A bicrystal cemented carbide and a method for producing the same

Abstract

This application belongs to the field of powder metallurgy technology, specifically a bicrystalline cemented carbide and its preparation method. The preparation method includes the following steps: mixing fine WC powder (2~4μm), Co powder, VC, and Cr3C2, followed by ball milling and spray granulation to obtain fine WC-Co composite powder; mixing coarse WC powder (8~12μm), Co powder, and ultrafine WC powder (0.15~0.25μm), followed by ball milling and spray granulation to obtain coarse WC-Co composite powder; and dry mixing, pressing, and sintering the fine WC-Co composite powder and the coarse WC-Co composite powder to obtain a bicrystalline cemented carbide with a Rockwell hardness of 87~90 HRA and a fracture toughness of 14~17 MPa·m. 1 / 2 The bending strength is 2500~3000MPa. This application prepares coarse and fine WC-Co composite powders separately, so that the inhibitor can effectively suppress the growth of fine WC grains during the sintering stage, while the ultrafine WC can promote the growth of coarse WC grains. This results in the prepared cemented carbide exhibiting a clear dual-scale WC grain distribution, while possessing both high hardness and high toughness. After dry mixing and pressing sintering, the prepared bicrystalline cemented carbide has high density.

Description

Technical Field

[0001] This application belongs to the field of powder metallurgy technology, specifically a double-crystal cemented carbide and its preparation method. Background Technology

[0002] Hard alloys consist of two phases: a hard phase and a binder phase. Because they combine the toughness of metals with the high hardness and wear resistance of ceramics, hard alloys are also known as metal ceramic materials. They are widely used in industries such as cutting tools, wire drawing dies, hot and cold rolling mill rolls, print heads, rock drill bits, and oil well drill bits.

[0003] Due to the inherent contradiction between hardness and toughness, it is generally difficult to simultaneously improve both in conventional cemented carbides. However, the combination of high hardness and good toughness is an indispensable requirement in industrial applications, and the manufacture of materials with these properties remains a significant challenge. Therefore, research on the joint enhancement of hardness and toughness in cemented carbides has become one of the research hotspots in the cemented carbide field in recent decades. Among these methods, the preparation of highly dense bicrystalline WC-Co cemented carbides is an effective approach. In bicrystalline cemented carbides, coarse WC particles possess higher toughness, while fine WC particles can compensate for the loss of hardness. Thus, bicrystalline cemented carbides can simultaneously achieve high strength and hardness. Currently, bicrystalline cemented carbides are mainly prepared by wet milling a mixture of coarse and fine WC powders and binder phase powder, followed by powder metallurgy processes. After being ball-milled and crushed, ultra-coarse WC is prone to recovering its coarse grain size during sintering, inducing abnormal growth and resulting in a more uneven microstructure. Simultaneously, fine WC dissolves rapidly and precipitates on the coarse WC grains, making it even more difficult to control the bicrystalline ratio and size. Summary of the Invention

[0004] To address the aforementioned problems, this application provides a bicrystalline cemented carbide and its preparation method. By using WC powder with a relatively small particle size difference, the excessive dissolution of fine WC grains is suppressed, while the growth and development of coarse WC grains are promoted. This solves the problems of insufficient performance in bicrystalline cemented carbides caused by uneven grain growth and excessively large differences in the size of the twin crystals. The bicrystalline cemented carbide prepared by this method exhibits a distinct dual-scale WC grain distribution and possesses high density and good mechanical properties.

[0005] According to a first aspect of this application, this application provides a method for preparing a bicrystalline cemented carbide, comprising the following steps:

[0006] S1. The first WC powder, the first Co powder and the vanadium-chromium powder are mixed and ball-milled, and then spray-granulated to obtain the first WC-Co composite powder. The vanadium-chromium powder is composed of VC and Cr3C2, and the particle size of the first WC powder is 2~4μm.

[0007] S2. The second WC powder, the second Co powder and the third WC powder are mixed and ball-milled, and then spray-granulated to obtain the second WC-Co composite powder. The particle size of the second WC powder is 8~12μm and the particle size of the third WC powder is 0.15~0.25μm.

[0008] S3. Dry mix the first WC-Co composite powder and the second WC-Co composite powder to obtain a mixed powder;

[0009] S4. The mixed powder is pressed and sintered, and after cooling, a bicrystalline hard alloy is obtained.

[0010] Furthermore, in the first WC-Co composite powder, the mass fraction of each component is: 86%~91% of the first WC powder, 8%~12% of the first Co powder and 1%~2% of the vanadium-chromium powder, wherein the mass ratio of VC to Cr3C2 in the vanadium-chromium powder is 1:(0.8~1.2).

[0011] Furthermore, in the second WC-Co composite powder, the mass fraction of each component is: 78%~88% of the second WC powder, 8%~12% of the second Co powder, and 2%~10% of the third WC powder.

[0012] Furthermore, in the mixed powder, the mass fraction of the first WC-Co composite powder is 50%~80%, and the mass fraction of the second WC-Co composite powder is 20%~50%.

[0013] Furthermore, the particle size of the first Co powder is 0.75~0.85μm, and the particle size of the vanadium-chromium powder is 0.8~1μm;

[0014] The particle size of the second Co powder is 0.75~0.85μm.

[0015] Furthermore, in the first WC-Co composite powder, the mass fraction of particles with a particle size of less than 100 mesh and greater than 270 mesh is greater than 70%;

[0016] In the second WC-Co composite powder, the mass fraction of particles with a particle size of less than 100 mesh and greater than 270 mesh is greater than 70%.

[0017] Furthermore, in step S1, the ball milling speed is 300~400 rpm, the time is 16~24 h, the ball-to-material ratio is (4~6):1, and the ball milling medium is alcohol;

[0018] In step S2, the ball milling speed is 200~300 rpm, the time is 8~12 h, the ball-to-material ratio is (3~5):1, and the ball milling medium is alcohol.

[0019] Furthermore, in step S4, the pressed mixed powder is sintered using a low-pressure argon sintering process, wherein the pressure of the low-pressure argon sintering process is 4~6MPa, the temperature is 1400~1450℃, and the time is 40~80min.

[0020] In the above technical solution, step S1 prepares fine WC-Co composite powder (first WC-Co composite powder) through wet milling and spray granulation. During spray granulation, VC and Cr3C2 in the vanadium-chromium powder act as inhibitors, which can be uniformly distributed on the surface of the fine WC powder (first WC powder) to form a covering layer. In the subsequent liquid phase sintering process, this layer can effectively inhibit the growth of fine WC grains, thereby controlling the size of the fine WC grains. At the same time, the inhibitors and Co powder have a shorter diffusion path and will quickly dissolve in the Co phase, thereby reducing the dissolution of fine WC grains. Step S2 prepares coarse WC-Co composite powder (second WC-Co composite powder) through wet milling and spray granulation. The highly active ultrafine WC powder (third WC powder) can be uniformly mixed with the coarse WC powder (second WC powder) and Co powder. During the sintering stage, the ultrafine WC powder will quickly dissolve in the binder phase and then precipitate on the nearby coarse WC grains, promoting the growth of coarse WC grains. In a specific embodiment, the order of steps S1 and S2 can be interchanged or performed simultaneously. In step S3, WC-Co mixtures with different coarse and fine particle ratios are prepared by dry mixing. By controlling the amount of coarse and fine WC-Co composite powder added, the ratio of coarse and fine WC grains in the mixture can be controlled. In addition, the WC-Co mixture prepared by the dry mixing method has a spherical shape. After pressing in step S4, the compact has higher strength and density, which is beneficial for preparing bicrystalline cemented carbide with higher density and better mechanical properties after sintering. Regarding the selection of raw materials, fine WC powder with a particle size of 2~4μm belongs to conventional fine and medium grains. After ball milling, it will not form ultrafine WC, so it is not easy to agglomerate and grow during sintering. With the addition of VC and Cr3C2 grain growth inhibitors, the resulting fine grain size can be stabilized at the submicron or micron level, avoiding the loss of fine grain strengthening effect due to complete coarsening of fine grains. At the same time, using conventional WC grains can reduce costs. On the other hand, coarse WC powder with a particle size of 8~12um will not be too fine even after ball milling. Therefore, it can effectively prevent rapid crack penetration, improve fracture toughness, and will not cause a sharp drop in hardness due to excessively coarse grains.

[0021] According to a second aspect of this application, this application provides a bicrystalline cemented carbide, which is prepared by the above-described method for preparing bicrystalline cemented carbide, wherein the fine WC grain size in the bicrystalline cemented carbide is 0.4~1μm and the coarse WC grain size is 1.5~4μm.

[0022] Furthermore, the bicrystalline cemented carbide has a Rockwell hardness of 87~90 HRA and a fracture toughness of 14~17 MPa·m. 1 / 2Its flexural strength is 2500~3000MPa.

[0023] This application proposes a bicrystalline cemented carbide and its preparation method, which produces the following beneficial effects: by preparing coarse and fine WC-Co composite powders separately, the inhibitor can effectively suppress the growth of fine WC grains during the sintering stage, while the ultrafine WC can promote the growth of coarse WC grains, so that the prepared cemented carbide exhibits a clear dual-scale WC grain distribution and has both high hardness and high toughness; by dry mixing and then pressing and sintering, the prepared bicrystalline cemented carbide has high density. Detailed Implementation

[0024] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0025] According to a first aspect of this application, this application provides a method for preparing a bicrystalline cemented carbide, comprising the following steps:

[0026] S1. The first WC powder, the first Co powder and the vanadium-chromium powder are mixed and ball-milled, and then spray-granulated to obtain the first WC-Co composite powder. The vanadium-chromium powder is composed of VC and Cr3C2, and the particle size of the first WC powder is 2~4μm.

[0027] Preferably, in the first WC-Co composite powder, the mass fractions of each component are: 86%~91% first WC powder, 8%~12% first Co powder, and 1%~2% vanadium-chromium powder; in the vanadium-chromium powder, the mass ratio of VC to Cr3C2 is 1:(0.8~1.2), preferably 1:1; the particle size of the first Co powder is 0.75~0.85μm, preferably 0.8μm; the particle size of the vanadium-chromium powder is 0.8~1μm; in the first WC-Co composite powder, the mass fraction of particles with a particle size less than 100 mesh and greater than 270 mesh is greater than 70%; the ball milling speed is 300~400rpm, the time is 16~24h, the ball-to-material ratio is (4~6):1, and the ball milling medium is alcohol.

[0028] S2. The second WC powder, the second Co powder and the third WC powder are mixed and ball-milled, and then spray-granulated to obtain the second WC-Co composite powder. The particle size of the second WC powder is 8~12μm and the particle size of the third WC powder is 0.15~0.25μm.

[0029] Preferably, in the second WC-Co composite powder, the mass fractions of each component are: 78%~88% second WC powder, 8%~12% second Co powder, and 2%~10% third WC powder; the particle size of the second Co powder is 0.75~0.85μm, preferably 0.8μm; in the second WC-Co composite powder, the mass fraction of particles with a particle size of less than 100 mesh and greater than 270 mesh is greater than 70%; the ball milling speed is 200~300rpm, the time is 8~12h, the ball-to-material ratio is (3~5):1, and the ball milling medium is alcohol.

[0030] S3. Dry mix the first WC-Co composite powder and the second WC-Co composite powder to obtain a mixed powder;

[0031] Preferably, in the mixed powder, the mass fraction of the first WC-Co composite powder is 50%~80%, and the mass fraction of the second WC-Co composite powder is 20%~50%. In some preferred embodiments of this application, the first WC-Co composite powder and the second WC-Co composite powder can be loaded into a three-dimensional mixer for dry mixing, and nitrogen gas is introduced and the pressure is controlled at 0.2~0.5 bar to reduce the oxidation of the mixed powder.

[0032] S4. Press and sinter the mixed powder, and obtain a bicrystalline hard alloy after cooling.

[0033] Preferably, the pressed mixed powder is sintered using a low-pressure argon sintering process, wherein the pressure of the low-pressure argon sintering process is 4~6MPa (preferably 5MPa), the temperature is 1400~1450℃ (preferably 1430℃), and the time is 40~80min (preferably 60min).

[0034] According to a second aspect of this application, this application provides a bicrystalline cemented carbide, which is prepared by the above-described method for preparing bicrystalline cemented carbide, wherein the fine WC grain size in the bicrystalline cemented carbide is 0.4~1μm and the coarse WC grain size is 1.5~4μm.

[0035] Preferably, the Rockwell hardness of the bicrystalline cemented carbide is 87~90 HRA, and the fracture toughness (K) is... IC The pressure is 14~17 MPa·m 1 / 2 Its flexural strength is 2500~3000MPa.

[0036] The technical solution of this application will be further described below with reference to specific embodiments.

[0037] Example 1

[0038] A method for preparing a bicrystalline cemented carbide includes the following steps:

[0039] S1. First WC powder (4μm), first Co powder (0.8μm), and vanadium-chromium powder (VC:Cr3C2 mass ratio 1:1) are mixed, ball-milled, and spray-granulated to obtain first WC-Co composite powder. The mass fractions of each component in the first WC-Co composite powder are: 88% first WC powder, 10% first Co powder, and 2% vanadium-chromium powder. The mass fraction of particles with a particle size less than 100 mesh and greater than 270 mesh in the first WC-Co composite powder is greater than 70%. The ball milling speed is 400 rpm, the time is 24 h, the ball-to-material ratio is 5:1, and the ball milling medium is alcohol.

[0040] S2. A mixture of 10μm second WC powder, 0.8μm second Co powder, and 0.2μm third WC powder is ball-milled and then spray-granulated to obtain a second WC-Co composite powder. The mass fractions of each component in the second WC-Co composite powder are: 85% second WC powder, 10% second Co powder, and 5% third WC powder. The mass fraction of particles with a particle size less than 100 mesh and greater than 270 mesh in the second WC-Co composite powder is greater than 70%. The ball milling speed is 300 rpm, the time is 12 h, the ball-to-particle ratio is 4:1, and the ball milling medium is alcohol.

[0041] S3. The first WC-Co composite powder and the second WC-Co composite powder are loaded into a three-dimensional mixer and dry-mixed with nitrogen to obtain a mixed powder, wherein the mass fraction of the first WC-Co composite powder is 70% and the mass fraction of the second WC-Co composite powder is 30%.

[0042] S4. The mixed powder is pressed and sintered using a low-pressure argon sintering process at a pressure of 5 MPa, a temperature of 1430℃, and a time of 60 min. After cooling, a bicrystalline hard alloy is obtained.

[0043] Testing revealed that the fine WC grain size in the bicrystalline cemented carbide prepared in this embodiment was 0.6~1μm, and the coarse WC grain size was 1.5~3.5μm. Its Rockwell hardness was 88.6HRA, K... IC 15.8 MPa·m 1 / 2 Its flexural strength is 2900MPa.

[0044] Example 2

[0045] The difference between the preparation method of this embodiment and that of Example 1 is only that in step S3, the mass fraction of the first WC-Co composite powder is 60% and the mass fraction of the second WC-Co composite powder is 40%.

[0046] Testing revealed that the fine WC grain size in the bicrystalline cemented carbide prepared in this embodiment was 0.6~1μm, and the coarse WC grain size was 1.5~3.5μm. Its Rockwell hardness was 88HRA, K...IC 16.2 MPa·m 1 / 2 Its flexural strength is 2780 MPa.

[0047] Example 3

[0048] The difference between the preparation method of this embodiment and that of Example 1 is that: in step S1, the particle size of the first WC powder is 2 μm; in step S2, the particle size of the second WC powder is 8 μm.

[0049] Testing revealed that the fine WC grain size in the bicrystalline cemented carbide prepared in this embodiment was 0.4~1μm, and the coarse WC grain size was 1.5~3.5μm. Its Rockwell hardness was 89HRA, K... IC 14.5 MPa·m 1 / 2 Its flexural strength is 2950 MPa.

[0050] Example 4

[0051] The difference between the preparation method of this embodiment and that of Example 1 is that: in step S1, the particle size of the first WC powder is 3 μm; in step S2, the particle size of the second WC powder is 12 μm; and in step S3, the mass fraction of the first WC-Co composite powder is 50% and the mass fraction of the second WC-Co composite powder is 50%.

[0052] Testing revealed that the fine WC grain size in the bicrystalline cemented carbide prepared in this embodiment was 0.6~1μm, and the coarse WC grain size was 2~4μm. Its Rockwell hardness was 87.5HRA, K... IC It is 16.7 MPa·m 1 / 2 Its flexural strength is 2630 MPa.

[0053] Example 5

[0054] The difference between the preparation method of this embodiment and that of Embodiment 1 is only that in step S3, the mass fraction of the first WC-Co composite powder is 80% and the mass fraction of the second WC-Co composite powder is 20%.

[0055] Testing revealed that the fine WC grain size in the bicrystalline cemented carbide prepared in this embodiment was 0.6~1μm, and the coarse WC grain size was 1.5~3.5μm. Its Rockwell hardness was 88.9HRA, K... IC It is 14.7 MPa·m 1 / 2 Its flexural strength is 2900MPa.

[0056] Comparative Example 1

[0057] The only difference between the preparation method of this comparative example and Example 1 is that in step S1, only the first WC powder and the first Co powder are used to prepare the first WC-Co composite powder.

[0058] Testing revealed that the fine WC grains in the cemented carbide prepared in this comparative example were excessively dissolved, and many abnormally grown grains appeared. The uniformity of WC grain distribution was poor. The size of the fine WC grains in the cemented carbide was 0.3~1μm, and the size of the coarse WC grains was 2.0~5μm. The bending strength was only 2250MPa.

[0059] Comparative Example 2

[0060] The difference between the preparation method of this comparative example and Example 1 is only that in step S2, only the second WC powder and the second Co powder are used to prepare the second WC-Co composite powder.

[0061] Testing revealed that the duodenal phenomenon in the cemented carbide prepared in this comparative example was not obvious, and the growth of coarse WC grains was also inhibited by the inhibitor. The size of fine WC grains in the cemented carbide was 0.6~1μm, and the size of coarse WC grains was 1.2~3μm, resulting in insufficient overall performance.

[0062] Comparative Example 3

[0063] The only difference between the preparation method of this comparative example and that of Example 1 is that in step S2, the particle size of the second WC powder is 4 μm.

[0064] Testing revealed that the WC grain size difference in the cemented carbide prepared in this comparative example was small, the twinning phenomenon was not obvious, and the WC grain size was 0.6~1.2μm.

[0065] Comparative Example 4

[0066] The only difference between the preparation method of this comparative example and that of Example 1 is that in step S1, the particle size of the first WC powder is 1 μm.

[0067] Testing revealed that the cemented carbide prepared in this comparative example contained numerous fine grains, with a significant size difference between the coarse and fine WC grains. Its Rockwell hardness was 88.9 HRA, K... IC 13.2 MPa·m 1 / 2 Its flexural strength is 2100MPa.

[0068] Comparative Example 5

[0069] The difference between the preparation method of this comparative example and that of Example 1 is that the first WC powder, the first Co powder, the vanadium-chromium powder, the second WC powder, the second Co powder, and the third WC powder are directly mixed and wet-milled and spray-granulated to obtain a mixed powder, which is then pressed and sintered.

[0070] Testing revealed that the bicrystalline structure of the cemented carbide prepared in this comparative example was disrupted, preventing the formation of distinct coarse and fine bimodal grains. The coarse WC grains exhibited abnormal growth, resulting in a significant decrease in microstructure uniformity. Its Rockwell hardness was 88.2 HRA, K... ICIt is 14.8 MPa·m 1 / 2 Its flexural strength is 2400MPa.

[0071] This application proposes a bicrystalline cemented carbide and its preparation method, which produces the following beneficial effects: by preparing coarse and fine WC-Co composite powders separately, the inhibitor can effectively suppress the growth of fine WC grains during the sintering stage, while the ultrafine WC can promote the growth of coarse WC grains, so that the prepared bicrystalline cemented carbide exhibits a clear dual-scale WC grain distribution and has both high hardness and high toughness; by dry mixing and then pressing and sintering, the prepared bicrystalline cemented carbide has high density.

[0072] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for preparing a bicrystalline cemented carbide, characterized in that, Includes the following steps: S1. The first WC powder, the first Co powder and the vanadium-chromium powder are mixed and ball-milled, and then spray-granulated to obtain the first WC-Co composite powder. The vanadium-chromium powder is composed of VC and Cr3C2, and the particle size of the first WC powder is 2~4μm. S2. The second WC powder, the second Co powder and the third WC powder are mixed and ball-milled, and then spray-granulated to obtain the second WC-Co composite powder. The particle size of the second WC powder is 8~12μm and the particle size of the third WC powder is 0.15~0.25μm. S3. Dry mix the first WC-Co composite powder and the second WC-Co composite powder to obtain a mixed powder; S4. The mixed powder is pressed and sintered, and after cooling, a bicrystalline hard alloy is obtained.

2. The method for preparing the bicrystalline cemented carbide according to claim 1, characterized in that, In the first WC-Co composite powder, the mass fraction of each component is: 86%~91% of the first WC powder, 8%~12% of the first Co powder and 1%~2% of the vanadium-chromium powder, wherein the mass ratio of VC to Cr3C2 in the vanadium-chromium powder is 1:(0.8~1.2).

3. The method for preparing the bicrystalline cemented carbide according to claim 1, characterized in that, In the second WC-Co composite powder, the mass fraction of each component is: 78%~88% of the second WC powder, 8%~12% of the second Co powder, and 2%~10% of the third WC powder.

4. The method for preparing the bicrystalline cemented carbide according to claim 1, characterized in that, In the mixed powder, the mass fraction of the first WC-Co composite powder is 50%~80%, and the mass fraction of the second WC-Co composite powder is 20%~50%.

5. The method for preparing the bicrystalline cemented carbide according to claim 1, characterized in that, The particle size of the first Co powder is 0.75~0.85μm, and the particle size of the vanadium-chromium powder is 0.8~1μm; The particle size of the second Co powder is 0.75~0.85μm.

6. The method for preparing the bicrystalline cemented carbide according to claim 1, characterized in that, In the first WC-Co composite powder, the mass fraction of particles with a particle size of less than 100 mesh and greater than 270 mesh is greater than 70%; In the second WC-Co composite powder, the mass fraction of particles with a particle size of less than 100 mesh and greater than 270 mesh is greater than 70%.

7. The method for preparing the bicrystalline cemented carbide according to claim 1, characterized in that, In step S1, the ball milling speed is 300~400 rpm, the time is 16~24 h, the ball-to-material ratio is (4~6):1, and the ball milling medium is alcohol; In step S2, the ball milling speed is 200~300 rpm, the time is 8~12 h, the ball-to-material ratio is (3~5):1, and the ball milling medium is alcohol.

8. The method for preparing the bicrystalline cemented carbide according to claim 1, characterized in that, In step S4, the pressed mixed powder is sintered using a low-pressure argon sintering process. The pressure of the low-pressure argon sintering process is 4~6MPa, the temperature is 1400~1450℃, and the time is 40~80min.

9. A bicrystalline cemented carbide, characterized in that, The bicrystalline cemented carbide is prepared by the preparation method of any one of claims 1 to 8, wherein the fine WC grain size in the bicrystalline cemented carbide is 0.4 to 1 μm and the coarse WC grain size is 1.5 to 4 μm.

10. The bicrystalline cemented carbide according to claim 9, characterized in that, The dual-crystal cemented carbide has a Rockwell hardness of 87~90 HRA and a fracture toughness of 14~17 MPa·m. 1 / 2 Its flexural strength is 2500~3000MPa.