowly added dropwise to the sodium tungstate solution using a dropping funnel. After the addition was complete, stirring was continued at the constant temperature for 1 hour, followed by aging for 15 hours to obtain Ag₂WO₄· n The H2O colloidal precipitate was filtered and washed until the filtrate was neutral. The washed precipitate was then dispersed in distilled water and ultrasonically vibrated to obtain Ag2WO4· n H2O sol;

[0047] S02. Weigh 800g of WC powder with an average particle size of 1μm and 175g of Ag powder with an average particle size of 50μm, and mix the WC powder and Ag2WO4· according to the ratio. n The H2O sol was loaded into a planetary ball mill jar, and the milling speed was set to 100 rpm for 1 hour for the first milling, so that Ag2WO4· nH2O sol fully encapsulates WC to obtain a two-phase mixed slurry. Ag powder and anhydrous ethanol are then added, and a second ball milling is performed at a speed of 200 rpm and a time of 2 h to obtain a uniform three-phase mixed slurry. The three-phase mixed slurry is then transferred to a spray dryer for spray granulation to obtain spherical composite feed with an average particle size of 50 μm. The feed is then vacuum dried at a vacuum degree of 10 Pa and a temperature of 80 °C for 12 h.

[0048] S03. The vacuum-dried composite feed is subjected to biaxial pressing at a pressure of 200MPa and a holding time of 30s to obtain a green body;

[0049] S04. Place the green billet in a sintering furnace and perform the following three-stage sintering treatment under an atmosphere of ammonia decomposition hydrogen with a dew point of -26℃: first, heat to 550℃ at a heating rate of 4℃ / min and hold for 10min to remove Ag2WO4· n The crystallization water of H2O yields a mixture of nano-Ag2WO4 and Ag / WC particles; this mixture is then heated to 750℃ at a heating rate of 2℃ / min and held for 1 h, allowing the nano-Ag2WO4 to undergo a solid-phase diffusion reaction with the WC particles, resulting in the in-situ generation of non-stoichiometric functional Ag4WO4 on the WC surface. x Interface, Ag4WO x x = 0.8-1.2; finally, heat to 900℃ at a heating rate of 8℃ / min, hold for 3 hours, and cool to room temperature with the furnace. This allows Ag particles to undergo grain boundary diffusion and surface diffusion for particle rearrangement, achieving efficient densification, Ag4WO3. x The interface phase combines with the Ag interface to obtain tungsten carbide silver contact blank material;

[0050] S05. The tungsten carbide silver contact blank material will be precision machined according to the dimensional accuracy requirements of the contact product to obtain the tungsten carbide silver contact material with the required dimensional accuracy.

[0051] Example 4

[0052] This embodiment provides a tungsten carbide silver contact material, which is composed of the following percentage by mass: WC 60%, Ag 38.5%, Ag4WO3 x 1.5%, Ag4WO x In the equation, x = 0.8 - 1.2.

[0053] The preparation method of the tungsten carbide silver contact material in this embodiment is the same as that in Example 1, except that the raw material ratio is different.

[0054] Example 5

[0055] This embodiment provides a tungsten carbide silver contact material, which is composed of the following percentage by mass: WC 80%, Ag 17.5%, Ag4WO3 x 2.5%, Ag4WO x In the equation, x = 0.8 - 1.2.

[0056] The preparation method of the tungsten carbide silver contact material in this embodiment is the same as that in Example 1, except that the raw material ratio is different.

[0057] Example 6

[0058] The composition of the tungsten carbide silver contact material in this embodiment is the same as that in Embodiment 1.

[0059] The preparation method of the tungsten carbide silver contact material in this embodiment is the same as that in Example 1, except that the sintering temperature in the last stage of the three-stage gradient heating sintering process in step S04 is adjusted to 900°C.

[0060] Comparative Example 1: Compared to Example 1, the contact material in this comparative example was made from the following percentage by weight composition: 70 wt% WC and 30 wt% Ag. During preparation, only the 70 wt% WC and 30 wt% Ag were mechanically mixed, and then processed using the same S03-S05 steps as in Example 1.

[0061] Comparative Example 2: Compared with Example 1, the contact material in this comparative example uses 2.0 wt% Ni powder to replace the Ag2WO4 precursor, while other process flows remain unchanged.

[0062] Comparative Example 3: Compared with Example 1, the contact material in this comparative example uses 2.0 wt% Co powder to replace the Ag2WO4 precursor, while other process flows remain unchanged.

[0063] Comparative Example 4: Compared with Example 1, the contact material in this comparative example uses 2.0 wt% Fe powder to replace the Ag2WO4 precursor, while other process flows remain unchanged.

[0064] Comparative Example 5: Compared with Example 1, the preparation method of the contact material in this comparative example is the same except that the sintering temperature of the third stage of step S04 is adjusted to 1100℃.

[0065] Comparative Example 6: Compared with Example 1, the amount of Ag2WO4 precursor added in this comparative example is 0.5 wt.% when preparing the contact material, and other process flows remain unchanged.

[0066] Comparative Example 7: Compared with Example 1, the amount of Ag2WO4 precursor added in this comparative example is 6 wt.%, and other process flows remain unchanged.

[0067] Comparative Example 8: Compared with Example 1, the three-stage sintering treatment in step S04 was omitted when preparing the contact material. Instead, the compact was directly heated to 930°C at a rate of 10°C / min and held for 150min. Other process flows remained unchanged.

[0068] Equal amounts of the tungsten carbide silver contact materials prepared in Examples 1, 4-6 and Comparative Examples 1-8 were taken, and their hardness, relative density, conductivity and anti-welding performance were tested respectively. The specific test results are shown in Table 1 below.

[0069] The following standards should be referenced for testing hardness, density, electrical conductivity, and resistance to welding during the testing process:

[0070] Referring to GB / T 4340.1 "Metallic materials Vickers hardness test - Part 1: Test method", the Vickers hardness indentation method is used to test the hardness; referring to GB / T 3850 "Density determination method of cemented carbide", the Archimedes displacement method is used to test the relative density; referring to GB / T 351 "Method for measuring resistivity of metallic materials", the four-probe method is used to measure the resistivity, which is then converted to the international standard conductivity of annealed copper (%IACS); referring to IEC 62271-1 "High voltage switchgear and controlgear - Part 1: General technical requirements", a switching cycle test is conducted under rated current and short-circuit current conditions, and the number of operations (electrical life) before contact failure is recorded to evaluate the resistance to welding.

[0071] Table 1. Schematic diagram comparing the performance of different contact materials

[0072]

[0073] As shown in Table 1, compared to the contact materials of Comparative Examples 1-4, the tungsten carbide silver contact material prepared using the composition and component ratio of the tungsten carbide silver contact material of this invention shows improvements in anti-welding performance, relative density, and conductivity, with the most significant improvement in anti-welding performance. Compared to the contact materials of Comparative Examples 5-8, the tungsten carbide silver contact material prepared using the method of this invention shows the most significant improvement in anti-welding performance. It is evident that the proportion of Ag2WO4 precursor added and the sintering process have a significant impact on the performance of the tungsten carbide silver contact material.

[0074] The analysis of the performance degradation mechanism of each comparison ratio is as follows.

[0075] Comparative Example 1: Due to the lack of interface modifier, the wettability between WC and Ag phases is extremely poor, resulting in a serious lack of interfacial bonding force and the formation of a large number of micropores. Under the action of electric arc, the pores become local hot spots and electrical stress concentration points, accelerating the evaporation and splashing of the silver matrix. At the same time, WC particles are easily detached from the matrix due to poor bonding, causing the contact material to fail rapidly.

[0076] Comparative Example 2: Although Ni improves interfacial wettability to some extent, its solid solution in the Ag matrix significantly scatters conduction electrons, severely reducing the overall conductivity of the material. The high resistivity leads to an aggravation of the Joule heating effect during operation, resulting in an increase in the overall temperature of the contact. Furthermore, at the high temperature of the electric arc, Ni is prone to react with WC to form a brittle phase, which worsens the interfacial toughness and ultimately leads to a decrease in resistance to arc erosion.

[0077] Comparative Example 3: Co exhibits better wettability to WC than Ni, but it also dissolves in Ag to form a high-resistivity solid solution, significantly sacrificing conductivity. Furthermore, the addition of Co tends to lead to excessively high viscosity of the Ag melt during the liquid-phase sintering stage, hindering the densification process and creating residual porosity. The interfacial phase formed by Co and WC is prone to microcracks and propagation under cyclic arc thermal shock, becoming a breakthrough point for arc erosion.

[0078] Comparative Example 4: Fe has extremely low solid solubility in Ag, and tends to segregate at grain boundaries to form isolated iron oxides or brittle phases. This not only severely hinders electron transport, leading to a deterioration in conductivity, but also disrupts the continuity of the Ag network. These brittle phases are prone to cracking and detaching under the thermal stress generated by the electric arc, and trigger severe particulate erosion, causing the material loss rate to accelerate dramatically.

[0079] Comparative Example 5: Excessively high sintering temperatures led to significant grain coarsening and even localized overburning in the Ag matrix, not only reducing matrix strength but also compromising the integrity of the conductive network. Simultaneously, the precursor decomposition reaction at high temperatures was too vigorous, resulting in Ag4WO3. 0.5 The interface layer is thick and uneven. Due to the excessively high junction temperature, it leads to severe over-reduction and severe oxygen loss in the interface phase. The x value is 0.5, which is far below the lower limit. The structure is unbalanced, and the thermal expansion mismatch between it and WC and Ag is aggravated. During the cooling process, internal stress microcracks are generated, causing the material to exhibit brittle fracture characteristics under the action of electric arc.

[0080] Comparative Example 6: Insufficient precursor addition amount cannot form a complete and continuous Ag4WO on the surface of WC particles. 1.5 Due to a severe deficiency in the amount of precursor added, the interface coating layer could not form a continuous interface layer, resulting in incomplete reaction and severe local oxygen enrichment. This led to a large amount of WC directly contacting Ag, and the fundamental problem of weak interfacial bonding remained unresolved. Under the thermal coupling effect of the electric arc, these unprotected interfaces became weak points, preferentially cracking and peeling off, thus accelerating the arc erosion rate.

[0081] Comparative Example 7: Excessive precursors generated excessively thick Ag4WO at the interface. 0.7Excessive precursor addition and an overly thick interfacial layer lead to uneven oxygen deficiency during the reaction, resulting in a low overall x-value. This layer significantly scatters electrons, severely reducing the material's conductivity. Furthermore, the excessively thick interfacial layer itself, due to its brittleness, becomes a source of microcrack initiation, easily fracturing under stress. This weakens the pinning reinforcement effect of WC particles, leading to overall performance degradation.

[0082] Comparative Example 8: The elimination of the medium- and low-temperature insulation stage resulted in the precursor failing to decompose stepwise and fully react with WC. Instead, it directly and rapidly decomposed at high temperatures to generate a high-x-value insulating phase, Ag4WO, similar to WO3. 1.7 This process causes the active components to be encapsulated by the Ag liquid phase before they even come into contact with WC, thus rendering their interfacial modification function ineffective. The resulting tissue is close to a mechanically mixed state without additives, with poor interfacial bonding and no improvement in any of the properties.

[0083] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A method of making a tungsten carbide-silver contact material, characterized by, It comprises the following steps: The silver nitrate solution is added to the sodium tungstate solution, constant temperature stirring, standing aging to obtain Ag2WO4· n H2O colloidal precipitate, washing by suction filtration, and then the washed precipitate is dispersed in distilled water, ultrasonic oscillation to obtain Ag2WO4· n H2O sol; The WC powder is added to Ag2WO4· n The two-phase mixed slurry is obtained by first ball milling in the H2O sol, the silver powder and the dispersant are added into the two-phase mixed slurry, second ball milling is performed to obtain a three-phase mixed slurry, and granulation and vacuum drying treatment are performed to obtain a composite feedstock; The composite feed is pressed to obtain a green body; The green body is placed in a sintering furnace and subjected to the following three-stage sintering treatment under a reducing atmosphere: first, heating to 400-550°C for sintering to remove Ag2WO4· n H2O crystallization water to obtain a mixture of nano Ag2WO4and Ag, WC particles; then heating to 700-750°C for sintering to make the nano Ag2WO4undergo solid-phase diffusion reaction with the WC particles to in-situ generate non-stoichiometric functional Ag4WO x interface phase, Ag4WO x wherein x=0.8-1.2; finally, heating to 900-950°C for sintering and furnace cooling to room temperature to make the Ag particles undergo grain boundary diffusion and surface diffusion for particle rearrangement to achieve high-efficiency densification, and the interface phase of Ag4WO x interface phase and the interface phase of Ag to obtain a tungsten carbide silver contact material; The tungsten carbide silver contact material consists of the following percentage mass components: WC 35-80%, Ag 15-60%, Ag4WO x 1-5%, the Ag4WO x x = 0.8-1.2; The sintering conditions of the three-stage gradient temperature sintering treatment are as follows: heating to 400-550 DEG C at a heating rate of 1-5 DEG C / min, sintering for 5-15 min; heating to 700-750 DEG C at a heating rate of 0.5-3 DEG C / min, sintering for 1-2 h; heating to 900-950 DEG C at a heating rate of 5-10 DEG C / min, sintering for 2-3 h.

2. The method of making a tungsten carbide silver contact material of claim 1, wherein: The preparation method further comprises the following steps: finishing or precision processing of the tungsten carbide silver contact material to achieve the required size and surface finish.

3. The method of making a tungsten carbide-silver contact material of claim 1, wherein: The concentration of the silver nitrate solution is 0.1-0.5 mol / L, the concentration of the sodium tungstate solution is 0.01-0.25 mol / L, and the constant temperature stirring conditions are as follows: temperature is 40-60 DEG C, stirring time is 1-3 h; the dispersing agent is anhydrous ethanol or acetone.

4. The method of making a tungsten carbide-silver contact material of claim 1, wherein: The filter washing is performed until the filtrate is neutral, the pH value of the filtrate is adjusted to 6.5-7.5 by dropwise adding dilute HNO3 or NH3·H2O during the filter washing process, and the standing aging time is 10-15 h.

5. The method of making a tungsten carbide-silver contact material of claim 1 wherein: The first ball milling conditions are as follows: rotation speed is 100-200 rpm, ball milling time is 2-5 h; the second ball milling conditions are as follows: rotation speed is 200-300 rpm, ball milling time is 1-2 h; the granulation treatment is performed in a spray dryer, and the vacuum drying treatment conditions are as follows: vacuum degree is less than or equal to 10 Pa, temperature is 80-120 DEG C, and drying time is 4-12 h.

6. The method of making a tungsten carbide-silver contact material of claim 1, wherein: The particle size of the WC powder is 1-20 μm, the particle size of the silver powder is 50-100 μm, and the particle size of the composite feed is 50-150 μm.

7. The method of making a tungsten carbide-silver contact material of claim 1, wherein: The pressing adopts bidirectional pressing forming, and the pressing conditions are as follows: pressure is 200-400 MPa, and pressure maintaining time is 10-30 s.

8. The method of making a tungsten carbide-silver contact material of claim 1 wherein: The WC phase size of the tungsten carbide silver contact material is 50-500 nm.

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