A composite ceramic with CoSi2 alloy toughened high-entropy carbide, its preparation method and application

Abstract

The application belongs to the technical field of composite ceramics, and discloses a CoSi2 alloy toughened high-entropy carbide composite ceramic and a preparation method and application thereof. 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 )C-CoSi2, wherein TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder, MoO3 powder and carbon powder are mixed to obtain mixed powder, the mixed powder is added into anhydrous ethanol for stirring to obtain slurry, the slurry is subjected to ball milling, drying and sieving, and then is dry-pressed into a green body, the green body is sintered at 1000-1600 DEG C under a protective atmosphere, high-entropy powder and CoSi2 powder are mixed, the mixture is subjected to ball milling, drying and sieving, and then is dry-pressed into a green body, and the green body is sintered by SPS at 1500-1700 DEG C under a uniaxial pressure of 25-30 MPa, so that the composite ceramic has the advantages of high density, high hardness and high fracture toughness, and can be applied in the field of preparation of cutting difficult-to-machine materials.

Description

Technical Field

[0001] This invention belongs to the field of composite ceramics technology, and more specifically, relates to a composite ceramic of CoSi2 alloy toughened high-entropy carbide, its preparation method and application. Background Technology

[0002] Compared to traditional mono- or binary transition metal carbide ceramics, high-entropy carbide ceramics exhibit higher hardness (~24 GPa), wear resistance, and high-temperature stability due to their unique high-entropy effect, making them ideal for manufacturing high-performance cutting tools, wear-resistant components, and other demanding applications in aerospace, military, and energy fields. However, due to their strong covalent bonds, low self-diffusion coefficient, and severe lattice distortion, high-entropy carbide ceramics suffer from high sintering temperatures and poor fracture toughness, which greatly limits their industrial applications.

[0003] Previous literature studies have shown that sintering with low-melting-point metal liquid phases can effectively reduce the densification temperature and improve the fracture toughness of high-entropy carbide ceramics, but it significantly sacrifices the high hardness advantage of high-entropy carbide ceramics. For example, (Hf-Ta-Ti-Nb-V)C and (Ti-V-Nb-Ta-W)C ceramics, with the addition of 19.2 vol.% Co and 12 vol.% Ni respectively, can achieve densification by sintering at 1400℃, and the fracture toughness of (Hf-Ta-Ti-Nb-V)C-19.2 vol.% Co and (TV-Nb-Ta-W)C-12 vol.% Ni ceramics can reach 8.5 MPa·m. 1 / 2 and 6.7 MPa·m 1 / 2 However, their Vickers hardness values ​​are relatively low, only 14.0 GPa and 14.3 GPa respectively. The residue of low-hardness metallic phase in the ceramic matrix after sintering is the main reason for the decrease in hardness of high-entropy carbide ceramics. Therefore, the urgent problem to be solved is how to maintain the inherent high hardness characteristics of high-entropy carbide ceramics while achieving low-temperature densification and improved fracture toughness. Summary of the Invention

[0004] In order to overcome the shortcomings and disadvantages of the existing technology, the primary objective of this invention is to provide a composite ceramic of CoSi2 alloy toughened high-entropy carbide.

[0005] Another objective of this invention is to provide a method for preparing composite ceramics of CoSi2 alloy-toughened high-entropy carbides obtained by the above method. This method introduces CoSi2 as a liquid-phase sintering aid, which significantly improves the fracture toughness of (Ti,Zr,Nb,Ta,Mo)C high-entropy ceramics while achieving low-temperature densification of the ceramics and maintaining the high hardness of the high-entropy carbide ceramics.

[0006] Another object of the present invention is to provide the application of the above-mentioned CoSi2 alloy toughened high-entropy carbide composite ceramic.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A composite ceramic of CoSi2 alloy toughened high-entropy carbide is (Ti 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 C-CoSi2 is prepared by mixing TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder, MoO3 powder and carbon powder in a molar ratio of 1:1:0.5:0.5:1:17 to obtain a mixed powder. This mixed powder is then added to anhydrous ethanol and stirred to obtain a slurry. After ball milling, drying, sieving, and dry pressing, it is formed into a green body A. Under a protective atmosphere, green body A is sintered at 1500–1600℃ to obtain (TiO2:0.5:0.5:1:17). 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 C high-entropy powder; the high-entropy powder and CoSi2 powder are mixed, anhydrous ethanol is added and ultrasonically stirred to obtain a slurry, which is then ball-milled, dried, sieved and dry-pressed into a green body B; the green body B is sintered at 1500-1700℃ under a uniaxial pressure of 25-30MPa by SPS.

[0009] Preferably, the composite ceramic has a Vickers hardness of 24.7–26 GPa and a fracture toughness of 5–5.5 MPa·m. 1 / 2 .

[0010] Preferably, the particle size of the TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder, and MoO3 powder is 1-2 μm; the particle size of the carbon powder is 100 nm-1 μm; and the particle size of the CoSi2 powder is 0.4-0.6 μm.

[0011] Preferably, the (Ti) 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 The volume ratio of high-entropy C powder to CoSi2 powder is (90-97.5):(2.5-10).

[0012] The preparation method of the CoSi2 alloy-toughened high-entropy carbide composite ceramic includes the following steps:

[0013] S1. TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder, MoO3 powder and carbon powder in a molar ratio of 1:1:0.5:0.5:1:17 are mixed to obtain a mixed powder.

[0014] S2. The mixed powder is added to anhydrous ethanol and ultrasonically stirred to obtain a slurry. Then, Si3N4 dielectric balls are added and the mixture is ball-milled, dried, sieved, and dry-pressed into a green body. Under a protective atmosphere, the green body is sintered at 1000–1600℃ to obtain (Ti 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 C high-entropy powder;

[0015] S3. (Ti) 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 High-entropy C powder and CoSi2 powder are mixed, and anhydrous ethanol is added and ultrasonically stirred to prepare a slurry. Then, silicon nitride dielectric balls are added, and the mixture is ball-milled, dried, sieved, and dry-pressed into a green body.

[0016] S4. A composite ceramic of CoSi2 alloy-toughened high-entropy carbide was prepared by SPS sintering at 1500–1700℃ under a uniaxial pressure of 25–30 MPa and holding at that temperature. The molecular formula was (Ti...). 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 )C-CoSi2.

[0017] Preferably, in step S2, the ball milling speed is 100-300 r / min, the ball milling time is 18-36 h, the drying temperature is 60-80 °C, and the drying time is 12-24 h.

[0018] Preferably, the heat treatment procedure for pressureless sintering in step S2 is as follows: first, the temperature is increased to 50-1000°C at a rate of 15-20°C / min, nitrogen is then introduced to 1 atmosphere, and the temperature is further increased to 1500-1600°C at a rate of 8-10°C / min; after the heating procedure is completed, the temperature is held for 0.5-1 hour, and then the temperature is decreased to 710-810°C at a rate of 8-15°C / min before being cooled down with the furnace.

[0019] Preferably, in step S3, the ball milling speed is 100-200 r / min, and the ball milling time is 18-36 h; the drying temperature is 60-80℃, and the drying time is 16-24 h.

[0020] Preferably, the SPS sintering process in step S4 is as follows: first, heat the temperature to 1500-1700℃ at a rate of 80-100℃ / min, hold for 10-15min, and then symmetrically cool down to below 710-800℃ with the furnace.

[0021] The application of the CoSi2 alloy-toughened high-entropy carbide composite ceramic in the preparation of difficult-to-machine ceramics.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. This invention employs a pressureless heat treatment process, which is simple, low-cost, and energy-saving.

[0024] 2. This invention uses CoSi2 alloy as a binder and employs SPS sintering process to promote the solid solution process of (Ti,Zr,Nb,Ta,Mo)C. Furthermore, a low-melting-point liquid phase is formed during sintering, which promotes the low-temperature densification process. This invention features fast sintering speed, reduced sintering temperature, and energy saving and environmental protection.

[0025] 3. The high-entropy carbide composite ceramic prepared by this invention improves fracture toughness while maintaining high hardness. Attached Figure Description

[0026] Figure 1 SEM images of the cross sections of the CoSi2 alloy-toughened high-entropy carbide composite ceramics prepared in Examples 1-3 and the high-entropy carbide ceramic of Comparative Example 1. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0028] The particle size of TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder and MoO3 powder used in this invention is 1 to 2 μm; the particle size of carbon powder is 100 nm to 1 μm; and the particle size of CoSi2 powder is 0.4 to 0.6 μm.

[0029] Example 1

[0030] 1. A mixed powder is prepared by mixing TiO2, ZrO2, Nb2O5, Ta2O5, MoO3 powders and carbon powder in a molar ratio of 1:1:0.5:0.5:1:17;

[0031] 2. Add anhydrous ethanol to the mixed powder, stir ultrasonically to obtain a slurry, then add silicon nitride media balls and ball mill them in a roller ball mill. After drying and sieving, the slurry is loaded into an iron mold and dry-pressed into a green blank.

[0032] 3. The green billet is first heated to 1000℃ at a rate of 20℃ / min, then nitrogen is introduced to 1 atmosphere, and the temperature is further increased to 1600℃ at a rate of 10℃ / min and held for 1 hour; then the temperature is decreased to 800℃ at a rate of 10℃ / min and cooled in the furnace. After being pulverized by a high-speed pulverizer and passed through a 100-mesh sieve, (Ti) is obtained. 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 C High-entropy powder.

[0033] 4. The volume ratio of (Ti) is 9:1. 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 High-entropy C powder and CoSi2 powder are mixed, and then anhydrous ethanol is added and ultrasonically stirred to obtain a slurry. The slurry is then ball-milled by a roller ball mill, dried, sieved, and then loaded into an iron mold and dry-pressed into a blank.

[0034] 5. The billet was subjected to SPS sintering at 1600℃ under a uniaxial pressure of 30MPa and a heating rate of 100℃ / min, and held for 10min. Then, it was symmetrically cooled below 600℃ in the furnace to obtain a CoSi2 alloy-toughened high-entropy carbide composite ceramic with the molecular formula (Ti...). 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 )C-CoSi2.

[0035] Example 2

[0036] 1. A mixed powder is prepared by mixing TiO2, ZrO2, Nb2O5, Ta2O5, MoO3 powders and carbon powder in a molar ratio of 1:1:0.5:0.5:1:17;

[0037] 2. The mixed powder is added to anhydrous ethanol and ultrasonically stirred to obtain a slurry. Then, silicon nitride media balls are added and the mixture is ball-milled in a roller ball mill. After drying and sieving, the mixture is loaded into an iron mold and dry-pressed into a blank.

[0038] 3. The green billet is first heated to 1000℃ at a rate of 20℃ / min, then nitrogen is introduced to 1 atmosphere. The temperature is then increased to 1600℃ at a rate of 10℃ / min and held for 1 hour. The temperature is then decreased to 800℃ at a rate of 10℃ / min and cooled with the furnace. After being pulverized by a high-speed pulverizer and passed through a 100-mesh sieve, (Ti) is obtained. 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 C High-entropy powder.

[0039] 4. (Ti) with a volume ratio of 97.5:2.5 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 A slurry was prepared by mixing high-entropy C powder and CoSi2 powder with anhydrous ethanol and ultrasonically stirring. Then, silicon nitride media balls were added and ball-milled in a roller mill. After drying and sieving, the slurry was loaded into an iron mold and dry-pressed into a blank.

[0040] 5. The billet was subjected to SPS sintering at 1600℃ with a uniaxial pressure of 30MPa and a heating rate of 100℃ / min, and held for 10min. The temperature was then symmetrically lowered below 800℃ during furnace cooling to obtain a CoSi2 alloy-toughened high-entropy carbide composite ceramic with the molecular formula (Ti...). 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 )C-CoSi2.

[0041] Example 3

[0042] 1. A mixed powder is prepared by mixing TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder, MoO3 powder and carbon powder in a molar ratio of 1:1:0.5:0.5:1:17;

[0043] 2. The mixed powder is added to anhydrous ethanol and ultrasonically stirred to obtain a slurry. Then, silicon nitride media balls are added and the mixture is ball-milled in a roller ball mill. After drying and sieving, the mixture is loaded into an iron mold and dry-pressed into a blank.

[0044] 3. The green billet is first heated to 1000℃ at a rate of 20℃ / min, then nitrogen is introduced to 1 atmosphere. The temperature is then increased to 1600℃ at a rate of 10℃ / min and held for 1 hour. The temperature is then decreased to 800℃ at a rate of 10℃ / min and cooled with the furnace. After being pulverized by a high-speed pulverizer and passed through a 100-mesh sieve, (Ti) is obtained. 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo0.2 C High-entropy powder.

[0045] 4. Mix Ti with a volume ratio of 95:5. 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 High-entropy C powder and CoSi2 powder are mixed, anhydrous ethanol is added and ultrasonically stirred to prepare a slurry, then silicon nitride dielectric balls are added, the mixture is ball-milled by a roller ball mill, dried, sieved and then loaded into an iron mold and dry-pressed into a blank.

[0046] 5. The billet was subjected to SPS sintering at 1600℃ with a uniaxial pressure of 10MPa and a heating rate of 100℃ / min, and held for 10min. The temperature was then symmetrically lowered below 800℃ during furnace cooling to obtain a CoSi2 alloy-toughened high-entropy carbide composite ceramic with the molecular formula (Ti...). 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 )C-CoSi2.

[0047] Comparative Example 1

[0048] 1. A mixed powder is prepared by mixing TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder, MoO3 powder and carbon powder in a molar ratio of 1:1:0.5:0.5:1:17;

[0049] 2. The mixed powder is added to anhydrous ethanol and ultrasonically stirred to obtain a slurry. Then, silicon nitride media balls are added and the mixture is ball-milled in a roller ball mill. After drying and sieving, the mixture is loaded into an iron mold and dry-pressed into a blank.

[0050] 3. The green billet is first heated to 1000℃ at a rate of 20℃ / min, then nitrogen is introduced to 1 atmosphere. The temperature is then increased to 1600℃ at a rate of 10℃ / min and held for 1 hour. The temperature is then decreased to 710–810℃ at a rate of 10℃ / min, followed by furnace cooling. The billet is then pulverized using a high-speed pulverizer and passed through a 100-mesh sieve to obtain (Ti). 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 C High-entropy powder.

[0051] 4. (Ti) 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2C high-entropy powder was added to anhydrous ethanol and ultrasonically stirred to prepare a slurry. Then, silicon nitride media balls were added and ball-milled in a roller ball mill. After drying and sieving, the slurry was loaded into an iron mold and dry-pressed into a blank.

[0052] 5. The green body is subjected to SPS sintering at 1600℃ with a uniaxial pressure of 10MPa and a heating rate of 100℃ / min, and held for 10min. The temperature is then symmetrically lowered below 800℃ during furnace cooling to obtain a high-entropy carbide ceramic with the molecular formula (Ti). 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 C.

[0053] Figure 1 SEM images of the cross-sections of the CoSi2 alloy-toughened high-entropy carbide composite ceramics prepared in Examples 1-3 and the high-entropy carbide ceramic of Comparative Example 1 are shown. (a) is the high-entropy carbide ceramic of Comparative Example 1. (b) is the CoSi2 alloy-toughened high-entropy carbide composite ceramic of Example 2. (c) is the CoSi2 alloy-toughened high-entropy carbide composite ceramic of Example 3. (d) is the CoSi2 high-entropy carbide composite ceramic of Example 1. Figure 1 As can be seen, the fracture mode of the CoSi2 alloy-toughened high-entropy carbide composite ceramic in Example 1 is intergranular fracture, while the fracture surface of the high-entropy carbide shows a fracture mode dominated by intergranular fracture. Meanwhile, "dimples" can be observed in the area indicated by the green dashed line, which is a major characteristic of grain pull-out, indicating that grain pull-out is the main toughening mechanism of the ceramic. Furthermore, some large grains ((Co3Mo3)C phase) are also present in this sample, and most of them exhibit transgranular fracture with smooth fracture surfaces, which weakens the fracture toughness of the material. Its fracture toughness is 3.47 ± 0.26 MPa·m. 1 / 2 The CoSi2 alloy-toughened high-entropy carbide composite ceramic of Example 2 has a porous structure with pore size comparable to grain size, which severely impairs the material's mechanical properties. This sample exhibits the lowest fracture toughness, at 2.81 ± 0.21 MPa·m. 1 / 2 The fracture mode of the CoSi2 alloy-toughened high-entropy carbide composite ceramic in Example 3 was also intergranular fracture, and many "dimples" were observed. This is a major characteristic of grain pull-out, indicating that grain pull-out is the main toughening mechanism of the ceramic and there are no large grains. Its fracture toughness is 5.23 ± 0.24 MPa·m. 1 / 2 It has a relative density of 100% and a Vickers hardness of 25±0.27GPa.

[0054] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A composite ceramic of CoSi2 alloy-toughened high-entropy carbide, characterized in that, The composite ceramic is (Ti) 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 C-CoSi2 is prepared by mixing TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder, MoO3 powder and carbon powder in a molar ratio of 1:1:0.5:0.5:1:17 to obtain a mixed powder. Anhydrous ethanol is added and stirred to obtain a slurry. After ball milling, drying, sieving, and dry pressing, the slurry is formed into a green body A. Under a protective atmosphere, the green body A is sintered at 1000~1600℃ to obtain (TiO2:0.5:0.5:1:17). 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 The high-entropy powder was mixed with CoSi2 powder, and anhydrous ethanol was added and ultrasonically stirred to obtain a slurry. The slurry was then ball-milled, dried, sieved, and dry-pressed into a green body B. The green body B was sintered at 1500-1700℃ under a uniaxial pressure of 25-30 MPa using SPS. The particle sizes of the TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder, and MoO3 powder were all 1-2 μm; the carbon powder had a particle size of 100 nm-1 μm; and the CoSi2 powder had a particle size of 0.4-0.6 μm. 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 The volume ratio of high-entropy C powder to CoSi2 powder is (90~97.5):(2.5~10).

2. The composite ceramic of CoSi2 alloy toughened high-entropy carbide according to claim 1, characterized in that, The composite ceramic has a Vickers hardness of 24.7~26 GPa and a fracture toughness of 5~5.5 MPa·m. 1 / 2 .

3. The method for preparing the composite ceramic of CoSi2 alloy toughened high-entropy carbide according to claim 1 or 2, characterized in that, Includes the following steps: S1. TiO2 powder, ZrO2 powder, Nb2O5 powder, Ta2O5 powder, MoO3 powder and carbon powder in a molar ratio of 1:1:0.5:0.5:1:17 are mixed to obtain a mixed powder. S2. The mixed powder was added to anhydrous ethanol and ultrasonically stirred to obtain a slurry. Then, Si3N4 dielectric balls were added and the mixture was ball-milled, dried, sieved, and dry-pressed into a green body. Under a protective atmosphere, the green body was sintered at 1500~1600℃ to obtain (Ti 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 C high-entropy powder; S3. (Ti) 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 High-entropy C powder and CoSi2 powder are mixed, and anhydrous ethanol is added and ultrasonically stirred to prepare a slurry. Then, silicon nitride dielectric balls are added, and the mixture is ball-milled, dried, sieved, and dry-pressed into a green body. S4. A composite ceramic of CoSi2 alloy-toughened high-entropy carbide was prepared by SPS sintering at 1500-1700℃ under a uniaxial pressure of 25-30 MPa and holding at that temperature to obtain a composite ceramic with the molecular formula (Ti). 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Mo 0.2 )C-CoSi2.

4. The method for preparing the composite ceramic of CoSi2 alloy toughened high-entropy carbide according to claim 3, characterized in that, In step S2, the ball milling speed is 100~300 r / min; the ball milling time is 18~36 h; the drying temperature is 60~80℃; and the drying time is 12~24 h.

5. The method for preparing the composite ceramic of CoSi2 alloy toughened high-entropy carbide according to claim 3, characterized in that, The heat treatment procedure for sintering described in step S2 is as follows: first, the temperature is raised to 50-1000℃ at a rate of 15-20℃ / min, nitrogen gas is then introduced to 1 atmosphere, and then the temperature is raised to 1500-1600℃ at a rate of 8-10℃ / min; after the heating procedure is completed, the temperature is held for 0.5-1 h, and then the temperature is lowered to 710-810℃ at a rate of 8-15℃ / min and then cooled with the furnace.

6. The method for preparing the composite ceramic of CoSi2 alloy toughened high-entropy carbide according to claim 3, characterized in that, In step S3, the ball milling speed is 100~200 r / min, and the ball milling time is 18~36 h; the drying temperature is 60~80℃, and the drying time is 16~24 h.

7. The method for preparing the composite ceramic of CoSi2 alloy toughened high-entropy carbide according to claim 3, characterized in that, The SPS sintering process described in step S4 is as follows: first, heat the temperature to 1500-1700℃ at a rate of 80-100℃ / min, hold for 10-15 min, and then symmetrically cool down to below 710-800℃ with the furnace.

8. The application of the composite ceramic of CoSi2 alloy toughened high-entropy carbide as described in claim 1 or 2 in the preparation of difficult-to-machine ceramics.

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