Anti-oxidation high-entropy diboride ceramic material with double protective layers and preparation method of anti-oxidation high-entropy diboride ceramic material

Abstract

The invention relates to the technical field of ceramic materials, and discloses an antioxidant high-entropy diboride ceramic material (HfZrTaCr) B2 with double protective layers as well as a preparation method and application of the antioxidant high-entropy diboride ceramic material. In order to solve the problems that an existing five-element high-entropy diboride (HfZrTaTiNb) B2 high-temperature oxidation layer is porous and poor in continuity, a quaternary system (HfZrTaCr) B2 capable of forming a single-phase solid solution is screened out through a Pall electronegativity difference factor. The preparation method comprises the following steps: adopting HfB2, ZrB2, TaB2 and CrB2 as raw materials, carrying out ball milling with absolute ethyl alcohol, drying, and carrying out spark plasma sintering to prepare the high-density (gt; according to the invention, Cr is introduced to realize element synergism, so that a unique CrTaO4 (at) (Hf, Zr) O2 / B2O3 double-layer protection structure is formed in situ during high-temperature oxidation. Pores of a (Hf, Zr) O2 framework of the inner layer are filled with CrTaO4 to form a compact barrier, and the surface of the outer layer is covered with molten B2O3 to cooperatively block oxygen diffusion. A thermogravimetric analysis experiment at the temperature of 1400 DEG C verifies that the weight gain rate of the (HfZrTaCr) B2 material is only 2.573%, is far superior to that of a contrast group (HfZrTaV) B2 and an existing (HfZrTaTiNb) B2 system, and has excellent oxidation resistance. In addition, the alloy also has single-phase stability and high density, and is suitable for ultra-high-temperature extreme environments such as aerospace engine hot end parts and nuclear reactor jackets.

Description

TECHNICAL FIELD

[0001] The application relates to the field of high-temperature structural materials, in particular to a quaternary single-phase high-entropy diboride ceramic material (HfZrTaCr)B2 with excellent high-temperature oxidation resistance and a preparation method thereof, and belongs to the technical field of high-entropy ceramic materials. BACKGROUND

[0002] With the development of extreme environment applications such as aerospace and nuclear energy, high-temperature structural materials need to have excellent oxidation resistance and mechanical stability. Traditional materials such as yttria partially stabilized zirconia (YSZ) will undergo phase transition, accelerate sintering and thermal insulation performance degradation when the temperature exceeds 1200 DEG C, resulting in material failure. Therefore, it is an urgent need to develop a new type of material that can serve stably at ultra-high temperature (>1200 DEG C) for a long time.

[0003] Transition metal diborides (such as HfB2, ZrB2) are considered as candidate materials for ultra-high temperature ceramics (UHTCs) due to their ultra-high melting point (>3000 DEG C) and good high-temperature oxidation resistance. However, the service temperature of traditional Y2O3 partially stabilized ZrO2 (YSZ) is limited below 1200 DEG C, because when the working temperature exceeds 1200 DEG C, YSZ will undergo high-temperature phase transition, accelerate sintering and thermal insulation performance degradation, and finally lead to material failure. In recent years, inspired by the concept of high-entropy alloys (HEAs), high-entropy diborides (HEBs) have also been successfully synthesized. This kind of material contains four or more main elements (each accounting for 5-35 at.%), forms a single-phase solid solution through entropy stabilization effect, and exhibits excellent comprehensive performance. However, the existing high-entropy diborides (HfZrTaTiNb)B2 still have significant defects such as poor continuity of oxides and generation of thermal stress in multi-phase structure at high temperature. Therefore, it is urgent to develop a high-entropy diboride with single-phase stability and multi-layer synergistic protection mechanism.

[0004] The application applies the design concept of high-entropy ceramics, selects Hf, Zr, Ta and Cr four elements which can form a single phase and play a synergistic role as high-entropy components, and obtains a high-density sample through an optimized process. It is hoped that through the synergistic effect between elements, an effective oxide protective layer is generated to improve the oxidation resistance. SUMMARY

[0005] The application provides a quaternary single-phase high-entropy diboride ceramic material (HfZrTaCr)B2 (hereinafter referred to as HZTC) with a CrTaO4@(Hf,Zr)O2 / B2O3 double protective layer structure to solve the technical bottleneck that the existing five-element high-entropy diboride (HfZrTaTiNb)B2 generates porous isolated oxides at high temperature, resulting in poor continuity of the protective layer and high oxidation weight gain rate. The material forms a dense gradient oxide layer through element synergistic effect, and significantly improves the ultra-high temperature oxidation resistance.

[0006] To achieve the above object, the present application is realized by the following technical solutions:

[0007] Through calculation based on Pauling electronegativity difference factor, the quaternary system (HfZrTaCr)B2 capable of forming stable single-phase solid solution is screened out, and thermal stress and oxidation unevenness caused by multi-phase structure are avoided. HfB2, ZrB2, TaB2 and CrB2 are used as starting powders, and after weighing, ball milling and drying according to the metering ratio obtained by theoretical calculation, the collected powder is placed into a mold, and sintering is carried out by using a spark plasma sintering furnace, so that the high-entropy diboride ceramic material with double protective layer oxidation resistance is obtained.

[0008] Preferably, the transition metal high-entropy diboride powder comprises HfB2, ZrB2, TaB2 and CrB2 four powders.

[0009] Preferably, the molar ratio of HfB2, ZrB2, TaB2 and CrB2 is 1:1:1:(0.5-1.5).

[0010] Preferably, the purity of HfB2, ZrB2, TaB2 and CrB2 is 99.5%, and the particle size range is 1-3 μm.

[0011] Preferably, the ball milling process uses anhydrous ethanol as the ball milling medium, and is added to completely immerse the powder.

[0012] Preferably, the ball milling process selects two kinds of agate grinding balls with diameters of 5 mm and 3 mm, and the mass ratio of each grinding ball to the powder is 1:1 during the grinding process, and the rotation speed is 200 rpm for sufficient mixing.

[0013] Preferably, the rotation speed of the ball mill is 200 rpm, and the ball milling time is 4-12 hours.

[0014] Preferably, the drying process uses a rotary evaporator to collect the mixed powder, and then the powder is dried at 70-90℃ for 1-3 hours.

[0015] Preferably, the sintering condition is vacuum, the sintering temperature is 1500-1800℃, the sintering pressure is 30-50 MPa, and the pressure holding time is 5-10 min.

[0016] The beneficial effects of the present application are:

[0017] 1. The present application accurately screens components by Pauling electronegativity difference factor, ensures the successful synthesis of uniform and stable single-phase solid solution, and avoids the problems of thermal stress and oxidation unevenness caused by the difference in thermal expansion coefficient of multi-phase structure at high temperature.

[0018] 2、The application can obtain dense high-entropy diboride ceramics with relative density >96% without adding any binder and sintering aid by optimizing the ball milling process (double size grinding balls, ethanol medium) and SPS sintering parameters (1750℃ / 50MPa / 10min), providing a reliable path for industrial production.

[0019] 3、The (HfZrTaCr)B2 prepared in the application can form a dense double-layer protective structure at high temperature: the first layer is formed by filling the (Hf, Zr)O2 skeleton pores with CrTaO4, and the second layer is formed by covering the material surface with molten B2O3, and this double-layer protection mechanism can synergistically block the diffusion of oxygen in the material interior. Therefore, in the thermogravimetric experiment at 1400℃, HZTC only increased by 2.573% (see the attached Figure 2 BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 XRD patterns of high-entropy diboride ceramic materials obtained in Examples 1, 2 and 3 of the application;

[0021] Figure 2 Thermogravimetric analysis curves of high-entropy diboride ceramic materials obtained in Examples 1, 2 and 3 of the application;

[0022] Figure 3 XRD patterns of high-entropy diboride ceramic materials obtained in Examples 1, 2 and 3 of the application after oxidation at 600, 900 and 1200℃ for 1h, respectively.

[0023] Figure 4 SEM patterns of high-entropy diboride ceramic materials obtained in Examples 1, 2 and 3 of the application, microstructure magnification images of HZTC and EDS patterns.

[0024] Figure 5 Microstructure magnification images and EDS patterns of HZTV and HZTTN obtained in Examples 2 and 3 of the application. Figure 6 TEM morphology image, local magnification images (a-c) of the oxidation protective film layer in Example 1 of the application, and selected area electron diffraction pattern corresponding to ① and ② regions in (c) and high-resolution TEM image of the junction between ① and ② regions. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with specific examples. The following examples are only used to illustrate the application and do not limit the scope of the application.

[0026] ​The test methods or test procedures described in the following examples are conventional methods unless otherwise specified; the reagents and materials are obtained from conventional commercial sources or prepared by conventional methods unless otherwise specified.

[0027] Example 1

[0028] Step 1: HfB2, ZrB2, TaB2, CrB2 powders were weighed separately with a molar ratio of 1:1:1:1, and the purity of the powders was 99.5%, and the particle size range was 1-3 μm.

[0029] Step 2: The weighed powder mixture was placed in a ball mill tank. Anhydrous ethanol was added as a ball milling medium until the powder was completely immersed. Grinding media was added to the ball mill tank, using maroon grinding balls with diameters of 5 mm and 3 mm (the two sizes of grinding balls had equal mass), and the total ball-to-charge mass ratio was maintained at 2:1. The ball mill tank was placed on a planetary ball mill, and ball milling was performed at a rotation speed of 200 rpm. The ball milling process used alternating rotation directions, with clockwise rotation for 0.5 hours, followed by counterclockwise rotation for 0.5 hours, for a total of 4 hours of ball milling. After ball milling was completed, the uniformly dispersed slurry was collected by a rotary evaporator and dried at 80°C for 2 hours to obtain a uniformly mixed (HfZrTaCr)B2 powder.

[0030] Step 3: A dry powder was subjected to densification sintering using a spark plasma sintering system. A carbon fiber mold was used to withstand the high temperature and high pressure during sintering. A uniaxial pressure of about 7.6 MPa was first applied to ensure good electrical contact. The sample was heated from room temperature to 1750°C at a heating rate of about 100°C / min. When the temperature reached 800°C, the applied pressure was increased to 50 MPa. After holding at 1750°C for 10 minutes, the sample was cooled in the furnace to obtain a dense (HfZrTaCr)B2 ceramic bulk body.

[0031] Step 4: The bulk density of the sintered body was measured using the Archimedes principle. The relative density was calculated to be 96.19%, indicating that a high-density HZTC ceramic was successfully obtained under the process conditions. The phase composition of the sintered sample was analyzed by X-ray diffraction. As shown in the attached figure (1), the XRD pattern only shows diffraction peaks of a single AlB2-type structure, without any detectable impurities, confirming the successful synthesis of a single-phase solid solution (HfZrTaCr)B2.

[0032] Step 5: After polishing the sample obtained in Step 4, phase structure determination, micro-morphology observation, element distribution analysis, and oxidation weight gain experiments were performed, and the X-ray diffraction pattern, scanning electron microscope image, energy spectrum results, and thermogravimetric curve are shown in the attached figures.

[0033] Example 2 (VB2 replaces CrB2 as a comparison)

[0034] Step 1: HfB2, ZrB2, TaB2, VB2 powders were weighed separately with a molar ratio of 1:1:1:1. The purity of the powders was 99.5%, and the particle size range was 1-3 μm.

[0035] Step 2: The weighed powder mixture was placed in a ball mill jar. Anhydrous ethanol was added as a ball milling medium until the powder was completely immersed. Grinding media was added to the ball mill jar, using maroon grinding balls with diameters of 5 mm and 3 mm (the two sizes of grinding balls had equal mass), maintaining a total ball-to-charge mass ratio of 2:1. The ball mill jar was placed on a planetary ball mill, and ball milling was performed at a rotation speed of 200 rpm. The ball milling process used alternating rotation directions, with clockwise rotation for 0.5 hours, followed by counterclockwise rotation for 0.5 hours, for a total of 4 hours of ball milling. After ball milling was completed, the uniformly dispersed slurry was collected by a rotary evaporator and dried at 80°C for 2 hours, obtaining a uniformly mixed (HfZrTaV)B2 powder (hereinafter referred to as HZTV).

[0036] Step 3: A dry powder was densified and sintered using a spark plasma sintering system. A carbon fiber mold was used to withstand the high temperature and high pressure during sintering. A uniaxial pressure of about 7.6 MPa was first applied to ensure good electrical contact. The sample was heated from room temperature to 1750°C at a heating rate of about 100°C / min. When the temperature reached 800°C, the applied pressure was increased to 50 MPa. After holding at 1750°C for 10 minutes, the sample was cooled in the furnace, obtaining a dense (HfZrTaV)B2 ceramic bulk.

[0037] Step 4: The bulk density of the sintered body was measured using the Archimedes principle. The relative density of (HfZrTaV)B2 was calculated to be 93.69%, indicating that a high-density HZTV ceramic was successfully obtained under the process conditions. The phase composition of the sintered sample was analyzed by X-ray diffraction. As shown in the attached figure (1), the XRD pattern only shows diffraction peaks of a single AlB2-type structure, without any detectable impurities, confirming the successful synthesis of a single-phase solid solution (HfZrTaV)B2.

[0038] Step 5: After polishing the sample obtained in Step 4, phase structure determination, micro-morphology observation, element distribution analysis, and oxidation weight gain experiments were performed, and the X-ray diffraction pattern, scanning electron microscope image, energy spectrum results, and thermogravimetric curve are shown in the attached figures.

[0039] Example 3 (existing high-entropy diboride)

[0040] Step 1: HfB2, ZrB2, TaB2, TiB2, NbB2 powders were weighed separately with a molar ratio of HfB2:ZrB2, TaB2:TiB2:NbB2 = 1:1:1:1:1. The purity of the powders was 99.5% and the particle size range was 1-3 μm.

[0041] Step 2: The weighed powder mixture was placed in a ball mill jar. Anhydrous ethanol was added as a milling medium until the powder was completely immersed. Grinding media was added to the ball mill jar, using maroon balls with diameters of 5 mm and 3 mm (the two sizes of balls had equal mass), maintaining a total ball-to-charge mass ratio of 2:1. The ball mill jar was placed on a planetary ball mill and milled at a speed of 200 rpm. The milling process used alternating rotational directions, with 0.5 hours of clockwise rotation followed by 0.5 hours of counterclockwise rotation, for a total of 4 hours of milling. After the milling was complete, the uniformly dispersed slurry was collected by a rotary evaporator and dried at 80°C for 2 hours, obtaining a uniformly mixed (HfZrTaTiNb)B2 powder (hereinafter referred to as HZTTN).

[0042] Step 3: A dry powder was densified and sintered using a spark plasma sintering system. A carbon fiber mold was used to withstand the high temperature and high pressure during sintering. A uniaxial pressure of about 7.6 MPa was first applied to ensure good electrical contact. The sample was heated from room temperature to 1750°C at a rate of about 100°C / min. When the temperature reached 800°C, the applied pressure was increased to 50 MPa. After holding at 1750°C for 10 minutes, the sample was cooled in the furnace, obtaining a dense (HfZrTaTiNb)B2 ceramic.

[0043] Step 4: The bulk density of the sintered body was measured using the Archimedes principle. The relative density of (HfZrTaTiNb)B2 was calculated to be 95.99%, indicating that a high-density HZTTN ceramic was successfully obtained under the process conditions. The phase composition of the sintered sample was analyzed by X-ray diffraction. As shown in the attached figure (1), the XRD pattern only shows diffraction peaks of a single AlB2-type structure, without any detectable impurities, confirming the successful synthesis of a single-phase solid solution (HfZrTaTiNb)B2.

[0044] Step 5: After polishing the sample obtained in step 4, phase structure determination, micro-morphology observation, element distribution analysis and oxidation weight gain experiment were performed, and the X-ray diffraction pattern, scanning electron microscope image, energy spectrum results and thermogravimetric curve are shown in the attached figures.

[0045] The X-ray diffraction pattern of the obtained high-entropy diboride ceramic material is shown in Figure 1

[0046] The thermogravimetric analysis curve of the obtained high-entropy diboride ceramic material is shown in​Figure 2 as shown.

[0047] X-ray diffraction patterns of the obtained high-entropy diboride ceramic materials after oxidation at 600, 900, 1200℃ for 1h are as shown. Figure 3 as shown.

[0048] SEM patterns of the obtained high-entropy diboride ceramic materials, microstructure magnification and EDS patterns of HZTC are as shown. Figure 4 as shown.

[0049] Microstructure magnification and EDS patterns of HZTV and HZTTN are as shown. Figure 5 as shown.

[0050] TEM morphology, local magnification and corresponding selected area electron diffraction patterns of the II layer (oxidation protection film layer) of the obtained HZTC are as shown. Figure 6 as shown.

[0051] The cross-section oxidation morphology of the obtained example 1 is as shown in the attached Figure 4 , it can be seen that the oxidation cross-section morphology of HZTC is divided into four layers: I layer (B2O3 liquid phase layer), II layer (oxidation protection film layer), III layer (oxidation product layer), IV layer (matrix layer). I layer is the outermost B2O3 liquid phase layer, which can play a certain role in filling pores and protecting the matrix. The II layer mainly contains elements Ta, Cr, and also contains Hf and Zr. TEM morphology and corresponding selected area electron diffraction patterns of the II layer are as shown in the attached Figure 6 . Further analysis shows that the oxidation region of the II layer is mainly composed of two phases, as seen from the image, the two phases are combined closely, only with a small amount of pores, this dense microstructure can efficiently block the transmission of oxygen, which is the main reason for the improved oxidation resistance of HZTC. SAED results show that the phase of region 1 is CrTaO4, and the phase of region 2 is (Hf, Zr)O2. HRTEM images show that the crystal plane spacing of the gray phase is 0.470 nm and 0.467 nm, respectively, corresponding to the (0 1 0) crystal plane and the (1 0 0) crystal plane of CrTaO4. In addition, the interface between CrTaO4 and (Hf, Zr)O2 is well combined, and the grain boundary thickness between the grains is only 4 nm, indicating that the lattice matching degree of the two phases is high and the structure is dense. Oxygen needs to diffuse through the bulk phase with a higher energy barrier than the grain boundary to pass through the CrTaO4@(Hf, Zr)O2 protection layer, greatly reducing the oxidation rate. In summary, a large amount of CrTaO4 precipitates and grows on the loose and porous (Hf, Zr)O2 structural framework and fills the pores, making it fully densified, thereby constructing a low oxygen diffusion rate CrTaO4@(Hf, Zr)O2 oxidation protection layer. Under the synergistic effect of the I and II liquid-solid protection layers, HZTC shows extremely low oxidation weight gain and excellent oxidation resistance.

[0052] The cross-section oxidation morphology of the obtained example 2 and 3 is shown in the attached figure Figure 5 The oxidation cross-section morphology of HZTV is divided into three layers, I layer (B2O3 liquid layer), II layer (oxidation product layer), III layer (matrix layer), the boundary between the three layers is clear, and the oxygen element forms an obvious diffusion gradient between I layer, II layer and III layer, which proves that the B2O3 liquid layer at this time has a good oxygen isolation effect, but the protection effect of only I layer is still limited. Compared with the microstructure of example 1, it is confirmed that Cr element is the key element to form double protective layer. The oxidation cross-section of HZTTN is also divided into I layer (B2O3 liquid layer), II layer (oxidation product layer), III layer (matrix layer), but the boundary between I layer and II layer is blurred, because a large amount of (Hf, Zr)O2, Nb2Zr6O 17 , Ta2O5, TiO2 generated by severe oxidation accumulates in I layer, and B2O3 liquid layer is difficult to completely cover, and the accumulated loose porous oxidation product to a certain extent destroys the hindering effect of B2O3 liquid layer on oxygen diffusion. In addition, a large number of holes are visible in II layer, the continuity of the oxidation layer is destroyed, and the holes become a rapid channel for oxygen diffusion from the outside. Therefore, the I layer and II layer of HZTTN cannot produce sufficient protection effect on III layer (matrix layer).

[0053] Example 1 and comparative examples (example 2, 3) fully prove that the preparation method provided by the present application can successfully synthesize high-density, single-phase quaternary (HfZrTaCr)B2 (HZTC) ceramic. The material can form a unique CrTaO4@(Hf,Zr)O2 / B2O3 double protective layer structure in situ under high temperature oxidation environment (especially > 1200℃), in which the CrTaO4 particles effectively fill the (Hf,Zr)O2 skeleton pores to form a dense inner layer, and the molten B2O3 outer layer provides dynamic sealing, and the synergistic effect of the two layers significantly inhibits oxygen diffusion, thereby endowing it with excellent ultrahigh temperature oxidation resistance (weight gain is only 2.573% under thermogravimetric analysis at 1400℃), and it is expected to become a candidate material for hot end parts of aerospace engine.

[0054] The above is only the preferred embodiment of the present application, it should be pointed out that the above preferred embodiment should not be regarded as limitation of the present application, the protection scope of the present application should be limited by the scope defined by the claims. For ordinary skilled in the art, several improvements and refinements can be made without departing from the spirit and scope of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A dual protective layer oxidation resistant high-entropy diboride ceramic material and a method of making the same, characterized in that, The double protective layer is CrTaO4@(Hf, Zr)O2 / B2O3 structure, the preparation method takes transition metal high-entropy diboride powder as raw material, the transition metal high-entropy diboride powder includes HfB2, ZrB2, TaB2 and CrB2, the molar ratio of HfB2, ZrB2, TaB2 and CrB2 is 1:1:1:(0.5-1.5), the purity of the powder is 99.5%, and the particle size range is 1-3 μm.

2. A method of preparing a dual protective layer oxidation resistant high-entropy diboride ceramic according to claim 1, characterized in that, The method comprises the following steps: S1: adding anhydrous ethanol as a ball milling medium, adding agate grinding balls for grinding, and uniformly mixing the four powders; S2: placing the mixed powder in S1 into a rotary evaporator, collecting the powder after drying; S3: loading the powder obtained after drying in S2 into a carbon fiber mold with graphite paper on the inner wall and both ends, and sintering in a spark plasma sintering furnace; S4: cooling to room temperature after sintering, and demolding the sintered high-entropy diboride ceramic.

3. The method of claim 2, wherein the method further comprises: The rotation speed of the ball mill in step S1 is 100-400 revolutions per minute, the ball milling time is 4-12 hours, and the mass ratio of the grinding balls to the powder is (1-5):

1.

4. The method of claim 2, wherein the method further comprises: The drying conditions in step S2 are: the drying temperature is 70-90 DEG C, and the drying time is 1-3 hours.

5. The method of claim 2, wherein the method further comprises: The sintering conditions in step S3 are: the atmosphere is vacuum or protective gas, the sintering temperature is 1500-1800 DEG C, the sintering pressure is 30-50 MPa, and the pressure holding time is 5-10 min.

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