A method for producing a fine-grained oxide-doped tungsten-based material

Abstract

The application discloses a preparation method of fine-grained oxide-doped tungsten-based material and relates to the technical field of powder metallurgy. The application provides a preparation method of oxide-doped tungsten, which comprises the following steps: S1. mixing tungsten powder and carbide nano powder, wet grinding, drying, and sieving to obtain dried powder material; S2. pressing the dried powder material to form a compact; and S3. sintering the compact in hydrogen. The carbide nano powder is ZrC nano powder, TiC nano powder or HfC nano powder. The method converts the carbide into oxide through a multi-stage sintering process, thereby avoiding the instability of the carbide. Under the premise of ensuring the density and shrinkage of the material, the growth of the grains is inhibited, so that the oxide-doped tungsten material has the characteristics of high density and fine grains. The process is simple and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, specifically relating to a method for preparing fine-grained oxide-doped tungsten-based materials. Background Technology

[0002] Tungsten possesses characteristics such as high melting point, high hardness, high thermal conductivity, low sputtering rate, good high-temperature strength, and a low coefficient of thermal expansion, making it widely used in defense, nuclear industry, and high-temperature applications. To further improve the material's strength and refine the grain size, doping is commonly employed, distributing dopant particles along the grain boundaries. This inhibits grain growth, thereby refining the grain size, and also prevents grain boundary slippage, improving high-temperature strength and significantly enhancing the material's high-temperature performance.

[0003] Typically, dopants are metal oxides (La₂O₃, Ce₂O₃, etc.) or carbides (ZrC, HfC, etc.). On the one hand, oxide doping has the advantage of stable phase chemistry, but its doping method is relatively complex. For example, patent CN109457159A proposes a method for preparing powder precursors using rare earth salts and polymers via liquid-phase chemical synthesis; another patent CN110560700B describes a method for preparing oxide composite powder precursors using ammonium metatungstate, rare earth nitrates, fuel, and ammonium nitrate as raw materials via low-temperature solution combustion synthesis. On the other hand, carbide-doped phases are unstable at high temperatures and may transform into other components (such as oxides) under specific atmospheres. During operation, this transformation may affect the material's performance. Furthermore, these methods involve complex formulations and processes, and some are even unsuitable for large-scale industrial production.

[0004] Currently, a new approach and process are needed to prepare high-density, fine-grained oxide-doped tungsten materials that are chemically stable, have simple doping methods, and can be mass-produced. Summary of the Invention

[0005] The technical problem solved by this invention is to avoid the complex formulations and processes of salt doping, and to provide a method for preparing fine-grained oxide-doped tungsten-based materials. This invention employs a carbide powder doping method, and then, during sintering, converts the carbide into oxide through appropriate processing methods, avoiding the instability of carbides in the finished product; thus providing a fine-grained oxide-doped tungsten-based material suitable for large-scale industrial production.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0007] This invention provides a method for preparing oxide-doped tungsten, comprising the following steps:

[0008] S1. Mix tungsten powder and carbide nanoparticles, wet grind, dry, and sieve to obtain dried powder material;

[0009] S2. Press the dried powder material into a compact;

[0010] S3. The compact is sintered in hydrogen to obtain a fine-grained oxide-doped tungsten-based material;

[0011] The carbide nanopowder includes one of ZrC nanopowder, TiC nanopowder, and HfC nanopowder.

[0012] In S1, the purity of the tungsten powder is 99.95%.

[0013] In S1, the particle size of the tungsten powder is 0.1 to 1.0 μm, preferably 0.1 to 0.6 μm, for example 0.1 μm.

[0014] In S1, the particle size of the carbide nanoparticles is 20-100 nm, preferably 20-50 nm, for example 50 nm.

[0015] In S1, the oxide in the fine-grained oxide-doped tungsten-based material accounts for 0.5% to 2.0% of the mass of the tungsten-based material; here, the required mass of carbide nanopowder should be calculated based on the mass of the oxide in the tungsten powder.

[0016] In S1, the oxide includes one of zirconium oxide, titanium oxide, or hafnium oxide; the oxide is obtained by oxidation of its corresponding carbide nanoparticles.

[0017] In this invention, the oxidant for the oxidation of carbide nanopowder comes from the oxygen adsorbed by tungsten powder in the dried powder material. The finer the particle size of the dried powder material, the higher its oxygen content. Because the metal elements and carbon elements in the carbide have higher chemical activity, they will react with the oxygen in the gaps between the tungsten powder in the dried powder material at high temperature to generate metal oxides and carbon dioxide, respectively.

[0018] In S1, the wet grinding is a conventional wet grinding method in the art, and a preferred method is to place the wet grinding media and cemented carbide balls in a ball mill for mixing and grinding.

[0019] In S1, the wet grinding medium is anhydrous ethanol.

[0020] In S1, the volume-to-mass ratio of the wet grinding media to the tungsten powder is 220–350 mL / kg; wherein, if the tungsten powder particle size becomes coarser, the amount of alcohol used can be reduced.

[0021] In S1, the tank for wet grinding is made of cemented carbide; the outer shell of the tank is made of steel, and the inner lining of the tank is made of cemented carbide plate.

[0022] In S1, the mass ratio of the cemented carbide ball to the tungsten powder is 2:1 to 8:1, preferably 3:1.

[0023] In S1, the wet milling speed is 60 r / min.

[0024] In S1, the wet milling time is 12 to 24 hours, for example, 24 hours; wherein, the purpose of wet milling is to obtain a fine and uniform distribution of dopant particles.

[0025] In S1, the drying temperature is 50-72°C, preferably 60-70°C, for example 65°C.

[0026] In S1, the drying time is 12 to 24 hours; drying is carried out until constant weight is achieved.

[0027] In S1, the sieving operation involves passing the material through a 60-mesh sieve twice.

[0028] In S2, the pressing method is cold isostatic pressing.

[0029] In S2, the pressing and molding process uses a rubber soft mold plus an outer steel mold; the outer steel mold serves to fix the shape.

[0030] In S2, the pressure for pressing is 160-240 MPa, preferably 180-220 MPa, for example 200 MPa.

[0031] In S2, the holding time for pressing is 5 to 10 minutes, preferably 10 minutes.

[0032] In step S3, the sintering is carried out in a high-purity hydrogen atmosphere; the flow rate of the hydrogen is 5–20 m³ / h. 3 / h; where hydrogen is used as a protective gas, it not only isolates the air and protects the tungsten from oxidation, but also significantly reduces the oxygen content in the powder; while the circulating hydrogen can promptly remove the generated water vapor and various low-melting-point impurities volatilized from the billet, all of which help to form a dense crystal structure and uniform grain size distribution, thus affecting the sintering process and microstructure of the material.

[0033] In S3, the heating rate of the sintering is 2 to 10 °C / min.

[0034] In S3, the sintering includes a heating process and high-temperature sintering.

[0035] In S3, the heating process includes four heating programs, with each temperature plateau held for 1 to 3 hours. The use of multiple temperature plateaus for holding is to allow sufficient time for impurity removal, oxygen reduction, and promotion of carbide nanoparticle conversion.

[0036] Furthermore, the heating process involves raising the temperature to 390–420°C, 720–760°C, 1000–1200°C, and 1520–1580°C, respectively, and holding the temperature for 1–2 hours; preferably, the temperature is raised to 400°C, 750°C, 1150°C, and 1550°C, and held for 2 hours.

[0037] In S3, the high-temperature sintering temperature is 1900-2100℃ and the time is 0.5-1.5h; wherein, using a lower sintering temperature and a shorter holding time can prevent grain coarsening and ensure the fine grain requirements of the material.

[0038] In this invention, the oxide-doped tungsten-based material has a carbon content of 5-10 ppm, a relative density (theoretical density calculated as ZrO2) greater than 98%, and an average grain size in the range of 1-5 μm.

[0039] The positive and progressive effects of this invention are as follows:

[0040] 1. This invention avoids the complex formulation and process of salt doping. Through a multi-stage sintering process, carbides are converted into oxides, thus avoiding the instability of carbides in the finished product. On the other hand, while ensuring that the material shrinks sufficiently and obtains the required density, the grain growth is suppressed to obtain fine-grained products.

[0041] 2. Oxide-doped tungsten-based materials have high density and fine grains. The carbon content in oxide-doped tungsten-based materials is only 5-10 ppm, and the density is 18.73-18.95 g / cm³. 3 The relative density (theoretical density calculated as ZrO2) is approximately 98.4%–98.5%, and the average grain size is approximately 1–5 μm.

[0042] 3. The doping method and production process of this invention are simple and can be industrialized for large-scale production. Attached Figure Description

[0043] Figure 1 This is a scanning electron microscope (SEM) image of the fracture surface of a tungsten-doped slab in Example 1.

[0044] Figure 2 This is a scanning electron microscope (SEM) image of the fracture surface of a tungsten-doped slab in Example 2.

[0045] Figure 3 This is a scanning electron microscope (SEM) image of the fracture surface of a tungsten-doped slab in Example 3.

[0046] Figure 4 This is a graph showing the XPS analysis results of tungsten doping in Example 2. Detailed Implementation

[0047] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0048] Unless otherwise specified, all raw materials and reagents used in the embodiments and comparative examples of this invention are commercially available.

[0049] In this invention, the carbon content is detected by a carbon-sulfur analyzer.

[0050] Example 1

[0051] Preparation of fine-grained W-0.5wt% ZrO2-doped tungsten slabs:

[0052] S1. Take 4.0 kg of tungsten powder with a purity of 99.95% and a particle size of 0.1 μm, 16.8 g of ZrC powder with a particle size of 50 nm, 1200 ml of anhydrous alcohol, and 12 kg of cemented carbide balls and put them into a ball mill jar. Wet mill for 24 h. Then dry in a vacuum drying oven at 65 °C for 16 h. Pass through a 60 mesh sieve twice to obtain dried powder.

[0053] S2. Press and mold under 200MPa pressure for 10 minutes;

[0054] S3. Then it enters the medium-frequency furnace and is kept for 5-10 minutes. 3 The hydrogen flow rate was 1 h, and the temperature was increased at a rate of 5 °C / min. The temperature was held for 2 h at four temperature plateaus: 400 °C, 750 °C, 1150 °C, and 1550 °C. Finally, the sintering was completed by holding at the highest sintering temperature of 2000 °C for 1 h, resulting in 3.80 kg of doped tungsten slab.

[0055] Testing revealed that the carbon content of the mixed powder before pressing was 700 ppm, and the carbon content of the tungsten slab after sintering was 8 ppm, which is comparable to the carbon content of pure tungsten slabs (typically 5–10 ppm). This indicates that the incorporated ZrC has been largely converted, and the carbon in the ZrC has mostly escaped. The density of the doped tungsten slab was measured to be 18.95 g / cm³. 3 The relative density (theoretical density calculated as ZrO2) is approximately 98.5%; the average grain size is approximately 2 μm. The resulting electron micrograph of the fracture surface of the doped tungsten slab is shown below. Figure 1 .

[0056] Example 2

[0057] Preparation of fine-grained W-1.0wt% ZrO2-doped tungsten slabs:

[0058] Except for the addition of 33.5g of ZrC powder in S1 and the highest sintering temperature of 2000℃ in S3, all other steps were the same as S1 to S3 in Example 1, resulting in 3.81kg of doped tungsten slab blank.

[0059] Testing revealed that the carbon content of the mixed powder before pressing was 1300 ppm, and the carbon content of the tungsten slab after sintering was 9 ppm, which is comparable to the carbon content of pure tungsten slabs (typically 5–10 ppm). This indicates that the incorporated ZrC has been largely converted, and the carbon in the ZrC has mostly escaped. The density of the doped tungsten slab was measured to be 18.86 g / cm³. 3 The relative density (theoretical density calculated as ZrO2) is approximately 98.4%; the average grain size is approximately 3–4 μm. The resulting electron micrographs of the fracture surface of the doped tungsten slab are shown below. Figure 1 .

[0060] Figure 4 In the spectrum, the Zr peak is at 184 eV, while the Zr peak of ZrC should be around 180 eV, indicating that Zr exists in the ZrO2 state, which is consistent with the full spectrum results.

[0061] Example 3

[0062] Preparation of fine-grained W-2.0wt% ZrO2-doped tungsten slabs:

[0063] Except for the addition of 67g of ZrC powder in S1 and the highest sintering temperature of 2050℃ in S3, all other steps were the same as S1 to S3 in Example 1, resulting in 3.83kg of doped tungsten slab blank.

[0064] Testing revealed that the carbon content of the mixed powder before pressing was 2500 ppm, and the carbon content of the tungsten slab after sintering was 9 ppm, which is comparable to the carbon content of pure tungsten slabs (typically 5–10 ppm). This indicates that the incorporated ZrC has been largely converted, and the carbon in the ZrC has mostly escaped. The density of the doped tungsten slab was measured to be 18.73 g / cm³. 3 The relative density (theoretical density calculated as ZrO2) is approximately 98.4%; the average grain size is approximately 3–4 μm. The resulting electron micrographs of the fracture surface of the doped tungsten slab are shown below. Figure 3 .

[0065] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a fine-grained oxide-doped tungsten-based material, characterized in that, It includes the following steps: S1. Tungsten powder and carbide nanopowder are mixed, wet-milled, dried, and sieved to obtain dried powder; the carbide nanopowder is one of ZrC nanopowder, TiC nanopowder, and HfC nanopowder; S2. Press the dried powder material into a compact; S3. The compact is sintered in hydrogen to obtain a fine-grained oxide-doped tungsten-based material; The sintering process includes a heating process and a high-temperature sintering process; the heating process involves heating to 390~420℃, 720~760℃, 1000~1200℃, and 1520~1580℃ respectively, and holding at these temperatures for 1~2 hours respectively; the high-temperature sintering process involves a temperature of 1900~2100℃ and a time of 0.5~1.5 hours. The oxidant for the oxidation of carbide nanopowder comes from the oxygen adsorbed by tungsten powder in the dried powder material. The oxygen in the gap between the carbide nanopowder and the tungsten powder generates oxides and carbon dioxide, respectively. The oxide in the fine-grained oxide-doped tungsten-based material accounts for 0.5% to 2.0% of the tungsten-based material by mass; the oxide includes one of zirconium oxide, titanium oxide, and hafnium oxide; The carbon content of the oxide-doped tungsten-based material is 5-10 ppm.

2. The method for preparing fine-grained oxide-doped tungsten-based materials as described in claim 1, characterized in that, The tungsten powder has a particle size of 0.1~1.0μm; The particle size of the carbide nanoparticles is 20~100nm.

3. The method for preparing fine-grained oxide-doped tungsten-based materials as described in claim 1, characterized in that, The wet grinding method involves placing wet grinding media and cemented carbide balls in a ball mill for mixing and grinding. The wet milling speed is 60 r / min; The wet milling time is 12-24 hours.

4. The method for preparing fine-grained oxide-doped tungsten-based materials as described in claim 3, characterized in that, The wet grinding medium is anhydrous ethanol; The volume-to-mass ratio of the wet grinding media to the tungsten powder is 220~350 mL / kg; The mass ratio of the cemented carbide ball to the tungsten powder is 2:1 to 8:

1.

5. The method for preparing fine-grained oxide-doped tungsten-based materials as described in claim 1, characterized in that, The drying temperature is 50~72℃; drying is carried out to constant weight. The pressing method is cold isostatic pressing; The pressing pressure is 160~240MPa; The pressure holding time for the pressing and molding process is 5-10 minutes.

6. The method for preparing fine-grained oxide-doped tungsten-based materials as described in claim 1, characterized in that, The sintering is carried out in a high-purity hydrogen atmosphere; The flow rate of the hydrogen gas is 5~20m³. 3 / h; The sintering heating rate is 2~10℃ / min.

7. The method for preparing fine-grained oxide-doped tungsten-based materials as described in claim 6, characterized in that, The heating process was carried out at 400℃, 750℃, 1150℃ and 1550℃ respectively, and held at that temperature for 2 hours each time.

8. The method for preparing fine-grained oxide-doped tungsten-based materials as described in claim 1, characterized in that, The relative density of the oxide-doped tungsten-based material is greater than 98%, and the average grain size is in the range of 1~5μm.

Images