Method for preparing high-entropy nitride ceramic with silicon carbide as sintering aid

Abstract

This invention discloses a method for preparing high-entropy nitride ceramics using silicon carbide as a sintering aid, comprising steps such as raw material preparation and treatment, powder synthesis, additive mixing and treatment, and ceramic sintering. This method uses HfO2, ZrO2, TiO2, Nb2O5, Ta2O5, and Si3N4 as raw materials, which are mechanically ball-milled for 5–10 hours, and then synthesized at 1800℃ to produce submicron-sized single-phase (HfO2) nitride ceramics. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 High-entropy powder (Hf) was then used as raw material, with SiC added as a sintering aid. The powder was sintered at 1900–2100 °C using SPS to prepare (Hf) powder with 5–15 mol% SiC. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 High-entropy ceramics. This invention relates to a method for preparing high-entropy nitride ceramics using silicon carbide as a sintering aid. By adding sintering aids and improving the preparation process of high-entropy nitride ceramics, the methods address the problems of difficult sintering and low density, while simultaneously improving the mechanical properties of the high-entropy nitride ceramics. The high-entropy ceramic with 10 mol% SiC added achieves a density of 98.32%, and its Vickers hardness, fracture toughness, and flexural strength are 23.34 ± 0.96 GPa, 3.84 ± 0.33 MPa·m, respectively. 1 / 2 And 409±41MPa.

Description

Technical Field

[0001] This invention relates to the field of ceramic production technology, specifically to a method for preparing high-entropy nitride ceramics using silicon carbide as a sintering aid. Background Technology

[0002] High-entropy ceramics typically refer to solid solutions formed by five or more ceramic components. Due to four major "high-entropy effects"—thermodynamic high-entropy effect, structural lattice distortion effect, kinetic hysteresis diffusion effect, and synergistic effect of the components—high-entropy ceramics exhibit superior properties and have become a research hotspot in the ceramics field in recent years. However, the preparation process of high-entropy ceramics still faces challenges such as difficulty in sintering and low density.

[0003] Sintering aids, also known as sintering promoters, are oxides or non-oxides added during the ceramic sintering process to promote densification. Their main functions are to form a solid solution with the sintered material, prevent crystal transformation, inhibit grain growth, and generate a liquid phase. During ceramic sintering, grain growth in the later stages plays a crucial role in densification. However, if secondary recrystallization or intermittent grain growth is too rapid, it can lead to coarser grains and wider grain boundaries, resulting in reverse densification and affecting the microstructure of the finished product. In such cases, adding sintering aids that inhibit abnormal grain growth can promote the densification process.

[0004] Therefore, it is necessary to improve the sintering aids and the preparation process of high-entropy nitride ceramics to address their difficulties in sintering and low density. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing high-entropy nitride ceramics with silicon carbide as a sintering aid. By adding sintering aids and improving the preparation process of high-entropy nitride ceramics, the method can improve the problems of difficult sintering and low density, while improving the microstructure of high-entropy nitride ceramics and improving their mechanical properties.

[0006] This invention provides a method for preparing high-entropy nitride ceramics using silicon carbide as a sintering aid, comprising the following steps:

[0007] (1) Raw material pretreatment: Weigh each component raw material according to the molar ratio HfO2:ZrO2:TiO2:Nb2O5:Ta2O5:Si3N4=2:2:2:1:1:10 and place them in a ball mill jar. Add grinding balls and an appropriate amount of anhydrous ethanol to make the solid content reach 65-75%. Then place the ball mill jar on a high-energy ball mill with a speed of 1200r / min and ball mill for 5-10h. After that, take out the slurry, separate the grinding balls and sieve to obtain the slurry. Place it in a constant temperature vacuum drying oven at 100℃ to dry. After drying, grind the powder with an agate mortar and pass it through a 60-mesh sieve. Then press it into block material using a hydraulic press.

[0008] (2) Powder synthesis: First, place a layer of graphite fiber felt at the bottom of the graphite crucible, then place graphite paper at the bottom and around the edges. Then, place the block material prepared in step (1) on the graphite paper. After placement, bend the surrounding strips of graphite paper downwards to support the layer of graphite fiber felt placed on top. Finally, place another piece of graphite paper and cover the crucible. Then, place the graphite crucible in a vacuum sintering furnace, protect it with Ar gas, heat it to 1800℃ at a rate of 10℃ / min, and hold it for 1 hour. After the furnace body cools naturally, grind the powder in an agate mortar and pass it through a 100-mesh sieve to obtain (Hf 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 High-entropy nitride powder;

[0009] (3) Additive mixing treatment: Weigh the high entropy nitride powder prepared in step (2), add 5-15 mol% SiC and place it in a polyurethane planetary ball mill jar. Add grinding balls and an appropriate amount of anhydrous ethanol and place it on a planetary ball mill with a speed of 400 r / min. Ball mill and mix for 10 h. Then take out the slurry, separate the grinding balls and sieve to obtain the slurry. Place it in a constant temperature vacuum drying oven at 100℃ to dry. After drying, grind the powder with an agate mortar and pass it through a 100-mesh sieve to obtain the mixed powder.

[0010] (4) Ceramic sintering: The mixed powder prepared in step (3) is placed in a graphite mold, and two rings of heat-insulating graphite fiber felt are wrapped around and on top. Then the mold is placed in a sintering furnace and a pressure of 10 MPa is applied. The powder becomes compacted under the action of the upper pressure head. Then the furnace door is closed, a vacuum is drawn, and the temperature is raised for sintering. The heated sintering includes three stages:

[0011] In the first stage, the temperature was increased from room temperature to 650℃ at a rate of 80℃ / min, while the pressure increased from 10MPa to 30MPa.

[0012] In the second stage, the temperature was increased from 650℃ to 1600℃ at a rate of 68℃ / min.

[0013] In the third stage, the temperature was increased to the sintering temperature of 1900-2100℃ at a rate of 37.5℃ / min, and the pressure was increased from 30MPa to 40MPa, and the temperature and pressure were kept stable for 8min.

[0014] In the fourth stage, the power output is cooled to 1500℃;

[0015] After sintering, the ceramic rough product is obtained by natural cooling in the furnace. The surface of the ceramic rough product is polished to remove the graphite paper on the surface. Then, a thickness of 0.5±0.1mm is removed by grinding to eliminate the influence of carbon in the graphite paper and graphite mold on the composition and properties of the block sample. Subsequently, the polished sample is cut and polished to obtain the ceramic product.

[0016] The pre-selected sintering temperature in step (4) is 2100°C.

[0017] Preferably, in steps (1) and (3), the grinding balls are ZrO2 balls with a diameter of 1-2 mm; the mass ratio of the grinding balls to the total amount of raw materials is 4:1; and the purity of the anhydrous ethanol is 99.9%.

[0018] Preferably, the block material mentioned in step (1) is a cylindrical block with a diameter of 2cm and a weight of 3-5g.

[0019] Preferably, the thickness of the graphite fiber felt in step (2) is 1 to 2 cm.

[0020] Preferably, the rate of power cooling in step (4) is 5 to 15 °C / min.

[0021] The working principle of this invention: The method for preparing high-entropy nitride ceramics with silicon carbide as a sintering aid of this invention uses metal oxides HfO2, ZrO2, TiO2, Nb2O5, Ta2O5 and Si3N4 as raw materials. After mechanical ball milling for 5-10 hours, submicron-sized single-phase (HfO2, ZrO2, TiO2, Nb2O5, Ta2O5 and Si3N4) are synthesized at 1800℃. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 High-entropy powder (Hf) was then used as raw material, with SiC added as a sintering aid. The powder was sintered at 1900–2100 °C using spark plasma sintering (SPS) at 1900–2100 °C to prepare (Hf) powder with 5–15 mol% SiC. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 In high-entropy ceramics, as the SiC addition amount increases within 10 mol%, the introduction of SiC particles suppresses (Hf) growth. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The grain coarsening and intracrystalline porosity formation of the high-entropy nitride phase increase the density of the high-entropy ceramic. After maintaining a stable temperature and pressure for 8 minutes at the sintering temperature, a cooling program with power was initiated to lower the temperature to 1500℃ to prevent cracking after sintering.

[0022] The beneficial effects of this invention: The preparation method of high-entropy nitride ceramics using silicon carbide as a sintering aid, by adding a sintering aid and improving the preparation process of high-entropy nitride ceramics, addresses the problems of difficult sintering and low density, while simultaneously improving the mechanical properties of high-entropy nitride ceramics. The addition of 10 mol% SiC (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The density of the N high-entropy ceramic reached 98.32%, and its Vickers hardness, fracture toughness, and flexural strength were 23.34±0.96 GPa, 3.84±0.33 MPa·m, respectively. 1 / 2 And 409±41MPa. Attached Figure Description

[0023] Figure 1 The sintering curves for high-entropy ceramics are: (a) 0S-2100, (b) 10S-2100.

[0024] Figure 2 To determine the density of high-entropy ceramics with different SiC contents;

[0025] Figure 3 (a) XRD pattern of high-entropy ceramics; (b) Grain size variation of high-entropy ceramics.

[0026] Figure 4 The surface morphologies of high-entropy ceramics are: (a) 0S-2100, (b) 2.5S-2100, (c) 5S-2100, (d) 7.5S-2100, (e) 10S-2100, (f) 12.5S-2100, (g) 15S-2100, (h) 20S-2100;

[0027] Figure 5 Fracture morphologies of high-entropy ceramics: (a) 0S-2100, (b) 2.5S-2100, (c) 5S-2100, (d) 7.5S-2100, (e) 10S-2100, (f) 12.5S-2100, (g) 15S-2100, (h) 20S-2100;

[0028] Figure 6 SEM images and corresponding EDS spectra of high-entropy ceramics with different SiC contents sintered at 2100℃: (a) 0S-2100 (b) 10S-2100;

[0029] Figure 7 The sintering curves for high-entropy ceramics are: (a) 10S-1900, (b) 10S-2000, and (c) 10S-2100.

[0030] Figure 8 Density of high-entropy ceramics at different sintering temperatures;

[0031] Figure 9 (a) XRD patterns and (b) grain size variation diagrams of high-entropy ceramics sintered at different temperatures;

[0032] Figure 10 The surface morphology of high-entropy ceramics is (a) 10S-1900, (b) 10S-2000, and (c) 10S-2100.

[0033] Figure 11 Fracture morphology of high-entropy ceramics: (a) 10S-1900, (b) 10S-2000, (c) 10S-2100;

[0034] Figure 12 SEM images and corresponding EDS spectra of high-entropy ceramics with 10 mol% SiC sintered at different temperatures: (a) 10S-1900, (b) 10S-2000, (c) 10S-2100.

[0035] Figure 13 TEM images of 10S-2100: (a) TEMBF image, (b) SAD of dark particles (high-entropy nitride particles) in (a), (c) SAD of bright particles (SiC particles) in (a), (d) HR-TEM image of the interface between high-entropy nitride and SiC grains.

[0036] Figure 14 EDS analysis of 10S-2100: (a) TEMEDS plot, (b) EDS spectrum of SiC grains, (c) EDS spectrum of high-entropy nitride grains.

[0037] Figure 15 This is a schematic diagram of the indentation.

[0038] Figure 16 This is a schematic diagram of three-point bending resistance. Detailed Implementation

[0039] To make the technical solution of the present invention easier to understand, the technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings and specific embodiments. I. Specific Implementation Methods

[0041] The method for preparing high-entropy nitride ceramics with silicon carbide as a sintering aid of the present invention includes the following steps:

[0042] (1) Raw material pretreatment: Weigh each component raw material according to the molar ratio HfO2:ZrO2:TiO2:Nb2O5:Ta2O5:Si3N4=2:2:2:1:1:10 and place them in a ball mill jar. Add ZrO2 grinding balls with a diameter of 2mm and an appropriate amount of anhydrous ethanol with a purity of 99.9% according to the ball-to-material ratio of 4:1 to make the solid content reach 70%. Then place the ball mill jar on a high-energy ball mill with a speed of 1200r / min and ball mill for 10h. After that, take out the slurry, separate the grinding balls and sieve to obtain the slurry. Place it in a constant temperature vacuum drying oven at 100℃ to dry. After drying, grind the powder with an agate mortar and pass it through a 60-mesh sieve. Then use a hydraulic press to press it into cylindrical blocks with a diameter of 2cm and a weight of 3g.

[0043] (2) Powder synthesis: First, place a layer of graphite fiber felt with a thickness of 2cm at the bottom of the graphite crucible, then place graphite paper at the bottom and around the sides, and then place the block material prepared in step (1) on the graphite paper. After placing it, bend the strip graphite paper around the sides downward to support the layer of graphite fiber felt placed on top. Finally, place another piece of graphite paper and cover it with a lid. Then, put the graphite crucible into a vacuum sintering furnace, protect it with Ar gas, heat it to 1800℃ at a rate of 10℃ / min and hold it for 1 hour. After the furnace body cools down naturally, grind the powder in an agate mortar and pass it through a 100-mesh sieve to obtain high-entropy nitride powder.

[0044] (3) Additive mixing treatment: Weigh the high entropy nitride powder prepared in step (2), add 0 mol% SiC and place it in a polyurethane planetary ball mill jar. Add ZrO2 grinding balls with a diameter of 2 mm and an appropriate amount of anhydrous ethanol with a purity of 99.9% according to the ball-to-material ratio of 4:1. Then place it on a planetary ball mill with a speed of 400 r / min and ball mill for 10 h. Then take out the slurry, separate the ball milling balls and sieve to obtain the slurry. Place it in a constant temperature vacuum drying oven at 100℃ to dry. After drying, grind the powder with an agate mortar and pass it through a 100-mesh sieve to obtain the mixed powder.

[0045] (4) Ceramic sintering: The mixed powder prepared in step (3) is placed in a graphite mold, and two rings of heat-insulating graphite fiber felt are wrapped around and on top. Then the mold is placed in a sintering furnace and a pressure of 10 MPa is applied. The powder becomes compacted under the action of the upper pressure head. Then the furnace door is closed, a vacuum is drawn, and the temperature is raised for sintering. The heated sintering includes three stages:

[0046] In the first stage, the temperature was increased from room temperature to 650℃ at a rate of 80℃ / min, while the pressure increased from 10MPa to 30MPa.

[0047] In the second stage, the temperature was increased from 650℃ to 1600℃ at a rate of 68℃ / min.

[0048] In the third stage, the temperature was increased to the sintering temperature of 2100℃ at a rate of 37.5℃ / min, the pressure was increased from 30MPa to 40MPa, and the temperature and pressure were kept stable for 8min.

[0049] In the fourth stage, the temperature is reduced to 1500℃ at a rate of 10℃ / min with power.

[0050] After sintering, the ceramic rough product is obtained by natural cooling in the furnace. The surface of the ceramic rough product is polished to remove the graphite paper on the surface. Then, a 0.5mm thickness is removed by grinding to eliminate the influence of carbon in the graphite paper and graphite mold on the composition and properties of the block sample. Subsequently, the polished sample is cut and polished to obtain the ceramic product.

[0051] Example 1:

[0052] In this embodiment: the amount of SiC added in step (3) is 0 mol%, the sintering temperature of the third stage in step (4) is 2100℃, and the ceramic sample prepared is numbered 0S-2100.

[0053] Example 2:

[0054] In this embodiment: the amount of SiC added in step (3) is 2.5 mol%, the sintering temperature in the third stage in step (4) is 2100℃, and the ceramic sample prepared is numbered 2.5S-2100.

[0055] Example 3:

[0056] In this embodiment: the amount of SiC added in step (3) is 5 mol%, the sintering temperature of the third stage in step (4) is 2100℃, and the ceramic sample prepared is numbered 5S-2100.

[0057] Example 4:

[0058] In this embodiment: the amount of SiC added in step (3) is 7.5 mol%, the sintering temperature of the third stage in step (4) is 2100℃, and the ceramic sample prepared is numbered 7.5S-2100.

[0059] Example 5:

[0060] In this embodiment: the SiC addition amount in step (3) is 10 mol%, the sintering temperature in the third stage in step (4) is 2100℃, and the ceramic sample prepared is numbered 10S-2100.

[0061] Example 6:

[0062] In this embodiment: the amount of SiC added in step (3) is 12.5 mol%, the sintering temperature of the third stage in step (4) is 2100℃, and the ceramic sample prepared is numbered 12.5S-2100.

[0063] Example 7:

[0064] In this embodiment: the amount of SiC added in step (3) is 15 mol%, the sintering temperature in the third stage in step (4) is 2100℃, and the ceramic sample prepared is numbered 15S-2100.

[0065] Example 8:

[0066] In this embodiment: the amount of SiC added in step (3) is 20 mol%, the sintering temperature in the third stage in step (4) is 2100℃, and the ceramic sample prepared is numbered 20S-2100.

[0067] Example 9:

[0068] In this embodiment: the amount of SiC added in step (3) is 10 mol%, the sintering temperature of the third stage in step (4) is 1900℃, and the ceramic sample prepared is numbered 10S-1900.

[0069] Example 10:

[0070] In this embodiment: the amount of SiC added in step (3) is 20 mol%, the sintering temperature of the third stage in step (4) is 2000℃, and the ceramic sample prepared is numbered 10S-2000.

[0071] II. Characterization Methods

[0072] 1. Sample processing

[0073] Before polishing, the sample needs to be fixed on the polishing device to ensure stability. First, select a flat surface and apply 40μm diamond polishing paste to the polishing cloth. Then, gently scrape the sample across the polishing cloth, maintaining uniform pressure and direction, until the surface roughness is reduced and becomes smooth. Next, repeat the above steps using 28μm diamond polishing paste for a second polishing treatment. This step further reduces surface roughness. Finally, perform a third polishing treatment using 10μm diamond polishing paste until the sample surface is smooth and even.

[0074] Finally, spray 1μm diamond polishing agent onto the polishing cloth, then place the sample on it and rotate it with appropriate pressure and direction until the sample surface is completely scratch-free and smooth. After polishing, the sample can be tested for hardness and microstructure observation.

[0075] 2. Characterization of phase and microstructure

[0076] In this experiment, XRD diffractometer was used to perform phase analysis on raw material powder, ball-milled mixed powder, and high-entropy nitride ceramics sintered at different temperatures. The XRD analysis test conditions were Cu-Kα radiation, accelerating voltage of 40 kV, current of 100 mA, scanning range of 10°–80°, and scanning rate of 4° / min. Substituting the XRD data into the Bragg equation and the interplanar spacing formula for cubic structures, the lattice constant α of the high-entropy nitride can be calculated, as shown in equations (2-1) and (2-2).

[0077] nλ=2dsinθ (2-1)

[0078]

[0079] According to formulas (2-1) and (2-2), five lattice parameters can be obtained. Next, the least squares method is used to optimize these five lattice parameters. The least squares method is a common optimization algorithm used to fit data and reduce errors. In this case, the actual measured values ​​of the five lattice parameters are compared with the values ​​calculated using the formulas, and the result with the smallest error is selected as the final lattice constant value. The final lattice constant value is the result obtained through the least squares method. This reduces errors and improves the accuracy of the lattice parameters.

[0080] The microstructure of powder and ceramic samples was analyzed using field emission scanning electron microscopy (FE-SEM). For powder samples, a loading voltage of 5 kV was used, while for bulk ceramic samples, a loading voltage of 15 kV was used. The fracture morphology and crack propagation paths of the ceramics were observed using FE-SEM to understand their fracture behavior and mechanical properties.

[0081] Transmission electron microscopy (TEM) was used to analyze the diffraction spots of the powder samples to further confirm the phase composition of individual powder particles. By analyzing the diffraction spots, the lattice parameters of the corresponding crystal planes can be determined, and formulas for calculating the interplanar spacing and interplanar angles can be used to obtain the crystal structure information of the powder.

[0082] In addition, energy dispersive spectroscopy (EDS) is used to perform point or area analysis on powder and ceramic samples to obtain the distribution of elements in the samples. EDS analysis can determine the content and distribution of each element in the sample, further elucidating the chemical composition of the sample.

[0083] 3. Grain size statistics and analysis

[0084] Particle size analysis of the raw material powder was performed using a laser particle size analyzer and the NanoMeasurer software, respectively. For particle size analysis, a laser particle size analyzer with a general refractive index range of 1.2–1.8 was selected. First, the sample and an appropriate amount of dispersant were added to an ultrasonically stabilized container. Under ultrasonically stable conditions, particle size analysis was then conducted. An appropriate concentration range was selected based on the test concentration, generally between 10% and 14%. The particle size distribution was obtained by measuring the intensity distribution of scattered light from the sample using a laser particle size analyzer.

[0085] For observing the grain size of synthesized powder particles, scanning electron microscopy (SEM) can be used. SEM samples of the synthesized powder and high-entropy ceramic samples are prepared and observed at magnifications of 5000x or 10000x. The grain size of the powder particles can be statistically analyzed using NanoMeasurer software. Generally, 150 samples are selected for statistical analysis to obtain more accurate results.

[0086] 4. Density test

[0087] After polishing, the sample is first ultrasonically cleaned in anhydrous ethanol for 15 minutes to remove surface impurities and dirt. After cleaning, the sample is removed and air-dried in a dust-free environment to ensure no residual solvent remains. Then, the sample is placed in a constant temperature drying oven and dried at 100℃ for 12 hours to completely remove moisture. The mass of the dried sample is recorded as dry weight m1. After heating the sample in distilled water, wait until the water boils for 30 minutes before removing the sample. Then, gently wipe the sample surface with a damp paper towel to remove any residue that may be adhering to the sample surface. This step aims to ensure the sample surface is clean to reduce interference with the bulk density test. Wiping the sample surface removes any impurities and water droplets, leaving the sample surface clean. After wiping, the subsequent bulk density test can be performed, and the measured mass is recorded as wet weight m2. Then, the sample is placed in distilled water, and the buoyant weight is measured and recorded as m3. The formula for calculating bulk density (ρb) is shown in equation (2-3).

[0088]

[0089] In the formula, p b —Sample bulk density (g / cm³) 3 )

[0090] m1 — Mass of the sample after drying (g)

[0091] m2 — Mass of the sample after water absorption (g)

[0092] m3 — Mass of the sample in water (g)

[0093] p0 — Density of distilled water (g / cm³) 3 )

[0094] The lattice constant α is obtained from XRD data, and the cell volume V of the cubic structure can be obtained. From this, the theoretical density (ρt) of the high-entropy ceramic can be calculated, and the sample packing density can be further obtained. The calculation formulas are shown in equations (2-4) and (2-5).

[0095] V = a³ (2-4)

[0096]

[0097] In the formula, V represents the unit cell volume (nm³).

[0098] a — lattice constant (nm)

[0099] W – Sample density (%)

[0100] Z – Number of molecules in a single unit cell

[0101] M—Molecular molar mass

[0102] NA – Avogadro's constant

[0103] Where ρw is the density of the liquid in the test, in g / m³. 3 Z is the number of molecules in a single unit cell, M is the relative molecular molar mass, and NA is Avogadro's constant, which is 6.02 × 10⁻⁶. 23 The density (ρr) is calculated from the bulk density and theoretical density, as shown in equation (2-6).

[0104]

[0105] In the formula, P b —Sample bulk density (g / cm³) 3 )

[0106] P t —Theoretical density of the sample (g / cm³) 3 )

[0107] 5. Ceramic mechanical property testing

[0108] (1) Hardness and fracture toughness

[0109] The samples were hardness tested using a Vickers hardness tester. The test load was 10 kgf (98 N). Each sample was tested three times, with 10 points randomly selected for each sample. The average and standard deviation were recorded. Simultaneously, after polishing, the samples were ultrasonically cleaned with alcohol for 15 minutes and then dried. During the testing process, the fracture toughness (KIC) of the ceramic could be calculated using Evans's equation based on the obtained hardness value and the above parameters. The formula for calculating fracture toughness is shown in (2-7).

[0110]

[0111] Where P is the load (N), C1 and C2 are the crack diagonal lengths (m), and β equals 68°, which is half the indenter angle. Figure 15 As shown.

[0112] (2) Bending strength

[0113] The coarsely ground ceramic block was cut into strips measuring 3mm x 4mm x 20mm. The surface of each strip was polished and chamfered, using fine sandpaper. Next, the bending strength was tested using a three-point bending method with a span of 16mm. Five tests were performed on each sample, and the average and standard deviation were recorded. The formula for calculating the bending strength (σf) is shown in (2-8).

[0114]

[0115] Where P is the load, L is the span, and b and h are the width (mm) and height (mm) of the specimen, respectively. Figure 16 As shown.

[0116] III. Results Analysis

[0117] (a) SiC addition amount versus (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The Influence of High-Entropy Ceramics

[0118] 1. Effect on the density of high-entropy ceramics

[0119] Figure 1 (a) and (b) are the curves showing the change of pressure head displacement and displacement rate with time (temperature) at a sintering temperature of 2100℃ in Examples 1 and 5, respectively. Figure 1 (a) No SiC added Figure 1 (b) The SiC addition amount is 10 mol%. Figure 1As shown in (a) and (b), in the initial stage of sintering, the pressure head drops by about 0.3 mm. From 1600 to 2100℃, the pressure head descent rate increases significantly during this stage, and the green body undergoes greater shrinkage deformation. Holding at 2100℃ for 8 minutes, the grains gradually grow, and the densification rate slows down. At this point, the pressure head displacement and displacement change rate remain essentially constant. The results show that the ceramic without SiC exhibits only a 2.1 mm pressure head displacement during sintering, while with the addition of 10 mol% SiC, the pressure head displacement reaches 3.6 mm, and the displacement change rate also increases significantly. The increased pressure head displacement indicates that (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 As the shrinkage of N ceramics increases, the ceramics become more compact.

[0120] Figure 2 For different SiC addition amounts (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The density curve of high-entropy ceramics is derived from... Figure 2 It can be seen that as the SiC addition amount varies from 0 to 20 mol%, the density of high-entropy ceramics first increases and then decreases. When the SiC addition amount increases to 10 mol%, the density reaches a maximum of 98.32%. When 20 mol% SiC is added, the resulting (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The density of the N high-entropy ceramic is only 91.70%, which is lower than the original sample's 93.08%.

[0121] 2. Effects on the microstructure of high-entropy ceramics

[0122] Figure 3 (a) is (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 XRD pattern of N high-entropy ceramic sintered body. From Figure 3 In (a), five diffraction peaks can be observed in the 2θ = 30-80° region, corresponding to the diffraction planes (111), (200), (220), (311), and (222) of the cubic phase unit cell, respectively. The sample sintered at 2100℃ exhibits a single-phase face-centered cubic structure, resulting in a single-phase high-entropy nitride. From... Figure 3 As shown in (b), increasing the amount of SiC leads to (Hf) 0.2 Zr0.2 Ti 0.2 Nb 0.2 Ta 0.2 The reduction in particle size in high-entropy ceramics is specifically manifested in a decrease in average grain size, because the addition of SiC inhibits excessive grain growth.

[0123] Figure 4 (a)~(h) and Figure 5 (a) to (h) represent the addition of 0-20 mol% SiC during sintering at 2100°C in Examples 1 to 8, respectively. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 Surface and fracture morphology of high-entropy ceramics. Figure 4 As shown in (a) to (h), the pores in sample 0S are mainly located between grain boundaries, while there are almost no pores inside the grains. With increasing SiC addition, the pores between grain boundaries are gradually expelled, and SiC begins to fill the pores at grain boundaries and some inside grains. When the SiC addition is 10 mol%, the sample density is the highest, reaching 98.32%, with the fewest pores at grain boundaries and inside grains. However, when the SiC addition increases to 20 mol%, the sample density decreases to 91.70%. The fracture surface diagram shows that the sample with 20 mol% SiC has the smallest grain size, possibly due to excessive SiC addition preventing uniform dispersion. Furthermore, the fracture mode is mainly intergranular fracture, with less transgranular fracture.

[0124] Figure 6 (a) and (b) show the surface scan and energy dispersive spectroscopy (EDS) analyses of the 0S and 10S samples sintered at 2100℃ in Examples 1 and 5, respectively. Figure 6 It can be seen that in the preparation of (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 In N high-entropy ceramics, the elemental distribution is relatively uniform. In particular, after adding 10 mol% SiC, the SiC grains are uniformly distributed among the high-entropy grains, forming a composite structure with the matrix material and improving the mechanical properties of the material.

[0125] 3. Effects on the mechanical properties of high-entropy ceramics

[0126] (Hf) with different SiC additive contents 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2The Vickers hardness, fracture toughness, and partial flexural strength of the SiC high-entropy ceramics are shown in Table 3-1. With increasing SiC content, the Vickers hardness gradually increases, from 19.16 GPa without SiC to 23.34 GPa with 10 mol% SiC. The effect of SiC addition on fracture toughness is not significant, remaining generally stable between 4.2 and 4.35 MPa·m. 1 / 2 Between. The flexural strength gradually increases with the increase of SiC content, reaching a maximum of 409 MPa.

[0127] Table 1 Mechanical properties of high-entropy ceramics with different SiC additions sintered at 2100℃

[0128]

[0129] (II) The effect of sintering temperature on the addition of SiC (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The Influence of High-Entropy Ceramics

[0130] 1. Effect on the density of high-entropy ceramics

[0131] Figure 7 The curves showing the changes in pressure head descent displacement and descent rate with sintering temperature during the sintering processes of (a)-(c) 10S-1900, 10S-2000 and 10S-2100 are shown. Figure 7 (a) is the sintering curve at 1900℃. The pressure head starts to decrease at 1300℃ and the displacement is 2mm at 1900℃. Figure 7 (b) shows the sintering curve at 2000℃. The indenter displacement of the sample remained essentially constant for the first 17 minutes. As the temperature increased to 1300℃, the indenter displacement began to increase significantly, reaching a maximum value of 2.6 mm at 32 minutes. During the later holding period, the indenter displacement and rate of change remained relatively stable. The total indenter displacement at 1900℃ and 2000℃ was approximately 3.6 mm and 3.8 mm, respectively. Figure 7 (c) The total indenter displacement at a sintering temperature of 2100℃ is approximately 6.0 mm. This indicates that the density of the sample is significantly improved at a sintering temperature of 2100℃. The sintering curves show a significant increase in the density of 10S-2100. Increasing the sintering temperature can effectively improve the (Hf) content of the SiC-added sample. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 Density of N high-entropy ceramics.

[0132] Figure 8To add 10 mol% SiC (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The density of high-entropy N-type ceramics at different sintering temperatures (1900–2100℃) was measured. The density of 10S-1900 was 91.09%, and that of 10S-2000 was 94.74%. It can be seen that as the sintering temperature increases, the density of (Hf) increases. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The density of N high-entropy ceramics is significantly improved, with the highest density of 98.32% at a sintering temperature of 2100℃.

[0133] 2. Influence on the phases and morphology of high-entropy ceramics

[0134] Figure 9 (a) and (b) are Hf samples sintered at 1900–2100 °C with 10 mol% SiC added. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 XRD pattern and grain size variation diagram of N high-entropy ceramic sintered body. Figure 9 (a) It can be seen that small impurity peaks still exist at 1900-2000℃, and XRD at 2100℃ shows a single-phase face-centered cubic structure, indicating the formation of a single-phase high-entropy nitride. With further increases in sintering temperature, (Hf...) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The density of high-entropy N ceramics tends to increase, and combined with XRD patterns, it can be observed that (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The optimal sintering temperature for high-entropy N-type ceramics can be considered to be around 2100℃. As shown in 3.9(b), with increasing temperature, when the SiC addition is 10 mol%, (Hf... 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The grain size of N high-entropy ceramics has also increased.

[0135] (Hf) with 10 mol% SiC added and sintered at 1900–2100℃ 0.2 Zr0.2 Ti 0.2 Nb 0.2 Ta 0.2 The surface and fracture morphology of high-entropy ceramics are as follows: Figure 10 and Figure 11 As shown. The SiC addition amount is 10 mol% (Hf) 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The grain size of high-entropy ceramics increases, and so does their density. Figure 3-11 The fracture morphology shows that the main fracture mode is transgranular fracture.

[0136] Figure 12 (a) to (c) show the EDS energy dispersive spectroscopy analysis of 10S samples sintered at 1900–2100 °C. Figure 12 It can be observed that at 1900℃, the distribution of SiC particles is uneven, and agglomeration occurs after sintering. However, at 2000℃ and 2100℃, the distribution of SiC gradually becomes more uniform, and the agglomeration decreases. This may be because at higher temperatures, the movement and diffusion rates of SiC particles increase, gradually reaching the sintering temperature of the SiC sintering aid, allowing it to be better and more uniformly distributed in the matrix, thus promoting matrix densification.

[0137] Figure 13 Images (a) to (d) are transmission electron micrographs of sample 10S-2100. Due to the weak electron scattering of light elements, [the following text appears to be incomplete and requires further context: "by..."] Figure 13 (a) It can be seen that the high-entropy nitride grains under dark contrast and the SiC grains under bright contrast are observed in the bright-field (BF) image. Selected-region diffraction (SAD) modes of the high-entropy nitride and SiC grains indicate that the high-entropy nitride has a face-centered cubic (fcc) structure, while SiC has a hexagonal structure, such as... Figure 13 As shown in (b) and (c). From Figure 13 (d) The HRTEM image of the sample shows that the interface between the high-entropy nitride and the SiC grains is very clear, and there is no transition layer between the two phases, indicating that SiC and the high-entropy phase are not dissolved and no new phase is formed.

[0138] Figure 14 (a) to (d) show the EDS analysis of sample 10S-2100, from... Figure 14 High-angle annular dark-field (HAADF) images show that the high-entropy nitride phase exhibits a bright contrast, while the SiC phase shows a dark contrast, due to the strong inelastic electron scattering from heavy elements. EDS analysis results for SiC grains and high-entropy nitride grains are shown below. Figure 14 As shown in (b) and (c), it can be clearly seen that no solid solution is formed between the high-entropy nitride and the SiC phase.

[0139] 3. Effects on the mechanical properties of high-entropy ceramics

[0140] Adding 10 mol% SiC to (Hf) at different SPS sintering temperatures 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The Vickers hardness, fracture toughness, and flexural strength of high-entropy ceramics are shown in Table 3-3. With increasing sintering temperature, Vickers hardness, flexural strength, and fracture toughness all show an increasing trend. At 1900℃, due to the relatively low temperature, maximum densification of the ceramic was not achieved, resulting in numerous intragranular and intergranular pores, and consequently, lower hardness, flexural strength, and fracture toughness. As the sintering temperature increased to 2100℃, grains gradually grew and grain boundaries migrated, significantly reducing intragranular and intergranular pores. Furthermore, the 10 mol% SiC sintering aid was uniformly dispersed in the high-entropy matrix, creating crack deflection or bridging conditions, thus improving strength and fracture toughness.

[0141] Table 2 (Hf) at different sintering temperatures 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 Mechanical properties of high-entropy ceramics

[0142]

[0143] (III) Conclusion Analysis:

[0144] In the examples, Hf was prepared by spark plasma sintering at different sintering temperatures of 1900–2100 °C and at different SiC addition amounts at 2100 °C. 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 High-entropy ceramics were prepared, and their microstructure and mechanical properties were characterized. The following conclusions were drawn: when the sintering temperature was 2100℃ and the SiC addition was 10 mol%, the density of the prepared high-entropy ceramic sample reached 98.32%, and the Vickers hardness, fracture toughness, and flexural strength were 23.34±0.96 GPa, 3.84±0.33 MPa·m, respectively. 1 / 2 The mechanical properties were 409±41 MPa, which was significantly improved compared to the sample sintered at 2100℃ without the addition of SiC sintering aid.

[0145] It should be noted that the embodiments described herein are only some embodiments of the present invention, and not all implementations of the present invention. These embodiments are merely illustrative and are intended only to provide a more intuitive and clear way to understand the content of the present invention, not to limit the technical solutions described herein. All other implementation methods that can be conceived by those skilled in the art without creative effort, as well as other simple substitutions and variations of the technical solutions of the present invention, without departing from the concept of the present invention, are within the protection scope of the present invention.

Claims

1. A method for preparing high-entropy nitride ceramics using silicon carbide as a sintering aid, characterized in that, Includes the following steps: (1) Raw material pretreatment: Weigh each component raw material according to the molar ratio HfO2:ZrO2:TiO2:Nb2O5:Ta2O5:Si3N4=2:2:2:1:1:10 and place them in a ball mill jar. Add grinding balls and an appropriate amount of anhydrous ethanol to make the solid content reach 65-75%. Then place the ball mill jar on a high-energy ball mill with a speed of 1200r / min and ball mill for 5-10h. After that, take out the slurry, separate the grinding balls and sieve to obtain the slurry. Place it in a constant temperature vacuum drying oven at 100℃ to dry. After drying, grind the powder with an agate mortar and pass it through a 60-mesh sieve. Then press it into block material using a hydraulic press. (2) Powder synthesis: First, place a layer of graphite fiber felt at the bottom of the graphite crucible, then place graphite paper at the bottom and around the edges. Then, place the block material prepared in step (1) on the graphite paper. After placement, bend the surrounding strips of graphite paper downwards to support the layer of graphite fiber felt placed on top. Finally, place another piece of graphite paper and cover the crucible. Then, place the graphite crucible in a vacuum sintering furnace, protect it with Ar gas, heat it to 1800℃ at a rate of 10℃ / min, and hold it for 1 hour. After the furnace body cools naturally, grind the powder in an agate mortar and pass it through a 100-mesh sieve to obtain (Hf 0.2 Zr 0.2 Ti 0.2 Nb 0.2 Ta 0.2 High-entropy nitride powder; (3) Additive mixing treatment: Weigh the high entropy nitride powder prepared in step (2), add 5-15 mol% SiC and place it in a polyurethane planetary ball mill jar. Add grinding balls and an appropriate amount of anhydrous ethanol and place it on a planetary ball mill with a speed of 400 r / min. Ball mill and mix for 10 h. Then take out the slurry, separate the grinding balls and sieve to obtain the slurry. Place it in a constant temperature vacuum drying oven at 100℃ to dry. After drying, grind the powder with an agate mortar and pass it through a 100-mesh sieve to obtain the mixed powder. (4) Ceramic sintering: The mixed powder prepared in step (3) is placed in a graphite mold, and two rings of heat-insulating graphite fiber felt are wrapped around and on top. Then the mold is placed in a sintering furnace and a pressure of 10 MPa is applied. The powder becomes compacted under the action of the upper pressure head. Then the furnace door is closed, a vacuum is drawn, and the temperature is raised for sintering. The heated sintering includes three stages: In the first stage, the temperature was increased from room temperature to 650℃ at a rate of 80℃ / min, while the pressure increased from 10MPa to 30MPa. In the second stage, the temperature was increased from 650℃ to 1600℃ at a rate of 68℃ / min. In the third stage, the temperature was increased to the sintering temperature of 1900-2100℃ at a rate of 37.5℃ / min, and the pressure was increased from 30MPa to 40MPa, and the temperature and pressure were kept stable for 8min. In the fourth stage, the power output is reduced to 1500℃; After sintering, the ceramic rough product is obtained by natural cooling in the furnace. The surface of the ceramic rough product is polished to remove the graphite paper on the surface. Then, a thickness of 0.5±0.1mm is removed by grinding to eliminate the influence of carbon in the graphite paper and graphite mold on the composition and properties of the block sample. Subsequently, the polished sample is cut and polished to obtain the ceramic product.

2. The method for preparing high-entropy nitride ceramics with silicon carbide as a sintering aid as described in claim 1, characterized in that, The sintering temperature in step (4) is 2100℃.

3. The method for preparing high-entropy nitride ceramics with silicon carbide as a sintering aid as described in claim 1, characterized in that, In steps (1) and (3), the grinding balls are ZrO2 balls with a diameter of 1-2 mm; the mass ratio of the grinding balls to the total amount of raw materials is 4:1; and the purity of the anhydrous ethanol is 99.9%.

4. The method for preparing high-entropy nitride ceramics with silicon carbide as a sintering aid as described in claim 1, characterized in that, The block material mentioned in step (1) is a cylindrical block with a diameter of 2cm and a weight of 3-5g.

5. The method for preparing high-entropy nitride ceramics with silicon carbide as a sintering aid as described in claim 1, characterized in that, The thickness of the graphite fiber felt in step (2) is 1 to 2 cm.

6. The method for preparing high-entropy nitride ceramics with silicon carbide as a sintering aid as described in claim 1, characterized in that, The rate of power-driven cooling in step (4) is 5 to 15 °C / min.

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