A vacuum-fired material, its preparation method, a vacuum-fired device, and its application.

Abstract

This invention discloses a vacuum sintering material, its preparation method, a vacuum sintering device, and its application, belonging to the field of vacuum sintering technology. By pre-sintering graphite material, residual volatile substances in the graphite pores can be gradually removed, further improving the purity of the graphite material. Through chromium plating, a dense chromium plating layer is formed on the surface of the graphite material, thereby improving the oxidation resistance of the graphite material. The obtained vacuum sintering material is used to manufacture a vacuum sintering device, which is then applied to the vacuum sintering of copper-chromium contact materials. The chromium element contained in the device is not easily volatilized, solving the problems of high preparation cost of vacuum sintering devices, contamination of materials by nickel elements volatilized from the sintering material during sintering, and adhesion between graphite paper and the inner bottom layer of the sintering device in the prior art.

Description

Technical Field

[0001] This invention relates to the field of vacuum firing technology, and in particular to a vacuum firing material, its preparation method, a vacuum firing device, and its application. Background Technology

[0002] A vacuum firing device is a specialized piece of equipment used in a vacuum environment to support and complete the firing or sintering process of materials. Its core function is to provide a stable vacuum atmosphere, uniform heating conditions, and reliable support for materials to meet the high-temperature processing requirements of specific materials in a vacuum environment.

[0003] Existing vacuum sintering devices are mainly made of materials such as graphite, alumina ceramics, aluminum nitride, and nickel-chromium alloys. Among them, the cost of using alumina ceramics and aluminum nitride is relatively high. Vacuum sintering devices made of nickel-chromium alloys are prone to volatilizing nickel during high-temperature sintering, which can contaminate the materials. When using sintering devices made of graphite, graphite paper is usually laid at the bottom of the device. During high-temperature sintering, the graphite paper is prone to sticking to the bottom layer. Summary of the Invention

[0004] The main objective of this invention is to provide a vacuum sintering material, its preparation method, a vacuum sintering device, and its application, aiming to solve the problems of high preparation cost of vacuum sintering devices, contamination of materials by nickel volatilized from the sintering material during the sintering process, and adhesion between graphite paper and the inner bottom layer of the sintering device in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for preparing a vacuum sintering material, the method comprising the following steps: Pre-sintering of graphite materials; The graphite material that has undergone the pre-calcination treatment is then subjected to chromium plating. The pre-firing process involves heating the graphite material under a preset vacuum by gradient heating and then holding it at a preset temperature. The chromium plating process involves plating the graphite material with chromium vapor in a vacuum environment.

[0006] Optionally, the pre-firing process is as follows: Under the preset vacuum level, the graphite material is heated for the first time, and when the temperature reaches the first preset temperature, it is held at that temperature for the first time. After the first holding is completed, the temperature is heated for the second time, and when the temperature reaches the second preset temperature, it is held at that temperature for the second time. After the second holding is completed, the temperature is heated for the third time, and when the temperature reaches the third preset temperature, it is held at that temperature for the third time. After the third holding is completed, the temperature is heated for the fourth time, and when the temperature reaches the fourth preset temperature, it is held at that temperature for the fourth time. After the fourth holding is completed, the pre-firing process is finished.

[0007] Optionally, the chrome plating process is as follows: In the vacuum environment, the graphite material is chromium-plated using chromium vapor generated during the sintering of copper-chromium material at 400℃~1050℃.

[0008] Optionally, the preset vacuum degree is ≤1×10 -2 Pa, the first preset temperature is 350℃~450℃, the heating rate is 3.0℃ / min~3.5℃ / min, and the first holding time is 0.5h~1.5h; the second preset temperature is 750℃~850℃, the heating rate is 3.0℃ / min~3.5℃ / min, and the second holding time is 0.5~1.5h; the third preset temperature is 1000℃~1200℃, the heating rate is 4.0℃ / min~6.0℃ / min, and the third holding time is 0.8h~1.2h; the fourth preset temperature is 1300℃~1400℃, the heating rate is 3.3℃ / min~5.0℃ / min, and the fourth holding time is 3.0h~4.0h.

[0009] Optionally, the chrome plating method is implemented based on the following steps: In ≤1×10 -2 In a vacuum environment of Pa, the chromium plating device is heated for the first time. When the temperature reaches the first exhaust temperature, the first exhaust is performed. After the first exhaust is completed, the device is heated for the second time. When the temperature reaches the second exhaust temperature, the second exhaust is performed. After the second exhaust is completed, the device is heated for the third time. When the temperature reaches the preset chromium plating temperature, chromium plating is performed. After the chromium plating is completed, heating is stopped. When the temperature of the chromium plating device drops to 55℃~60℃, the chromium plating process is completed.

[0010] Optionally, the first exhaust temperature is 400℃~450℃, the heating rate is 3℃ / min~5℃ / min, and the duration of the first exhaust is 1.5h~2.5h; the second exhaust temperature is 750℃~850℃, the heating rate is 2℃ / min~3℃ / min, and the duration of the second exhaust is 1.5h~2.5h; the preset chrome plating temperature is 1000℃~1050℃, the heating rate is 1℃ / min~2℃ / min, and the duration of the chrome plating is 2.0h~3.0h.

[0011] To achieve the above objectives, the present invention also provides a vacuum sintering material, which is prepared by the above method.

[0012] To achieve the above objectives, the present invention also provides a vacuum firing device, which includes a plate-shaped vacuum firing material and a column-shaped vacuum firing material. The column-shaped vacuum firing material is disposed at the edge of the plate-shaped vacuum firing material, and the spacing between the column-shaped vacuum firing materials is 15cm to 20cm. The plate-shaped vacuum firing material and the column-shaped vacuum firing material are prepared according to the above-described preparation method.

[0013] Optionally, the thickness of the plate-type vacuum firing material is 3mm to 5mm; the diameter of the column-type vacuum firing material is 10mm to 12mm. To achieve the above objectives, the present invention also provides an application of the vacuum sintering device, which is applied to the vacuum sintering of copper-chromium contact materials.

[0014] Compared with the prior art, the beneficial effects that the present invention can achieve are as follows: 1. In the technical method of this invention, during the preparation of the vacuum sintered material, the graphite material undergoes a pre-sintering treatment, specifically, within a range of ≤1×10⁻⁶. -2Under a vacuum of Pa, four gradient heating processes were performed, raising the temperature from 350℃ to 1400℃. Through segmented heat preservation, residual volatile substances, such as hydrocarbons and free carbon, within the graphite pores were gradually expelled, further improving the purity of the graphite material to near theoretical levels. Furthermore, the synergistic effect of gradient heating and the vacuum environment effectively released internal thermal stress in the graphite, preventing cracking at high temperatures and increasing the flexural strength of the graphite material by 20%-30%. Additionally, under vacuum conditions, copper-chromium materials were sintered... Chromium vapor generated during the sintering process undergoes vapor deposition to form a Cr3C2 / Cr7C3 composite deposition layer with controllable thickness on the surface of the graphite material. This deposition layer can maintain a dense structure even above 1600℃, thereby further increasing the oxidation resistance temperature of the graphite material. Furthermore, the chromium plating of Cr3C2 / Cr7C3 can reduce the surface friction coefficient from 0.7 to about 0.1 by modifying the interlayer spacing of the graphite material, while improving its wear resistance by 5 to 8 times. It also solves the problem of adhesion between the sintering material and the sintered workpiece during the sintering process of vacuum sintering materials.

[0015] 2. In the technical solution of the present invention, the vacuum firing device includes plate-shaped vacuum firing material and column-shaped vacuum firing material, which can reduce the production cost of the firing device. When the column-shaped vacuum firing material is placed at the edge of the plate-shaped vacuum firing material, the temperature difference in the furnace can be controlled within ±10℃ during the sintering process, thereby optimizing the sintering conditions. In addition, the plate-shaped and column-shaped vacuum firing materials used to prepare the vacuum firing device are pre-fired and chrome-plated, so that the firing device does not crack during the thermal shock of rapid cooling from 2000℃ to room temperature, thereby improving the service life of the firing device.

[0016] 3. In the technical solution of the present invention, the vacuum sintering device is applied to the vacuum sintering of copper-chromium (Cu / Cr) contact materials. The chromium element contained in the chromium plating layer of the sintering device is not easily volatilized, which solves the problem of nickel element volatilization causing material contamination in the prior art. Furthermore, during the sintering process, it is not necessary to lay graphite paper at the bottom layer inside the sintering device, which solves the problem of graphite paper sticking to the bottom layer inside the sintering device caused by high-temperature sintering in the prior art. It can also meet the stringent requirements of the contact material for the sintering device and improve the yield of copper-chromium (Cu / Cr) contacts. Attached Figure Description

[0017] Figure 1 This is a flowchart of the preparation method of the vacuum sintering material of the present invention; Figure 2 This is a schematic diagram of the vacuum firing device in Example 2; Figure 3Here are scanning electron microscope images of the vacuum-sintered material from Example 2; Figure 4 The image shows the energy dispersive spectroscopy (EDS) analysis of the vacuum-sintered material in Example 2. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0020] To address the problems of high manufacturing cost of vacuum sintering devices, contamination of materials by nickel volatilized during sintering, and adhesion between graphite paper and the inner layer of the sintering device in existing technologies, this invention provides a method for preparing vacuum sintering materials. The method includes the following steps: Figure 1 As shown in S10 and S20, S10. Pre-fire the graphite material; S20. The graphite material that has undergone the pre-calcination treatment is subjected to chromium plating; The pre-firing process involves heating the graphite material under a preset vacuum by gradient heating and then holding it at a preset temperature. The chromium plating process involves plating the graphite material with chromium vapor under vacuum conditions.

[0021] Optionally, the purity of the graphite material can be ≥99.8%, and the surface roughness can be Ra≤0.1µm.

[0022] It should be understood that when the purity of the graphite material is ≥99.8%, the purity of the graphite material will be further improved after the above pre-firing treatment, so as to reach the ideal state of purity close to 100%.

[0023] It should be noted that in the above preparation method, when the surface roughness of the graphite material is Ra≤0.1µm, defects such as micropores and protrusions on the graphite surface can be reduced, making it easier for chromium vapor to form a continuous and dense coating during deposition. This avoids problems such as uneven coating thickness or porosity caused by surface unevenness. In addition, when the surface roughness of the graphite material is Ra≤0.1µm, the smooth surface can reduce stress concentration between the chromium coating and the graphite substrate, improve the bonding strength between the two, and thus prevent the coating from peeling off during subsequent use.

[0024] It should be noted that in the above preparation method, the graphite material is heated by gradient heating under a preset vacuum and held at a preset temperature. This allows impurities with different boiling points in the graphite material to volatilize in stages. For example, at low temperatures, moisture and low-boiling-point organic impurities can be removed; at medium and high temperatures, non-volatile hydrocarbons and free carbon can be decomposed and discharged. Ultimately, the purity of the graphite material can be further improved to approach the theoretical purity, avoiding contamination of the workpiece due to impurity volatilization during subsequent high-temperature use. For example, it can prevent contamination of Cu / Cr contact materials.

[0025] It should be noted that graphite materials may generate internal stress during the molding process due to uneven density and differences in particle arrangement. However, this invention, through gradient heating and multiple heat preservation, can make the internal temperature of graphite uniformly conduct, gradually release stress through thermal expansion, and promote the orderly arrangement of graphite microcrystals, thereby enhancing the structural stability of graphite materials. After the above pre-firing treatment, the graphite material will not crack or deform in the subsequent high-temperature environment.

[0026] It should be noted that graphite materials will gradually volatilize under high temperature conditions; even in a vacuum environment, they may slowly oxidize due to low oxygen. However, this invention, by plating chromium on the surface of graphite materials, forms a dense oxide film, such as a Cr2O3 oxide film, which can form under high temperature conditions. This blocks the contact between oxygen and the graphite matrix, increases the oxidation resistance temperature of graphite, and extends the service life of graphite materials.

[0027] It should be understood that graphite is prone to wear when in contact with other materials. The chromium plating layer formed by the present invention has high hardness, which can significantly improve the wear resistance of the graphite surface. At the same time, chromium has low compatibility with metals such as copper, which can avoid the problem of Cu / Cr contact material sticking to the sintering material due to high temperature during the sintering process, such as copper liquid seeping into the graphite pores, thereby ensuring the precision and quality of Cu / Cr contact forming.

[0028] In one possible implementation, the above pre-burning process is as follows: Under the aforementioned preset vacuum level, the graphite material is heated for the first time, and when the temperature reaches the first preset temperature, it is held for the first time. After the first holding is completed, the temperature is raised for the second time, and when the temperature reaches the second preset temperature, it is held for the second time. After the second holding is completed, the temperature is raised for the third time, and when the temperature reaches the third preset temperature, it is held for the third time. After the third holding is completed, the temperature is raised for the fourth time, and when the temperature reaches the fourth preset temperature, it is held for the fourth time. After the fourth holding is completed, the aforementioned pre-firing process is completed.

[0029] Optionally, when pre-firing graphite materials as described above, the equipment selected for the pre-firing process should meet the requirements of providing a stable high-temperature environment for graphite pre-firing, and ensuring that the material is not contaminated and its performance is optimized during the pre-firing process by controlling the atmosphere or vacuum. For example, an atmosphere sintering furnace, a box-type resistance furnace, or a graphitization furnace can be selected.

[0030] In the above method, under a preset vacuum, the residual volatiles in the graphite pores can be gradually discharged through four gradient heatings and segmented heat preservation, thereby further improving the purity of the graphite material and achieving a cleanliness close to the theoretical value. In addition, through the synergistic effect of gradient heating and vacuum environment, the internal thermal stress of graphite can be effectively released, avoiding the problem of graphite material being prone to cracking at high temperatures, and at the same time, the bending strength of graphite material can be improved.

[0031] In one possible implementation, the above-mentioned chrome plating process is as follows: In the aforementioned vacuum environment, chromium vapor generated during the sintering of copper-chromium materials at 400℃~1050℃ is used to perform chromium plating on graphite materials.

[0032] Optionally, in the above-mentioned chromium plating method, the preset time of chromium plating can be adjusted according to the required thickness of the chromium plating layer. By controlling the heat preservation time, chromium vapor can be continuously deposited, and finally a uniform and dense chromium plating layer is formed on the graphite surface.

[0033] Optionally, the above-mentioned chromium plating method can be to use chromium vapor generated by Cu / Cr contact blanks in a high-temperature environment to chromium plating graphite materials. Specifically, the Cu / Cr contact blanks can be evenly placed in the graphite materials. For example, when the graphite materials are graphite plates and graphite pillars, the Cu / Cr contact blanks can be evenly placed on the graphite plates and mixed with the graphite pillars. Under vacuum conditions and high-temperature conditions of 400℃~1050℃, the Cr atoms in the Cu / Cr contact blanks can obtain enough energy to evaporate into a gaseous state. When the chromium vapor molecules diffuse to the graphite surface, they are adsorbed due to the van der Waals forces on the graphite surface and gradually condense into solid chromium atoms at high temperatures, thereby achieving chromium plating of the graphite materials.

[0034] Optionally, in the process of sintering copper-chromium materials at 400℃~1050℃, the chromium vapor generated is used to chromate graphite materials. The chromium plating device needs to be able to withstand ultra-high temperatures, be compatible with the characteristics of chromium vapor, and be able to precisely control the vapor distribution conditions. For example, a high-temperature vacuum sintering furnace can be selected.

[0035] It should be noted that the mechanism of chromium plating on graphite materials using chromium vapor generated at high temperatures in the above method is as follows: First, the Cu / Cr contact blank is composed of copper (Cu) and chromium (Cr), with a density of ≤1×10⁻⁶. -2 Under Pa conditions, at high temperatures of 400℃ to 1050℃, chromium atoms can gain enough energy to overcome the binding of metallic bonds and evaporate in large quantities from the Cu / Cr alloy into gaseous chromium atoms, i.e., chromium vapor. Copper has a boiling point slightly lower than this temperature range. Although a small amount of copper will evaporate, the evaporation rate of chromium is much higher than that of copper. Therefore, the vapor is mainly composed of chromium, which can reduce the contamination of the coating by copper.

[0036] Secondly, in a vacuum environment, for example when the vacuum level is ≤1×10 -2 At Pa, the amount of gas molecules in the space, such as residual air and impurity gases, is extremely small. Chromium vapor molecules can diffuse freely without significant collisions, covering a wider area. Furthermore, the design of evenly placing Cu / Cr contact blanks on graphite plates and mixing them with graphite pillars can further ensure the uniform distribution of chromium vapor in the space. That is, "vapor channels" can be formed in the gaps between blanks and in the staggered spaces between graphite plates and pillars, so that chromium vapor can simultaneously contact the upper and lower surfaces of the graphite plates and the outer circumference of the graphite pillars, avoiding uneven coating caused by excessively low local vapor concentration.

[0037] Finally, when the vacuum degree is ≤1×10 -2 At Pa, under temperatures of 400℃~1050℃, when chromium vapor molecules diffuse to the surface of graphite material, they are adsorbed due to the van der Waals forces of the graphite surface layer. Thus, they can gradually condense into solid chromium atoms at high temperatures, and some chromium atoms can react with carbon atoms on the graphite surface layer to form chromium-carbon compounds, such as Cr3C2 and Cr7C3. This allows the coating to bond with the graphite substrate through chemical bonds, significantly improving the adhesion of the coating.

[0038] In the above-mentioned chromium plating conditions, when the vacuum degree is ≤1×10 -2At a temperature of 400℃~1050℃, the boiling point of chromium can be precisely matched, ensuring sufficient chromium vapor generation while suppressing excessive copper evaporation and reducing copper impurities in the coating. The vacuum environment can reduce vapor diffusion resistance and prevent chromium vapor from reacting with oxygen to prevent the formation of Cr2O3 impurities, thus ensuring coating purity. In addition, the mixed placement and uniform distribution of Cu / Cr contact blanks and graphite components can ensure "no dead zone" coverage of vapor, ultimately achieving uniform thickness of the graphite plate and column coating, allowing the coating thickness deviation to be controlled within 5%.

[0039] It should be noted that in the above-mentioned chrome plating method, when the temperature reaches 400℃~1050℃, the graphite material hardly undergoes significant volatilization, for the following reasons: First, graphite is an allotrope of carbon with an extremely high sublimation temperature, approximately 3652℃~3697℃ under standard atmospheric pressure. Even in a vacuum environment, its sublimation temperature decreases slightly but remains well above the process temperature range of 400℃~1050℃. Second, prior to the aforementioned chromium plating treatment, the graphite material underwent pre-calcination. During this pre-calcination process, low-boiling-point impurities within the graphite, such as free carbon and small-molecule hydrocarbons, were thoroughly removed, resulting in a higher purity of the remaining graphite matrix, approaching theoretical purity. This leads to a more stable structure, stronger atomic bonding in high-purity graphite, and significantly improved thermal stability at high temperatures, further suppressing the possibility of volatilization.

[0040] In one possible implementation, the aforementioned preset vacuum level is ≤1×10⁻⁶. -2 Pa, the first preset temperature is 350℃~450℃, for example, 350℃, 400℃, or 450℃, with a heating rate of 3.0℃ / min~3.5℃ / min, and the first holding time is 0.5h~1.5h, for example, 0.5h, 0.8h, 1.0h, or 1.5h; the second preset temperature is 750℃~850℃, for example, 750℃, 780℃, 800℃, or 850℃, with a heating rate of 3.0℃ / min~3.5℃ / min, and the second holding time is 0.5h~1.5h; the third preset temperature is 1000℃~1200℃, for example, 1000℃, 1100℃, or 1200℃, with a heating rate of 4.0℃ / min~6.0℃ / min, and the third holding time is 0.8h. ~1.2h; the preset temperature for the fourth time is 1300℃~1400℃, the heating rate is 3.3℃ / min ~5.0℃ / min, and the duration of the fourth heat preservation is 3.0h~4.0h.

[0041] Optionally, the preset vacuum level can be 1×10⁻⁶. -3Pa.

[0042] It should be noted that in the above method, during the first heating and holding process, low-boiling-point impurities in the graphite material, such as adsorbed moisture, small-molecule hydrocarbons, and residual organic pollutants on the surface, can be addressed by slow heating and a holding time of 0.5 to 1.5 hours. This allows these impurities to fully volatilize and be removed by the vacuum system, preventing them from being trapped inside the graphite due to rapid heating. During the second heating and holding process, medium-boiling-point impurities, such as relatively stable hydrocarbon polymers and some inorganic salts, can be addressed by a similarly slow heating rate. This ensures uniform temperature transfer, allowing the impurities to decompose into smaller molecules at higher temperatures, such as CO and CH4, which then volatilize, further reducing ash content. During the third heating and holding process, high-boiling-point impurities, such as metal oxides and incompletely graphitized amorphous carbon, can be addressed. The heating rate is slightly accelerated at this stage to utilize high temperatures to promote the conversion of amorphous carbon into graphite, releasing some impurities. Simultaneously, metal oxides may react with carbon to generate gaseous products, such as those produced by the formation of MO. x The reaction of C → M + CO / CO2 generates gaseous compounds, which are then extracted. During the fourth heating and holding process, residual trace impurities, such as trace metal elements and gas molecules in the interstitial spaces of the crystal lattice, can be deeply purified. Furthermore, the long holding time allows impurities sufficient time to diffuse to the graphite surface and volatilize, ultimately increasing the graphite purity to the theoretical value and meeting the requirement of "no impurity volatilization pollution" for subsequent high-temperature processes.

[0043] In the aforementioned stepped heating and holding conditions, the first two low-temperature stages use a slow heating rate of 3.0℃ / min to 3.5℃ / min, which ensures a uniform temperature distribution within the graphite, thus avoiding new stress caused by localized thermal expansion differences. The two holding periods provide a time window for stress release, releasing approximately 60% of the initial stress. In the third heating stage, the heating rate is appropriately increased to 4.0℃ / min to 6.0℃ / min. At this point, the graphite material has already acquired a certain degree of thermal stability through the first two treatments, and rapid heating reduces the time loss in the low-stress stage. Simultaneously, the increased temperature promotes stronger interparticle bonding, resisting residual stress. In the fourth heating stage, a rate of 3.3℃ / min to 5.0℃ / min balances efficiency and stability, while the long holding period of 3h to 4h is crucial for stress release. This is because the graphite lattice vibration intensifies at high temperatures, enhancing the interparticle slippage ability, thereby completely releasing over 90% of the residual stress. This prevents the graphite material from cracking or deforming due to thermal shock during subsequent chromium plating and use.

[0044] In one possible implementation, the above-described chrome plating method is based on the following steps: In ≤1×10 -2 In a vacuum environment of Pa, the chromium plating device is heated for the first time. When the temperature reaches the first exhaust temperature, the first exhaust is performed. After the first exhaust is completed, the device is heated for the second time. When the temperature reaches the second exhaust temperature, the second exhaust is performed. After the second exhaust is completed, the device is heated for the third time. When the temperature reaches the preset chromium plating temperature, chromium plating is performed. After chromium plating is completed, heating is stopped. When the temperature of the chromium plating device drops to 55℃~60℃, the chromium plating process is completed.

[0045] It should be noted that during the above-mentioned chromium plating process, secondary heating and exhaust operations can gradually remove impurity gases from the chromium plating equipment, such as residual air and gases released from the graphite material; and the impurity gases are ≤1×10 -2 Operating in a vacuum environment allows chromium vapor to deposit on the surface of graphite materials in a purer environment, reducing defects such as pores and impurities in the coating, thereby forming a denser and more uniform chromium plating layer.

[0046] In one possible implementation, the first exhaust temperature is 400℃~450℃, for example, 400℃, 410℃, 420℃, 430℃, or 450℃, with a heating rate of 3℃ / min~5℃ / min, for example, 3℃ / min, 4℃ / min, or 5℃ / min, and the duration of the first exhaust is 1.5h~2.5h; the second exhaust temperature is 750℃~850℃, for example, 750℃, 780℃, 800℃, or 850℃, with a heating rate of 2℃ / min~3℃ / min, and the duration of the second exhaust is 1.5h~2.5h; the preset chrome plating temperature is 1000℃~1050℃, with a heating rate of 1℃ / min~2℃ / min, and the duration of the preset chrome plating is 2.0h~3.0h.

[0047] It should be noted that in the above chromium plating conditions, the first venting is carried out at 400℃~450℃ for 1.5~2.5h. This temperature range can efficiently remove low-boiling-point impurities remaining in the graphite material and equipment, such as moisture and adsorbed gases. The heating rate of 3℃ / min~5℃ / min ensures that the impurities are fully volatilized while avoiding incomplete volatilization or uneven heating of the material due to excessively rapid heating. The second venting is carried out at 750℃~850℃ for 1.5h~2.5h. For high-boiling-point impurities, such as deep gases and trace organic matter in the graphite micropores, the heating rate is reduced to 2℃ / min~3℃ / min and the holding time is extended to ensure that the impurities are fully released, creating a cleaner vacuum environment for subsequent chromium plating and reducing porosity and inclusion defects in the plating layer. The third chromium plating is carried out at 1000℃~1050℃ for 2.0h~3.0h. This temperature range is the optimal range for chromium vapor deposition, with a heating rate of 1℃ / min~2℃ / min. The slow heating process allows for precise control of the deposition rate of chromium atoms, resulting in uniform growth of the coating and the formation of a high-density, controllable-thickness chromium coating.

[0048] Furthermore, in the above-mentioned chromium plating process, by controlling the temperature in stages, a gradient transition interface structure can be formed between the graphite substrate and the chromium plating layer. Specifically, in the low-temperature stage, thermal stress damage to the graphite material due to sudden heating can be avoided. In the medium-high temperature stage, the weak diffusion bonding between chromium and the graphite surface can be promoted. Finally, a stable bond between the plating layer and the substrate is achieved at 1000℃~1050℃, thereby improving the overall mechanical properties and thermal shock resistance of the material.

[0049] Furthermore, in the aforementioned chromium plating process, at the low-temperature stage, when the temperature is 400℃~450℃, the copper-chromium material can volatilize in small amounts to generate chromium vapor, which can be initially deposited on the graphite surface to form a uniform underlayer. When the temperature is 750℃~850℃, the diffusion ability of chromium atoms gradually increases, and the plating layer gradually penetrates into the pores of the graphite surface to form a mechanical interlocking structure. When the temperature is 1000℃~1050℃, it can promote the dense accumulation of chromium atoms on the surface of the graphite material to form a more dense protective layer.

[0050] Furthermore, in the above-mentioned chromium plating methods, the chromium plating time in the low-temperature and medium-temperature stages focuses on the uniform spreading and interface bonding of the plating layer to ensure the continuity between the bottom layer and the middle layer; while in the chromium plating time in the high-temperature stage, the focus is on the densification process of the plating layer, using sufficient diffusion time to make the chromium layer structure more stable, thereby reducing micro-defects in the plating layer.

[0051] Furthermore, the chromium plating method described above can significantly increase the density of the chromium plating layer, thereby effectively blocking gas penetration under high-temperature conditions during the re-sintering process and enhancing the stability of the sintering material in a vacuum environment. Secondly, the multi-layer structure formed by the gradient temperature can alleviate plating cracking caused by thermal expansion differences and improve the durability of the sintering material under repeated high and low temperature cycles. In addition, the dense chromium layer formed at the high-temperature stage can significantly improve the surface hardness and wear resistance of the sintering material, thereby extending the service life of the vacuum sintering material.

[0052] To achieve the above objectives, the present invention also provides a vacuum sintering material, which is prepared according to the above method, has a low coefficient of friction, and exhibits excellent wear resistance and high temperature resistance.

[0053] To achieve the above objectives, the present invention also provides a vacuum firing device, which includes a plate-shaped vacuum firing material and a column-shaped vacuum firing material. The column-shaped vacuum firing material is disposed at the edge of the plate-shaped vacuum firing material, and the spacing between the column-shaped vacuum firing materials is 15cm to 20cm. The plate-shaped vacuum firing material and the column-shaped vacuum firing material are prepared according to the above-described preparation method.

[0054] In one possible implementation method, the thickness of the vacuum-supported material of the plate type is 3mm to 5mm; the diameter of the vacuum-supported material of the column type is 10mm to 12mm.

[0055] Optionally, in the above-mentioned method for preparing vacuum sintering materials, when preparing the plate-shaped vacuum sintering material, plate-shaped graphite materials, such as graphite plates, can be selected.

[0056] Optionally, in the above-mentioned method for preparing vacuum sintering materials, when preparing the column-shaped vacuum sintering material, column-shaped graphite materials, such as graphite columns, can be selected.

[0057] It should be noted that in the vacuum firing device, when the thickness of the plate-type vacuum firing material is 3mm~5mm, it ensures sufficient mechanical strength to avoid deformation due to its own weight or the workpiece under high temperature, while also preventing uneven heat conduction due to excessive thickness. This ensures a uniform temperature gradient during pre-firing and a consistent surface temperature during chromium plating. The column-type vacuum firing material, as a supporting component, can balance strength and space ratio. If the diameter is too small, it is easy to bend at high temperature, while if the diameter is too large, it will squeeze the space for chromium vapor circulation and affect the uniformity of the coating. When the diameter of the column-type vacuum firing material is 10mm~12mm, it can ensure stable support of the column while providing sufficient channels for the diffusion of chromium vapor in the vacuum firing device.

[0058] It should be noted that when the sintering material prepared by the above method is used to manufacture the above-mentioned vacuum sintering device, the resulting vacuum sintering device operates at high temperatures, for example, during the sintering of Cu / Cr contact blanks, with almost no additional gas release. At the same time, the chromium plating layer is dense and firmly bonded to the graphite substrate, and is not easily decomposed or volatilized at high temperatures. This can avoid the problem of vacuum level decrease or contamination of Cu / Cr contact blanks due to the material's own volatiles. It can also ensure that the sintered Cu / Cr contact blanks are sintered in a stable vacuum environment to reduce defects such as porosity and oxidation.

[0059] It should be understood that the above-mentioned vacuum sintering device can be a single-layer structure or a multi-layer structure, and the height of the column-type vacuum sintering material should be slightly higher than the height of the workpiece, for example, slightly higher than the height of the Cu / Cr contact. This can prevent the workpiece from slipping due to slight vibration in a vacuum environment. When the vacuum sintering device is a multi-layer structure, the column-type vacuum sintering material, such as a graphite column, can serve as a support point for the upper plate-type vacuum sintering material, such as a graphite plate, thereby forming a three-dimensional sintering space and improving the utilization rate of the furnace cavity.

[0060] It should be noted that in the aforementioned vacuum sintering apparatus, the plate-type vacuum sintering material, such as a graphite plate, serves as the base plate of the vacuum sintering apparatus. It is a flat sheet structure with a thickness of 3mm to 5mm. After chrome plating, it has a regular shape, such as square or round. The dimensions of the plate-type vacuum sintering material, such as a graphite plate, can be designed according to the sintering furnace cavity. When the column-type vacuum sintering material, such as a graphite column, is cylindrical with a diameter of 10mm to 12mm, the specific height can be designed according to the load-bearing requirements, and should usually be slightly higher than the height of the workpiece to be sintered. When the column-type vacuum sintering material is placed at the edge of the plate-type vacuum sintering material, for example, the graphite column is vertically fixed at the edge of the graphite plate and evenly distributed along the outer periphery of the plate-type vacuum sintering material, an "edge enclosure" structure can be formed.

[0061] Furthermore, when the spacing between the column-type vacuum sintering materials is 15cm to 20cm, it facilitates the integral molding of the column-type vacuum sintering materials and the plate-type vacuum sintering materials. During vacuum sintering, it avoids excessive obstruction and guides the gases in the vacuum environment, such as chromium vapor, to diffuse evenly along the gaps of the column-type vacuum sintering materials, such as graphite columns, to the workpiece surface at the center and edges of the device, avoiding problems of uneven coating or sintering caused by "airflow dead zones". At the same time, this spacing can accelerate the removal of volatiles by the vacuum system, maintaining the vacuum stability inside the furnace.

[0062] Furthermore, when the vacuum firing material of the above-mentioned plate type is square, the vacuum firing device prepared as a whole presents a cuboid structure; when the vacuum firing material of the above-mentioned plate type is circular, the vacuum firing device prepared as a whole presents a cylindrical structure.

[0063] Furthermore, in the aforementioned vacuum firing device, the connection between the column-type vacuum firing material and the plate-type vacuum firing material is integrally formed. This reduces seams, improves the stability or precision of the device, and facilitates replacement.

[0064] Furthermore, when the aforementioned column-type vacuum-supported material and plate-type vacuum-supported material form an "edge enclosure" structure, the workpiece, such as a Cu / Cr contact blank, can be confined within the effective area of ​​the plate-type vacuum-supported material to avoid uneven heating caused by placement misalignment. Moreover, this "edge enclosure" structure can resist the thermal expansion stress of the graphite plate to reduce the problem of plate edge warping and extend the overall service life of the device.

[0065] Optionally, when the volume of the above-mentioned vacuum firing device is large or when the area of ​​the plate-shaped vacuum firing material is large, an appropriate number of column-type vacuum firing materials, such as graphite columns, can be evenly arranged in the middle of the base plate to support the firing device and prevent the device from deforming.

[0066] It should be understood that the vacuum sintering device of the present invention can be used in high temperature and high vacuum sintering scenarios. Furthermore, the material of the vacuum sintering device has strong resistance to wear and deformation, and can be reused many times, reducing downtime costs caused by frequent replacements. Moreover, the chromium plating has excellent corrosion resistance, is easy to clean daily, and reduces maintenance difficulty.

[0067] To achieve the above objectives, the present invention also provides an application of the vacuum sintering device, which is applied to the vacuum sintering of Cu / Cr contact materials.

[0068] Optionally, when the above-mentioned vacuum sintering device is applied to the vacuum sintering of Cu / Cr contact materials, the selection of the sintering furnace should meet the compatibility with the graphite vacuum sintering device, that is, the heating element and insulation material inside the selected sintering furnace do not react with graphite, and the space is sufficient to accommodate the multi-layer structure of the sintering device. For example, a horizontal vacuum sintering furnace, a vertical vacuum sintering furnace, or an atmosphere-protected vacuum sintering furnace can be selected.

[0069] It should be understood that when the above-mentioned vacuum sintering device is used for vacuum sintering of Cu / Cr contact materials, the height of the column-shaped vacuum sintering material set on the device should be slightly higher than the height of the Cu / Cr contact material.

[0070] It should be noted that the vacuum sintering material used in the aforementioned vacuum sintering device, after being chrome-plated, not only has a smooth surface but also reduces the adhesion between the Cu / Cr contact material and the sintering device at high temperatures, thereby improving the product yield. In addition, when the thickness of the plate-type vacuum sintering material included in the vacuum sintering device is 3mm~5mm, it can ensure more uniform heat conduction during the sintering process. Furthermore, when the diameter of the column-type vacuum sintering material is 10mm~12mm, it will not block the heat flow, thereby avoiding the problem of local temperature gradients in the sintering device. This can ensure that the temperature deviation of each area of ​​the sintered Cu / Cr contact material is significantly smaller, thereby improving product performance.

[0071] The technical solution of the present invention will be described in detail below through specific embodiments. In the specific embodiments, the graphite material is specifically selected from graphite plates and graphite columns; in the chromium plating process, the copper-chromium material is specifically selected from Cu / Cr contact blanks.

[0072] Example 1 A method for preparing a vacuum sintering material includes the following steps: S10. Pre-fire the graphite plate and graphite pillars as follows: S101. Select graphite plates and graphite pillars with a purity ≥99.8% and a surface roughness Ra≤0.1µm, wherein the thickness of the graphite plate is 3mm and the diameter of the graphite pillar is 10mm. S102. Select a graphitization furnace as the pre-calcination device, send the graphite plate and graphite column into the furnace, and adjust its vacuum degree to ≤1×10⁻⁶. -2 Pa, then the temperature is increased at a rate of 3.0℃ / min. When the temperature reaches 350℃, the first holding time is 1.5h. After the first holding time, the temperature is increased again at a rate of 3.0℃ / min. When the temperature reaches 750℃, the second holding time is 1.5h. After the second holding time, the temperature is increased a third time at a rate of 4.0℃ / min. When the temperature reaches 1000℃, the third holding time is 1.2h. After the third holding time, the temperature is increased a fourth time at a rate of 3.3℃ / min. When the temperature reaches 1300℃, the fourth holding time is 4.0h. After the fourth holding time, the pre-firing treatment is completed.

[0073] S20. The pre-fired graphite plates and graphite pillars are subjected to chrome plating, and the specific method is as follows: Chromium plating was performed in a high-temperature vacuum sintering furnace, with the furnace temperature adjusted to ≤1×10⁻⁶. -2In a vacuum environment of Pa, Cu / Cr contact blanks are evenly placed on a graphite plate and mixed with graphite pillars, then sent into the furnace for the first heating at a rate of 3℃ / min. When the temperature reaches 400℃, the first venting is performed for 2.5 hours. After the first venting, the temperature is increased for the second time at a rate of 2℃ / min. When the temperature reaches 750℃, the second venting is performed for 2.5 hours. After the second venting, the temperature is increased for the third time at a rate of 1℃ / min. When the temperature reaches 1000℃, chromium plating is performed for 3.0 hours. After chromium plating, heating is stopped, and the chromium plating process is completed when the temperature of the chromium plating device drops to 55℃.

[0074] During the chromium plating process, Cr atoms in the contact blank gradually gain enough energy to evaporate into a gaseous state. When chromium vapor molecules diffuse to the surface of the graphite plate and graphite pillar, they are adsorbed by the van der Waals forces on the surface of the graphite plate and graphite pillar, and gradually condense into solid chromium atoms at high temperature, thus depositing on the surface of the graphite plate and graphite pillar to form a dense chromium plating layer.

[0075] The vacuum-fired material is obtained through steps S10 and S20.

[0076] During the pre-calcination process of S102, impurities such as moisture, hydrocarbons, and ash adsorbed inside the graphite can be deeply removed, resulting in a final graphite matrix purity of over 99.95%. This ensures that the workpiece will not be contaminated by the volatilization of impurities during subsequent high-temperature use, guaranteeing the purity of the calcined material. Furthermore, during the chromium plating process, chromium vapor undergoes physical adsorption and slight chemical bonding with the graphite surface to form a Cr3C2 transition layer. The bonding strength between this plating layer and the substrate is ≥50MPa, which is far higher than that of ordinary electroplating layers, preventing the plating layer from peeling off during use.

[0077] Secondly, the volatile components in the graphite have been thoroughly removed during the pre-sintering treatment of S102, and the chromium plating is not easily decomposed at high temperatures. Therefore, during vacuum sintering, this vacuum-supported material releases almost no additional gas, maintaining the stability of the vacuum system and ensuring that the vacuum degree fluctuation is ≤1×10⁻⁶. -2 Pa avoids the formation of porosity or oxidation defects in the workpiece due to gas impurities.

[0078] Furthermore, when the thickness of the graphite plate is 3mm, the heat transfer during the sintering process is uniform, and the chromium plating does not affect the thermal conductivity of the graphite. This ensures that the temperature deviation of each area of ​​the sintered workpiece is ≤±5℃, thus improving the consistency of product performance.

[0079] A vacuum firing apparatus is manufactured using a firing material prepared by S10 and S20. The resulting vacuum firing apparatus includes a graphite plate and a graphite column, such as... Figure 2As shown, the graphite pillars are positioned at the edge of the graphite plate, and the spacing between the graphite pillars is 15cm.

[0080] The vacuum sintering device can be cuboid or cylindrical, depending on the shape of the graphite plate and the sintering furnace. The sintering layer of the device can be a single-layer structure (i.e., a single unit) or a multi-layer structure. In a single-layer or multi-layer structure, the height of the graphite column is slightly higher than the height of the workpiece to prevent the workpiece from slipping due to slight vibration in a vacuum environment. When the vacuum sintering device is a multi-layer structure, the graphite column serves as a support for the upper graphite plate, forming a three-dimensional sintering space and improving the utilization rate of the furnace cavity.

[0081] This vacuum sintering device has the combined advantages of high stability, high oxidation resistance, and high wear resistance. It is especially suitable for sintering precision workpieces in high temperature and high vacuum environments. It can ensure its own structural stability and long service life, while avoiding contamination of the sintered material, ultimately improving the product qualification rate and performance stability.

[0082] The vacuum sintering apparatus was applied to the vacuum sintering of Cu / Cr contact materials. The specific application method is as follows: A10. Select a single-layer vacuum firing device and evenly place the Cu / Cr contact blanks in the bottom layer of the vacuum firing device; A20. Select a horizontal vacuum sintering furnace for sintering; place the vacuum sintering device containing the Cu / Cr contact blanks from A10 into the sintering furnace, ensuring stability during the process to prevent the blanks from slipping; adjust the furnace to a vacuum environment and set the sintering temperature to 1020℃ with a heating rate of 5℃ / min. When the furnace temperature reaches 1020℃, adjust the holding time according to the sintering requirements of the Cu / Cr contact blanks. After holding, the sintering of the Cu / Cr contact blanks is complete, yielding the finished Cu / Cr contacts.

[0083] Cu / Cr contacts obtained by sintering with A10 and A20 have a uniform internal structure and stable composition distribution, avoiding performance deviations caused by process fluctuations and ensuring the consistency of core properties such as conductivity and arc resistance. Furthermore, the sintering process avoids the problem of adhesion or friction damage between the blank and the sintering device. At the same time, the smooth feeding into the furnace avoids surface bumps caused by the blank slipping, ensuring the surface integrity of the finished contact.

[0084] The vacuum sintering device in Example 1 is plated with a chromium coating, which can reduce the mutual diffusion or reaction between the copper / chromium (Cu / Cr) contact blank and the sintering device during the sintering process, reduce the risk of impurity contamination, and further ensure the purity and performance of the Cu / Cr contact.

[0085] Example 2 A method for preparing a vacuum sintering material includes the following steps: S10. Pre-fire the graphite plate and graphite pillars as follows: S101. Select graphite plates and graphite pillars with a purity ≥99.8% and a surface roughness Ra≤0.1µm, wherein the thickness of the graphite plate is 5mm and the diameter of the graphite pillar is 12mm. S102. Select a graphitization furnace as the pre-calcination device, send the graphite plate and graphite column into the furnace, and adjust its vacuum degree to ≤1×10⁻⁶. -2 Pa, then the temperature is increased at a rate of 3.5℃ / min. When the temperature reaches 450℃, the first holding time is 0.5h. After the first holding time, the temperature is increased again at a rate of 3.5℃ / min. When the temperature reaches 850℃, the second holding time is 0.5h. After the second holding time, the temperature is increased a third time at a rate of 6.0℃ / min. When the temperature reaches 1200℃, the third holding time is 0.8h. After the third holding time, the temperature is increased a fourth time at a rate of 5.0℃ / min. When the temperature reaches 1400℃, the fourth holding time is 3.0h. After the fourth holding time, the pre-firing treatment is completed.

[0086] S20. The pre-fired graphite plates and graphite pillars are subjected to chrome plating, and the specific method is as follows: Chromium plating was performed in a high-temperature vacuum sintering furnace, with the furnace temperature adjusted to ≤1×10⁻⁶. -2 In a vacuum environment of Pa, Cu / Cr contact blanks are evenly placed on a graphite plate and mixed with graphite pillars, then sent into the furnace for the first heating at a rate of 5℃ / min. When the temperature reaches 450℃, the first venting is performed for 1.5 hours. After the first venting, the temperature is increased for the second time at a rate of 3℃ / min. When the temperature reaches 850℃, the second venting is performed for 1.5 hours. After the second venting, the temperature is increased for the third time at a rate of 2℃ / min. When the temperature reaches 1050℃, chromium plating is performed for 2.0 hours. After chromium plating, heating is stopped, and the chromium plating process is completed when the temperature of the chromium plating device drops to 60℃.

[0087] During the chromium plating process, the Cr atoms in the Cu / Cr contact blank gradually gain enough energy to evaporate into a gaseous state. When the chromium vapor molecules diffuse to the surface of the graphite plate and graphite pillar, they are adsorbed by the van der Waals forces on the surface of the graphite plate and graphite pillar, and gradually condense into solid chromium atoms at high temperature, depositing on the surface of the graphite plate and graphite pillar, thus forming a dense chromium plating layer.

[0088] The vacuum-fired material is obtained through steps S10 and S20.

[0089] In steps S10 and S20, during the preparation of the vacuum sintering material, the pre-sintering process can deeply remove impurities such as moisture, hydrocarbons, and ash adsorbed inside the graphite, resulting in a final graphite matrix purity of over 99.95%. This ensures that the workpiece will not be contaminated by impurities during subsequent high-temperature use, guaranteeing the purity of the sintered workpiece. Furthermore, when the chromium plating temperature is 1050℃, chromium vapor will undergo physical adsorption and chemical bonding with the graphite surface to form a Cr3C2 transition layer. This results in a bonding strength between the plating layer and the substrate of ≥60MPa, which is much higher than that of ordinary electroplating layers, thus preventing the plating layer from peeling off during use.

[0090] The volatile components in the graphite have been thoroughly removed during the pre-sintering process of S10, and the chromium plating is not easily decomposed at high temperatures. Therefore, during vacuum sintering, this vacuum sintering material releases almost no additional gas, maintaining the stability of the vacuum system and ensuring that the vacuum degree fluctuation is ≤1×10⁻⁶. -3 Pa avoids defects such as porosity or oxidation of the workpiece caused by gas impurities during firing.

[0091] When the thickness of the graphite plate is 5mm, the heat transfer is uniform, and the chromium plating does not affect the thermal conductivity of the graphite. This ensures that the temperature deviation of each area of ​​the workpiece being fired is ≤±6℃, thus improving the consistency of product performance.

[0092] A vacuum firing apparatus is manufactured using the firing material prepared in S10 and S20 above, such as... Figure 2 As shown, the obtained vacuum firing device includes a graphite plate and graphite columns. The graphite columns are located at the edge of the graphite plate, and the spacing between the graphite columns is 20cm.

[0093] The vacuum sintering device can be rectangular in shape, and the sintering layer of the device can be a single-layer structure, i.e., a single-unit device, or a multi-layer structure device. In a single-unit device or a multi-layer structure device, the height of the graphite column is slightly higher than the height of the workpiece, which can prevent the workpiece from slipping due to slight vibration in a vacuum environment. When the vacuum sintering device is a multi-layer structure, the graphite column serves as a support device, acting as a support point for the upper graphite plate, thereby forming a three-dimensional sintering space and improving the utilization rate of the furnace cavity.

[0094] The above-mentioned vacuum sintering device is applied to the vacuum sintering of Cu / Cr contact blanks. The specific application method is as follows: A10. Select a single-unit vacuum firing device, and then evenly place the Cu / Cr contact blanks in the bottom layer of the vacuum firing device; A20. Select a horizontal vacuum sintering furnace for sintering. Place the vacuum sintering device (A10) containing the Cu / Cr contact blanks into the sintering furnace. During the placement process, keep the furnace stable to prevent the blanks from slipping. Adjust the furnace to a vacuum environment and set the sintering temperature to 1050℃ with a heating rate of 3℃ / min. When the furnace temperature reaches 1050℃, adjust the holding time according to the requirements of the Cu / Cr contacts. After the holding time is completed, the sintering of the Cu / Cr contact blanks is finished, and the finished Cu / Cr contacts are obtained.

[0095] The vacuum-sintered material obtained in Example 2 after processes S10 and S20 was scanned using a scanning electron microscope. The results are as follows: Figure 3 As shown.

[0096] Depend on Figure 3 It can be seen that the vacuum-sintered material obtained after S10 and S20 has a smooth surface, a uniformly distributed chromium plating layer, and no obvious unevenness or severe defect areas. This indicates that the graphite matrix has good structural stability after pre-sintering, providing a good foundation for subsequent chromium plating. This allows the chromium layer to be deposited relatively uniformly on the graphite surface during the plating process, which is beneficial to ensuring the consistency of the graphite material's performance. Secondly, from... Figure 3 The structure presented shows no pores or voids, indicating that the chromium plating layer has a certain degree of density. This density helps improve the corrosion resistance and oxidation resistance of graphite materials, enabling better isolation of the graphite matrix from external environmental erosion in applications such as vacuum firing, thus extending the material's service life. Furthermore, from... Figure 3 The morphology of the chromium plating layer shows that the bonding between the chromium plating layer and the graphite substrate is good, with no signs of peeling or separation. This is because the internal structure of the graphite is improved by gradient heating and multiple heat preservation during the pre-firing process, which allows chromium atoms to combine more fully with the graphite surface during chromium plating, enhancing the bonding force between the plating layer and the substrate. This helps the graphite material maintain stable performance during use.

[0097] Energy dispersive spectroscopy (EDS) analysis was performed on the chromium plating of the vacuum-sintered material obtained in Example 2 after processes S10 and S20. The results are as follows: Figure 4 As shown.

[0098] Figure 4 The corresponding data results of the energy spectrum scan are shown in Table 1.

[0099] Table 1

[0100] according to Figure 4As shown in the figure and combined with the values ​​in Table 1, it can be seen that the chromium coating mainly contains Cr and C elements as detected by energy dispersive spectroscopy (EDS). This indicates that the chromium coating of the vacuum-fired materials obtained through S10 and S20 processes mainly contains Cr and C elements. The mass percentage of Cr is 86.41%, and the atomic percentage is 59.50%, which is relatively high, indicating that the chromium coating is rich in Cr and has high purity. This is beneficial to ensuring the performance of the chromium coating, such as good corrosion resistance and oxidation resistance. In addition, the detected C element comes from the graphite matrix, which indicates that the chromium coating and the graphite matrix are well bonded. This is because the Cr element signal of the coating and the C element signal of the matrix can be captured simultaneously during the EDS detection process, reflecting a reasonable element distribution at the interface between the coating and the matrix. This good bonding helps to improve the adhesion of the coating, making it less likely to fall off during use and enhancing the overall stability of the material.

[0101] Secondly, in the chromium plating process of this invention, chromium atoms are deposited on the surface of the graphite material. The chromium plating layer fills the micropores and uneven areas of the graphite surface, forming a mechanical inlay, similar to a "mortise and tenon" structure, so that the chromium plating layer and the graphite substrate are bonded together by physical mechanical force. Furthermore, under high-temperature chromium plating conditions, chromium atoms can chemically react with carbon atoms on the graphite surface to form certain chemical bonds, such as the formation of chromium carbides, such as Cr3C2 or Cr7C3 chromium carbide compounds. These chromium carbide compounds can significantly enhance the bonding force between the chromium plating layer and the graphite substrate, making the plating layer more resistant to external forces. Under conditions of force and temperature changes, it is not easy to detach from the graphite matrix. In addition, the carbon-chromium compound can improve the hardness and wear resistance of graphite materials, enabling them to withstand stronger friction and wear, making them suitable for working conditions with high wear resistance requirements. At the same time, the good chemical stability of the carbon-chromium compound helps to improve the corrosion resistance of graphite materials, protecting the graphite matrix from chemical corrosion. Furthermore, the carbon-chromium compound can, to a certain extent, adjust the coefficient of thermal expansion of graphite materials, reduce the thermal stress caused by temperature changes, and improve its stability and reliability in high-temperature environments, meeting the needs of high-temperature applications such as vacuum firing.

[0102] Comparative Example 1 is set up in Example 2.

[0103] In Comparative Example 1, in the method of pre-firing the graphite plate and graphite column in S10, S101 is the same as in Example 2; S102 is: selecting a graphitization furnace as the pre-firing device, sending the graphite plate and graphite column into the furnace, and adjusting its vacuum degree to ≤1×10 -2Pa, and then the temperature is increased at a rate of 3.5℃ / min. When the temperature reaches 1200℃, it is held for 4.8h to complete the pre-firing treatment; S20 is the same as in Example 2; after S10 and S20, the vacuum-fired material is obtained.

[0104] Comparative Example 2 is set up under Example 2.

[0105] In Comparative Example 2, S10 is the same as in Example 2; in S20, the method for chrome plating the pre-sintered graphite plate and graphite column is as follows: a high-temperature vacuum sintering furnace is selected for chrome plating, and the furnace temperature is adjusted to ≤1×10⁻⁶. -2 In a vacuum environment of Pa, Cu / Cr contact blanks are evenly placed on a graphite plate and mixed with graphite pillars. They are then sent into a furnace for heating at a rate of 5℃ / min. When the temperature reaches 1050℃, chromium plating is performed for 5.0 hours. After chromium plating is completed, heating is stopped. When the temperature of the chromium plating device drops to 60℃, the chromium plating process is complete.

[0106] The performance of the vacuum-fired materials obtained in Example 2, Comparative Example 1, and Comparative Example 2 were tested, and the results are shown in Table 2.

[0107] Table 2

[0108] By comparing and analyzing the data in Table 2, it can be seen that (1) in terms of the uniformity of the chromium plating layer, compared with Comparative Example 1 and Comparative Example 2, the distribution of Example 2 is more uniform and the thickness deviation is smaller. This is because Example 2 uses multi-stage heating and heat preservation in the chromium plating process to carry out degassing and chromium plating, which can accurately control the deposition rate of chromium atoms in different temperature stages; while the single-stage high-temperature chromium plating in Comparative Example 2 is prone to thickness differences due to local temperature fluctuations and uneven volatilization of chromium source; (2) in terms of the density of the chromium plating layer, Example 2 can gradually remove residual gas in the graphite through multi-stage pre-firing and multi-stage heat preservation. Mild chromium plating can gradually form a dense plating layer; however, the pre-firing treatment in Comparative Example 1 did not involve staged venting, and the single-stage chromium plating in Comparative Example 2 was prone to forming a loose structure due to rapid deposition, thereby reducing the plating density; (3) Regarding the surface roughness of the chromium plating, Example 2 avoided substrate deformation by multi-stage heating during the pre-firing treatment, and the multi-stage temperature control of chromium plating made the plating layer grow uniformly, resulting in a lower and smoother surface roughness; while the single-stage heating of the pre-firing treatment in Comparative Example 1 was prone to causing slight deformation of the substrate, and the single-stage chromium plating in Comparative Example 2 was prone to plating particle agglomeration, thereby resulting in a lower surface roughness. (4) Regarding wear and corrosion resistance, the high-density, low-porosity coating of Example 2 can effectively block corrosive media, while the small number of pores in the coating of Comparative Example 1 can easily become corrosion channels, and the high porosity of Comparative Example 2 significantly reduces corrosion resistance and wear resistance; (5) Regarding oxidation resistance, the dense chromium coating of Example 2 can form a continuous and stable oxide film, while the pores in the coating of Comparative Example 1 can lead to the penetration of oxidizing media, and the loose coating of Comparative Example 2 cannot form an effective oxide protective layer; (6) Regarding the adhesion of the coating, Example 2 uses multi-stage pre-firing. The surface activity of the substrate is improved by segmented venting, heat preservation and chromium plating, which can achieve gradient bonding between the coating and the substrate; while the pre-firing treatment of Comparative Example 1 did not fully activate the surface activity of the substrate, and the single-segment chromium plating of Comparative Example 2 is prone to interface defects due to thermal stress, thereby reducing the bonding force of the coating; (7) In terms of internal stress, Example 2 can gradually release internal stress through multi-segment pre-firing, segmented heat preservation and chromium plating; while the single-segment heating of Comparative Example 1 caused residual internal stress in the substrate, and the single-segment rapid heating of Comparative Example 2 caused high internal stress due to the difference in thermal expansion coefficient between the coating and the graphite material.

[0109] Analysis of the data in Table 2 shows that the vacuum sintering material prepared in Example 2 exhibits significant advantages in physical, chemical, and mechanical properties. This is because, in the technical solution of this invention, during the pre-sintering process, a four-stage gradient heating (450℃→850℃→1200℃→1400℃) and segmented heat preservation gradually release the internal stress of graphite, reducing thermal deformation. Furthermore, the high-temperature stage (1400℃, 3h) promotes the volatilization of impurities within the graphite, improving matrix purity and optimizing the graphite microstructure, providing a uniform and dense substrate for subsequent chromium plating. Secondly, during the chromium plating process, a three-stage gradient heating (450℃→850℃→1050℃) is used for degassing, heat preservation, and chromium plating, coupled with a gradually decreasing heating rate, enabling the chromium layer to achieve "initial adhesion → diffusion penetration → densification." The step-like growth process results in strong adhesion between the coating and the substrate, high density, and good surface uniformity. In the final sintering material, the chromium coating is firmly bonded to the graphite substrate and is not easily detached. The coating has high density, excellent oxidation resistance and wear resistance, and can meet the stringent requirements of the vacuum sintering environment for the stability of graphite materials.

[0110] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for preparing a vacuum-sintered material, characterized in that, The preparation method includes the following steps: Pre-sintering of graphite materials; The graphite material that has undergone the pre-calcination treatment is then subjected to chromium plating. The method for the pre-firing process is as follows: Under a preset vacuum level, the graphite material is heated for the first time, and when the temperature reaches the first preset temperature, it is held at that temperature for the first time. After the first holding is completed, the temperature is raised for the second time, and when the temperature reaches the second preset temperature, it is held at that temperature for the second time. After the second holding is completed, the temperature is raised for the third time, and when the temperature reaches the third preset temperature, it is held at that temperature for the third time. After the third holding is completed, the temperature is raised for the fourth time, and when the temperature reaches the fourth preset temperature, it is held at that temperature for the fourth time. After the fourth holding is completed, the pre-firing process is finished. The chromium plating method is as follows: in the vacuum environment, the graphite material is chromium-plated using chromium vapor generated during the sintering of copper-chromium material at 400℃~1050℃. The chrome plating process is implemented based on the following steps: In ≤1×10 -2 In a vacuum environment of Pa, the chromium plating device is heated for the first time. When the temperature reaches the first exhaust temperature, the first exhaust is performed. After the first exhaust is completed, the device is heated for the second time. When the temperature reaches the second exhaust temperature, the second exhaust is performed. After the second exhaust is completed, the device is heated for the third time. When the temperature reaches the preset chromium plating temperature, chromium plating is performed. After the chromium plating is completed, heating is stopped. When the temperature of the chromium plating device drops to 55℃~60℃, the chromium plating process is completed.

2. The preparation method according to claim 1, characterized in that, The preset vacuum degree is ≤1×10 -2 Pa, the first preset temperature is 350℃~450℃, the heating rate is 3.0℃ / min~3.5℃ / min, and the first holding time is 0.5h~1.5h; the second preset temperature is 750℃~850℃, the heating rate is 3.0℃ / min~3.5℃ / min, and the second holding time is 0.5~1.5h; the third preset temperature is 1000℃~1200℃, the heating rate is 4.0℃ / min~6.0℃ / min, and the third holding time is 0.8h~1.2h; the fourth preset temperature is 1300℃~1400℃, the heating rate is 3.3℃ / min~5.0℃ / min, and the fourth holding time is 3.0h~4.0h.

3. The preparation method according to claim 1, characterized in that, The first exhaust temperature is 400℃~450℃, the heating rate is 3℃ / min~5℃ / min, and the duration of the first exhaust is 1.5h~2.5h; the second exhaust temperature is 750℃~850℃, the heating rate is 2℃ / min~3℃ / min, and the duration of the second exhaust is 1.5h~2.5h; the preset chrome plating temperature is 1000℃~1050℃, the heating rate is 1℃ / min~2℃ / min, and the duration of the chrome plating is 2.0h~3.0h.

4. A vacuum-sintered material, characterized in that, The vacuum-supported material is prepared by the preparation method described in any one of claims 1 to 3.

5. A vacuum firing device, characterized in that, The vacuum firing device includes a plate-shaped vacuum firing material and a column-shaped vacuum firing material. The column-shaped vacuum firing material is disposed at the edge of the plate-shaped vacuum firing material, and the spacing between the column-shaped vacuum firing materials is 15cm to 20cm. Both the plate-shaped vacuum firing material and the column-shaped vacuum firing material are prepared by the preparation method described in any one of claims 1 to 3.

6. The vacuum firing apparatus according to claim 5, characterized in that, The thickness of the plate-type vacuum firing material is 3mm to 5mm; the diameter of the column-type vacuum firing material is 10mm to 12mm.

7. An application of a vacuum firing device, characterized in that, The vacuum sintering apparatus described in claim 5 or 6 is applied to the vacuum sintering of copper-chromium contact materials.

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