A carburized tungsten tetraboride superhard material and its preparation method

Abstract

The present invention relates to a carburized tungsten tetraboride superhard material, which is composed of WB4 phase and T ‑B two-phase composition of WB4‑ T B bulk material; and the Vickers hardness of the material under a load of 0.49 N is 63.05 GPa, and the electrical conductivity is 1.7×10 5 S / m, the fracture toughness measured by the single-side pre-cracked beam method is 4.7 ± 0.5 MPa•m 1 / 2 At the same time, the present invention also discloses a method for preparing the material. The WB4- T β material has ultra-high hardness and conductivity. At the same time, the preparation equipment is simple, the preparation process is mild, and it is economical and practical. It has important application prospects in the fields of wear-resistant materials and mechanical processing.

Description

Technical Field

[0001] The present invention relates to the technical field of superhard materials, and in particular to a carburized tungsten tetraboride superhard material and a preparation method thereof. Background Art

[0002] Superhard materials (Vickers hardness greater than 40 GPa) have numerous applications, including high-performance cutting tools and wear-resistant materials. Modern industry is increasingly demanding high-performance, highly stable, and more affordable superhard materials, exposing the limitations of traditional superhard materials synthesized under harsh conditions. Therefore, the search for superhard materials that can be synthesized under mild and affordable conditions is not only of great scientific significance but also has significant application value.

[0003] Inspired by the superhardness and superincompressibility of diamond, there are two main methods for designing superhard materials: one is to form strong covalent bonds with light elements such as boron, carbon, nitrogen or oxygen, such as c-BN, B6O, BC2N, etc.; the other is to combine the incompressibility of high-valent electron density metals (osmium, rhenium and tungsten) with short covalent bonds constructed by light elements to achieve the superhard properties of the material.

[0004] People have extensively explored transition metal-light element compounds. Among them, the first material discovered to have superhard properties was the transition metal boride - rhenium diboride (ReB2), which has a Vickers hardness of up to 48 GPa. Studies have shown that the TMs-B and BB short bonds formed by the boron element play a crucial role in the superhardness of the material. Therefore, tungsten tetraboride (WB4) with a high proportion of boron structure has become a current research hotspot. According to first-principles predictions, the theoretical hardness of the WB4 structure is 41.2-42.2 GPa, making it a potential superhard material. In 2008, Gu et al. first prepared WB4 bulk material using arc melting and reported its Vickers hardness of 46 GPa (Advanced Materials, 2008. 20(19): p. 3620-3626). Then in 2010, Mohammadi et al. also used the arc melting method to synthesize WB4 bulk with a Vickers hardness of 43.3 GPa, and reported that the synthesized sample was composed of two phases, WB4 and amorphous boron (Proc Natl Acad Sci USA, 2011.108(27): p. 10958-62). Since then, people have used other synthesis methods to prepare WB4 materials, such as reactive hot pressing sintering, high temperature and high pressure mechanochemical synthesis, and laser pulse deposition, but the hardness and purity of WB4 materials prepared by these methods are not ideal.

[0005] In order to explore WB4 materials with higher hardness, the effects of transition metal ions (Re, Mn, Cr, Mo, Zr, Hf, Ta) on the hardness of WB4 were studied according to the solid solution strengthening mechanism, and WB4 with a Vickers hardness of 57.3 GPa was prepared. 0.93 Ta 0.02 Cr 0.05 The Vickers hardness of WB4 solid solution increased from 43.3 GPa to over 50 GPa (J Am Chem Soc, 2012. 134(51): p.20660-8). However, adding dispersed second phases (TaB2, MnB4, ZrB2, MoB4) to WB4 material does not effectively increase its hardness. This is partly because the added second phases have a low hardness, and partly because the WB4 material is affected by the dispersed second phase B.

[0006] At present, domestic patents have reported on the preparation technology of superhard WB4 materials and their composite materials. Chinese patent CN106116593A publicly reports a method for preparing tungsten tetraboride ceramic powder, using hot pressing and sintering to prepare a single WB4 phase powder material. Chinese patent CN108424146A publicly reports a method for preparing tungsten tetraboride-based ceramics, using metal nickel powder or cobalt powder as a sintering aid, and hot pressing and sintering to prepare tungsten tetraboride-based ceramics. The sintering aid reduces the difficulty of WB4 sintering and improves the purity and density of the WB4 block. Chinese patent CN108726526A publicly reports a method for preparing rhenium-doped tungsten tetraboride material. Chinese patent CN108557834A publicly reports a method for preparing chromium-doped tungsten tetraboride superhard material. Chinese patent CN110483057A publicly reports a tungsten tetraboride material doped with tantalum, its preparation method and application. The above patents report the preparation of tungsten tetraboride materials by doping transition metal elements. The purpose is to improve the hardness and thermal stability of mechanical properties by improving the microstructure of WB4, but the synthesized new superhard materials are generally lower than traditional superhard materials. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a carburized tungsten tetraboride superhard material with good performance.

[0008] Another technical problem to be solved by the present invention is to provide a method for preparing the carburized tungsten tetraboride superhard material.

[0009] In order to solve the above problems, the present invention provides a carburized tungsten tetraboride superhard material, characterized in that: the material is composed of WB4 phase and T -B two-phase composition WB4- T B bulk material; and the Vickers hardness of the material under a load of 0.49 N is 63.05 GPa, and the electrical conductivity is 1.7×105 S / m, the fracture toughness measured by the single-side pre-cracked beam method is 4.7 ± 0.5 MPa•m 1 / 2 .

[0010] The method for preparing a carburized tungsten tetraboride superhard material is characterized in that: 10-12.5% ​​of B powder and 87.5-90% of W powder of different particle sizes are mixed in a planetary high-energy ball mill with WC balls in a molar ratio to obtain a mixed powder; the mixed powder is placed in a graphite mold, and two 0.5 mm graphite sheets are placed on the upper and lower sides of the powder column respectively, and then the powder is sintered in a spark plasma sintering furnace (SPS). After sintering, it is naturally cooled to room temperature to obtain WB4- T B bulk material.

[0011] The purity of the B powder is greater than 99%, and the particle size is <500 nm; the purity of the W powder is greater than 99%, and the particle size is <500 nm.

[0012] The ball milling mixing conditions are as follows: a ball-to-material ratio of 4:1, a rotation speed of 250 r / min, and a mixing time of 4 h.

[0013] The spark plasma sintering conditions are as follows: a heating rate of 100°C / min, a vacuum degree of 15-20 Pa, a temperature of 1600-1800°C, a pressure of 30 MPa, and a holding time of 2-10 min.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. The present invention utilizes the characteristics of SPS sintering to bombard carbon elements into the raw materials through high-energy pulses, and generates ultra-high hardness with the excess boron in the raw materials. T -B phase, thereby obtaining carburized WB4- T β superhard material.

[0016] 2. WB4- T The β material is composed of WB4 phase and tetragonal phase B, and has superhard properties. Its Vickers hardness is as high as 63GPa and its electrical conductivity is 1.7×10 5 S / m, fracture toughness is 4.7 ± 0.5 MPa•m 1 / 2 .

[0017] 3. WB4- T Beta material is currently the hardest, electrically conductive, and reprocessable inexpensive superhard material.

[0018] 4. The preparation equipment of the present invention is simple, the preparation process is mild, economical and practical, and has important application prospects in the fields of wear-resistant materials and mechanical processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0020] Figure 1 For the present invention WB4- T X-ray diffraction patterns of β and WB4-βB materials.

[0021] Figure 2 For the present invention WB4- T STEM characterization images of β and WB4-βB materials.

[0022] Figure 3 For the present invention WB4- T Hardness test chart of β and WB4-βB materials.

[0023] Figure 4 For the present invention WB4- T Loading force and displacement curves of β and WB4-βB materials. DETAILED DESCRIPTION

[0024] A carburized tungsten tetraboride superhard material, which is composed of WB4 phase and T -B two-phase composition WB4- T B bulk material; and the Vickers hardness of the material under a load of 0.49 N is 63.05 GPa, and the electrical conductivity is 1.7×10 5 S / m, the fracture toughness measured by the single-side pre-cracked beam method is 4.7 ± 0.5 MPa•m 1 / 2 .

[0025] Its preparation method is as follows: 10~12.5% ​​B powder and 87.5~90% W powder of different particle sizes are mixed in a planetary high-energy ball mill with WC balls in molar ratio. The ball-to-material ratio is 4:1, the rotation speed is 250 r / min, and the mixing time is 4 h. After uniform mixing, a mixed powder is obtained; the mixed powder is loaded into a graphite mold, and two 0.5 mm graphite sheets are placed on the upper and lower sides of the powder cylinder respectively, and then the powder is sintered in a spark plasma sintering furnace (SPS). The conditions of spark plasma sintering are a heating rate of 100 ℃ / min, a vacuum degree of 15~20 Pa, a temperature of 1600~1800 ℃, a pressure of 30 MPa, and a holding time of 2~10 min. After sintering, it is naturally cooled to room temperature to obtain WB4- T B bulk material.

[0026] The graphite gasket above the powder in the graphite mold is the carbon source. During the sintering process, the carbon element is bombarded and infiltrated into the material by a high-energy electron beam.

[0027] Among them: the purity of B powder is greater than 99%, and the particle size is <500 nm; the purity of W powder is greater than 99%, and the particle size is <500 nm.

[0028] Example A carburized tungsten tetraboride superhard material (WB4- T B) Preparation method:

[0029] Step 1, mixing:

[0030] The tungsten powder and boron powder are mixed in a molar ratio of 1:9 and evenly mixed to obtain a mixed powder; the tungsten powder has a purity greater than 99% and a particle size of <500 nm; the boron powder has a purity greater than 99% and a particle size of <500 nm.

[0031] Step 2, loading:

[0032] After attaching graphite paper to the inner wall of a cylindrical graphite mold, the mixed powder is placed in the mold and two layers of graphite paper are placed above and below the powder. The statically pressed filled mold is placed in an SPS sintering furnace.

[0033] Step 3, carburizing and sintering:

[0034] (1) Evacuate the SPS sintering furnace, maintain the vacuum degree at 10~15 Pa, heat it to 1600~1800℃ at a heating rate of 100℃ / min, and then sinter it at a pressure of 30 MPa for 2~10 min;

[0035] (2) After the end of the heat preservation, the pressure was immediately released to 5 MPa and naturally cooled to room temperature to obtain WB4- T B block;

[0036] Step 4, finished product: remove the graphite paper on the surface of the block, and then use a diamond sand tray and diamond grinding paste for mechanical polishing. The surface roughness of the polished sample is 0.025 μm.

[0037] Comparative Example A method for preparing a WB4-βB superhard material:

[0038] Step 1, mixing:

[0039] The tungsten powder and boron powder are mixed in a molar ratio of 1:9 to obtain a mixed powder. The purity of the tungsten powder is greater than 99% and the particle size is 1 μm. The purity of the boron powder is greater than 99% and the particle size is 1 μm.

[0040] Step 2, loading:

[0041] After attaching graphite paper to the inner wall of a cylindrical graphite mold, the mixed powder is placed in the mold and two layers of graphite paper are placed above and below the powder. The statically pressed filled mold is placed in an SPS sintering furnace.

[0042] Step 3, carburizing and sintering:

[0043] (1) Evacuate the SPS sintering furnace, maintain the vacuum degree at 10~15 Pa, heat it to 1600~1800℃ at a heating rate of 100℃ / min, and then sinter it at a pressure of 30 MPa for 2~10 min;

[0044] (2) Immediately after the heat preservation, the pressure was released to 5 MPa and the mixture was naturally cooled to room temperature to obtain WB4-βB blocks;

[0045] Step 4, finished product: remove the graphite paper on the surface of the block, and then use a diamond sand tray and diamond grinding paste for mechanical polishing. The surface roughness of the polished sample is 0.025 μm.

[0046]

WB4- T Structural analysis of B and WB4-βB bulk materials

[0047] Preparation of WB4- T B and WB4-βB materials were characterized by X-ray diffraction, as Figure 1 As shown, WB4- T The B and WB4-βB material samples only have diffraction peaks of the WB4 phase, and no other crystallization peaks.

[0048] STEM Characterization WB4- T B and WB4-βB sample microstructure and crystallographic information, such as Figure 2 As shown. Tungsten boride in the two samples exists in the WB4 structure, WB4- T The remaining boron phase in the B sample is tetragonal boron, and the remaining boron phase in the WB4-βB sample is hexagonal boron.

[0049]

Mechanical properties of materials

[0050] 1. Hardness test:

[0051] Test method: Use Vickers microhardness tester to test WB4- T The hardness of β and WB4-βB materials was tested under the conditions of 0.49 N, 0.98 N, 1.96 N, 4.9 N, and 9.8 N, with a loading duration of 10 s. Figure 3 shown.

[0052] Test results: WB4- T The hardness range of β material is 63 ~ 29.4 GPa,

[0053] The hardness range of WB4-βB material is 46.7 ~ 27.7 GPa.

[0054] 2. Fracture toughness test:

[0055] Test method: Use the single-side pre-cracked beam method to test WB4- T The fracture toughness of β and WB4-βB materials was tested under the following conditions: 3 mm × 4 mm × 18 mm sample, 16 mm span, 2 mm notch depth, and 0.5 mm / min pressing speed. The load force and displacement curve is shown in Figure 2. Figure 4 shown.

[0056] Test results: WB4- T The fracture toughness of material β is 4.7 ± 0.5 MPa•m 1 / 2 .

[0057] The fracture toughness of WB4-βB material is 2.8 ± 0.7 MPa•m 1 / 2 .

Claims

1. A carburized tungsten tetraboride superhard material, characterized in that: The material is composed of WB4 phase and T -B two-phase composition WB4- T B block material; the preparation method of the material is as follows: 10-12.5% ​​W powder of different particle sizes and 87.5-90% B powder are mixed in a planetary high-energy ball mill with WC balls according to a molar ratio, and mixed evenly to obtain a mixed powder; the mixed powder is placed in a graphite mold, and two 0.5 mm graphite sheets are placed on the upper and lower sides of the powder column respectively, and then the powder is sintered in a spark plasma sintering furnace. After sintering, it is naturally cooled to room temperature to obtain WB4- T B bulk material; the conditions of the spark plasma sintering are a heating rate of 100°C / min, a vacuum degree of 10~15 Pa, a temperature of 1600~1800°C, a pressure of 30 MPa, and a holding time of 2~10 min; the particle sizes of the B powder and the W powder are both <500 nm.

2. The carburized tungsten tetraboride superhard material according to claim 1, wherein: The purity of the B powder is greater than 99%, and the purity of the W powder is greater than 99%.

3. The carburized tungsten tetraboride superhard material according to claim 1, wherein: The ball milling mixing conditions are as follows: a ball-to-material ratio of 4:1, a rotation speed of 250 r / min, and a mixing time of 4 h.

4. The carburized tungsten tetraboride superhard material according to claim 1, wherein: The material has a Vickers hardness of 63.05 GPa under a load of 0.49 N and a conductivity of 1.7×10 5 S / m, the fracture toughness measured by the single-side pre-cracked beam method is 4.7±0.5 MPa•m 1 / 2 .

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