A nickel-tungsten master alloy and its preparation method by multi-step heat treatment.

Abstract

This invention discloses a multi-step heat treatment method for preparing nickel-tungsten master alloys. The method includes: 1. Selecting high-purity, low-oxygen-content nickel powder and tungsten powder with specific particle sizes as raw materials; 2. Mixing the nickel powder and tungsten powder with anhydrous ethanol to obtain a mixed powder; 3. Preparing a green blank by cold isostatic pressing of the mixed powder; 4. Obtaining a sintered body by sintering and multi-step heat treatment of the green blank; 5. Obtaining the nickel-tungsten master alloy after machining. This invention, through strict control of the sintering and multi-step heat treatment processes, promotes the reaction between the nickel solid solution phase and tungsten, as well as the continued reaction of the reaction products with tungsten. This achieves the ablation of the high-melting-point, high-density elemental tungsten phase in the alloy, promotes the uniform distribution of nickel and tungsten elements, and realizes the preparation of low-cost, high-efficiency, and high-purity nickel-tungsten master alloys. The final product meets the requirements for applications in nickel-based high-temperature alloy smelting. The method is simple and easy to implement.

Description

Technical Field

[0001] This invention belongs to the field of alloy preparation technology, specifically relating to a nickel-tungsten master alloy and its multi-step heat treatment preparation method. Background Technology

[0002] Nickel-based superalloys possess excellent structural stability, oxidation resistance, hot corrosion resistance, and high-temperature mechanical properties, making them widely used in aerospace, shipbuilding, and other industries. With the advancement of nickel-based superalloy generations, the elemental composition of the alloys has changed significantly, and the alloys' heat resistance has gradually improved accordingly.

[0003] Currently, refractory elements are indispensable in commercially available nickel-based superalloys, with tungsten accounting for 3-7 wt%. The addition of tungsten, through the combined effects of solid solution strengthening and carbide grain boundary dispersion strengthening, results in excellent high-temperature mechanical properties in nickel-based superalloys. Compared to nickel, tungsten has a larger atomic radius (135 pm), a higher melting point (3422℃), and a higher density (19.26 g / cm³). 3 ), high surface tension of the liquid phase (σ) W The nickel-based superalloys prepared by melting have characteristics such as 2300mN / m and T=3695K, which leads to severe tungsten segregation in the alloys and thus adversely affects the performance of the final product.

[0004] To facilitate the addition of high-melting-point tungsten, prevent metal overheating, shorten smelting time, and reduce metal burn-off, nickel-tungsten master alloys with uniform and accurate composition are of great significance for obtaining nickel-based superalloys. According to the nickel-tungsten binary alloy phase diagram, nickel-tungsten master alloys with a tungsten content of less than 62 wt% have a melting point of 1455℃~1655℃, close to the smelting temperature of pure nickel, making them suitable for smelting nickel-based superalloys.

[0005] Currently, there are four publicly disclosed methods for preparing nickel-tungsten master alloys: vacuum induction melting, electron beam melting, aluminothermic melting, and powder sintering. Invention patents with publication numbers CN106756243A, CN109182843A, and CN110358947A disclose technologies for preparing nickel-tungsten master alloys using vacuum induction melting, electron beam melting, and aluminothermic melting, respectively. Among these, nickel-tungsten master alloys prepared by the melting method are prone to tungsten segregation and have high energy consumption and cost; nickel-tungsten master alloys prepared by the aluminothermic melting method have poor density, unstable composition, and are prone to introducing impurities such as aluminum and oxygen.

[0006] Compared to the aforementioned smelting methods and the out-of-furnace aluminothermic method, nickel-tungsten master alloys prepared by powder sintering have advantages such as uniform composition and low cost. Invention patents CN109825752A and CN102312132A have successively disclosed technologies for preparing nickel-tungsten master alloys using a vacuum high-temperature sintering method. The former uses tungsten powder accounting for 38wt%~55wt% of the total alloy weight, with a sintering temperature of 800℃~1450℃. However, due to the large particle size of the selected powder and the lack of carbon and oxygen isolation measures during alloy sintering, the final product exhibits uneven composition distribution and excessive levels of impurities such as carbon, oxygen, and nitrogen. Comparing the processes, the latter adds a ball milling process, thereby reducing the particle size of the nickel-tungsten powder, promoting the formation of the nickel-tungsten master alloy, and ensuring the uniformity of the nickel-tungsten powder mixing. However, the production capacity of the ball milling process limits its large-scale application, and the mutual impact between the grinding balls during ball milling can also introduce additional impurities into the alloy. Meanwhile, sintering temperatures of 1250℃ to 1350℃ are insufficient to eliminate the elemental tungsten phase. To address this, patent CN102329973A, based on patent CN102312132A, added a high-temperature melting process. While this high-temperature melting method successfully eliminated the elemental tungsten phase in the nickel-tungsten alloy, it also significantly increased the cost. Summary of the Invention

[0007] The technical problem to be solved by this invention is to provide a multi-step heat treatment preparation method for nickel-tungsten master alloys, addressing the shortcomings of the prior art. This method involves mixing nickel powder and tungsten powder, pressing the mixture into a compact, and then sequentially performing sintering and multi-step heat treatment. By strictly controlling the sintering and multi-step heat treatment processes, the high-melting-point, high-density elemental tungsten phase in the alloy is ablated, promoting the uniform distribution of nickel and tungsten elements. This achieves low-cost, high-efficiency preparation of nickel-tungsten master alloys, solving the problems of high cost, uneven composition and segregation of nickel-tungsten master alloys, and high levels of impurities found in existing methods.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a multi-step heat treatment preparation method for nickel-tungsten master alloy, characterized in that the method includes the following steps:

[0009] Step 1: Raw material selection: Select nickel powder with a purity of 99.9% or higher, a particle size of less than 100μm, and an oxygen content of no more than 1000ppm, and tungsten powder with a purity of 99.9% or higher, a particle size of less than 25μm, and an oxygen content of no more than 1000ppm as raw materials;

[0010] Step 2, Powder Mixing: Based on the composition of the target product, nickel-tungsten master alloy, weigh the nickel powder and tungsten powder from Step 1 and mix them with anhydrous ethanol in a mixer to obtain a mixed powder.

[0011] Step 3, Green body forming: After drying the mixed powder obtained in step 2, it is placed into a rubber mold, vacuum sealed, and then placed in a cold isostatic press. It is held under pressure of 200MPa~300MPa for 10 minutes to obtain the green body.

[0012] Step 4, sintering and multi-step heat treatment: The green blank obtained in step 3 is placed in a vacuum sintering furnace and sintered at a vacuum of 0.001 Pa to 0.05 Pa and a temperature of 1400°C to 1600°C for 2 hours. Then, multi-step heat treatment is performed: first, the temperature is lowered to 1030°C to 1060°C and held for 1 hour to 3 hours, then the temperature is lowered to 1005°C to 1025°C and held for 1 hour to 3 hours. The blank is then cooled to room temperature in the furnace to obtain the sintered body.

[0013] Step 5, Machining: The sintered body obtained in Step 4 is machined to remove a surface thickness of 1mm to 2mm to obtain a nickel-tungsten master alloy.

[0014] The above-mentioned multi-step heat treatment preparation method for a nickel-tungsten master alloy is characterized in that the particle size ratio of nickel powder to tungsten powder in step one is 1~2:1. During powder mixing, the particle size, density, and content of different powders all affect the uniformity of powder mixing. Based on practical experience in powder mixing, it is known that when the product of the particle size, density, and content of different powders is close, the powder mixing uniformity is better. Furthermore, because the diffusion rate of tungsten (W) in nickel (Ni) at the same temperature is much higher than that of nickel in tungsten (the diffusion coefficient of tungsten in nickel at 1450℃ is 1.2×10⁻⁶), this method is particularly beneficial. -13 m 2 / s~1.6×10 - 13 m 2 / s, which is much higher than its diffusion coefficient of 1.5×10 in tungsten. -13 m 2 / s~3.0×10 -22 m 2 This invention, by controlling the particle size ratio of nickel powder to tungsten powder, ensures both thorough mixing of the two powders and that the tungsten powder particles are smaller than the nickel powder particles. This allows tungsten to fully dissolve in elemental nickel and dissolve within a short time during the subsequent sintering process, significantly improving the diffusion capacity of tungsten. This ensures the uniform distribution of the high-melting-point elemental tungsten phase in the finished nickel-tungsten master alloy and promotes the full dissolution of excess elemental tungsten phase in the nickel matrix.

[0015] The above-mentioned multi-step heat treatment preparation method for a nickel-tungsten master alloy is characterized in that, in the powder mixing process of step two, nickel powder and 5% anhydrous ethanol by mass of nickel powder are first placed in a mixer and run at a barrel speed of 20 rpm to 60 rpm for 30 minutes. After standing for 15 minutes, tungsten powder is added, and the mixture is run at a barrel speed of 20 rpm to 60 rpm for 3 hours to 5 hours. This invention uses anhydrous ethanol as a binder. The first mixing process achieves sufficient spreading of anhydrous ethanol on the surface of the nickel powder. Then, a second mixing process is used to bond small-diameter tungsten powder particles on the surface of the nickel powder. Simultaneously, the addition of anhydrous ethanol reduces the flowability of the powder, thereby maintaining the uniformity of the mixed powder and ensuring the uniform distribution of nickel-tungsten elements and high-melting-point elemental tungsten phase in the finished nickel-tungsten master alloy.

[0016] The above-mentioned multi-step heat treatment preparation method for a nickel-tungsten master alloy is characterized in that, after the mixed powder is prepared in step two, the green blank forming process in step three is completed within 8 hours. This invention avoids particle segregation of density-preserving tungsten powder due to prolonged standing by limiting the time between mixing nickel and tungsten powder and cold isostatic pressing. This prevents the loss of uniformity in the mixing of the nickel-tungsten alloy powder, which in turn affects the forming of the green blank and the uniformity of the alloy composition, and causes segregation of the high-melting-point elemental tungsten phase in the alloy.

[0017] The above-mentioned multi-step heat treatment preparation method for a nickel-tungsten master alloy is characterized in that, during sintering in step four, a tantalum sheet with a purity of 99% or higher is first used to wrap the blank, and then sponge titanium with a purity of 99.5% or higher is placed in the furnace cavity of a vacuum sintering furnace. Based on oxide free energy diagrams and related binary phase diagrams, this invention selects tantalum sheets and sponge titanium to isolate impurities such as carbon and oxygen from contaminating the nickel-tungsten alloy. According to the oxide free energy diagram, compared with nickel and tungsten, titanium and tantalum react more readily with elements such as carbon, oxygen, and sulfur to form carbides, oxides, and sulfides; according to the binary phase diagram, nickel and titanium can form nickel-titanium intermediate compounds on the titanium-rich side at a temperature of 942℃. Therefore, this invention selects tantalum sheets, which do not react with nickel and tungsten, to wrap the blank, and selects sponge titanium, which readily reacts with elements such as carbon, oxygen, and sulfur, to absorb impurity gases in the furnace, thereby ensuring the purity of the nickel-tungsten master alloy after sintering.

[0018] The above-mentioned multi-step heat treatment preparation method for a nickel-tungsten master alloy is characterized in that, in the multi-step heat treatment process described in step four, an infrared thermometer combined with a K-type thermocouple equipped in a vacuum sintering furnace is used to monitor and control the temperature of each heat treatment step. Because the temperature range of the multi-step heat treatment is too narrow, this invention uses an infrared thermometer combined with a K-type thermocouple equipped in a sintering furnace to monitor and control the temperature of each heat treatment step, utilizing manual assistance to control the heat treatment temperature in order to ensure the accuracy of the heat treatment temperature.

[0019] This invention is based on Figure 1Based on the Ni-W binary alloy phase diagram shown, the sintering and heat treatment process of the nickel-tungsten master alloy was designed. Specifically, the cold isostatically pressed green blank was first sintered at a vacuum of 0.001 Pa to 0.05 Pa and a temperature of 1400°C to 1500°C for 2 hours. Utilizing the high solid solubility (approximately 40 wt%) and diffusion ability of tungsten in nickel at high temperatures, the formation of the nickel-tungsten solid solution phase was promoted, thereby ensuring the dissolution of most of the tungsten element. Simultaneously, according to... Figure 1 As shown in the Ni-W binary alloy phase diagram, although the content of high-melting-point elemental tungsten is extremely low (approximately 1wt% to 5wt%) in the temperature range of 1068℃ to 1495℃, elemental tungsten is a thermodynamically stable phase and cannot be eliminated simply by high-temperature heat treatment sintering. To eliminate the small amount of elemental tungsten phase remaining after high-temperature sintering of the nickel-tungsten master alloy, this invention requires further multi-step heat treatment, and the heat treatment temperature needs to be controlled between 1002℃ and 1068℃ to ensure that elemental tungsten reacts with the nickel solid solution phase (1068℃) and the NiW phase (1027℃), thereby achieving the consumption of residual elemental tungsten at high temperatures. Specifically, this invention first cools the alloy to 1030℃~1060℃ and holds for 1h~2h to ensure that the nickel solid solution phase reacts with the remaining tungsten components to generate a NiW phase with a lower melting point. Then, it cools the alloy to 1005℃~1025℃ and holds for 1h~2h to ensure that the NiW phase reacts fully with the remaining tungsten to generate a NiW2 phase with a lower melting point. Since the NiW phase in the later reaction is a product of the previous reaction, ensuring the formation of the NiW phase through multi-step heat treatment is key to achieving the dissolution of excess elemental tungsten phase in the alloy. Next, during the furnace cooling to room temperature, the NiW and NiW2 phases formed by the heat treatment react with the nickel solid solution phase to form a Ni4W phase. Ultimately, all excess elemental tungsten phase in the alloy is dissolved, with some dissolving in elemental nickel and the rest reacting with nickel to generate NiW, NiW2, or Ni4W phases, thus avoiding the residue of elemental tungsten phase.

[0020] In addition, the present invention also discloses a nickel-tungsten master alloy prepared by the method described above, characterized in that the elemental mass fraction of the nickel-tungsten master alloy is: Ni 40%~62%, with the balance being W and unavoidable impurities. The unavoidable impurities include non-metallic impurities O, C, and S with a mass fraction of less than 0.01%, and metallic impurities Al, Mo, Pb, Sn, Ta, and Ti with a mass fraction of less than 0.01%. The phase composition of the nickel-tungsten master alloy includes Ni4W phase and other nickel-tungsten phases, which are derived from the solid solution phase of nickel, NiW phase, and NiW2 phase. The nickel-tungsten elements are uniformly distributed in the nickel-tungsten master alloy, and there is no tungsten element segregation.

[0021] In addition, the present invention also discloses a nickel-tungsten master alloy prepared by the method described above, characterized in that the elemental mass fraction of the nickel-tungsten master alloy is: Ni 40%~62%, with the balance being W and unavoidable impurities. The unavoidable impurities include non-metallic impurities O, C, and S with a mass fraction of less than 0.01%, and metallic impurities Al, Mo, Pb, Sn, Ta, and Ti with a mass fraction of less than 0.01%. The phase composition of the nickel-tungsten master alloy includes Ni4W phase and other nickel-tungsten phases, which are derived from the solid solution phase of nickel, NiW phase, and NiW2 phase. The nickel-tungsten elements are uniformly distributed in the nickel-tungsten master alloy, and there is no tungsten element segregation. This invention comprehensively considers the melting point of the alloy and the characteristics of subsequent multi-step heat treatment processes. By controlling the Ni mass fraction in the nickel-tungsten master alloy to not exceed 62%, it ensures that its melting characteristics meet the requirements of the smelting process. Furthermore, during the research process, it was discovered that when the Ni mass fraction in the nickel-tungsten master alloy is below 40%, W can be completely dissolved in the Ni matrix after high-temperature sintering, eliminating the need for subsequent multi-step heat treatment. However, when the Ni mass fraction in the nickel-tungsten master alloy is above 40%, W residue inevitably occurs after high-temperature sintering. The subsequent multi-step heat treatment process of this invention can effectively eliminate the W residue. Therefore, this invention controls the elemental mass fraction of the nickel-tungsten master alloy to be: Ni 40%~62%, with the balance being W and unavoidable impurities. This satisfies both the alloy melting point's requirement for compositional constraints and adapts to the specific Ni content requirements of subsequent multi-step heat treatment processes.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. This invention selects nickel powder and tungsten powder, mixes them evenly and presses them into a compact, and then performs sintering and multi-step heat treatment in sequence. By strictly controlling the sintering and multi-step heat treatment process, the high melting point and high density elemental tungsten phase in the alloy is ablated, which promotes the uniform distribution of nickel and tungsten elements. This enables the preparation of low-cost and high-efficiency nickel-tungsten master alloys, and the final product meets the application requirements in the smelting of nickel-based high-temperature alloys.

[0024] 2. Compared with the disadvantages of ball mill mixing in existing technologies, such as increased cost, reduced efficiency, and decreased alloy purity, this invention ensures the uniformity of powder mixing and the density of the formed blank by controlling the particle size and purity of nickel and tungsten powders, adding wetting agents, and controlling the powder mixing and forming process. Combined with the powder sintering process to prepare nickel-tungsten master alloy, the compositional uniformity and controllability of the nickel-tungsten master alloy are guaranteed. This method is simple, more economical and efficient, and avoids the serious tungsten element segregation caused by the large atomic radius, high melting point, high density, and high liquid phase surface tension of tungsten element during the smelting process.

[0025] 3. In the sintering process of this invention, by using tantalum sheets to wrap and place sponge titanium, the contamination of the alloy by elements such as carbon, sulfur, and oxygen that may be generated in the sintering environment is isolated, thus ensuring the purity of the nickel-tungsten master alloy.

[0026] 4. Compared with the shortcomings of existing technologies that directly cool to room temperature in the furnace after high-temperature sintering, resulting in the residue of high-melting-point tungsten phase in the alloy, this invention adds a multi-step heat treatment process after high-temperature sintering. Through the reaction of elemental tungsten with the solid solution phase of nickel and the reaction product NiW phase with elemental tungsten, the excess high-melting-point tungsten phase in the alloy is dissolved, thereby obtaining a high-quality nickel-tungsten master alloy.

[0027] 5. Compared with the disadvantage of the existing furnace aluminothermic method which easily introduces impurity elements, the powder sintering process of the present invention does not use aluminum powder as a reducing agent and the sintering process is in a high vacuum state, which effectively avoids the introduction of impurity elements. Therefore, the nickel-tungsten master alloy prepared by the method of the present invention has lower content of elements such as aluminum, carbon, oxygen, and sulfur, and higher purity.

[0028] 6. The phase composition of the nickel-tungsten master alloy of the present invention consists of one or more of the following: Ni4W phase, nickel solid solution phase, NiW phase, and NiW2 phase. The nickel-tungsten elements are uniformly distributed in the nickel-tungsten master alloy, and there is no tungsten element segregation. It is suitable for the preparation of nickel-based high-temperature alloys.

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0030] Figure 1 This is the phase diagram of a Ni-W binary alloy.

[0031] Figure 2 The image shows the XRD pattern of the green blank prepared in Example 1 of this invention after sintering and direct furnace cooling to room temperature.

[0032] Figure 3 The image shows the XRD pattern of the nickel-tungsten master alloy prepared in Example 1 of this invention.

[0033] Figure 4a This is a secondary electron diagram of the nickel-tungsten master alloy prepared in Example 1 of the present invention.

[0034] Figure 4b This is the Ni element energy spectrum scan of the nickel-tungsten master alloy prepared in Example 1 of the present invention.

[0035] Figure 4c This is the W element energy spectrum scan of the nickel-tungsten master alloy prepared in Example 1 of the present invention. Detailed Implementation

[0036] Example 1

[0037] The preparation method of this embodiment includes the following steps:

[0038] Step 1: Raw material selection: Select nickel powder with a purity of 99.9% or higher, a particle size of 1μm, and an oxygen content of no more than 1000ppm, and tungsten powder with a purity of 99.9% or higher, a particle size of 1μm, and an oxygen content of no more than 1000ppm as raw materials;

[0039] Step 2, Powder Mixing: Based on the composition of the target product, nickel-tungsten master alloy, Ni-38wt%W, weigh nickel powder and 5% anhydrous ethanol (by weight of nickel powder) and place them in a mixer. Run the mixer at a drum speed of 20 rpm for 30 minutes, let it stand for 15 minutes, then add tungsten powder and continue running the mixer at a drum speed of 20 rpm for 3 hours.

[0040] Step 3, Green blank forming: The mixed powder obtained in step 2 is dried in an oven at 120℃ for 30 minutes, then placed into a rubber mold, vacuum sealed, and placed in a cold isostatic press. It is held under pressure of 300MPa for 10 minutes to obtain the green blank.

[0041] After the mixed powder is prepared in step two, the green body forming process in step three is completed within 8 hours.

[0042] Step 4, Sintering and Multi-Step Heat Treatment: The green blank obtained in Step 3 is placed in a vacuum sintering furnace. The green blank is wrapped with tantalum sheets of 99% or higher purity, and sponge titanium of 99.5% or higher purity is placed in the furnace cavity. Sintering is then carried out at a vacuum of 0.001 Pa to 0.05 Pa and a temperature of 1400°C for 2 hours. Subsequently, multi-step heat treatment is performed: first, the temperature is lowered to 1030°C and held for 1 hour, then lowered to 1005°C and held for 1 hour, and then cooled to room temperature with the furnace to obtain the sintered body. During the multi-step heat treatment, an infrared thermometer combined with a K-type thermocouple equipped in the vacuum sintering furnace is used to monitor and control the temperature of each heat treatment step.

[0043] Step 5, Machining: The sintered body obtained in Step 4 is machined to remove a 1mm thick layer from the surface, resulting in a nickel-tungsten master alloy.

[0044] Figure 2 The XRD pattern of the green body prepared in this embodiment, after sintering and direct furnace cooling to room temperature, is shown below. Figure 2 As can be seen from the figure, in addition to the main phases Ni4W and NiW, there is still a secondary phase W, indicating that the elemental W phase is in a thermodynamically stable state at high temperatures.

[0045] Figure 3 The XRD pattern of the nickel-tungsten master alloy prepared in this embodiment is shown below. Figure 3As can be seen from the figure, the peak of the W phase has disappeared, indicating that the W element in the nickel-tungsten master alloy has been completely dissolved in the Ni phase or has undergone an alloying reaction with Ni, that is, the elemental W phase has been completely dissolved.

[0046] Figure 4a This is a secondary electron diagram of the nickel-tungsten master alloy prepared in this embodiment. Figures 4b-4c The above are the energy dispersive spectral density (EDS) images of Ni and W elements in the nickel-tungsten master alloy prepared in this embodiment, combined with... Figures 4a-4c As can be seen from the figure, the nickel and tungsten elements are evenly distributed, and there is no segregation or residue of high-melting-point elemental tungsten, indicating the high homogeneity of the nickel-tungsten master alloy, that is, the nickel and tungsten elements are evenly distributed without segregation.

[0047] The composition of the nickel-tungsten master alloy prepared in this embodiment was analyzed, and the results are shown in Table 1 below.

[0048] Table 1

[0049]

[0050] As shown in Table 1, the nickel-tungsten master alloy prepared in this embodiment has very low levels of impurity elements such as Al, Mo, Pb, Si, Sn, Ta, and Ti. This indicates that the present invention effectively improves the purity of the nickel-tungsten master alloy by controlling the purity and particle size of the raw tungsten powder and nickel powder. At the same time, the impurity elements such as C, O, and S in the nickel-tungsten master alloy are far below 0.01 wt%, indicating that the present invention effectively suppresses the contamination of the sintering environment (graphite furnace cavity, air, etc.) on the nickel-tungsten master alloy product by using tantalum sheet wrapping and sponge titanium placement.

[0051] Example 2

[0052] The preparation method of this embodiment includes the following steps:

[0053] Step 1: Raw material selection: Select nickel powder with a purity of 99.9% or higher, a particle size of 2μm, and an oxygen content of no more than 1000ppm, and tungsten powder with a purity of 99.9% or higher, a particle size of 1μm, and an oxygen content of no more than 1000ppm as raw materials;

[0054] Step 2, Powder Mixing: Based on the composition of the target product, nickel-tungsten master alloy, Ni-50wt%W, weigh nickel powder and 5% anhydrous ethanol (by weight of nickel powder) and place them in a mixer. Run the mixer at a drum speed of 20 rpm for 30 minutes, let it stand for 15 minutes, then add tungsten powder and continue running the mixer at a drum speed of 40 rpm for 4 hours.

[0055] Step 3, Green blank forming: The mixed powder obtained in step 2 is dried in an oven at 120℃ for 30 minutes, then placed into a rubber mold, vacuum sealed, and placed in a cold isostatic press. It is held under pressure of 250MPa for 10 minutes to obtain the green blank.

[0056] After the mixed powder is prepared in step two, the green body forming process in step three is completed within 8 hours.

[0057] Step 4, Sintering and Multi-Step Heat Treatment: The green blank obtained in Step 3 is placed in a vacuum sintering furnace. The green blank is wrapped with tantalum sheets with a purity of 99% or higher, and sponge titanium with a purity of 99.5% or higher is placed in the furnace cavity. Sintering is then carried out at a vacuum of 0.001 Pa to 0.05 Pa and a temperature of 1500°C for 2 hours. Subsequently, multi-step heat treatment is performed. First, the temperature is lowered to 1045°C and held for 2 hours, then lowered to 1015°C and held for 2 hours. The furnace is then cooled to room temperature to obtain the sintered body. During the multi-step heat treatment, an infrared thermometer combined with a K-type thermocouple equipped in the vacuum sintering furnace is used to monitor and control the temperature of each heat treatment step.

[0058] Step 5: Machining: The sintered body obtained in Step 4 is machined to remove a 1.5mm thick surface layer, resulting in a nickel-tungsten master alloy.

[0059] The composition of the nickel-tungsten master alloy prepared in this embodiment was analyzed, and the results are shown in Table 2 below.

[0060] Table 2

[0061]

[0062] As shown in Table 2, the nickel-tungsten master alloy prepared in this embodiment has very low levels of impurity elements such as Al, Mo, Pb, Si, Sn, Ta, and Ti. This indicates that the present invention effectively improves the purity of the nickel-tungsten master alloy by controlling the purity and particle size of the raw tungsten powder and nickel powder. At the same time, the impurity elements such as C, O, and S in the nickel-tungsten master alloy are far below 0.01 wt%, indicating that the present invention effectively suppresses the contamination of the sintering environment (graphite furnace cavity, air, etc.) on the nickel-tungsten master alloy product by using tantalum sheet wrapping and sponge titanium placement.

[0063] Upon testing, the phase composition of the nickel-tungsten master alloy prepared in this embodiment consists of a nickel solid solution phase, a Ni4W phase, and a NiW phase. Furthermore, the nickel and tungsten elements are uniformly distributed in the nickel-tungsten master alloy, and there is no tungsten segregation. The reason for this is that, under equilibrium conditions, the phase composition of the nickel-tungsten master alloy includes both the Ni4W and NiW phases. However, due to the influence of kinetic factors, complete thermodynamic equilibrium cannot be achieved. Therefore, the final phase composition of the nickel-tungsten master alloy consists of three phases: a nickel solid solution phase, a Ni4W phase, and a NiW phase.

[0064] Example 3

[0065] The preparation method of this embodiment includes the following steps:

[0066] Step 1: Raw material selection: Select nickel powder with a purity of 99.9% or higher, a particle size of 1μm, and an oxygen content of no more than 1000ppm, and tungsten powder with a purity of 99.9% or higher, a particle size of 1μm, and an oxygen content of no more than 1000ppm as raw materials;

[0067] Step 2, Powder Mixing: Based on the composition of the target product, nickel-tungsten master alloy, Ni-60wt%W, weigh nickel powder and 5% anhydrous ethanol (by weight of nickel powder) and place them in a mixer. Run the mixer at a drum speed of 20 rpm for 30 minutes, let it stand for 15 minutes, then add tungsten powder and continue running the mixer at a drum speed of 60 rpm for 5 hours.

[0068] Step 3, Green blank forming: The mixed powder obtained in step 2 is dried in an oven at 120℃ for 30 minutes, then placed into a rubber mold, vacuum sealed, and placed in a cold isostatic press. It is held under pressure of 200MPa for 10 minutes to obtain the green blank.

[0069] After the mixed powder is prepared in step two, the green body forming process in step three is completed within 8 hours.

[0070] Step 4, Sintering and Multi-Step Heat Treatment: The green blank obtained in Step 3 is placed in a vacuum sintering furnace. The green blank is wrapped with tantalum sheets of 99% or higher purity. Sponge titanium of 99.5% or higher purity is placed in the furnace cavity. Sintering is then carried out at a vacuum of 0.001 Pa to 0.05 Pa and a temperature of 1600°C for 2 hours. Subsequently, multi-step heat treatment is performed. First, the temperature is lowered to 1060°C and held for 3 hours, then lowered to 1025°C and held for 3 hours. The furnace is then cooled to room temperature to obtain the sintered body. During the multi-step heat treatment, an infrared thermometer combined with a K-type thermocouple equipped in the vacuum sintering furnace is used to monitor and control the temperature of each heat treatment step.

[0071] Step 5, Machining: The sintered body obtained in Step 4 is machined to remove a 2mm thick surface layer, resulting in a nickel-tungsten master alloy.

[0072] The composition of the nickel-tungsten master alloy prepared in this embodiment was analyzed, and the results are shown in Table 3 below.

[0073] Table 3

[0074]

[0075] As shown in Table 3, the nickel-tungsten master alloy prepared in this embodiment has very low levels of impurity elements such as Al, Mo, Pb, Si, Sn, Ta, and Ti. This indicates that the present invention effectively improves the purity of the nickel-tungsten master alloy by controlling the purity and particle size of the raw tungsten powder and nickel powder. At the same time, the impurity elements such as C, O, and S in the nickel-tungsten master alloy are far below 0.01 wt%, indicating that the present invention effectively suppresses the contamination of the sintering environment (graphite furnace cavity, air, etc.) on the nickel-tungsten master alloy product by using tantalum sheet wrapping and sponge titanium placement.

[0076] Testing revealed that the nickel-tungsten master alloy prepared in this embodiment consists of a Ni4W phase and a nickel solid solution phase, and the nickel and tungsten elements are evenly distributed in the nickel-tungsten master alloy without any tungsten segregation.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for the production of a nickel tungsten intermediate alloy by a multi-step heat treatment, characterized in that, The method comprises the following steps: Step one, raw material selection: selecting nickel powder with a mass purity of 99.9% or above, a particle size of 100 microns or below, and an oxygen content of no more than 1000 ppm, and tungsten powder with a mass purity of 99.9% or above, a particle size of 25 microns or below, and an oxygen content of no more than 1000 ppm as raw materials; Step two, powder mixing: according to the composition of the target product nickel-tungsten intermediate alloy, the nickel powder and the tungsten powder in step one are weighed and mixed uniformly with anhydrous ethanol in a mixer to obtain a mixed powder; Step three, green compact forming: the mixed powder obtained in step two is dried and then loaded into a rubber mold, and after vacuum packaging, it is placed in a cold isostatic pressing machine under a pressure of 200 MPa to 300 MPa for 10 minutes to obtain a green compact; Step four, sintering and multi-step heat treatment: the green compact obtained in step three is placed in a vacuum sintering furnace and sintered at a vacuum degree of 0.001 Pa to 0.05 Pa and a temperature of 1400 ℃ to 1600 ℃ for 2 hours, and then subjected to multi-step heat treatment, first cooled to 1030 ℃ to 1060 ℃ for 1 hour to 3 hours, then cooled to 1005 ℃ to 1025 ℃ for 1 hour to 3 hours, and cooled to room temperature in the furnace, to obtain a sintered body; during sintering, the green compact is first wrapped with tantalum sheets with a mass purity of 99% or above, and a titanium sponge with a mass purity of 99.5% or above is placed in the furnace cavity of the vacuum sintering furnace; Step five, machining: the sintered body obtained in step four is machined to remove a thickness of 1 mm to 2 mm from the surface to obtain a nickel-tungsten intermediate alloy.

2. The method according to claim 1, wherein the method is characterized by, The particle size ratio of the nickel powder to the tungsten powder in step one is 1 to 2:

1.

3. The multi-step heat treatment preparation method for a nickel-tungsten master alloy according to claim 1, characterized in that, In the powder mixing process in step two, the nickel powder is first placed in a mixer with 5% of the mass of the nickel powder of anhydrous ethanol, and the barrel rotation speed is operated at 20 revolutions per minute to 60 revolutions per minute for 30 minutes, and after standing for 15 minutes, the tungsten powder is added, and the barrel rotation speed is continued to be operated at 20 revolutions per minute to 60 revolutions per minute for 3 hours to 5 hours.

4. The method of claim 1, wherein the multi-step heat treatment of the nickel tungsten intermediate alloy is characterized by, After the mixed powder is prepared in step two, the green compact forming process in step three is completed within 8 hours.

5. The method of claim 1, wherein the multi-step heat treatment of the nickel tungsten intermediate alloy is characterized by: In the multi-step heat treatment process in step four, an infrared temperature measuring instrument is used in combination with a K-type thermocouple equipped with the vacuum sintering furnace to monitor and control the temperature of each step of heat treatment.

6. A nickel-tungsten master alloy produced by the method of any one of claims 1 to 5, characterized in that The mass fraction of the nickel-tungsten intermediate alloy is: Ni 40% to 62%, the balance being W and unavoidable impurities, the unavoidable impurities including non-metallic impurities O, C, and S each with a mass fraction of 0.01% or below, and metallic impurities Al, Mo, Pb, Sn, Ta, and Ti each with a mass fraction of 0.01% or below, and the phase composition of the nickel-tungsten intermediate alloy includes Ni4W phase and other nickel-tungsten phases, the other nickel-tungsten phases being derived from nickel solid solution phase, NiW phase, and NiW2 phase, the nickel-tungsten elements in the nickel-tungsten intermediate alloy are uniformly distributed, and there is no tungsten element segregation.

Images