A high-temperature self-lubricating high-entropy rare earth boride ceramic material and its preparation method

Abstract

The present invention relates to a high-temperature self-lubricating high-entropy rare-earth boride ceramic material. The ceramic material is in a bulk form, and its friction coefficient at 800 - 1200 °C is 0.10 - 0.24. It has the following chemical composition: REB6, where RE is selected from at least five of the lanthanide rare-earth elements La, Nd, Sm, Eu, Gd, Dy, Ho, Yb, Sc, and Y. At the same time, the present invention also discloses a preparation method of the ceramic material. The present invention adopts the design concept of high-entropy materials and introduces rare-earth elements. The material composition and performance have a large adjustable space. The prepared bulk material has excellent high-temperature self-lubricating performance, which can promote the multi-functional integration development and diversified application of rare-earth materials, and promote the comprehensive utilization of rare-earth resources in China.

Description

Technical Field

[0001] The present invention relates to the technical field of high-entropy ceramics, and particularly to a high-temperature self-lubricating high-entropy rare-earth boride ceramic material and a preparation method thereof. Background Art

[0002] With the rapid development of China's aerospace, nuclear power and other cutting-edge technologies, the service conditions of mechanical moving parts in high-end equipment such as aeroengines and hypersonic aircraft are becoming increasingly harsh, facing serious high-temperature friction and wear problems. Under high-temperature extreme conditions, traditional liquid lubricants are prone to volatilization or oxidation failure. The ceramic materials that can achieve high-temperature self-lubrication have good lubrication performance at high temperatures and can maintain high strength and hardness at the same time, which are suitable for solving the high-temperature friction and wear problems of the mechanical systems of high-end equipment.

[0003] High-entropy rare-earth boride ceramics have the characteristics of high melting point, high hardness, good electrical and thermal conductivity, excellent high-temperature stability, etc., and have attracted wide attention due to their unique physical, chemical and thermo-mechanical properties. Patent CN112408409 B discloses a preparation method of (Y 1 / 5 Sm 1 / 5 Eu 1 / 5 Yb 1 / 5 Er 1 / 5 )B6 ceramic powder, and studies its microwave absorption performance, obtaining a high-temperature resistant high-entropy microwave absorption ceramic material. Patent CN 117700235 A discloses a preparation method of a high-entropy rare-earth boride ceramic material, and a high-entropy diboride containing one rare-earth element (Sm or Lu or Er or Ho or Y or Tm) is obtained by adopting an electric field sintering technology. Patent CN 119059824 A discloses a preparation method of hexa-boride RE(AE) x B6 containing rare-earth metal element RE and alkaline-earth metal element AE at the same time, and studies its optical properties. The literature [J. Adv.Ceram, 2021, 10(1): 62-77] synthesized high-entropy rare-earth hexa-boride powder by a one-step method and studied its electromagnetic wave absorption performance, believing that REB6 ceramic material has good high-temperature stability, oxidation resistance and corrosion resistance, and is a new type of electromagnetic wave absorption material that can meet the requirements of high-temperature or corrosive service environments.

[0004] At present, the research on high-entropy rare-earth boride ceramic materials is still in its infancy. The research mainly focuses on the preparation of powders or porous materials, and there is less research on dense bulk materials, especially the lack of research on tribological properties. In addition, by carrying out research on the preparation and properties of rare-earth ceramic materials, promoting the multi-functional integration development and diversified application of rare-earth materials helps to promote the comprehensive utilization of China's rare-earth resources. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-temperature self-lubricating high-entropy rare-earth boride ceramic material with excellent performance.

[0006] Another technical problem to be solved by the present invention is to provide a preparation method for the high-temperature self-lubricating high-entropy rare-earth boride ceramic material.

[0007] To solve the above problems, a high-temperature self-lubricating high-entropy rare-earth boride ceramic material according to the present invention is characterized in that: the ceramic material is in a block form, and its friction coefficient at 800-1200 °C is 0.10-0.24, and it has the following chemical composition: REB6, where: RE is selected from at least five of the lanthanide rare-earth elements La, Nd, Sm, Eu, Gd, Dy, Ho, Yb, Sc, and Y.

[0008] A preparation method for the high-temperature self-lubricating high-entropy rare-earth boride ceramic material as described above is characterized in that: the method refers to using RE2O3 powder and B4C powder as production raw materials, where the RE2O3 powder is at least five of La2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Dy2O3, Ho2O3, Yb2O3, Sc2O3, and Y2O3; first, the RE2O3 powder and the B4C powder are mixed evenly by wet ball milling, dried, and sieved through a 100-120 mesh sieve to obtain a mixed powder; after the mixed powder is sintered by pressureless solid-state reaction and cooled to room temperature, it is ground and sieved through a 100-120 mesh sieve to obtain a high-entropy rare-earth boride ceramic powder material; then the high-entropy rare-earth boride ceramic powder material is sintered by spark plasma sintering to obtain a high-entropy rare-earth boride ceramic block material.

[0009] The mass percentage of the RE2O3 powder is 60-70%, and the mass percentage of the B4C powder is 30-40%.

[0010] The purity of the RE2O3 powder is not less than 99.9%, and the particle size is 1-10 μm; the purity of the B4C powder is not less than 98%, and the particle size is 1-10 μm.

[0011] The conditions for the pressureless solid-state reaction sintering refer to a temperature of 1650-1800 °C, a holding time of 1-3 h, a heating rate of 10-20 °C / min, and a sintering atmosphere of vacuum.

[0012] The conditions for the spark plasma sintering refer to a sintering temperature of 1750-1900 °C, a holding time of 5-20 min, a heating rate of 75-150 °C / min, a sintering pressure of 25-35 MPa, and a sintering atmosphere of vacuum or argon protection atmosphere.

[0013] The present invention has the following advantages compared with the prior art:

[0014] 1. The present invention adopts the design concept of high-entropy materials and introduces rare earth elements. The material composition and performance have a large adjustable space, which can promote the integrated development and diversified application of rare earth materials, and contribute to the comprehensive utilization of China's rare earth resources.

[0015] 2. The present invention uses rare earth oxides and boron carbide powder as raw materials, and the raw material cost is low.

[0016] 3. The preparation process of the present invention is simple and has a short cycle, which is conducive to large-scale production.

[0017] 4. The high-entropy rare earth boride ceramic block prepared by the present invention has excellent high-temperature self-lubricating performance through tribological performance testing, and the friction coefficient at 800 - 1200 °C is 0.10 - 0.24. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following further elaborates on the specific embodiments of the present invention with reference to the accompanying drawings.

[0019] Figure 1 It is the XRD pattern of the high-entropy rare earth boride ceramic powder material synthesized by the reaction of the present invention.

[0020] Figure 2 It is the XRD pattern and sintered sample block of the high-entropy rare earth boride ceramic block material in Example 3 of the present invention.

[0021] Figure 3 It is the friction coefficient - time curve of the high-entropy rare earth boride ceramic block material in Example 3 of the present invention when rubbing against different mating materials at room temperature.

[0022] Figure 4 It is the friction coefficient - time curve of the high-entropy rare earth boride ceramic block material in Example 3 of the present invention from room temperature to 1200 °C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] A high-temperature self-lubricating high-entropy rare earth boride ceramic material, the ceramic material is in block form, and the friction coefficient at 800 - 1200 °C is 0.10 - 0.24. It has the following chemical composition: REB6, where RE is selected from at least five of the lanthanide rare earth elements La, Nd, Sm, Eu, Gd, Dy, Ho, Yb, Sc, and Y.

[0024] Preparation method of the high-temperature self-lubricating high-entropy rare-earth boride ceramic material: Using RE2O3 powder and B4C powder as raw materials, where the RE2O3 powder is at least five of La2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Dy2O3, Ho2O3, Yb2O3, Sc2O3 and Y2O3; the purity of the RE2O3 powder is not less than 99.9%, and the particle size is 1-10 μm; the purity of the B4C powder is not less than 98%, and the particle size is 1-10 μm.

[0025] First, the RE2O3 powder and the B4C powder are mixed evenly by wet ball milling. The mass percentage (g / g) of the RE2O3 powder is 60-70%, and the mass percentage (g / g) of the B4C powder is 30-40%. After drying to constant weight at 60-80 °C and passing through a 100-120 mesh sieve, a mixed powder is obtained; the mixed powder is placed in a graphite crucible, and the graphite crucible is moved into a vacuum sintering furnace. Under the conditions of a temperature of 1650-1800 °C, a holding time of 1-3 h, a heating rate of 10-20 °C / min, and a sintering atmosphere of vacuum, pressureless solid-phase reaction sintering is carried out. After cooling to room temperature, it is ground and passed through a 100-120 mesh sieve to obtain a high-entropy rare-earth boride ceramic powder material (REB6 powder material). Chemical reaction: RE2O3 + 3B4C → 2REB6 + 3CO. Then, the high-entropy rare-earth boride ceramic powder material is placed in a graphite mold, and under the conditions of a sintering temperature of 1750-1900 °C, a holding time of 5-20 min, a heating rate of 75-150 °C / min, a sintering pressure of 25-35 MPa, and a sintering atmosphere of vacuum or argon protection atmosphere, spark plasma sintering is carried out to obtain a high-entropy rare-earth boride ceramic bulk material (REB6 bulk material).

[0026] Example 1

[0027] By mass percentage (g / g), 8.8% Nd2O3, 15.5% Sm2O3, 13.7% Eu2O3, 13.1% Yb2O3, 13.9% Y2O3 rare-earth oxide powders with a particle size of 5 μm and 35% B4C powder with a particle size of 5 μm are placed in a ball milling tank, and 20 wt.% of absolute ethanol is added as a wet ball milling medium. After ball milling, mixing, drying, and sieving, a mixed powder is obtained; the mixed powder is placed in a graphite crucible, and the graphite crucible is moved into a vacuum sintering furnace for pressureless solid-phase reaction sintering. It is heated to 1650 °C at a heating rate of 10 °C / min, held for 3 h, and the sintering atmosphere is vacuum. After the holding ends, it is cooled to room temperature with the furnace, ground, and sieved to obtain a high-entropy rare-earth boride ceramic powder material. The phase composition of the powder is as Figure 1 shown, and the main component of the powder is REB6.

[0028] The high-entropy rare-earth boride ceramic powder material is placed into a graphite mold, and using a spark plasma sintering furnace, it is kept warm for 5 minutes under the conditions of a sintering temperature of 1900 °C, a heating rate of 100 °C / min, and a sintering pressure of 25 MPa, thus obtaining the high-entropy rare-earth boride ceramic bulk material.

[0029] Example 2

[0030] By mass percentage (g / g), 9.3% Nd2O3, 16.1% Sm2O3, 14.4% Eu2O3, 13.9% Yb2O3, 14.3% Y2O3 rare-earth oxide powders with a particle size of 1 μm and 32% B4C powder with a particle size of 10 μm are placed into a ball mill tank, and 20 wt.% of absolute ethanol is added as a wet ball milling medium. After ball milling, mixing, drying, and sieving, a mixed powder is obtained; the mixed powder is placed into a graphite crucible, and the graphite crucible is moved into a vacuum sintering furnace for pressureless solid-phase reaction sintering. It is heated to 1750 °C at a heating rate of 15 °C / min, with a holding time of 2 h, and the sintering atmosphere is vacuum. After the holding ends, it is cooled to room temperature with the furnace, and then ground and sieved to obtain the high-entropy rare-earth boride ceramic powder material. The phase composition of the powder is as Figure 1 shown, with almost no impurity peaks and the powder purity improved.

[0031] The high-entropy rare-earth boride ceramic powder material is placed into a graphite mold, and using a spark plasma sintering furnace, it is kept warm for 10 minutes under the conditions of a sintering temperature of 1800 °C, a heating rate of 150 °C / min, and a sintering pressure of 30 MPa, thus obtaining the high-entropy rare-earth boride ceramic bulk material.

[0032] Example 3

[0033] By mass percentage (g / g), 9.1% Nd2O3, 15.8% Sm2O3, 14.1% Eu2O3, 13.5% Yb2O3, 14.2% Y2O3 rare-earth oxide powders with a particle size of 10 μm and 33.3% B4C powder with a particle size of 1 μm are placed into a ball mill tank, and 20 wt.% of absolute ethanol is added as a wet ball milling medium. After ball milling, mixing, drying, and sieving, a mixed powder is obtained; the mixed powder is placed into a graphite crucible, and the graphite crucible is moved into a vacuum sintering furnace for pressureless solid-phase reaction sintering. It is heated to 1800 °C at a heating rate of 20 °C / min, with a holding time of 1 h, and the sintering atmosphere is vacuum. After the holding ends, it is cooled to room temperature with the furnace, and then ground and sieved to obtain the high-entropy rare-earth boride ceramic powder material. The phase composition of the powder is as Figure 1 shown, obtaining a REB6 powder with high purity.

[0034] The high-entropy rare earth boride ceramic powder material is placed in a graphite mold and sintered in a spark plasma sintering furnace at a sintering temperature of 1750 °C, a heating rate of 75 °C / min, and a sintering pressure of 35 MPa for 15 min to obtain the high-entropy rare earth boride ceramic bulk material. The phase composition of the bulk is as shown in Figure 2 , which is consistent with the powder composition, and good phase stability is maintained during the high-temperature sintering process.

[0035] The friction and wear properties of the prepared high-entropy rare earth boride ceramic bulk material in an atmospheric environment are evaluated using a GF-Ⅰ high-temperature reciprocating friction and wear testing machine: the friction pairs are Si3N4, Al2O3, and SiC ceramic balls, the friction load is 10 N, the amplitude is 5 mm, the frequency is 5 Hz, the test temperatures are room temperature, 800 °C, 1000 °C, and 1200 °C, and the test time is 30 min. The test results are as shown in Figure 3 and 4 . At room temperature, when forming friction pairs with Si3N4, Al2O3, and SiC ceramic balls respectively, it has a stable friction coefficient, approximately 0.50 ( Figure 3 ); when rubbing against the Si3N4 ceramic ball, the friction coefficient at 800 °C is approximately 0.15, the friction coefficient at 1000 °C decreases to 0.10, and it still has a relatively low friction coefficient at 1200 °C, approximately 0.24. The experimental results show that the prepared high-entropy rare earth boride ceramic bulk material has excellent high-temperature self-lubrication performance.

[0036] Above, the embodiments of the present invention have been illustrated by examples. However, any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention shall be included within the protection scope of the present invention. The protection scope of the present invention shall be subject to the appended claims. The content not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. A method for preparing a high-temperature self-lubricating high-entropy rare earth boride ceramic material, characterized in that: The method is to use RE2O3 powder and B4C powder as production raw materials, wherein the RE2O3 powder is five kinds of Nd2O3, Sm2O3, Eu2O3, Yb2O3 and Y2O3; firstly, the RE2O3 powder and the B4C powder are mixed evenly by wet ball milling, and then dried and passed through a 100-120 mesh sieve to obtain a mixed powder; after the mixed powder is sintered by a pressureless solid phase reaction, it is cooled to room temperature, ground and passed through a 100-120 mesh sieve to obtain a high entropy rare earth boride ceramic powder material; then the high entropy rare earth boride ceramic powder material After spark plasma sintering, REB6 high entropy rare earth boride ceramic block material is obtained; the mass percentage of the RE2O3 powder is 60~70%, the mass percentage of Nd2O3 is 8.8%~9.3%, the mass percentage of Sm2O3 is 15.5%~16.1%, the mass percentage of Eu2O3 is 13.7%~14.4%, the mass percentage of Yb2O3 is 13.1%~13.9%, and the mass percentage of Y2O3 is 13.9%~14.3%; the mass percentage of the B4C powder is 30~40%.

2. The method for preparing a high-temperature self-lubricating high-entropy rare earth boride ceramic material according to claim 1, characterized in that: The purity of the RE2O3 powder is not less than 99.9%, and the particle size is 1-10 μm; the purity of the B4C powder is not less than 98%, and the particle size is 1-10 μm.

3. The method for preparing a high-temperature self-lubricating high-entropy rare earth boride ceramic material according to claim 1, characterized in that: The conditions of the pressureless solid phase reaction sintering are a temperature of 1650-1800°C, a holding time of 1-3 h, a heating rate of 10-20°C / min, and a vacuum sintering atmosphere.

4. The method for preparing a high-temperature self-lubricating high-entropy rare earth boride ceramic material according to claim 1, characterized in that: The conditions of the spark plasma sintering are that the sintering temperature is 1750-1900°C, the holding time is 5-20 min, the heating rate is 75-150°C / min, the sintering pressure is 25-35 MPa, and the sintering atmosphere is a vacuum or argon protective atmosphere.

5. A high-temperature self-lubricating high-entropy rare earth boride ceramic material prepared by the method according to any one of claims 1 to 4, characterized in that: The ceramic material is in the form of a block, has a friction coefficient of 0.10-0.24 at 800-1200° C., and has the following chemical composition: REB6, wherein RE is selected from five of the lanthanide rare earth elements Nd, Sm, Eu, Yb and Y.

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