A method for preparing high-density tungsten based on oscillating hot-pressing process low-temperature sintering and a product thereof

Abstract

The application belongs to the technical field of powder metallurgy, and discloses a method for preparing high-density tungsten based on an oscillation hot-pressing process and a product, wherein tungsten powder is placed in a vacuum environment with a vacuum degree less than 10 Pa; the tungsten powder is heated to 1500-1600 DEG C, and a constant pressure of 2-5 MPa is applied to the tungsten powder during the heating process; then, the tungsten powder is kept for 1-2 hours for sintering, and an oscillation pressure is applied to the tungsten powder during the keeping process; after the sintering is completed, the obtained product is decompressed and cooled. The application can realize the preparation of tungsten sheets with high density, small grain size and good mechanical properties at a low sintering temperature.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, and relates to the preparation of high-density tungsten, and particularly to a low-temperature sintering technology for preparing high-density tungsten based on an oscillating hot pressing process. Background Technology

[0002] Tungsten (W) is a rare transition metal with advantages such as high melting point, high hardness, corrosion resistance, and chemical stability, making it widely used in industries such as instrumentation, medical equipment, aerospace, and machinery. As a sputtering target, tungsten requires high density and good mechanical properties to ensure high sputtering efficiency during coating. High-density tungsten also possesses characteristics such as a low coefficient of thermal expansion, good electrical and thermal conductivity, a high sputtering threshold, and non-reaction with tritium, making it considered one of the most promising plasma-oriented materials. However, tungsten exhibits a notch-sensitive effect, easily leading to crack propagation and deepening, and its low impurity tolerance, recrystallization brittleness, and low-temperature brittleness can easily cause material cracking. Therefore, improving the mechanical properties of tungsten and extending its service life is crucial.

[0003] Refining grain structure is an effective means of improving the mechanical properties of materials. In the preparation of metallic materials, grain size and grain boundary structure are controlled by manipulating raw material composition, heat treatment processes, deformation methods, and rates. In the preparation of ceramic materials, grain size and grain boundary structure are controlled by manipulating sintering temperature, time, pressure application method, and pressure magnitude, thereby optimizing the mechanical properties of the material. Generally, the smaller the raw material particle size, the smaller the grain size of the prepared material. However, during the sintering of micron- or even nano-sized raw materials, powder agglomeration often occurs. Agglomerates preferentially sinter, leading to uneven structure in the sintered body, abnormal grain growth, and difficulty in eliminating closed pores, resulting in reduced material density. Therefore, pressure sintering is often used to break powder agglomeration. However, the inherent driving force provided by static pressure sintering (such as hot pressing, hot isostatic pressing, and spark plasma sintering) is insufficient to effectively break agglomerates and eliminate closed pores. Even increasing the sintering temperature and extending the holding time cannot reduce pores by promoting grain growth; instead, it can lead to abnormal grain growth. Summary of the Invention

[0004] The purpose of this invention is to address the problems of low density and poor mechanical properties of tungsten by providing a method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot pressing process. This method can achieve the preparation of tungsten sheets with high density and excellent mechanical properties at a relatively low sintering temperature.

[0005] Hot oscillatory pressing (HOP) is a novel sintering technology that utilizes adjustable sinusoidal dynamic pressure during the sintering process to provide a higher sintering driving force. The sinusoidal dynamic pressure effectively breaks up powder agglomeration and growth during sintering, eliminating the formation of intragranular pores. Furthermore, the equipment is simple to operate and offers good controllability. Therefore, this application employs hot oscillatory pressing to prepare tungsten. Under oscillatory pressure, particle rearrangement and volume shrinkage are accelerated in the early stages of sintering, resulting in a higher packing density. In the middle and later stages of sintering, increased grain rotation, slip, and plastic flow accelerate the densification rate, effectively suppressing grain growth, lowering the sintering temperature, improving the microstructure of tungsten, and enhancing its density and mechanical properties.

[0006] To achieve the above objectives, the present invention provides a method for preparing high-density tungsten based on a low-temperature sintering process using oscillating hot pressing, comprising the following steps:

[0007] S1 places the tungsten powder in a vacuum environment with a vacuum degree of less than 10 Pa;

[0008] S2 is heated to 1500-1600℃, and a constant pressure of 2-5 MPa is applied to the tungsten powder during the heating process; then it is held at this temperature for sintering for 1-2 hours, during which an oscillating pressure is applied to the tungsten powder.

[0009] After the S3 sintering is completed, the resulting product is depressurized and cooled.

[0010] The tungsten powder used in this invention has a particle size of approximately 1–5 μm and a purity of ≥99.99%.

[0011] In step S2 above, the heating process includes two stages. The first stage involves heating from room temperature to 1000℃ at a rate of 8–10℃ / min. The second stage involves further heating to 1500–1600℃ at a rate of 5–8℃ / min. The heating rate in the first stage is greater than that in the second stage. During the heat preservation process, the oscillation pressure parameters include: median pressure of 30–60 MPa, amplitude of ±5–±15 MPa, and oscillation frequency of 0.5–10 Hz.

[0012] In step S3 above, after sintering is completed, the oscillation program is ended, the pressure of the obtained product is reduced, and then the product is cooled to room temperature in the furnace to obtain the final product.

[0013] The tungsten products prepared by the above method can achieve a density of over 96%, a purity of ≥99.95%, a grain size of approximately 3.83–4.29 μm, and a bending strength of approximately 885–1200 MPa.

[0014] Compared with existing technologies, the method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot-pressing process provided by this invention has the following beneficial effects:

[0015] (1) The present invention adopts an oscillating pressure sintering process, which is a sintering process assisted by a thermal field and a force field. Its pressure is a sinusoidal dynamic pressure with adjustable frequency and amplitude, which provides a high sintering driving force, improves grain boundary strength, promotes particle rearrangement, and realizes plastic deformation. It effectively solves the problem of particle agglomeration and elimination of closed pores that are difficult to break under static pressure. It can realize the preparation of tungsten sheets with high density, small grain size and good mechanical properties at a lower sintering temperature.

[0016] (2) The pure tungsten sample prepared by the present invention has a density of over 96%, a grain size of approximately 3.83 to 4.29 μm, and a bending strength of approximately 885 to 1200 MPa. Compared with pure tungsten samples prepared by other processes, it has higher density, finer grain size, and better mechanical properties. Attached Figure Description

[0017] Figure 1 This diagram illustrates the heating and holding sintering process in the low-temperature sintering method for preparing high-density tungsten based on oscillating hot pressing, as described in this invention. An example is a sintering process with a temperature of 1600℃, an oscillation pressure of 60±15MPa, and a frequency of 1Hz. The small graph in the upper right corner shows the pressure change over time at a frequency of 1Hz. The temperature is increased to 1000℃ at a heating rate of 10℃ / min, then increased to 1600℃ at a heating rate of 7.5℃ / min, with a constant pressure of 5MPa applied during the heating phase. At the 1600℃ holding phase, the temperature is maintained for 2 hours, while an oscillation pressure of 60MPa, an amplitude of ±15MPa, and a frequency of 1Hz is applied. At the end of the holding phase, the pressure is released, the oscillation program is terminated, and the sample is then cooled to room temperature with the furnace.

[0018] Figure 2 The XRD patterns of the pure tungsten samples prepared in Examples 1-7 are shown.

[0019] Figure 3 The images show SEM images of the three-point bending cross-sections of pure tungsten samples prepared in Examples 1 to 7; where (a) corresponds to Example 1, (b) corresponds to Example 2, (c) corresponds to Example 3, (d) corresponds to Example 4, (e) corresponds to Example 5, (f) corresponds to Example 6, and (g) corresponds to Example 7.

[0020] Figure 4 The image shows the grain size distribution of the pure tungsten samples prepared in Examples 1 to 7; where (a) corresponds to Example 1, (b) corresponds to Example 2, (c) corresponds to Example 3, (d) corresponds to Example 4, (e) corresponds to Example 5, (f) corresponds to Example 6, and (g) corresponds to Example 7. Detailed Implementation

[0021] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0022] The W powder used in the following examples was purchased from Beijing Huawiruike Chemical Co., Ltd., with an average particle size of approximately 1 μm and a purity of 99.99%.

[0023] Example 1

[0024] The method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot-pressing process provided in this embodiment includes the following steps:

[0025] S1. Take 14.5g of pure tungsten powder and load it into a cylindrical graphite mold with a diameter of Φ20mm, positioning the mold in the center of the worktable with its center aligned with the middle of the heating element. Adjust the pressure head downwards until it just touches the mold. Close the furnace door, ensuring all valves are closed. Start the mechanical pump to create a vacuum. Once the mechanical pump is running stably, open the upper valve and evacuate to below 10Pa. Then, start the heating and pressurization process.

[0026] S2 was heated to 1000℃ at a rate of 10℃ / min, then to 1600℃ at a rate of 7.5℃ / min, with a holding time of 2 hours. During the heating process, a constant pressure of 5MPa was applied to the sample at a loading rate of 5MPa / min. At 1600℃, an oscillation program was initiated until the holding time ended, with a median oscillation pressure of 60MPa, an amplitude of ±15MPa, and a frequency of 0.5Hz. After the holding time, the furnace was cooled and depressurized. After cooling to room temperature, the vacuum was broken, the furnace door was opened, and the graphite mold was removed by controlling the pressure head to move upwards. The sample was then taken out.

[0027] The graphite paper on the sample obtained from sintering in step S1 was removed using a grinding machine, and the sample was then cleaned, dried, and packaged. The pure tungsten sample prepared by sintering had a relative density of 96.33%, a grain size of 3.95 μm, and a bending strength of 988.5 MPa.

[0028] Example 2

[0029] The method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot-pressing process provided in this embodiment includes the following steps:

[0030] S1. Take 14.5g of pure tungsten powder and load it into a cylindrical graphite mold with a diameter of Φ20mm, positioning the mold in the center of the worktable with its center aligned with the middle of the heating element. Adjust the pressure head downwards until it just touches the mold. Close the furnace door, ensuring all valves are closed. Start the mechanical pump to create a vacuum. Once the mechanical pump is running stably, open the upper valve and evacuate to below 10Pa. Then, start the heating and pressurization process.

[0031] S2 was heated to 1000℃ at a heating rate of 10℃ / min, then to 1600℃ at a heating rate of 7.5℃ / min, with a holding time of 2 hours. During the heating process, a constant pressure of 5MPa was applied to the sample at a loading rate of 5MPa / min. At 1600℃, an oscillation program was initiated until the holding time ended, with a median oscillation pressure of 60MPa, an amplitude of ±15MPa, and a frequency of 1Hz. After the holding time, the furnace was cooled and depressurized. After cooling to room temperature, the vacuum was broken, the furnace door was opened, and the graphite mold was removed by controlling the pressure head to move upwards. The sample was then taken out.

[0032] The graphite paper on the sample obtained from sintering in step S1 was removed using a grinding machine, and the sample was then cleaned, dried, and packaged. The pure tungsten sample prepared by sintering had a relative density of 99.30%, a grain size of 3.90 μm, and a bending strength of 1200 MPa.

[0033] Example 3

[0034] The method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot-pressing process provided in this embodiment includes the following steps:

[0035] S1. Take 14.5g of pure tungsten powder and load it into a cylindrical graphite mold with a diameter of Φ20mm, positioning the mold in the center of the worktable with its center aligned with the middle of the heating element. Adjust the pressure head downwards until it just touches the mold. Close the furnace door, ensuring all valves are closed. Start the mechanical pump to create a vacuum. Once the mechanical pump is running stably, open the upper valve and evacuate to below 10Pa. Then, start the heating and pressurization process.

[0036] S2 was heated to 1000℃ at a heating rate of 10℃ / min, then to 1600℃ at a heating rate of 7.5℃ / min, with a holding time of 2 hours. During the heating process, a constant pressure of 5MPa was applied to the sample at a loading rate of 5MPa / min. At 1600℃, an oscillation program was initiated until the holding time ended, with a median oscillation pressure of 60MPa, an amplitude of ±15MPa, and a frequency of 2Hz. After the holding time, the furnace was cooled and depressurized. After cooling to room temperature, the vacuum was broken, the furnace door was opened, and the graphite mold was removed by controlling the pressure head to move upwards. The sample was then taken out.

[0037] The graphite paper on the sample obtained from sintering in step S1 was removed using a grinding machine, and the sample was then cleaned, dried, and packaged. The pure tungsten sample prepared by sintering had a relative density of 96.99%, a grain size of 3.87 μm, and a bending strength of 957.6 MPa.

[0038] Example 4

[0039] The method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot-pressing process provided in this embodiment includes the following steps:

[0040] S1. Take 14.5g of pure tungsten powder and load it into a cylindrical graphite mold with a diameter of Φ20mm, positioning the mold in the center of the worktable with its center aligned with the middle of the heating element. Adjust the pressure head downwards until it just touches the mold. Close the furnace door, ensuring all valves are closed. Start the mechanical pump to create a vacuum. Once the mechanical pump is running stably, open the upper valve and evacuate to below 10Pa. Then, start the heating and pressurization process.

[0041] S2 was heated to 1000℃ at a heating rate of 10℃ / min, then to 1600℃ at a heating rate of 7.5℃ / min, with a holding time of 2 hours. During the heating process, a constant pressure of 5MPa was applied to the sample at a loading rate of 5MPa / min. At 1600℃, an oscillation program was initiated until the holding time ended, with a median oscillation pressure of 60MPa, an amplitude of ±15MPa, and a frequency of 5Hz. After the holding time, the furnace was cooled and depressurized. After cooling to room temperature, the vacuum was broken, the furnace door was opened, and the graphite mold was removed by controlling the pressure head to move upwards. The sample was then taken out.

[0042] The graphite paper on the sample obtained from sintering in step S1 was removed using a grinding machine, and the sample was then cleaned, dried, and packaged. The pure tungsten sample prepared by sintering had a relative density of 97.03%, a grain size of 3.83 μm, and a bending strength of 947.0 MPa.

[0043] Example 5

[0044] The method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot-pressing process provided in this embodiment includes the following steps:

[0045] S1. Take 14.5g of pure tungsten powder and load it into a cylindrical graphite mold with a diameter of Φ20mm, positioning the mold in the center of the worktable with its center aligned with the middle of the heating element. Adjust the pressure head downwards until it just touches the mold. Close the furnace door, ensuring all valves are closed. Start the mechanical pump to create a vacuum. Once the mechanical pump is running stably, open the upper valve and evacuate to below 10Pa. Then, start the heating and pressurization process.

[0046] S2 was heated to 1000℃ at a rate of 10℃ / min, then to 1600℃ at a rate of 7.5℃ / min, with a holding time of 2 hours. During the heating process, a constant pressure of 5MPa was applied to the sample at a loading rate of 5MPa / min. At 1600℃, an oscillation program was initiated until the holding time ended, with a median oscillation pressure of 60MPa, an amplitude of ±10MPa, and a frequency of 1Hz. After the holding time, the furnace was cooled and depressurized. After cooling to room temperature, the vacuum was broken, the furnace door was opened, and the graphite mold was removed by controlling the pressure head to move upwards. The sample was then taken out.

[0047] The graphite paper on the sample obtained from sintering in step S1 was removed using a grinding machine, and the sample was then cleaned, dried, and packaged. The pure tungsten sample prepared by sintering had a relative density of 99.21%, a grain size of 4.29 μm, and a bending strength of 944.5 MPa.

[0048] Example 6

[0049] The method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot-pressing process provided in this embodiment includes the following steps:

[0050] S1. Take 14.5g of pure tungsten powder and load it into a cylindrical graphite mold with a diameter of Φ20mm, positioning the mold in the center of the worktable with its center aligned with the middle of the heating element. Adjust the pressure head downwards until it just touches the mold. Close the furnace door, ensuring all valves are closed. Start the mechanical pump to create a vacuum. Once the mechanical pump is running stably, open the upper valve and evacuate to below 10Pa. Then, start the heating and pressurization process.

[0051] S2 was heated to 1000℃ at a rate of 10℃ / min, then to 1600℃ at a rate of 7.5℃ / min, with a holding time of 2 hours. During the heating process, a constant pressure of 5MPa was applied to the sample at a loading rate of 5MPa / min. At 1600℃, an oscillation program was initiated until the holding time ended, with a median oscillation pressure of 60MPa, an amplitude of ±10MPa, and a frequency of 2Hz. After the holding time, the furnace was cooled and depressurized. After cooling to room temperature, the vacuum was broken, the furnace door was opened, and the graphite mold was removed by controlling the pressure head to move upwards. The sample was then taken out.

[0052] The graphite paper on the sample obtained from sintering in step S1 was removed using a grinding machine, and the sample was then cleaned, dried, and packaged. The pure tungsten sample prepared by sintering had a relative density of 99.23%, a grain size of 4.04 μm, and a bending strength of 921.8 MPa.

[0053] Example 7

[0054] The method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot-pressing process provided in this embodiment includes the following steps:

[0055] S1. Take 14.5g of pure tungsten powder and load it into a cylindrical graphite mold with a diameter of Φ20mm, positioning the mold in the center of the worktable with its center aligned with the middle of the heating element. Adjust the pressure head downwards until it just touches the mold. Close the furnace door, ensuring all valves are closed. Start the mechanical pump to create a vacuum. Once the mechanical pump is running stably, open the upper valve and evacuate to below 10Pa. Then, start the heating and pressurization process.

[0056] S2 was heated to 1000℃ at a heating rate of 10℃ / min, then to 1600℃ at a heating rate of 7.5℃ / min, with a holding time of 2 hours. During the heating process, a constant pressure of 5MPa was applied to the sample at a loading rate of 5MPa / min. At 1600℃, an oscillation program was initiated until the holding time ended, with a median oscillation pressure of 60MPa, an amplitude of ±10MPa, and a frequency of 5Hz. After the holding time, the furnace was cooled and depressurized. After cooling to room temperature, the vacuum was broken, the furnace door was opened, and the graphite mold was removed by controlling the pressure head to move upwards. The sample was then taken out.

[0057] The graphite paper on the sample obtained from sintering in step S1 was removed using a grinding machine, and the sample was then cleaned, dried, and packaged. The pure tungsten sample prepared by sintering had a relative density of 98.43%, a grain size of 3.91 μm, and a bending strength of 967.3 MPa.

[0058] Example 8

[0059] The method for preparing high-density tungsten based on low-temperature sintering using an oscillating hot-pressing process provided in this embodiment includes the following steps:

[0060] S1. Take 14.5g of pure tungsten powder and load it into a cylindrical graphite mold with a diameter of Φ20mm, positioning the mold in the center of the worktable with its center aligned with the middle of the heating element. Adjust the pressure head downwards until it just touches the mold. Close the furnace door, ensuring all valves are closed. Start the mechanical pump to create a vacuum. Once the mechanical pump is running stably, open the upper valve and evacuate to below 10Pa. Then, start the heating and pressurization process.

[0061] S2 was heated to 1000℃ at a rate of 10℃ / min, then to 1500℃ at a rate of 7.5℃ / min, with a holding time of 2 hours. During the heating process, a constant pressure of 5MPa was applied to the sample at a loading rate of 5MPa / min. At 1500℃, an oscillation program was initiated until the holding time ended, with a median oscillation pressure of 60MPa, an amplitude of ±15MPa, and a frequency of 1Hz. After the holding time, the furnace was cooled and depressurized. After cooling to room temperature, the vacuum was broken, the furnace door was opened, and the graphite mold was removed by controlling the pressure head to move upwards. The sample was then taken out.

[0062] The graphite paper on the sample obtained from sintering in step S1 was removed using a grinding machine, and the sample was then cleaned, dried, and packaged. The pure tungsten sample prepared by sintering had a relative density of 98.33%, a grain size of 5.60 μm, and a bending strength of 885.6 MPa.

[0063] The pure tungsten samples prepared in Examples 1 to 7 were subjected to structural and performance analysis.

[0064] XRD analysis was performed on the pure tungsten samples prepared in Examples 1 to 7, and the results are as follows: Figure 2 As shown. From Figure 2 It can be seen that all prepared pure tungsten samples are pure tungsten phase. ICP analysis, hydrogen oxygen nitrogen analysis, and carbon sulfur analysis showed that the impurity element content was less than 0.05%, therefore the purity of the pure tungsten samples is ≥99.95%.

[0065] SEM tests were performed on the pure tungsten samples prepared in Examples 1 to 7, and the test results are as follows: Figure 3 As shown. From Figure 3 The results show that the pure tungsten samples sintered by oscillation hot pressing have almost no porosity between grains, high density, and transgranular fracture is the dominant fracture mode. They exhibit high grain boundary strength, smooth fracture surfaces, and numerous dissociation cracks left by transgranular fracture. The density of the pure tungsten samples ranges from 96.99% to 99.30%, the grain size from 3.83 to 4.29 μm, and the flexural strength from 885.6 to 1200 MPa. The main difference between Examples 1-4 and Examples 5-7 lies in the oscillation frequency. It can be seen that both excessively high and low oscillation frequencies negatively impact the density and mechanical properties of the test samples. The difference between Examples 1 and 5 lies in the oscillation amplitude; increasing the oscillation amplitude promotes densification and improves mechanical properties.

[0066] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing high density tungsten by low temperature sintering based on oscillating hot pressing process, characterized in that, The method comprises the following steps: S1: placing tungsten powder in a vacuum environment with a vacuum degree less than 10 Pa; S2: heating to 1500-1600 ℃, and applying a constant pressure of 2-5 MPa to the tungsten powder during the heating process; then, sintering for 1-2 h, and applying an oscillating pressure to the tungsten powder during the sintering process; The heating process comprises two stages, the first stage is heating from room temperature to 1000 ℃ at a rate of 8-10 ℃ / min, and the second stage is continuously heating to 1500-1600 ℃ at a rate of 5-8 ℃ / min; During the sintering process, the oscillating pressure parameters comprise: a median pressure of 60 MPa, an amplitude of ±5-±15 MPa, and an oscillating frequency of 0.5-10 Hz; S3: after the sintering is completed, discharging pressure and cooling the obtained product.

2. The method for preparing high density tungsten by low temperature sintering based on an oscillating hot press process according to claim 1, characterized in that, The tungsten powder used has a particle size of 1-5 μm and a purity of ≥99.99%.

3. A tungsten product prepared by the method of claim 1 or 2.

4. The tungsten product of claim 3, wherein, The tungsten product has a density of ≥96%, a purity of ≥99.95%, a grain size of 3.83-4.29 μm, and a bending strength of 885-1200 MPa.

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