A method for preparing non-isotropic high-entropy silicide ceramic material

Abstract

The present invention relates to a preparation method of a non-isotropic high entropy silicide ceramic material, comprising the steps of mixing Ti powder, V powder, Nb powder, Mo powder, W powder and Si powder, adding anhydrous ethanol as a ball milling medium, grinding in an argon protective atmosphere to obtain a mixed powder; drying the mixed powder, pressing the mixed powder into a shape, and then performing spark plasma sintering; and cooling the mixed powder after the sintering is completed to obtain a target product Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2. After testing, this high-entropy ceramic has high hardness and good oxidation resistance at high temperatures, and has potential application prospects in extremely harsh working conditions such as high temperature and high load.

Description

Technical Field

[0001] The present invention relates to a non-equivalent high entropy silicide Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) The invention relates to a preparation method of Si2 and its bulk ceramics, specifically a hexagonal structure high-temperature resistant metal ceramic material with multiple metal elements and its preparation method, which belongs to the technical field of high entropy compounds and high-temperature ceramic material preparation. Background Art

[0002] With the rapid development of high-tech fields, the demand for advanced, high-performance materials capable of withstanding harsh operating conditions (such as ultra-high temperatures, ultra-high speeds, high loads, and heavy loads) is growing exponentially. Aviation and aerospace applications, in particular, place ever-higher demands on components for high-temperature mechanical properties, oxidation resistance, and wear resistance. In recent years, the emergence of high-entropy ceramics has significantly expanded the scope for component selection and performance control in ultra-high-temperature ceramic materials. As a novel ceramic material, these materials possess numerous unparalleled properties, making them a growing research hotspot. High-entropy ceramics reported so far include silicides, carbides, oxides, borides, and nitrides. Among them, high-entropy transition metal silicides exhibit exceptional high-temperature oxidation resistance, electrical conductivity, and thermal conductivity, holding great promise for their applications as high-temperature protective materials, electrodes, and high-temperature structural components.

[0003] At the same time, due to the limited research on high-entropy ceramics, the preparation methods for high-entropy ceramics are still in the exploratory stage. The literature "A new class of high-entropy perovskite oxides[J].Scripta Materialia 2018,104:116-120." uses ball milling combined with heat treatment to prepare oxide high-entropy ceramics, but the density is low. The literature "Multicomponent equiatomic rare earth oxides[J].2017,5:102-109." uses spray granulation to prepare oxide high-entropy ceramics with good uniformity. However, this method uses nitrate as the raw material, which is somewhat dangerous and has a low production yield, thus limiting its application. The literature "High-Entropy Metal Diborides:A New Classof High-Entropy Materials and a New Type of UltrahighTemperature Ceramics[J].Scientific Reports,2016,6:37946." uses a method combining high-energy ball milling and discharge plasma to prepare high-entropy boride ceramics with high hardness and good oxidation resistance in a short time. Although this method has been applied to borides, few people have applied it to the preparation of high-entropy silicides. The literature "Characterizationofmulti-principal-element(TiZrNbHfTa)N and (TiZrNbHfTa)C coatings forbiomedicalapplications.[J].Journal of the Mechanical Behavior of BiomedicalMaterials,2012,10(10):197." uses magnetron sputtering to prepare high-entropy carbide films, but it is impossible to prepare bulk ceramics. This method greatly limits the application of high-entropy ceramics. Summary of the Invention

[0004] The present invention discloses a non-isotropic high entropy ceramic material Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2 and its preparation method, through a simple and green preparation process, obtain bulk ceramic materials with excellent mechanical properties, high-temperature oxidation resistance, high-temperature resistance and high wear resistance, which meet the safe and reliable service requirements of mechanical components under harsh working conditions such as high temperature and high load.

[0005] 1. Non-isotropic high entropy ceramic material Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Preparation of Si2

[0006] 1) Mo powder, V powder, Nb powder, Ti powder, W powder, and Si powder were weighed in a molar ratio of 4.0:1.5:1.5:1.5:1.5:20, and 5%-10% anhydrous ethanol was added as a ball milling medium. The mixture was ground under argon protection to obtain a mixed powder. The purity of the raw materials Ti powder, V powder, Nb powder, Mo powder, W powder, and Si powder was ≥99%, and the particle size was 1-3 μm.

[0007] Grinding is to place the raw materials in the ball mill of a ball mill and add tungsten carbide grinding balls to grind them into mixed powder; during grinding, the mass ratio of grinding balls to mixed materials is 5:1~20:1; the speed of the ball mill is 200~600 r / min; the ball milling time is 8~15 hours;

[0008] The purpose of ball milling is to make the powder and the grinding balls in the jar collide and rub against each other at high speed, so as to achieve the effects of crushing, grinding, mixing and dispersing the sample.

[0009] 2) Place the mixed powder obtained in step 1) in a vacuum drying oven and dry at 60-80°C for 1-3 hours to obtain the desired target mixed powder;

[0010] 3) The target mixed powder obtained in step 2) is pressed into a green body, and then the green body is subjected to spark plasma sintering. After sintering, it is cooled to obtain the target product Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2 bulk ceramics;

[0011] During the spark plasma sintering process, the vacuum pressure is 1.5~30 MPa and the vacuum degree is less than 10 0 Pa, the heating rate is 80~150 ℃ / min, the sintering temperature is 1400~1600 ℃, and the sintering time is 5min~30min.

[0012] The synthesis mechanism of this invention involves using transition metal TM (Ti, V, Nb, Mo, W, etc.) powder and Si powder as raw materials. Based on the reaction of TM(s) + Si(s) → HE-MSi2(s), mechanical grinding and spark plasma sintering are used to induce in-situ synthesis of a uniformly distributed high-entropy silicide ceramic material. Temperature significantly influences the synthesis of non-isotropic high-entropy ceramic materials. The sintering temperature directly affects the diffusion rate and grain growth of the raw powders. Excessively low temperatures result in loose sintering and the failure to synthesize a single phase. Excessively high temperatures can cause melting and metal outflow. Failure to achieve the desired ball milling speed and time can also lead to inadequate mixing of the powders, resulting in uneven elemental distribution in the synthesized sample, impacting its performance.

[0013] 2. Non-isotropic high entropy ceramic material Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Structure and properties of Si2

[0014] The present invention synthesizes a new type of non-isotropic high entropy ceramic material with the molecular formula Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2, the crystal structure belongs to the hexagonal system, and the unit cell parameters are a = 4.66359(15) Å, c = 6.49215(22)Å. Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 The crystal structure diagram of Si2 is as follows Figure 1 shown.

[0015] Structural characterization

[0016] Figure 2 The XRD pattern of the non-isotropic high entropy ceramic material synthesized by the present invention is Figure 2 It can be seen that the prepared Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2 ceramics are pure hexagonal phase, without other impurity phases, and its refinement results confirm that its structure is reliable. R p = 5.63%, Rwp = 8.10 %.

[0017] Figure 3 The energy spectrum of the non-equivalent high entropy ceramic material synthesized by the present invention is Figure 3 It can be seen that the Mo synthesized by the method of the present invention 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 The proportion of Si2 ceramic elements is consistent with the proportion of raw materials.

[0018] Figure 4 This is the SEM image of the novel non-isotropic high entropy ceramic material synthesized by the present invention. Figure 5 The EDS spectrum element distribution diagram of the non-equivalent high entropy ceramic material synthesized by the present invention; Figure 4 The microscopic morphology shows that the Mo synthesized by the present invention 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2 ceramics are denser and have fewer defects; as shown in Figure 5, the Mo synthesized by the present invention 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 The six constituent elements of Si2 ceramics are evenly distributed.

[0019] Performance evaluation

[0020] 1. Density and mechanical properties

[0021] (1) The density and compactness of the material were measured using the Archimedes principle. The test results showed that the bulk density of the prepared bulk material was 5.6692 g / cm 3 The theoretical density is 6.147 g / cm 3 , its density reaches 92.2%.

[0022] (2) Using nanoindentation instrument to test Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Nanohardness of Si2 ceramics. Test conditions: 6 test points were randomly selected, load was 6 mN, and loading duration was 10 s;

[0023] The hardness of the material was tested using a Vickers microhardness tester. The test conditions were: load 200 gf, loading duration 10 s. The test results are shown in Table 1.

[0024] Table 1 Hardness of the high entropy ceramic material of the present invention at room temperature

[0025] 2. High temperature antioxidant performance

[0026] The high temperature oxidation resistance was evaluated by a synchronous thermal analyzer. The test conditions were air environment, the test temperature was room temperature ~ 1000 ℃, the heating rate was 10 ℃ / min, and the test time was 100 min. The experimental results showed that the prepared Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2 ceramics have excellent oxidation resistance at high temperatures, such as Figure 6 shown.

[0027] 3. Non-isotropic high entropy ceramic material Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Application of Si2

[0028] Mo synthesized by the present invention 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 The Vickers hardness of Si2 ceramics is higher than that of the commercial disilicides of various metal elements and the isotropic high entropy silicide ceramics (Mo 0.2 Ti 0.2 V 0.2 Nb 0.2 W 0.2 )Si2, the results are shown in Table 2. At the same time, due to Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2 ceramic materials have better antioxidant properties than MoSi2 in high-temperature environments, and are expected to be used as high-temperature thermal protection materials and high-temperature structural parts. They have great application potential in structural components serving in extreme working conditions of aerospace and marine engines.

[0029] Table 2 Vickers hardness of the high entropy ceramic materials of the present invention and the corresponding transition metal disilicides

[0030]

[0031] In summary, the initial materials used in the method of the present invention are relatively economical and cost-saving. The raw materials used are simple, available on the market, easy to obtain and cheap, and convenient for process implementation. Compared with commercial disilicide, the Mo prepared by the present invention is 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 The presence of five metallic elements in the unit cell of Si2 ceramic bulk material gives it a higher entropy value, resulting in superior mechanical properties. Furthermore, the method of the present invention offers advantages such as a simple preparation process, strong controllability, and ease of scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Mo prepared by the present invention 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Schematic diagram of the crystal structure of Si2 ceramics.

[0033] Figure 2 Mo prepared in the embodiment of the present invention 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 XRD pattern and Rietveld refinement results of Si2 ceramics.

[0034] Figure 3 Mo prepared in the embodiment of the present invention 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Energy spectrum of Si2 ceramics.

[0035] Figure 4 Mo prepared in the embodiment of the present invention 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 SEM image of Si2 ceramics.

[0036] Figure 5 Mo prepared in the embodiment of the present invention 0.4(Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 EDS spectrum element distribution diagram of Si2 ceramics.

[0037] Figure 6 Mo prepared in the embodiment of the present invention 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Thermogravimetric curve of Si2 ceramics. DETAILED DESCRIPTION

[0038] The present invention is described below by way of examples. 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 The synthesis method of Si2 ceramic bulk materials is described in detail. Example

[0039] 1) Mo powder, V powder, Nb powder, Ti powder, W powder, and Si powder were prepared in a ratio of 4.0:1.5:1.5:1.5:1.5:20, with a total weight of approximately 20 g. The raw materials were placed in a ball mill with a ratio of tungsten carbide grinding balls to mixed material of 5:1. 10% anhydrous ethanol was added as the milling medium, and the mill was placed in a planetary ball mill. The mixture was milled at 500 r / min under argon protection for 9 h to obtain a mixed powder.

[0040] (2) Place the mixed powder obtained in step (1) in a drying oven and dry at 60°C for 0.5 h. Sieve out the dried mixed powder using a 200-mesh sieve.

[0041] (3) The dry mixed powder obtained in step (2) is pressed into a shape to obtain a green body, and then spark plasma sintering is performed. Spark plasma sintering is performed in a vacuum, and the sintering furnace is evacuated for 10 minutes to make the vacuum reading value <10 0 Pa, then the furnace temperature was raised from room temperature to 1500℃ at a heating rate of 120℃ / min and kept at this temperature for 10 min; then the power was turned off and naturally cooled to room temperature to obtain Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2 ceramics. Structure and properties such as Figures 2 to 6 shown.

[0042] Prepared Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 The density of Si2 ceramics is 5.6692 g / cm 3 , the theoretical density is 6.147 g / cm 3 , density is 92.2%, nanohardness is 17.9±3.8 GPa, elastic modulus is 419.3±96.05 GPa, and Vickers hardness is 12.2±0.3 GPa.

Claims

1. A method for preparing a non-isotropic high entropy silicide ceramic material, characterized in that: The following steps are involved: 1) Mo powder, V powder, Nb powder, Ti powder, W powder, and Si powder were weighed in a molar ratio of 4.0:1.5:1.5:1.5:1.5:20, and anhydrous ethanol (5% to 10% by weight of the total weight of the mixed powder) was added as a ball milling medium. The mixed powder was ground under argon protection to obtain a mixed powder; 2) Place the mixed powder obtained in step 1) in a vacuum drying oven and dry at 60-80°C for 1-3 hours to obtain the desired target mixed powder; 3) The target mixed powder obtained in step 2) is pressed into a green body, and then the green body is subjected to spark plasma sintering. After sintering, it is cooled to obtain the target product Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2 bulk ceramics.

2. The method for preparing a non-isotropic high entropy silicide ceramic material according to claim 1, wherein: In step 1), the purity of the raw materials Ti powder, V powder, Nb powder, Mo powder, W powder and Si powder is ≥99%, and the particle size is 1-3 μm.

3. The method for preparing a non-isotropic high entropy silicide ceramic material according to claim 1, wherein: In step 1), the raw materials are placed in a ball mill jar and tungsten carbide grinding balls are added to grind the raw materials into a mixed powder. During grinding, the mass ratio of the grinding balls to the mixed materials is 5:1 to 20:

1. The rotation speed of the ball mill is 200 to 600 r / min. The ball milling time is 8 to 15 hours.

4. The method for preparing a non-isotropic high entropy silicide ceramic material according to claim 1, wherein: In step 3), the spark plasma sintering process is vacuumed with a pressure of 1.5~30 MPa and a vacuum degree of <10 0 Pa, the heating rate is 80~150℃ / min, the sintering temperature is 1500~1600℃, and the sintering time is 5min~30min.

5. A non-isotropic high entropy silicide ceramic material prepared by the method of claim 1, wherein the molecular formula is Mo 0.4 (Ti 0.25 V 0.25 Nb 0.25 W 0.25 ) 0.6 Si2, the crystal structure belongs to the hexagonal system, the unit cell parameters are a = 4.66359(15) Å, c =6.49215(22)Å.

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