A cemented carbide with cobalt-aluminum intermetallic compound CoAl as a bonding phase and a preparation method thereof

Abstract

The present invention belongs to the technical field of cemented carbide manufacturing, and discloses a cemented carbide with a cobalt-aluminum intermetallic compound CoAl as a bonding phase and a preparation method thereof. The cemented carbide is composed of a cobalt-aluminum intermetallic compound CoAl as a bonding phase and a hard phase WC. When the molar ratio of the added Co element and the Al element is 1:1 or 3:2, respectively, a cemented carbide with the intermetallic compound CoAl as a bonding phase is obtained. The mixed powder is evenly mixed by ball milling, and then spark plasma sintering is performed to finally obtain a dense cemented carbide with the cobalt-aluminum intermetallic compound CoAl as a bonding phase. The material composition of the present invention is reasonably designed, the preparation process is simple and controllable, the production cost is low, and large-scale industrial production and application are possible.

Description

Technical Field

[0001] The present invention relates to the technical field of cemented carbide manufacturing, in particular to a cemented carbide with a cobalt-aluminum intermetallic compound CoAl as a bonding phase and a preparation method thereof. Background Art

[0002] Cemented carbide is one of the most widely used powder metallurgy products in the world. Traditional tungsten-cobalt cemented carbide is a composite material with high strength, high hardness and high wear resistance, made of WC with a high melting point, high hardness and high chemical stability as the hard phase and Co with good toughness as the binder phase, prepared using powder metallurgy technology. Tungsten-cobalt cemented carbide tools are widely used in the mechanical manufacturing and processing industry, mainly for the production of cutting tools, wear-resistant parts and molds. However, tungsten-cobalt cemented carbide has poor high-temperature oxidation resistance and corrosion resistance, and the binder phase Co has disadvantages such as high cost, poor corrosion resistance, domestic resource scarcity, biological toxicity and carcinogenicity, which has aroused people's interest in finding new binder phase components to partially or completely replace the binder phase Co. The binder phase Al is low in price, abundant in raw materials, and environmentally friendly. More importantly, the binder phase Al has a low melting point and can form intermetallic compounds with the binder phase Co.

[0003] At present, cemented carbides with Co and Al as bonding phases have the following main deficiencies or defects: ① Al is easily oxidized to obtain Al2O3 during sintering, which affects the density of the alloy; ② The bonding phase obtained is not mainly composed of the intermetallic compound CoAl phase, but intermetallic compounds of other cobalt and aluminum components; ③ The average size of the WC grains of the prepared cemented carbide is large and does not reach ultrafine grains (<500nm) or nanocrystalline (<200nm); ④ The shape of the WC grains is relatively sharp, resulting in reduced performance of the cemented carbide.

[0004] The present invention addresses the aforementioned shortcomings and drawbacks by further optimizing the molar ratio of Co to Al in the binder phase to produce a cemented carbide with the intermetallic compound CoAl as the binder phase. Furthermore, replacing Co with the intermetallic compound CoAl as the binder phase not only improves the carbide's hardness and fracture toughness, but also reduces environmental hazards, the cost of cemented carbide powder, and the amount of Co used. Summary of the Invention

[0005] The present invention aims to address the current problems of tungsten-cobalt cemented carbides, such as poor high-temperature oxidation resistance and corrosion resistance, and the susceptibility of Co and Al powders as binder phases to oxidation and poor performance. This invention proposes preparing a cemented carbide with a cobalt-aluminum intermetallic compound, CoAl, as the binder phase. This intermetallic compound, CoAl, replaces Co and acts as the binder phase in the cemented carbide. This not only improves the carbide's hardness and fracture toughness, but also reduces the environmental impact of Co and lowers the cost of the cemented carbide powder.

[0006] The technical solution of the present invention is as follows: a cemented carbide with a cobalt-aluminum intermetallic compound CoAl as a binder phase, mainly composed of a hard phase WC and an intermetallic compound CoAl as a binder phase; the cemented carbide components are prepared according to the following powder raw material component ratio: the total amount of Co and Al elements in the binder phase is 5-20wt% of the total mass of the powder raw material, and the balance is the hard phase WC, and the mass fraction of WC is 100wt%-(Co+Al)wt%; the content of Co and Al elements in the binder phase is proportioned according to the molar fraction of the total amount of the binder phase, the molar fraction of Co powder is 40%-60%, and the molar fraction of Al powder is (100%-Co%); and the molar ratio of Co powder to Al powder is selected to be 1:1 or 3:2.

[0007] The bonding phase is a CoAl intermetallic compound with a B2 ordered structure and a bcc crystal structure.

[0008] A method for preparing a cemented carbide with a cobalt-aluminum intermetallic compound CoAl as a binder phase comprises the following steps: mixing powder raw materials, ball milling, vacuum drying and sieving the powder to obtain a mixed powder; and sintering the mixed powder to prepare a cemented carbide with the cobalt-aluminum intermetallic compound CoAl as a binder phase.

[0009] The sintering method is spark plasma sintering: the mixed powder is loaded into a graphite mold, and the graphite mold containing the mixed powder is placed in a spark plasma sintering furnace for sintering. After the sintering cavity is evacuated to below 10 Pa, the temperature is increased at a heating rate of 100°C / min. When the temperature reaches the sintering temperature, the temperature is maintained. At the same time, a sintering pressure of 30 to 100 MPa is applied, and the sintering temperature is 1000 to 1300°C. The temperature is maintained for 5 minutes under the sintering pressure, and finally the furnace is cooled to room temperature to obtain a dense cemented carbide with a cobalt-aluminum intermetallic compound CoAl as a bonding phase.

[0010] The average particle size of the WC powder in the powder raw material is 0.1 to 0.5 μm; the average particle size of the Co powder and the Al powder is in the range of 0.1 to 1 μm.

[0011] The WC powder has an average particle size of 200 nm or 400 nm; the Co powder has an average particle size of 100 nm; and the Al powder has an average particle size of 400 nm.

[0012] The temperature of the vacuum drying is 60-100° C., and the heat preservation time of the vacuum drying is 480-600 minutes. The sieve for sieving the powder has a mesh size of 80-200, and the powder is stored under vacuum conditions.

[0013] When the molar ratio of Co:Al is 1:1 or 3:2, an intermetallic compound with CoAl as the main phase is obtained. Furthermore, this intermetallic compound has the advantages of low density, high hardness, and high oxidation resistance, making it an ideal material to replace the traditional binder phase Co.

[0014] The average WC grain size of cemented carbide has a crucial impact on its performance. When the average WC grain size is reduced to ultrafine grains (<500nm) and nanocrystalline grains (<200nm), the strength and hardness of the cemented carbide are significantly improved. Spark plasma sintering, due to its unique electrical effect, not only removes impurities from the powder surface but also slows the growth of WC grains.

[0015] The cemented carbide uses WC as a hard phase and a cobalt-aluminum intermetallic compound CoAl as a bonding phase. By regulating the alloy composition and adopting spark plasma sintering, a cemented carbide with the cobalt-aluminum intermetallic compound CoAl as a bonding phase is prepared.

[0016] In the above technical solution, the ball milling process is as follows: the mass ratio of ball milling beads to mixed powder is 10:1, 40wt% alcohol is added as a wet milling medium, the rotation speed is 180r / min, and the wet milling time is 10-100 hours. The mixed slurry after ball milling is placed in a vacuum oven at 60-100°C for vacuum drying for 480-600 minutes. The dried mixed powder is separated through an 80-200 mesh sieve and stored under vacuum conditions.

[0017] The method of the present invention includes four steps: raw material preparation, ball milling, drying and screening the powder, and sintering. The sintering method is spark plasma sintering, which produces a cemented carbide with a cobalt-aluminum intermetallic compound (CoAl) as the binder phase. Ball milling increases the powder's reactivity, internal energy, and surface energy, thereby reducing the sintering temperature. Furthermore, because spark plasma sintering can heat to a higher temperature in a shorter time, it achieves rapid sintering, reduces WC grain growth, and removes impurities on the powder surface. Therefore, the ball milling combined with spark plasma sintering process can quickly produce a dense cemented carbide structure with finer, more uniformly sized grains at a lower temperature.

[0018] The present invention has the following beneficial effects: The molar ratio of Co and Al in the binder phase is determined, i.e., the molar ratio of Co to Al is 1:1 or 3:2, respectively, to prepare a cemented carbide with a cobalt-aluminum intermetallic compound CoAl as the binder phase; a cemented carbide with nanocrystalline or ultrafine WC grains is prepared; spark plasma sintering is used to reduce Al oxidation and improve the density of the cemented carbide; the intermetallic compound CoAl can inhibit WC grain growth and has a relatively simple crystal structure and diffusion uniformity, thereby improving the alloy's fracture toughness while also enhancing the hardness and strength of the cemented carbide; the cost of the alloy raw material powder and its hazards to the human body and the environment are reduced. Because the intermetallic compound CoAl can inhibit WC grain growth and has a relatively simple crystal structure and diffusion uniformity, the average WC grain size can be reduced and the hardness and strength of the cemented carbide can be improved; and because the cobalt-aluminum intermetallic compound CoAl formed by the addition of Al replaces Co as the binder phase, the amount of Co used is reduced, thereby reducing the cost of the cemented carbide powder material and also reducing the hazards of Co to the human body and the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a microstructure diagram of a nanocrystalline cemented carbide prepared at 1250° C. using a cobalt-aluminum intermetallic compound CoAl (Co:Al molar ratio of 1:1) as a binder phase, using WC powder with a powder size of 200 nm.

[0020] Figure 2 This is a microstructure diagram of a nanocrystalline cemented carbide prepared at 1250° C. using a cobalt-aluminum intermetallic compound CoAl (Co:Al molar ratio of 3:2) as a binder phase, using WC powder with a powder particle size of 200 nm.

[0021] Figure 3 This is a microstructure diagram of an ultrafine-grained cemented carbide in which a cobalt-aluminum intermetallic compound CoAl (Co:Al molar ratio of 1:1) is used as a binder phase to prepare WC powder with a powder particle size of 400 nm at 1200° C. in Example 3 of the present invention.

[0022] Figure 4 This is a microstructure diagram of an ultrafine-grained cemented carbide in which a cobalt-aluminum intermetallic compound CoAl (Co:Al molar ratio of 3:2) is used as a binder phase to prepare WC powder with a powder particle size of 400 nm at 1200° C. in Example 4 of the present invention.

[0023] Figure 5 3 is a comparison chart of Vickers hardness between the embodiment and the comparative example. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The embodiments of the present invention are intended to enable those skilled in the art to better understand the present invention and are not intended to limit the present invention in any way. The workflow and working principle of the present invention will be further described below using a preferred embodiment of the present invention.

[0025] Comparative Example 1

[0026] A 90wt% WC powder with a nano-scale diameter of 200nm was selected. The molar fractions of Co and Al powders in the binder phase were 80% and 20%, respectively (a molar ratio of 1:4, i.e., 8.97wt% Co and 1.03wt% Al, the sum of which accounts for 10wt% of the total powder material). The cemented carbide contains a WC hard phase and a binder phase free of the intermetallic compounds CoAl.

[0027] Cemented carbide and its preparation method are carried out according to the following steps:

[0028] (1) a cemented carbide raw material to which Co and Al powders are added is prepared, wherein the molar fractions of Co and Al powders are 80% and 20%, respectively (molar ratio 1:4, i.e., 8.97 wt% Co and 1.03 wt% Al, the sum of which is 10 wt% of the total raw material), and 90 wt% of WC powder;

[0029] (2) The above raw materials were mixed and added into a planetary high-energy ball mill for wet grinding at a ball-to-material ratio of 10:1, alcohol as the wet grinding medium, a rotation speed of 180 r / min, and a wet grinding time of 48 h. The mixture was kept in a vacuum drying oven at 80°C for 480 min, separated by a 100-mesh sieve, and stored under vacuum conditions;

[0030] (3) The powder was weighed and placed into a graphite mold with a diameter of 15 mm, and then placed in a spark plasma sintering furnace and vacuumed to 10 -4 Pa, the temperature was raised to 1200°C, a pressure of 50 MPa was applied, the heating rate was 100°C / min, and the mixture was kept at this temperature for 5 minutes before being cooled to room temperature with the furnace to obtain a cemented carbide having a binder phase free of the intermetallic compound CoAl.

[0031] Example 1

[0032] The difference between Example 1 and Comparative Example 1 lies in the addition of Al powder (molar ratio of Co:Al = 1:1) in Step 1 and the sintering temperature of 1250°C in Step 3. The alloy composition of Comparative Example 1 of the present invention is as follows: 90 wt% WC powder of 200 nm nanometer size is selected, and the molar fractions of Co and Al powder in the binder phase are 50% and 50%, respectively (molar ratio of 1:1, i.e., 6.86 wt% Co and 3.14 wt% Al, the sum of which is 10 wt% of the total raw material). The binder phase is composed of the cobalt-aluminum intermetallic compound CoAl, and the cemented carbide contains a WC hard phase and the intermetallic compound CoAl binder phase.

[0033] The present invention provides a cemented carbide having a cobalt-aluminum intermetallic compound CoAl as a binder phase and a preparation method thereof, which is carried out in the following steps:

[0034] (1) a cemented carbide raw material to which Co and Al powders are added is prepared, wherein the molar fractions of Co and Al powders are 50% and 50% respectively (molar ratio 1:1, i.e., 6.86 wt% Co and 3.14 wt% Al, the sum of which is 10 wt% of the total raw material), and 90 wt% of WC powder;

[0035] (2) The above raw materials were mixed and added into a planetary high-energy ball mill for wet grinding at a ball-to-material ratio of 10:1, alcohol as the wet grinding medium, a rotation speed of 180 r / min, and a wet grinding time of 48 h. The mixture was kept in a vacuum drying oven at 80°C for 480 min, separated by a 100-mesh sieve, and stored under vacuum conditions;

[0036] (3) The powder was weighed and placed into a graphite mold with a diameter of 15 mm, and then placed in a spark plasma sintering furnace and vacuumed to 10 -4 Pa below, and then began to heat up to 1250 ° C, applied a pressure of 50 MPa, and heated at a rate of 100 ° C / min. After holding for 5 minutes, it was cooled to room temperature with the furnace to obtain a cemented carbide with cobalt-aluminum intermetallic compound CoAl as the binder phase. Figure 1 shown.

[0037] Example 2

[0038] The difference between Example 2 and Comparative Example 1 lies in the addition of Al powder (molar ratio of Co:Al = 3:2) in Step 1 and the sintering temperature of 1250°C in Step 3. The alloy composition of Comparative Example 2 is as follows: 85 wt% WC powder, 200 nm in size, is selected, and the molar fractions of Co and Al powder in the binder phase are 60% and 40%, respectively (molar ratio of 3:2, i.e., 11.49 wt% Co and 3.51 wt% Al, the sum of which accounts for 15 wt% of the total raw material). The binder phase is composed of the cobalt-aluminum intermetallic compound CoAl, and the cemented carbide contains both WC and the intermetallic compound CoAl binder phase.

[0039] The present invention provides a cemented carbide having a cobalt-aluminum intermetallic compound CoAl as a binder phase and a preparation method thereof, which is carried out in the following steps:

[0040] (1) a cemented carbide raw material to which Co and Al powders are added is prepared, wherein the molar fractions of Co and Al powders are 60% and 40%, respectively (molar ratio 3:2, i.e., 11.49 wt% Co and 3.51% wt% Al, the sum of which is 15 wt% of the total raw material), and 85 wt% of WC powder;

[0041] (2) The above raw materials were mixed and added to a planetary high-energy ball mill for wet grinding at a ball-to-material ratio of 10:1, alcohol as the wet grinding medium, a rotation speed of 180 r / min, and a wet grinding time of 60 h. The mixture was kept in a vacuum drying oven at 100°C for 600 min, separated by a 100-mesh sieve, and stored under vacuum conditions;

[0042] (3) The powder was weighed and placed into a graphite mold with a diameter of 15 mm, and then placed in a spark plasma sintering furnace and vacuumed to 10 -4 Pa below, and then began to heat up to 1250 ° C, applied a pressure of 50 MPa, and heated at a rate of 100 ° C / min. After holding for 5 minutes, it was cooled to room temperature with the furnace to obtain a cemented carbide with cobalt-aluminum intermetallic compound CoAl as the binder phase. Figure 2 shown.

[0043] Example 3

[0044] The differences between Example 3 and Comparative Example 1 are that ultrafine 400nm WC powder is selected in step 1, Al powder is added (molar ratio of Co:Al = 1:1), and the sintering temperature in step 3 is 1200°C. The alloy composition of Comparative Example 3 of the present invention is as follows: 90wt% ultrafine 400nm WC powder is selected, and the molar fractions of Co and Al powder in the binder phase are 50% and 50%, respectively (molar ratio of 1:1, i.e., 6.86wt% Co and 3.14wt% Al, the sum of which is 10wt% of the total raw material). The binder phase is composed of the cobalt-aluminum intermetallic compound CoAl, and the cemented carbide contains a WC hard phase and the intermetallic compound CoAl binder phase.

[0045] The present invention provides a cemented carbide having a cobalt-aluminum intermetallic compound CoAl as a binder phase and a preparation method thereof, which is carried out in the following steps:

[0046] (1) a cemented carbide raw material to which Co and Al powders are added is prepared, wherein the molar fractions of Co and Al powders are 50% and 50% respectively (molar ratio 1:1, i.e., 6.86 wt% Co and 3.14 wt% Al, the sum of which is 10 wt% of the total raw material), and 90 wt% of WC powder;

[0047] (2) The above raw materials were mixed and added into a planetary high-energy ball mill for wet grinding at a ball-to-material ratio of 10:1, alcohol as the wet grinding medium, a rotation speed of 180 r / min, and a wet grinding time of 48 h. The mixture was kept in a vacuum drying oven at 80°C for 480 min, separated by an 80-mesh sieve, and stored under vacuum conditions;

[0048] (3) The powder was weighed and placed into a graphite mold with a diameter of 15 mm, and then placed in a spark plasma sintering furnace and vacuumed to 10 -4 Pa below, and then began to heat up to 1200 ° C, applied a pressure of 50 MPa, and heated at a rate of 100 ° C / min. After holding for 5 minutes, it was cooled to room temperature with the furnace to obtain a cemented carbide with cobalt-aluminum intermetallic compound CoAl as the binder phase. Figure 3 shown.

[0049] Example 4

[0050] The differences between Example 4 and Comparative Example 1 are that ultrafine 400nm WC powder is selected in step 1, Al powder is added (molar ratio of Co:Al = 3:2), and the sintering temperature in step 3 is 1200°C. The alloy composition of Comparative Example 4 is as follows: 85wt% ultrafine 400nm WC powder is selected, and the molar fractions of Co and Al powder in the binder phase are 60% and 40%, respectively (molar ratio of 3:2, i.e., 11.49wt% Co and 3.51wt% Al, the sum of which is 15wt% of the total raw material). The binder phase is composed of the cobalt-aluminum intermetallic compound CoAl, and the cemented carbide contains both WC and the intermetallic compound CoAl binder phase.

[0051] The present invention provides a cemented carbide having a cobalt-aluminum intermetallic compound CoAl as a binder phase and a preparation method thereof, which is carried out in the following steps:

[0052] (1) a cemented carbide raw material to which Co and Al powders are added is prepared, wherein the molar fractions of Co and Al powders are 60% and 40%, respectively (molar ratio 3:2, i.e., 11.49 wt% Co and 3.51% wt% Al, the sum of which is 15 wt% of the total raw material), and 85 wt% of WC powder;

[0053] (2) The above raw materials were mixed and added to a planetary high-energy ball mill for wet grinding at a ball-to-material ratio of 10:1, alcohol as the wet grinding medium, a rotation speed of 180 r / min, and a wet grinding time of 60 h. The mixture was kept in a vacuum drying oven at 100°C for 600 min, separated by an 80-mesh sieve, and stored under vacuum conditions;

[0054] (3) The powder was weighed and placed into a graphite mold with a diameter of 15 mm, and then placed in a spark plasma sintering furnace and vacuumed to 10 -4 Pa below, and then began to heat up to 1200 ° C, applied a pressure of 50 MPa, and heated at a rate of 100 ° C / min. After holding for 5 minutes, it was cooled to room temperature with the furnace to obtain a cemented carbide with cobalt-aluminum intermetallic compound CoAl as the binder phase. Figure 4 shown.

Claims

1. A cemented carbide having a cobalt-aluminum intermetallic compound CoAl as a binder phase, characterized in that: The cemented carbide mainly consists of a hard phase WC and an intermetallic compound CoAl as a binder phase. The cemented carbide components are prepared according to the following powder raw material composition ratio: the total amount of Co and Al elements in the binder phase is 5-20wt% of the total mass of the powder raw material, the balance is the hard phase WC, and the mass fraction of WC is 100wt%-(Co+Al)wt%. The contents of Co and Al elements in the binder phase are proportioned by molar fraction according to the total amount of the binder phase, with the molar fraction of Co powder being 40%-60% and the molar fraction of Al powder being (100%-Co%). The molar ratio of Co powder to Al powder is selected to be 1:1 or 3:2 respectively. The binder phase is a CoAl intermetallic compound with a B2 ordered structure and a bcc crystal structure.

2. A method for preparing a cemented carbide with a cobalt-aluminum intermetallic compound CoAl as a binder phase according to claim 1, characterized in that: The powder raw materials are mixed, ball-milled, vacuum-dried and sieved to obtain a mixed powder; the mixed powder is subjected to spark plasma sintering to prepare a cemented carbide with a cobalt-aluminum intermetallic compound CoAl as a binder phase.

3. The preparation method according to claim 2, characterized in that The spark plasma sintering method specifically comprises the following steps: loading the mixed powder into a graphite mold, placing the graphite mold containing the mixed powder in a spark plasma sintering furnace for sintering, evacuating the sintering cavity to below 10 Pa, and then heating the cavity at a heating rate of 100° C. / min. When the temperature reaches the sintering temperature, the temperature is maintained, while applying a sintering pressure of 30 to 100 MPa, the sintering temperature is 1000 to 1300° C., and the temperature is maintained for 5 minutes under the sintering pressure. Finally, the cavity is cooled to room temperature in the furnace to obtain a dense cemented carbide with a cobalt-aluminum intermetallic compound CoAl as a binder phase.

4. The preparation method according to claim 3, characterized in that The average particle size of the WC powder in the powder raw material is 0.1 to 0.5 μm; the average particle size of the Co powder and the Al powder is in the range of 0.1 to 1 μm.

5. The preparation method according to claim 4, characterized in that The WC powder has an average particle size of 200 nm or 400 nm; the Co powder has an average particle size of 100 nm; and the Al powder has an average particle size of 400 nm.

6. The preparation method according to claim 5, characterized in that The temperature of the vacuum drying is 60-100° C., and the heat preservation time of the vacuum drying is 480-600 minutes. The sieve for sieving the powder has a mesh size of 80-200, and the powder is stored under vacuum conditions.

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