High-density fine-grain pure tungsten crucible and method for manufacturing the same

Abstract

The application discloses a high-density fine-grain pure tungsten crucible and a preparation method thereof, and belongs to the technical field of pure tungsten crucibles. The preparation method comprises the following steps: mixing two kinds of pure tungsten powder with different average particle sizes to obtain mixed raw materials with an average particle size of 3.5-5.5 mu m and a diameter distance of 1.8-2, isostatic pressing is performed under a pressure of 210-250 MPa, sintering treatment is performed on the obtained crucible blank, and a high-density fine-grain pure tungsten crucible is obtained; the sintering treatment comprises the following steps: the crucible blank is raised to a highest temperature of 2350-2370 DEG C through multiple temperature rising and holding stages, and then is lowered to a second highest temperature of 2250-2300 DEG C and is subjected to long-time holding. The preparation process is simple, the preparation efficiency is high, the obtained pure tungsten crucible has a density greater than 18.5 g / cm 3 , an average grain size less than 30 mu m, a uniform microstructure without defects, a long service life and stability.

Description

Technical Field

[0001] This invention relates to the technical field of pure tungsten crucibles, and particularly to a high-density fine-grained pure tungsten crucible and its preparation method. Background Technology

[0002] Pure tungsten crucibles, as a crucial high-temperature container, are widely used in harsh operating environments ranging from 1500℃ to 2100℃. Within this temperature range, the material must possess excellent high-temperature strength, high density (typically requiring no less than 18.3 g / cm³), and a highly uniform microstructure to ensure its service stability and lifespan. Currently, the industry commonly employs powder metallurgy to prepare pure tungsten crucibles. This involves using pure tungsten powder as raw material, sequentially undergoing processes such as powder loading, pressing, and high-temperature sintering to obtain a semi-finished product, which is then machined to obtain the final product.

[0003] Despite significant improvements in the overall service life of pure tungsten crucibles over the years, several issues remain in practical applications, including: substantial differences in service life between individual crucibles, resulting in significant variations in lifespan; and some crucibles exhibiting cracking early in their service life, leading to abnormal failure. Analysis indicates that this cracking primarily stems from minute defects within or on the surface of the material. Under repeated cyclic thermal stress, these micro-defects gradually expand into macroscopic cracks, ultimately causing crucible breakage. Cyclic thermal stress is mainly determined by actual operating conditions, while the minute defects are often caused by a combination of external mechanical impact, chemical corrosion, and internal structural defects within the material.

[0004] To address these challenges, there is an urgent need to develop a pure tungsten crucible with higher density (greater than 18.5 g / cm³), finer grain size, and virtually no sintering defects. However, its preparation process presents significant difficulties: pursuing higher density often results in abnormal grain growth, making it difficult to simultaneously achieve both high density and fine grain structure—two key indicators. Furthermore, conventional tungsten powder often exhibits fine particle agglomeration, which can easily induce localized structural inhomogeneities and even defects during sintering, directly affecting the uniformity of material properties. Simultaneously, strict control of powder particle size distribution is required during preparation to ensure sufficient strength in the green body to meet the requirements of subsequent processing and treatment.

[0005] Therefore, there is an urgent need in the field for a stable preparation method for pure tungsten crucibles that can obtain high-density, fine-grained and uniform microstructure. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a high-density fine-grained pure tungsten crucible and its preparation method. This invention can solve the problems of lifespan fluctuations, premature cracking and failure leading to high scrap costs, and rare earth resource consumption in the process of sapphire crystal growth and rare earth smelting and purification, thereby obtaining a pure tungsten crucible with a high-density fine-grained structure and uniform structure.

[0007] The technical solution of the present invention is as follows: A method for preparing a high-density, fine-grained pure tungsten crucible includes the following steps: (1) Two kinds of pure tungsten powders with different average particle sizes and no fine particle agglomeration are mixed to obtain a mixed raw material. The average particle size of the mixed raw material is 3.5-5.5μm and the diameter is 1.8-2, so as to ensure the strength of the pressed blank. (2) The mixed raw materials are subjected to isostatic pressing at a pressure of 210-250 MPa to obtain a crucible blank; (3) The crucible blank is sintered to obtain the high-density fine-grained pure tungsten crucible; the sintering process includes: raising the crucible blank to the highest temperature through multiple heating and holding stages, holding it briefly for 0.5-3 hours, and then lowering it to the second highest temperature and holding it for 12-15 hours; wherein the highest temperature is 2350-2370℃ and the second highest temperature is 2250-2300℃.

[0008] The preparation method of this invention effectively ensures the strength of the pressed compact by mixing pure tungsten powder with different average particle sizes. At the same time, combined with a specific sintering process, it significantly improves the density and grain refinement and homogenization of the obtained pure tungsten crucible, and improves the thermal shock resistance, permeability resistance and thermal stability of the product. This makes it more adaptable and stable in rare earth smelting conditions with high corrosive environment, extremely fast heating and cooling rates and frequent thermal cycles.

[0009] According to some preferred embodiments of the present invention, the pure tungsten powder includes a first pure tungsten powder with an average particle size of 3-4 μm and a diameter spacing of 1.2-1.5 μm and a second pure tungsten powder with an average particle size of 1-2 μm and a diameter spacing of 1.2-1.5 μm.

[0010] According to some preferred embodiments of the present invention, the pure tungsten powder includes a first pure tungsten powder with an average particle size of 3-4 μm and a diameter spacing of 1.2-1.5 μm and a third pure tungsten powder with an average particle size of 4-8 μm and a diameter spacing of 1.2-1.5 μm.

[0011] In the two preferred methods above, the combination of the first pure tungsten powder and the second pure tungsten powder is preferably used to prepare a high-density fine-grained pure tungsten crucible with a relatively low operating temperature, while the combination of the first pure tungsten powder and the third pure tungsten powder is preferably used to prepare a high-density fine-grained pure tungsten crucible with a relatively high operating temperature.

[0012] According to some preferred embodiments of the present invention, the sintering process includes: heating the crucible blank from room temperature to 450-550°C for 0.5-1 h, then heating it to 950-1050°C for 2-3 h and holding it at that temperature for 1-3 h, then heating it to 1150-1250°C for 0.5-2.5 h, then heating it to 1450-1550°C for 1-3 h, then heating it to 1750-1850°C for 1-3 h, then heating it to 2050-2150°C for 2-3 h, then heating it to 2350-2370°C for 5-8 h and holding it briefly for 0.5-3 h, then cooling it to 2250-2300°C and holding it at that temperature for 12-15 h, and then cooling it down with the furnace.

[0013] The above-mentioned preferred embodiments of the present invention effectively coordinate the effects of sintering temperature and porosity on oxygen removal rate, enabling rapid heating and holding at a temperature range of approximately 450-1000℃ to remove oxygen, thereby achieving rapid and sufficient oxygen removal. Furthermore, based on the influence of different temperature ranges on the product structure, a process of heating to the highest temperature at different rates was designed to ensure that the crucible during sintering reaches a density of over 70% and is in a uniform, porous, and highly active sintering state. Subsequently, considering that the promoting effect of temperature on grain growth is far greater than that of time, the temperature is lowered to a slightly higher temperature, allowing the crucible to rapidly sinter to a uniform, porous, and highly active sintering state before being lowered to a slightly higher temperature platform for long-term holding, in order to obtain a high-density, fine-grained pure tungsten crucible.

[0014] The highest and / or second-highest temperatures can be further adjusted flexibly based on the operating temperature and density of the high-density fine-grained pure tungsten crucible.

[0015] The temperature of the second highest temperature can be determined based on the different temperatures of rare earth smelting and the average particle size and diameter of the powder after mixing. The higher the ambient temperature, the higher the second highest temperature should be selected, and the more suitable it is to use mixed raw materials with larger average particle size and diameter after mixing.

[0016] According to some preferred embodiments of the present invention, the sintering process includes: heating the crucible blank from room temperature to 500°C for 0.5-1 h, then heating it to 1000°C for 2-3 h and holding it at that temperature for 1.5-2.5 h, then heating it to 1200°C for 0.5-1.5 h, then heating it to 1500°C for 1-2 h, then heating it to 1800°C for 1.5-2.5 h, then heating it to 2100°C for 2-3 h, then heating it to 2350°C for 5.5-6.5 h and holding it briefly for 1.5-2.5 h, then cooling it to 2250°C and holding it at that temperature for 12-13 h, and then cooling it down with the furnace.

[0017] According to some preferred embodiments of the present invention, the sintering process includes: heating the crucible blank from room temperature to 500°C for 0.5-1 h, then heating it to 1000°C for 2-3 h and holding it at that temperature for 1.5-2.5 h, then heating it to 1200°C for 0.5-1.5 h, then heating it to 1500°C for 1-2 h, then heating it to 1800°C for 1.5-2.5 h, then heating it to 2100°C for 2-3 h, then heating it to 2360°C for 5.5-6.5 h and holding it briefly for 1.5-2.5 h, then cooling it to 2300°C and holding it at that temperature for 12-13 h, and then cooling it down with the furnace.

[0018] The present invention further provides a high-density fine-grained pure tungsten crucible prepared according to the above preparation method.

[0019] According to some preferred embodiments of the present invention, the high-density fine-grained pure tungsten crucible has an average grain size of 15-28 μm and is basically free of microstructural defects.

[0020] This invention has the following beneficial effects: It effectively combines the technique of mixing pure tungsten powder of different particle sizes with a specific sintering method (multi-stage rapid heating to the highest temperature to obtain a uniform, porous, highly active tungsten crucible, followed by long-term holding at a lower temperature for sintering), resulting in a density greater than 18.5 g / cm³. 3 The resulting pure tungsten crucible has an average grain size of less than 30 μm. Furthermore, the microstructure of the obtained pure tungsten crucible is more uniform and the pore distribution is finer and more uniform than that of crucibles sintered by conventional multi-stage heating and multi-stage holding processes. It has superior performance, stability and longer service life. Attached Figure Description

[0021] Figure 1 The sintering curve is the result of sintering treatment in Example 1.

[0022] Figure 2 This is a SEM image of the microstructure of the high-density fine-grained pure tungsten crucible obtained in Example 1.

[0023] Figure 3 The image shows the microstructure of the comparative pure tungsten crucible obtained in Example 1 using SEM.

[0024] Figure 4 The sintering curve is the result of sintering treatment in Example 2.

[0025] Figure 5 This is a SEM image of the microstructure of the high-density fine-grained pure tungsten crucible obtained in Example 2.

[0026] Figure 6 The image shows the SEM image of the microstructure of the pure tungsten crucible obtained in Example 2.

[0027] Figure 7 The sintering curves of the pure tungsten crucible are shown in the examples for comparison. Detailed Implementation

[0028] The technical solutions of the present invention will be further described below with reference to embodiments thereof. The embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0029] Example 1 High-density, fine-grained pure tungsten crucibles are prepared using the following process: (1) Pure tungsten powder A and pure tungsten powder B, which are free from agglomeration as shown in Table 1, are mixed at a mass ratio of 8:2 to obtain a mixed raw material. The average particle size of the mixed raw material is 3.5 μm and the diameter is 1.4. There is no agglomeration of fine particles. (2) The mixed raw materials were subjected to isostatic pressing at a pressure of 220 MPa to obtain a high-strength pressed blank; (3) As per the appendix Figure 1 The sintering curves shown illustrate the sintering process of the crucible blank. Specifically, the temperature was increased from room temperature to 500℃ in 0.5 hours, then increased from 500℃ to 1000℃ in 2.5 hours and held for 2 hours. Subsequently, the temperature was increased from 1000℃ to 1200℃ in 1 hour, from 1200℃ to 1500℃ in 1.5 hours, from 1500℃ to 1800℃ in 2 hours, from 1800℃ to 2100℃ in 2.5 hours, from 2100℃ to 2350℃ in 6 hours and held briefly for 2 hours. Afterward, the temperature was lowered in the furnace to 2250℃ and held for 12 hours. Finally, the temperature was lowered in the furnace to obtain a high-density, fine-grained pure tungsten crucible.

[0030] Furthermore, for comparative testing, the crucible blank obtained in step (2) above was prepared according to... Figure 7 The conventional sintering treatment curve shown was used for sintering (the specific sintering procedure was as follows: 5 hours to 1000℃ from room temperature and 2 hours to hold; 3 hours to 1200℃ from 1000℃ and 2 hours to hold; 6 hours to 1500℃ from 1200℃ and 4 hours to hold; 4 hours to 1650℃ from 1500℃ and 6 hours to hold; 4 hours to 1800℃ from 1650℃ and 6 hours to hold; 4 hours to 2100℃ from 1800℃ and 6 hours to hold; 4 hours to 2280℃ from 2100℃ and 4 hours to hold; 4 hours to 2360℃ from 2280℃ and 4 hours to hold; then the furnace was cooled to room temperature and removed from the furnace), resulting in a comparative pure tungsten crucible.

[0031] Table 1 Comparison of raw material composition and compact strength

[0032] The density of the obtained high-density fine-grained pure tungsten crucible was measured to be 18.56 g / cm³. 3 Greater than 18.5 g / cm³ 3 The average grain size is 20 μm, and its microstructure is shown in the attached figure. Figure 2 As shown, through the attached Figure 2 It can be seen that the grain size is mainly concentrated between 15 and 25 μm, and the average grain size measured by the intercept method is about 22 μm, which is significantly lower than the average grain size of 30 μm in conventional sintering, and is more uniform. The residual pores after sintering are also more uniformly distributed, and are basically <5 μm. In contrast, the microstructure of a pure tungsten crucible is shown in the attached figure. Figure 3 As shown, its grain size is larger, and the pores are larger and unevenly distributed. Testing revealed that the density of the control crucible was 18.4 g / cm³. 3 It is significantly less than the density of a high-density fine-grained pure tungsten crucible.

[0033] Furthermore, through actual use testing, the service life of the obtained high-density fine-grained pure tungsten crucible has been improved from the unstable use of conventional pure tungsten crucibles for 100-300 heats to a stable service life of over 300 heats.

[0034] Meanwhile, tests showed that the prepared crucible has superior performance in terms of thermal shock resistance, thermal stability, and impermeability, and exhibits greater adaptability and stability in rare earth smelting conditions characterized by high corrosiveness, extremely rapid heating and cooling rates, and frequent thermal cycles.

[0035] Example 2 High-density, fine-grained pure tungsten crucibles are prepared using the following process: (1) Pure tungsten powder A and pure tungsten powder B, which are free from agglomeration as shown in Table 2, are mixed at a mass ratio of 6.5:3.5 to obtain a mixed raw material. The average particle size of the mixed raw material is 5.2 μm and the diameter is 1.99. There is no agglomeration of fine particles. (2) The mixed raw materials were subjected to isostatic pressing at a pressure of 210 MPa to obtain a high-strength crucible blank; (3) As per the appendix Figure 4 The sintering curves shown illustrate the sintering process of the crucible blank. Specifically, the temperature was increased from room temperature to 500℃ in 0.5h, then increased from 500℃ to 1000℃ in 2.5h and held for 2h; then increased from 1000℃ to 1200℃ in 1h, from 1200℃ to 1500℃ in 1.5h, from 1500℃ to 1800℃ in 2h, from 1800℃ to 2100℃ in 2.5h, from 2100℃ to 2360℃ in 6h and held briefly for 2h, then cooled in the furnace to 2300℃ and held for 14h, and finally cooled in the furnace to obtain a high-density, fine-grained pure tungsten crucible.

[0036] Furthermore, for comparative testing, the crucible blank obtained in step (2) above was prepared according to... Figure 7 The conventional sintering treatment curve shown was used for sintering (the specific sintering procedure was as follows: 5 hours to 1000℃ from room temperature and 2 hours to hold; 3 hours to 1200℃ from 1000℃ and 2 hours to hold; 6 hours to 1500℃ from 1200℃ and 4 hours to hold; 4 hours to 1650℃ from 1500℃ and 6 hours to hold; 4 hours to 1800℃ from 1650℃ and 6 hours to hold; 4 hours to 2100℃ from 1800℃ and 6 hours to hold; 4 hours to 2280℃ from 2100℃ and 4 hours to hold; 4 hours to 2360℃ from 2280℃ and 4 hours to hold; then the furnace was cooled to room temperature and removed from the furnace), resulting in a comparative pure tungsten crucible.

[0037] Table 2 Raw material composition

[0038] The density of the obtained high-density fine-grained pure tungsten crucible was measured to be 18.53 g / cm³. 3 Greater than 18.5 g / cm³ 3 The average grain size is approximately 24 μm, and its microstructure is shown in the attached image. Figure 5 As shown, through the attached Figure 5 It can be seen that the grain size is mainly concentrated between 18 and 28 μm, and the average grain size measured by the intercept method is about 24 μm, which is significantly lower than the 35 μm average grain size of conventional sintering, and is more uniform. The residual pores after sintering are also more uniformly distributed, and are basically <5 μm. The microstructure of a pure tungsten crucible is shown in the attached figure. Figure 6 As shown, the grain size is larger, and the pores are larger and unevenly distributed. The density of the sintered crucible was measured to be 18.36 g / cm³. 3 It is significantly less than the density of a high-density fine-grained pure tungsten crucible.

[0039] Meanwhile, tests showed that the prepared crucible has superior performance in terms of thermal shock resistance, thermal stability, and impermeability, and exhibits greater adaptability and stability in rare earth smelting conditions characterized by high corrosiveness, extremely rapid heating and cooling rates, and frequent thermal cycles.

[0040] It should be noted that the above descriptions are merely preferred embodiments of the present invention and should not limit the scope of protection of the technical solutions of the present invention. Any modifications made to the technical solutions described in the foregoing embodiments, or equivalent substitutions of technical features, by those skilled in the art within the spirit and principles of the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-density, fine-grained pure tungsten crucible, characterized in that, It includes the following steps: (1) Two kinds of pure tungsten powders with different average particle sizes and no fine particle agglomeration are mixed to obtain a mixed raw material, wherein the average particle size of the mixed raw material is 3.5-5.5 μm and the diameter is 1.8-2 μm; wherein the pure tungsten powder includes a first pure tungsten powder with an average particle size of 3-4 μm and a diameter of 1.2-1.5 μm and a second pure tungsten powder with an average particle size of 1-2 μm and a diameter of 1.2-1.5 μm; or, the pure tungsten powder includes a first pure tungsten powder with an average particle size of 3-4 μm and a diameter of 1.2-1.5 μm and a third pure tungsten powder with an average particle size of 4-8 μm and a diameter of 1.2-1.5 μm. (2) The mixed raw materials are subjected to isostatic pressing at a pressure of 210-250 MPa to obtain a crucible blank; (3) The crucible blank is sintered to obtain the high-density fine-grained pure tungsten crucible; the sintering process includes: heating the crucible blank from room temperature to 450-550℃ for 0.5-1h, then heating it to 950-1050℃ for 2-3h and holding it for 1-3h, then heating it to 1150-1250℃ for 0.5-2.5h, then heating it to 1450-1550℃ for 1-3h, then heating it to 1750-1850℃ for 1-3h, then heating it to 2050-2150℃ for 2-3h, then heating it to 2350-2370℃ for 5-8h and holding it briefly for 0.5-3h, then cooling it to 2250-2300℃ and holding it for 12-15h, and then cooling it down with the furnace. The density of the high-density fine-grained pure tungsten crucible is greater than 18.5 g / cm³. 3 The average grain size is 15-28 μm.

2. The preparation method according to claim 1, characterized in that, The sintering process includes: heating the crucible blank from room temperature to 500°C for 0.5-1 h, then heating it to 1000°C for 2-3 h and holding it at that temperature for 1.5-2.5 h, then heating it to 1200°C for 0.5-1.5 h, then heating it to 1500°C for 1-2 h, then heating it to 1800°C for 1.5-2.5 h, then heating it to 2100°C for 2-3 h, then heating it to 2350°C for 5.5-6.5 h and holding it briefly for 1.5-2.5 h, then cooling it to 2250°C and holding it at that temperature for 12-13 h, followed by furnace cooling.

3. The preparation method according to claim 1, characterized in that, The sintering process includes: heating the crucible blank from room temperature to 500°C for 0.5-1 h, then heating it to 1000°C for 2-3 h and holding it at that temperature for 1.5-2.5 h, then heating it to 1200°C for 0.5-1.5 h, then heating it to 1500°C for 1-2 h, then heating it to 1800°C for 1.5-2.5 h, then heating it to 2100°C for 2-3 h, then heating it to 2360°C for 5.5-6.5 h and holding it briefly for 1.5-2.5 h, then cooling it to 2300°C and holding it at that temperature for 12-13 h, followed by furnace cooling.

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