A method for preparing a tungsten-based composite material with high hardness, low oxygen content and a network grain boundary pinning structure

Abstract

A method for preparing a tungsten-based composite material with high hardness, low oxygen content and a network grain boundary pinning structure relates to the technical field of tungsten-boron composite material preparation. First, a W-B composite powder is obtained by mixing powder in a mixer with argon filling, and then a W-B tungsten-based composite material is prepared by optimizing spark plasma sintering and regulating the grain boundary structure. Boron elements combine with oxygen elements at the tungsten grain boundaries during spark plasma sintering to form low-melting-point compounds, which evaporate at high temperatures, reducing the oxygen concentration and reducing the weakening effect of O on the grain boundary cohesion. The prepared W-B tungsten-based composite material has a relative density of more than 95.0%, and a microhardness value of 493.2 to 697.4 HV, which is better than pure tungsten material (microhardness 360 to 420 HV). At the same time, the oxygen content (4.0 to 32.4 ppm) is significantly lower than the oxygen content (124.6 to 248.9 ppm) of tungsten-boron composite materials prepared by high-energy mechanical ball milling.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of tungsten-boron composite materials, and in particular to a preparation method of a tungsten-based composite material with high hardness, low oxygen content and a network grain boundary pinning structure. Background Art

[0002] Tungsten (W) has a high melting point (3683K), high density (19.3g.cm -3 ), high thermal conductivity (174W(mk) -1 ), low thermal expansion coefficient (4.5x10 -6 K -1 ) and a low sputtering threshold, making them considered the most promising plasma-facing materials (PFMs) for fusion devices. In the ITER (International Nuclear Confinement Research Institute), PFMs must withstand harsh operating conditions such as high heat loads, plasma shock, and neutron irradiation. These conditions can cause severe damage to the material, such as cracking, melting, and blistering, which severely impact reactor operation.

[0003] However, tungsten's inherent brittleness is a significant contributor to these damages. The high Peierls stress of the BCC crystal structure and poor grain boundary cohesion contribute to tungsten's low-temperature limited plasticity. A primary factor contributing to the low-temperature limited plasticity of refractory metals like tungsten and molybdenum is the material's high sensitivity to interstitial impurities, which tend to segregate at grain boundaries, reducing grain boundary cohesion and leading to grain boundary brittleness.

[0004] Therefore, researchers are considering adding grain boundary cohesion enhancers to tungsten-based materials to remove the brittle element oxygen at the grain boundaries and further improve the grain boundary bonding strength of the material. The current strategy to reduce the concentration of free oxygen at the grain boundaries is mainly to add active elements that easily form stable compounds with oxygen, such as titanium (Ti), zirconium (Zr), hafnium (Hf), etc. Researchers have shown through simulation calculations that boron (B) has the highest strengthening potential at tungsten grain boundaries and is a very effective grain boundary cohesion enhancer. Boron can potentially remove and replace oxygen at the tungsten grain boundaries, improve the grain boundary bonding strength of the material, and thus strengthen the tungsten grain boundaries.

[0005] Mechanical ball milling to prepare second-phase reinforced tungsten-based composites is an effective method for material structural design, capable of regulating desired structures and properties, making it particularly suitable for the preparation of nanomaterials. However, the powder is susceptible to oxidation due to local overheating during the mechanical alloying collision process. This leads to oxygen segregation at grain boundaries during subsequent sintering, resulting in deterioration of material properties. Therefore, reducing the material's oxygen content and preparing tungsten-based composites with excellent comprehensive mechanical properties is a hot topic among researchers. Summary of the Invention

[0006] In order to solve the problem that the mechanical ball milling method can easily achieve the regulation of material structure and the preparation of multi-element powder, but introduces defects such as oxygen impurities during the mechanical alloying process, the present invention proposes a preparation method for a tungsten-based composite material with high hardness, low oxygen content and a network grain boundary pinning structure. First, a WB composite powder is obtained by mixing powder in a mixer with argon filling. Then, the WB tungsten-based composite material is prepared by optimizing spark plasma sintering and regulating the grain boundary structure, so as to significantly improve the hardness of the tungsten-based composite material and reduce its oxygen content.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is:

[0008] A method for preparing a tungsten-based composite material having high hardness, low oxygen content and a network grain boundary pinning structure, comprising the following steps:

[0009] Step 1: Flour making:

[0010] W powder, B powder and an appropriate amount of WC cemented carbide balls are placed in a plastic solid bottle according to the proportion, filled with argon in a glove box, sealed and placed in a mixer for powder mixing; after mixing, the composite powder is vacuumed and stored to obtain WB composite powder;

[0011] Step 2: Powder filling:

[0012] The WB composite powder obtained in step 1 is filled into a graphite mold. Before filling the mold with powder, carbon paper needs to be evenly rolled and laid. The carbon paper is tightly attached to the inner wall of the mold, and the distance between the upper and lower punches and the mold is just filled with carbon paper. The upper and lower punches are adjusted so that the powder is located in the center of the mold. The mold after powder filling is pre-pressed under a tablet press. The pre-pressed mold is assembled with thermal insulation carbon felt, and the mold temperature measuring hole is adjusted to align with the reserved hole of the thermal insulation carbon felt.

[0013] Step 3: Spark plasma sintering:

[0014] The graphite mold filled with the powder in step 2 is placed in a spark plasma sintering furnace chamber, and the furnace chamber is vacuumed; sintering is started to prepare a tungsten-boron composite material block, that is, a tungsten-based composite material with high hardness, low oxygen content and a network grain boundary pinning structure.

[0015] As a preferred technical solution of the present invention, in the preparation method:

[0016] In step 1, the proportion of B powder is 0.5-1.0% by mass, with the remainder being W powder. The argon pressure in the plastic solid bottle is 0.01-0.02 MPa. The mixer speed is 50-60 rpm, and the W and B powders are mixed for 10-15 hours. The diameter of the WC cemented carbide balls is 4-6 mm. The product of the number of WC cemented carbide balls added and their diameter is equal to 2 / 3 of the height of the plastic solid bottle. The resulting number is the number of WC cemented carbide balls added.

[0017] In step 2, the mass of the WB composite powder loaded was 12-18 g. The carbon paper loaded was 12.7 mm long, 3-4 mm wider than the mold length, and 0.1 mm thick. The mold pre-pressing pressure was 5 MPa, and the pre-pressing time was 3-5 minutes. The assembled carbon felt had a thickness of 0.5 mm.

[0018] In step 3, after the furnace chamber is evacuated, the vacuum level is 10 Pa. The specific steps of spark plasma sintering are: heating to 1300°C at 100°C / min and holding for 5-10 minutes, then increasing the temperature to 1600-1700°C at 100°C / min and holding for 5 minutes. After the holding period, heating is immediately stopped, the furnace is cooled to room temperature, and the tungsten-boron composite material block is obtained after demolding. The mold load during spark plasma sintering is 0.5 tons.

[0019] Compared with the prior art, the beneficial effects of the present invention are mainly manifested in:

[0020] 1. Under the specified raw material ratios and sintering process parameters, a WB composite powder is obtained by mixing with argon-filled powders. Spark plasma sintering is then used to obtain a WB composite block with a network-like grain boundary pinning structure. During spark plasma sintering, boron combines with oxygen at the tungsten grain boundaries to form a low-melting-point compound. This low-melting-point compound evaporates at high temperatures, reducing the oxygen concentration and thus the weakening effect of oxygen on grain boundary cohesion.

[0021] 2. The WB tungsten-based composite material prepared by the present invention has a relative density exceeding 95.0% and a microhardness of 493.2 to 697.4 HV, which is superior to pure tungsten (microhardness 360 to 420 HV). Furthermore, the oxygen content of the WB tungsten-based composite material prepared by the present invention is 4.0 to 32.4 ppm, significantly lower than the oxygen content of tungsten-boron composite materials prepared by high-energy mechanical ball milling (124.6 to 248.9 ppm). BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1This is a SEM image of a bulk W-1.0 wt.% B tungsten-based composite material prepared by spark plasma sintering in Example 1. (a) shows the fracture morphology, and (b) shows the network-like second-phase pinning structure at the grain boundaries. This demonstrates the preparation of a tungsten-based composite material with a grain-boundary reinforcement network-like second-phase pinning structure.

[0023] Figure 2 a, b, and c are metallographic images of the W-xB tungsten-based composite materials prepared by spark plasma sintering in Examples 1, 2, and 3, respectively. It can be seen that the volume fraction of the second phase in the W-xB tungsten-based composite materials increases with the increase in the addition amount of the B element.

[0024] Figure 3 The relative density and microhardness of the W-xB tungsten-based composites prepared after spark plasma sintering in Examples 1, 2, and 3 are shown. It can be seen that the densification temperature of the W-xB tungsten-based composites increases with the increase of the addition amount of element B, and the hardness of the W-xB tungsten-based composites increases with the increase of the addition amount of element B. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with embodiments and drawings.

[0026] Example 1:

[0027] In this embodiment, the method for preparing the low-oxygen and high-hardness WB tungsten-based composite material comprises the following steps:

[0028] 1. Powder making: W powder (0.5 μm, Xiamen Jinlu Special Alloy Co., Ltd.), B powder (D 50 =10-20 μm, Aladdin, purity ≥99%) and an appropriate amount of WC carbide balls are placed in a 100 mL plastic solid bottle; the plastic solid bottle is filled with argon in a glove box to a pressure of 0.02 MPa; the argon-filled solid bottle is sealed; the sealed solid bottle is placed in a mixer for powder mixing at a mixer speed of 60 rpm for 12 hours; the mixed composite powder is vacuum-evacuated to obtain a WB composite powder.

[0029] 2. Powder loading: Fill 15 g of the WB composite powder obtained in step 1 into a graphite mold with an inner diameter of 20 mm. Before filling the mold with powder, a 0.1 mm thick carbon paper needs to be evenly rolled and laid. The carbon paper fits tightly against the inner wall of the mold, and the distance between the upper and lower punches and the mold is just filled with carbon paper; adjust the position of the upper and lower punches so that the powder is located in the center of the mold; pre-press the powder-filled mold under a tablet press with a pre-pressing pressure of 5 MPa and a pre-pressing time of 5 min; assemble the pre-pressed mold with insulating carbon felt with a thickness of 0.5 mm, and adjust the mold temperature measuring hole to align with the reserved hole in the insulating carbon felt.

[0030] 3. Spark plasma sintering: Place the graphite mold filled with powder in step 2 in the spark plasma sintering furnace chamber, and evacuate the furnace chamber (10Pa); after starting sintering, heat to 1300℃ at 100℃ / min and keep warm for 10 minutes, then increase the temperature to 1700℃ at 100℃ / min and keep warm for 5 minutes; after the insulation is completed, stop heating immediately, cool to room temperature with the furnace, and demold to obtain a tungsten-boron composite material block (the load borne by the mold during the sintering process is 0.5t).

[0031] Comparative Example 1:

[0032] 1. High-energy mechanical ball milling:

[0033] W powder, B powder and WC carbide balls were loaded into a ball mill, and then an appropriate amount of anhydrous ethanol, a process control agent, was added to the mixed powder. The ball mill was filled with argon and the ball milling parameters were set: the ball milling speed was 400 rpm, and the ball milling time was 12 h. The slurry after ball milling was dried to obtain a WB composite powder. Based on the mass percentage of the mixed powder, the proportion of B powder was 1.0%, and the balance was W powder.

[0034] 2. Powder filling: same as step 2 in Example 1.

[0035] 3. Powder filling: same as step 3 of Example 1.

[0036] See also Figures 1 to 3 As shown, the W-1.0 wt.% B composite prepared by spark plasma sintering in Example 1 exhibits a network of second-phase pinning structures at the grain boundaries, enhancing grain boundary bonding. The addition of B also reduces the oxygen content in the matrix material. The W-1.0 wt.% B composite has an oxygen content of 24.0 ppm, lower than the 124.6 ppm of the W-1.0 wt.% B composite prepared by high-energy mechanical ball milling in Comparative Example 1.

[0037] Meanwhile, the W-1.0wt.%B tungsten-based composite material prepared by sintering at 1700°C in Example 1 has a relative density of 99.9% and a microhardness of 672.1±15.6HV, which is better than pure tungsten material (microhardness 360-420HV).

[0038] Example 2:

[0039] In this embodiment, the method for preparing the low-oxygen and high-hardness WB tungsten-based composite material comprises the following steps:

[0040] 1. Powder making: W powder (0.5 μm, Xiamen Jinlu Special Alloy Co., Ltd.), B powder (D 50 =10-20 μm, Aladdin, purity ≥99%) and an appropriate amount of WC carbide balls are placed in a 100 mL plastic solid bottle; the plastic solid bottle is filled with argon in a glove box to a pressure of 0.02 MPa; the argon-filled solid bottle is sealed; the sealed solid bottle is placed in a mixer for powder mixing at a mixer speed of 60 rpm for 12 hours; the mixed composite powder is vacuum-evacuated to obtain a WB composite powder.

[0041] 2. Powder loading: Fill 15 g of the WB composite powder obtained in step 1 into a graphite mold with an inner diameter of 20 mm. Before filling the mold with powder, a 0.1 mm thick carbon paper needs to be evenly rolled and laid. The carbon paper fits tightly against the inner wall of the mold, and the distance between the upper and lower punches and the mold is just filled with carbon paper; adjust the position of the upper and lower punches so that the powder is located in the center of the mold; pre-press the powder-filled mold under a tablet press with a pre-pressing pressure of 5 MPa and a pre-pressing time of 5 min; assemble the pre-pressed mold with insulating carbon felt with a thickness of 0.5 mm, and adjust the mold temperature measuring hole to align with the reserved hole in the insulating carbon felt.

[0042] 3. Spark plasma sintering: Place the graphite mold filled with powder in step 2 in the spark plasma sintering furnace chamber, and evacuate the furnace chamber (10Pa); after starting sintering, heat to 1300℃ at 100℃ / min and keep warm for 10 minutes, then increase the temperature to 1600℃ at 100℃ / min and keep warm for 5 minutes; after the insulation is completed, stop heating immediately, cool to room temperature with the furnace, and demold to obtain a tungsten-boron composite material block (the load borne by the mold during the sintering process is 0.5t).

[0043] Comparative Example 2:

[0044] 1. High-energy mechanical ball milling:

[0045] W powder, B powder and WC carbide balls were loaded into a ball mill, and then an appropriate amount of anhydrous ethanol, a process control agent, was added to the mixed powder. The ball mill was filled with argon and the ball milling parameters were set: the ball milling speed was 400 rpm, and the ball milling time was 12 h. The slurry after ball milling was dried to obtain a WB composite powder. Based on the mass percentage of the mixed powder, the proportion of B powder was 1.0%, and the balance was W powder.

[0046] 2. Powder filling: same as step 2 in Example 2.

[0047] 3. Powder filling: same as step 3 in Example 2.

[0048] See also Figures 1 to 3 As shown, the W-1.0 wt.% B composite prepared by spark plasma sintering in Example 2 exhibits a network of second-phase pinning structures at the grain boundaries, enhancing grain boundary bonding. The addition of element B also reduces the oxygen content in the matrix material. The W-1.0 wt.% B composite has an oxygen content of 24.6 ppm, lower than the 126.8 ppm of the W-1.0 wt.% B composite prepared by high-energy mechanical ball milling in Comparative Example 2.

[0049] Meanwhile, the W-1.0wt.%B tungsten-based composite material prepared by sintering at 1600°C in Example 2 has a relative density of 95.9% and a microhardness of 526.6±18.8HV, which is better than pure tungsten material (microhardness 360-420HV).

[0050] Example 3:

[0051] In this embodiment, the method for preparing the low-oxygen and high-hardness WB tungsten-based composite material comprises the following steps:

[0052] 1. Powder making: W powder (0.5 μm, Xiamen Jinlu Special Alloy Co., Ltd.), B powder (D 50 =10-20 μm, Aladdin, purity ≥99%) and an appropriate amount of WC carbide balls are placed in a 100 mL plastic solid bottle; the plastic solid bottle is filled with argon in a glove box to a pressure of 0.02 MPa; the argon-filled solid bottle is sealed; the sealed solid bottle is placed in a mixer for powder mixing at a mixer speed of 60 rpm for 12 hours; the mixed composite powder is vacuum-evacuated to obtain a WB composite powder.

[0053] 2. Powder loading: Fill 15 g of the WB composite powder obtained in step 1 into a graphite mold with an inner diameter of 20 mm. Before filling the mold with powder, a 0.1 mm thick carbon paper needs to be evenly rolled and laid. The carbon paper fits tightly against the inner wall of the mold, and the distance between the upper and lower punches and the mold is just filled with carbon paper; adjust the position of the upper and lower punches so that the powder is located in the center of the mold; pre-press the powder-filled mold under a tablet press with a pre-pressing pressure of 5 MPa and a pre-pressing time of 5 min; assemble the pre-pressed mold with insulating carbon felt with a thickness of 0.5 mm, and adjust the mold temperature measuring hole to align with the reserved hole in the insulating carbon felt.

[0054] 3. Spark plasma sintering: Place the graphite mold filled with powder in step 2 in the spark plasma sintering furnace chamber, and evacuate the furnace chamber (10Pa); after starting sintering, heat to 1300℃ at 100℃ / min and keep warm for 10 minutes, then increase the temperature to 1600℃ at 100℃ / min and keep warm for 5 minutes; after the insulation is completed, stop heating immediately, cool to room temperature with the furnace, and demold to obtain a tungsten-boron composite material block (the load borne by the mold during the sintering process is 0.5t).

[0055] Comparative Example 3:

[0056] 1. High-energy mechanical ball milling:

[0057] W powder, B powder and WC carbide balls were loaded into a ball mill, and then an appropriate amount of anhydrous ethanol, a process control agent, was added to the mixed powder. The ball mill was filled with argon and the ball milling parameters were set for ball milling: the ball milling speed was 400 rpm and the ball milling time was 12 h. The slurry after ball milling was dried to obtain WB composite powder. Based on the mass percentage of the mixed powder, the proportion of B powder was 0.5%, and the balance was W powder.

[0058] 2. Powder filling: same as step 2 in Example 3.

[0059] 3. Powder filling: same as step 3 in Example 3.

[0060] See also Figures 1 to 3 As shown, the W-0.5 wt.% B composite prepared by spark plasma sintering in Example 3 exhibits a network of second-phase pinning structures at the grain boundaries, enhancing grain boundary bonding. The addition of B also reduces the oxygen content in the matrix material. The W-0.5 wt.% B composite has an oxygen content of 28.3 ppm, lower than the 214.5 ppm in the W-0.5 wt.% B composite prepared by high-energy mechanical ball milling in Comparative Example 3.

[0061] Meanwhile, the W-0.5wt.%B tungsten-based composite material prepared by sintering at 1600°C in Example 3 has a relative density of 96.7% and a microhardness of 506.5±10.9HV, which is better than that of pure tungsten material (microhardness 360-420HV).

[0062] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a tungsten-based composite material having high hardness, low oxygen content and a network grain boundary pinning structure, characterized in that: Here are the steps: Step 1: Flour making: W powder, B powder and an appropriate amount of WC cemented carbide balls are placed in a plastic solid bottle according to the proportion, filled with argon in a glove box, sealed and placed in a mixer for powder mixing; after mixing, the composite powder is vacuumed and stored to obtain WB composite powder; Step 2: Powder filling: The WB composite powder obtained in step 1 is filled into a graphite mold. Before filling the mold with powder, carbon paper needs to be evenly rolled and laid. The carbon paper is tightly attached to the inner wall of the mold, and the distance between the upper and lower punches and the mold is just filled with carbon paper. The upper and lower punches are adjusted so that the powder is located in the center of the mold. The mold after powder filling is pre-pressed under a tablet press. The pre-pressed mold is assembled with thermal insulation carbon felt, and the mold temperature measuring hole is adjusted to align with the reserved hole of the thermal insulation carbon felt. Step 3: Spark plasma sintering: The graphite mold filled with the powder in step 2 is placed in a spark plasma sintering furnace chamber, and the furnace chamber is vacuumed; sintering is started to prepare a tungsten-boron composite material block, that is, a tungsten-based composite material with high hardness, low oxygen content and a network grain boundary pinning structure.

2. The preparation method according to claim 1, wherein In step 1, the proportion of B powder is 0.5-1.0% by mass, and the remainder is W powder.

3. The preparation method according to claim 1, wherein In the step 1, the argon filling pressure in the plastic solid bottle is 0.01-0.02 MPa.

4. The preparation method according to claim 1, wherein In step 1, the rotation speed of the mixer is 50-60 rpm, and the mixing time of W powder and B powder is 10-15 hours.

5. The preparation method according to claim 1, wherein In step 2, the mold pre-pressing pressure is 5 MPa, and the pre-pressing time is 3 to 5 minutes.

6. The preparation method according to claim 1, wherein The thickness of the assembled carbon felt in step 2 is 0.5 mm.

7. The preparation method according to claim 1, wherein After the furnace chamber is evacuated in step 3, the vacuum degree is 10 Pa.

8. The preparation method according to claim 1, wherein The specific steps of spark plasma sintering in step 3 are: heating to 1300°C at 100°C / min and keeping warm for 5-10 minutes, then heating to 1600-1700°C at 100°C / min and keeping warm for 5 minutes; after the insulation is completed, heating is immediately stopped, cooling to room temperature with the furnace, and demolding to obtain a tungsten-boron composite material block.

9. The preparation method according to claim 8, wherein The load borne by the mold during the spark plasma sintering process is 0.5t.

Images