A multi-component refractory metal carbide-co composite powder and a preparation method of a high-entropy ceramic composite material thereof

Abstract

The application relates to a multi-component refractory metal carbide-Co composite powder and a preparation method of high-entropy ceramic composite material thereof, and belongs to the field of powder metallurgy. In the application, multi-component refractory metal oxides, cobalt oxides and carbon sources are mixed, vacuum carbothermal reduction is carried out at 1000-1300 DEG C, and a composite powder of uniformly dispersed refractory metal carbide and metal cobalt is generated in situ in one step. The reduction temperature is 200-500 DEG C lower than that of the same system without cobalt. The composite powder is formed, sintered in an Ar atmosphere at 1350-1500 DEG C and 2-10 MPa of air pressure, and a dense refractory metal carbide high-entropy ceramic-Co composite material is prepared. The sintering temperature is more than 400 DEG C lower than that required for sintering the corresponding carbide powder without cobalt. Through the introduction of cobalt, the preparation temperature is greatly reduced, the average grain size of the obtained composite material is less than 3 mu m, and the fracture toughness is more than one time higher than that of the same high-entropy ceramic material without Co. The application is suitable for high-performance cutting tools and wear-resistant parts, and has the advantages of energy saving and consumption reduction and high toughness.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, specifically relating to a method for preparing a multi-component refractory metal carbide-Co composite powder and its high-entropy ceramic composite material. Background Technology

[0002] Refractory metal carbide high-entropy ceramics refer to solid solutions formed by four or more refractory metal carbide ceramic components in equimolar or near-equimolar ratios. Their properties defy the predictions of traditional "mixing rules," typically exhibiting high hardness, excellent wear resistance, and outstanding high-temperature stability, demonstrating broad application prospects in aerospace, high-end equipment, and other fields.

[0003] However, the industrial application of such materials still faces the following major technical bottlenecks: (1) High powder synthesis temperature: Due to the high kinetic energy barrier of multi-component oxide reduction, the temperature of multi-component carbide powder synthesized by traditional carbothermal reduction method usually exceeds 1500℃, resulting in large energy consumption and easy to cause abnormal grain growth; (2) Difficulty in solid solution and densification of high-entropy materials: The extremely high melting point of refractory metal carbides and the kinetic lag diffusion effect make it difficult to form a single-phase solid solution and densify. Even under a pressure of 30-50 MPa, the sintering densification temperature is generally higher than 1800℃, which further aggravates grain coarsening and performance inhomogeneity; (3) The problem of intrinsic room temperature brittleness has not been solved: Although high entropy can improve some performance, it has not improved the intrinsic room temperature brittleness of carbide ceramics, which restricts its reliability in actual service.

[0004] To improve toughness, metallic phases such as Co are often introduced as toughening phases. However, current mainstream processes mostly employ mechanical mixing, which involves mixing pre-synthesized multi-component carbide powder with metallic Co powder. This method struggles to achieve uniform component distribution and easily leads to microscopic agglomeration, thus limiting further improvements in the material's overall performance.

[0005] Therefore, developing a technology that enables low-temperature synthesis of multi-component refractory metal carbide-Co composite powder, low-temperature sintering preparation of refractory metal carbide high-entropy ceramic-Co composite materials, and achieving uniform and controllable microstructure has become one of the urgent problems to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing multi-component refractory metal carbide-Co composite powder with low process energy consumption, which can synthesize the powder in situ and ultimately obtain fine-grained, high-toughness refractory metal carbide high-entropy ceramic-Co composite material.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a multi-component refractory metal carbide-Co composite powder, characterized by comprising the following steps:

[0009] (1) Raw material mixing: According to the target chemical composition, the multi-component refractory metal oxide, cobalt oxide and carbon source are uniformly mixed; the multi-component refractory metal oxide contains at least four different refractory metal elements, and the refractory metal elements are selected from four or more of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W; the amount of each refractory metal oxide added should make the molar fraction of each refractory metal carbide in the final product 5-35% of all refractory metal carbides; the amount of cobalt oxide added should make the mass fraction of Co in the final composite powder 3-30%; the amount of carbon source used is 95-105% of the theoretical carbon amount required to completely reduce all oxides to generate the corresponding most stable refractory metal carbide and metallic Co (calculated with CO as the gaseous product);

[0010] (2) Carbothermic reduction: The mixture obtained in step (1) is subjected to carbothermic reduction reaction at 1000-1300℃ under vacuum conditions of 0.1-100 Pa to prepare a composite powder of multi-component refractory metal carbide and metal Co in one step in situ.

[0011] In a second aspect, the present invention provides a multi-component refractory metal carbide-Co composite powder prepared by the method described in the first aspect.

[0012] Thirdly, the present invention provides a method for preparing a refractory metal carbide high-entropy ceramic-Co composite material, characterized by comprising the following steps: molding the multi-component refractory metal carbide-Co composite powder as described in the second aspect, and then sintering it at a temperature of 1350-1500℃ and an Ar atmosphere with a pressure of 2-10 MPa to obtain the refractory metal carbide high-entropy ceramic-Co composite material.

[0013] Fourthly, the present invention provides a refractory metal carbide high-entropy ceramic-Co composite material prepared by the method described in the third aspect.

[0014] Furthermore, in the method described in the first aspect, the temperature of the carbothermic reduction reaction in step (2) is 200-500°C lower than the temperature required to completely reduce the multi-component refractory metal oxide and generate the corresponding stable refractory metal carbide under the same conditions without cobalt oxide; the composition of the multi-component refractory metal oxide should be such that the refractory metal carbide portion in the composite powder generated in step (2) is a multi-component carbide powder that can be sintered to form a single-phase carbide high-entropy ceramic solid solution; the refractory metal carbide-Co composite powder obtained by the method has an average particle size of less than 500 nanometers for the multi-component refractory metal carbide, and metal Co particles are dispersed therein.

[0015] Furthermore, in the method described in the third aspect, the sintering temperature is more than 400°C lower than the temperature required for densifying the corresponding refractory metal carbide powder obtained by carbothermal reduction of cobalt oxide-free raw materials; the average grain size of the obtained refractory metal carbide high-entropy ceramic-Co composite material is less than 3 μm, and its fracture toughness is more than twice that of the corresponding high-entropy ceramic material without Co.

[0016] Beneficial technical effects of the present invention:

[0017] (1) Low temperature energy saving: By introducing cobalt oxide into the reduction system, the activation energy of the carbothermic reduction reaction of refractory metal oxides is significantly reduced, which greatly reduces the reduction temperature and subsequent sintering temperature, effectively reducing energy consumption and production costs.

[0018] (2) In-situ synthesis: One-step in-situ generation of multi-component carbide and Co composite powder avoids pollution and agglomeration in multi-step processing, and provides highly active powder raw materials for obtaining high-performance composite materials.

[0019] (3) Low-temperature and low-pressure sintering: Thanks to the high-activity composite powder and the effect of liquid Co during the sintering process, the sintering temperature of high-entropy ceramics can be reduced to 1350-1500℃, which is more than 400℃ lower than the sintering temperature of traditional Co-free high-entropy ceramics. The required pressure is only 2-10 MPa, which greatly reduces the requirements for equipment and energy.

[0020] (4) Toughening with fine grain structure and Co binder phase: The low synthesis and sintering temperature effectively inhibited grain growth and obtained a fine microstructure at the submicron level. The introduction of the metallic Co phase significantly improved the fracture toughness of the material through mechanisms such as plastic deformation and crack bridging. Compared with pure high-entropy carbides, the toughness was increased by more than 1 times.

[0021] (5) Simple process and easy to promote: The entire process is short and suitable for large-scale production. Attached Figure Description

[0022] Figure 1 Scanning electron microscope (SEM) image, corresponding energy dispersive spectroscopy (EDS) analysis image, and particle size distribution image of the ultrafine multi-component carbide-Co composite powder prepared by in-situ reaction according to the present invention.

[0023] Figure 2 The microstructure, corresponding energy dispersive spectroscopy (EDS) and XRD patterns of (TiNbTaMo)C-10Co% prepared in Example 1 are shown. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the following embodiments are provided to further describe the invention in detail. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0025] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0026] Example 1

[0027] The raw materials used were TiO2 (99 wt.%, 2-3 μm purity), Nb2O5 (99.9 wt.%, 1 μm purity), Ta2O5 (99.5 wt.%, 1 μm purity), MoO2 (99 wt.%, 1 μm purity), Co3O4 (99.5 wt.%, 5 μm purity), and carbon black (99.9 wt.%, 100 nm purity). The amount of carbon black added was 97% of the theoretical carbon content required for the complete reduction of the oxides to generate the corresponding refractory metal carbides and CO gas. The refractory metals in the final system were designed to be in equimolar ratio, and the Co content was 10 wt%. The masses of TiO2, Nb2O5, Ta2O5, MoO2, Co3O4, and carbon black were 6.03 g, 10.03 g, 16.67 g, 9.65 g, 5.26 g, and 11.99 g, respectively. The mixed raw material powder was compressed into briquettes and placed in a graphite crucible. Under a vacuum of 10 Pa, the temperature was increased to 1100℃ at a rate of 5℃ / min and held for 60 min, followed by furnace cooling. X-ray diffraction (XRD) analysis confirmed the product to be a mixture of TiC, NbC, TaC, Mo2C, and Co. Oxygen, nitrogen, and hydrogen analyzers showed an oxygen content of only 0.25%. Scanning electron microscopy (SEM) analysis indicated that TiC, NbC, TaC, Mo2C, and Co were uniformly distributed. Figure 1 a). The particle size obtained statistically from SEM images is approximately 150 nm ( Figure 1 b).

[0028] The prepared composite powder was pressed into shape and sintered in a low-pressure sintering furnace at 1410℃ and 6 MPa Ar gas pressure for 120 min. X-ray diffraction (XRD) analysis revealed that the composite material consisted of a single-phase high-entropy refractory metal carbide solid solution (TiNbTaMo)C and Co. Energy dispersive spectroscopy (EDS) analysis determined that the light gray and gray phases in the scanned images were (TiNbTaMo)C and Co, respectively. Figure 2 The relative density of the material, measured by the water displacement method, is >99.0%. The average grain size of the high-entropy carbide ceramic phase is approximately 2 μm. Its fracture toughness, determined by indentation, is 7.2 MPa·m¹ / ².

[0029] Example 2

[0030] Example 2 is basically the same as Example 1, except that:

[0031] The designed refractory metal carbide components include TiC, VC, NbC, TaC, and Mo2C, with a Co content of 20 wt% in the composite material. V2O5 (purity 99.6 wt.%, 1 μm) was used as the V source. Carbon black, representing 98% of the theoretical carbon required for complete reduction of all oxides, was added as the carbon source. The mass ratios of TiO2, V2O5, Nb2O5, Ta2O5, MoO2, Co3O4, and carbon black were 3.90 g, 4.44 g, 6.47 g, 10.80 g, 6.29 g, 8.68 g, and 9.43 g, respectively. The reduction preparation temperature for the refractory metal carbide-Co composite powder was 1050℃, the sintering temperature was 1480℃, the sintering pressure was 8 MPa, and the holding time was 60 min.

[0032] The product of vacuum carbothermal reduction was a mixed powder of TiC, VC, NbC, TaC, Mo2C, and Co, with an average particle size of approximately 150 nm. Sintering yielded a composite material of (TiVNbTaMo)C and Co, with a relative density >99.0%. The average grain size of the (TiVNbTaMo)C phase was approximately 1.8 μm, and the fracture toughness obtained by indentation testing was 9.1 MPa·m¹ / ².

[0033] Example 3

[0034] Example 3 is basically the same as Example 2, except that:

[0035] The designed carbide components included TiC, HfC, VC, NbC, TaC, and Mo2C, with a Co content of 6 wt% in the composite material. HfO2 (99 wt.% purity, 1-3 μm) was used as the Hf source. Carbon black, representing 102% of the theoretical carbon required for complete reduction of all oxides, was added as the carbon source. The mass ratios of TiO2, HfO2, V2O5, Nb2O5, Ta2O5, MoO3, Co3O4, and carbon black were 3.49 g, 9.21 g, 3.98 g, 5.80 g, 9.69 g, 5.64 g, 2.71 g, and 9.47 g, respectively. The reduction preparation temperature for the refractory metal carbide-Co composite powder was 1250℃, the sintering temperature was 1480℃, the sintering gas pressure was 5 MPa, and the holding time was 150 min.

[0036] The product of vacuum carbothermal reduction was a mixed powder of TiC, HfC, VC, NbC, TaC, Mo2C, and Co, with an average particle size of approximately 260 nm. Sintering yielded a composite material of (TiHfVNbTaMo)C and Co, with a relative density >99.0%. The average grain size of the (TiHfVNbTaMo)C phase was approximately 3 μm, and the fracture toughness obtained by indentation testing was 6.2 MPa·m¹ / ².

[0037] Comparative Example 1

[0038] The same four metal oxides, carbon black, and raw material ratios as in Example 1 were used, but Co3O4 was not added. The masses of TiO2, Nb2O5, Ta2O5, MoO2, and carbon black were 5.60 g, 9.30 g, 15.53 g, 9.04 g, and 10.53 g, respectively. XRD results showed that no oxide diffraction peaks were observed in the product at a reduction temperature of 1500 °C, and the product was a mixture of TiC, NbC, TaC, and Mo2C. However, oxygen, nitrogen, and hydrogen analysis showed that the oxygen content was as high as 1.05%. Compared with Example 1, this indicates that the introduction of Co lowered the carbothermic reduction temperature of TiO2, Nb2O5, Ta2O5, and MoO2 by more than 400 °C. Furthermore, the composite powder was subjected to rapid hot pressing sintering at 1800℃ and 50 MPa, and the resulting (TiNbTaMo)C high-entropy ceramic material had a relative density of 98.1%, an average grain size of approximately 5.3 μm, and a fracture toughness of 2.9 MPa·m¹ / ².

[0039] Comparative Example 1 shows that, without the addition of Co, obtaining dense (TiNbTaMo)C high-entropy ceramics requires sintering conditions far exceeding those of this invention (1800°C, 50 MPa), which inevitably leads to grain coarsening (approximately 5.3 μm). Comparing the data from Example 1, it is evident that by introducing Co, this invention not only lowers the densification temperature by approximately 390°C, allowing sintering under milder conditions (1410°C, 6 MPa), but also achieves a fine-grained structure (approximately 2 μm) and a uniformly distributed toughening Co phase. The synergistic effect of these two factors ultimately results in a significant improvement in fracture toughness (approximately 150%).

Claims

1. A method for preparing a multi-component refractory metal carbide-Co composite powder, characterized in that, Includes the following steps: (1) Raw material mixing: According to the target chemical composition, the multi-component refractory metal oxide, cobalt oxide and carbon source are uniformly mixed; the multi-component refractory metal oxide contains at least four different refractory metal elements, and the refractory metal elements are selected from four or more of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W; the amount of each refractory metal oxide added should make the molar fraction of each refractory metal carbide in the final product 5-35% of all refractory metal carbides; the amount of cobalt oxide added should make the mass fraction of Co in the final composite powder 3-30%; the amount of carbon source used is 95-105% of the theoretical carbon required to completely reduce all oxides to generate the corresponding most stable refractory metal carbide and metallic Co, with CO as the gaseous product. (2) Carbothermic reduction: The mixture obtained in step (1) is subjected to carbothermic reduction reaction at 1000-1300℃ under vacuum conditions of 0.1-100 Pa to prepare a composite powder of multi-component refractory metal carbide and metal Co in one step in situ.

2. A multi-component refractory metal carbide-Co composite powder prepared by the method of claim 1.

3. A method for preparing a refractory metal carbide high-entropy ceramic-Co composite material, characterized in that, The process includes the following steps: molding the multi-component refractory metal carbide-Co composite powder as described in claim 2, and then sintering it at a temperature of 1350-1500℃ and an Ar atmosphere with a pressure of 2-10 MPa to obtain the refractory metal carbide high-entropy ceramic-Co composite material.

4. A refractory metal carbide high-entropy ceramic-Co composite material prepared by the method of claim 3.

5. The preparation method according to claim 1, characterized in that, The temperature of the carbothermic reduction reaction in step (2) is 200-500°C lower than the temperature required to completely reduce the multi-component refractory metal oxide and generate the corresponding stable refractory metal carbide under the same conditions without cobalt oxide; the composition of the multi-component refractory metal oxide should be such that the refractory metal carbide portion in the composite powder generated in step (2) is a multi-component carbide powder that can be sintered to form a single-phase carbide high-entropy ceramic solid solution; the refractory metal carbide-Co composite powder obtained by the method has an average particle size of less than 500 nanometers for the multi-component refractory metal carbide, and the metal Co particles are dispersed therein.

6. The preparation method according to claim 3, characterized in that, The sintering temperature is more than 400°C lower than the temperature required to densify the corresponding refractory metal carbide powder obtained by carbothermal reduction of raw materials without cobalt oxide to >99%.

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