CN106854080B - Preparation method for reducing sintering temperature of compact superfine crystal boron carbide ceramic material - Google Patents

Preparation method for reducing sintering temperature of compact superfine crystal boron carbide ceramic material Download PDF

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CN106854080B
CN106854080B CN201611003083.5A CN201611003083A CN106854080B CN 106854080 B CN106854080 B CN 106854080B CN 201611003083 A CN201611003083 A CN 201611003083A CN 106854080 B CN106854080 B CN 106854080B
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boron carbide
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袁铁锤
张梅
李瑞迪
周志辉
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Central South University
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Abstract

The invention discloses a compact superfine crystal boron carbide ceramicThe preparation method for reducing the sintering temperature of the ceramic material comprises the following steps: selecting coarse boron carbide powder with the average particle size of less than 20 mu m, and carrying out ball milling and sedimentation to obtain boron carbide superfine powder with the particle size of less than 1 mu m; mixing boron carbide superfine powder with MnNiCoCrFexMixing high-entropy alloy powder and ball-milling to obtain B4C‑MnNiCoCrFexMixing the powder; and (3) carrying out pressure sintering on the mixed powder to obtain the compact superfine crystal boron carbide ceramic material with reduced sintering temperature. According to the invention, MnNiCoCrFex high-entropy alloy powder is added into the boron carbide substrate, so that a liquid phase can be formed during high-temperature sintering to fill pores, the sintering densification temperature of the boron carbide ceramic material is effectively reduced, and the energy consumption is reduced; the boron carbide product with the density of more than 99 percent can be obtained by heat preservation for five minutes below 1900 ℃, the temperature is reduced by 200 ℃ compared with the prior sintering temperature, and the heat preservation time is greatly shortened.

Description

Preparation method for reducing sintering temperature of compact superfine crystal boron carbide ceramic material
Technical Field
The invention relates to a compact superfine crystal boron carbide material, in particular to a preparation method capable of reducing the sintering temperature of a compact superfine crystal boron carbide ceramic material.
Background
Boron carbide has the molecular formula of B4C, black gray powder at normal temperature and normal pressure, high hardness (Mohs hardness 9.3, second only to diamond and cubic boron nitride), and low density (theoretical density 2.52 g/cm)3The lightest ceramic material), high melting point (2350 ℃) and good thermal stability. Therefore, the boron carbide material can be used as a friction, drilling and polishing material.
One extremely important application of boron carbide is as bearing material for gyroscopic hydrodynamic motors. The gyroscope is used as a sensor for sensing angular displacement and angular velocity, and is an indispensable component of an inertial guidance system of aerospace equipment. Boron carbide is firstly adopted as an air floatation gyro bearing material by British Smith instruments company in the seventies of the last century to replace the prior 300 series ball bearing rate gyro, and the boron carbide has good mechanical property and low specific gravity and is used up to now.
As a bearing material for gyroscopes, the major wear of boron carbide comes from the bearing start and stop. In the starting and stopping processes, a set of sliding self-friction pairs are formed between the boron carbide bearing and the shaft sleeve, so that the bearing and the shaft sleeve are inevitably worn. At present, the boron carbide bearing material has the following technical problems:
(1) preparing nano boron carbide powder less than 1 mu m: the average grain size of the prepared boron carbide gyroscope bearing material is less than 1 mu m, so that the raw material, namely boron carbide powder, is at least less than 1 mu m;
(2) the boron carbide has a high melting point of 2350 ℃, is sintered under the conventional non-pressure, and needs 2200 ℃ or keeps the temperature for a long time if reaching full compactness, so that the boron carbide has high energy consumption and harsh production conditions, and is difficult to reach under common conditions. The product has low relative density, more residual pores inside, low hardness, fracture toughness, bending strength and frictional wear strength, and can not be applied by adopting low sintering temperature or low heat preservation time.
(3) The prepared pure boron carbide bearing material adopts the traditional pressure sintering, namely hot pressure sintering or discharge plasma sintering, the sintering temperature is reduced, but 2100 ℃ is needed, the temperature is higher, the production condition is still harsh, the crystal grain growth is obvious when the heat preservation time in the sintering process is too long, the average crystal grain size is larger than 5 mu m, the bending strength is low, the internal cracks of the bearing are more, and the hardness and the wear resistance are poor.
Therefore, it is necessary to develop a preparation method capable of reducing the sintering temperature of the dense ultra-fine grain boron carbide ceramic material.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects and shortcomings in the background technology and providing a preparation method for reducing the sintering temperature of a dense superfine crystal boron carbide ceramic material.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a preparation method of a dense superfine crystal boron carbide ceramic material for reducing sintering temperature comprises the following steps:
(1) selecting coarse boron carbide powder with the average particle size of less than 20 mu m, and carrying out ball milling and sedimentation to obtain boron carbide superfine powder with the particle size of less than 1 mu m;
(2) mixing the boron carbide superfine powder obtained in the step (1) with MnNiCoCrFe with different iron contentsxMixing high-entropy alloy powder and ball-milling to obtain B4C-MnNiCoCrFexMixing the powder, wherein x is more than 0 and less than or equal to 2;
(3) b obtained in the step (2)4C-MnNiCoCrFexAnd (3) performing pressure sintering on the mixed powder to obtain the compact superfine crystal boron carbide ceramic material with reduced sintering temperature.
In the above preparation method, preferably, in the step (2), the MnNiCoCrFexThe high-entropy alloy powder is prepared by adopting an air atomization method; the MnNiCoCrFexThe particle size of the high-entropy alloy powder is not higher than 15 mu m.
Preferably, in the preparation method described above, in the step (1), a planetary ball mill is used for ball milling in the ball milling process, the ball milling medium is deionized water, and the mass ratio of ball materials is (8-15):1, the rotating speed is 480-.
In the preparation method, preferably, before the sedimentation, the boron carbide powder is firstly pickled by concentrated hydrochloric acid and then washed by deionized water; settling in a glass container with the height of 1-2m, wherein the settling medium is deionized water, and after the boron carbide particles naturally settle in the deionized water completely and uniformly, taking the upper suspension, and dropwise adding hydrochloric acid to promote the settling of the boron carbide fine particles; finally, pouring out the supernatant, and drying at 80 ℃ to obtain boron carbide superfine powder with the average grain diameter less than 1 mu m.
Preferably, in the step (2), the ball milling process adopts a planetary ball mill, the ball milling medium is alcohol, the ball milling rotation speed is 160r/min, the ball milling time is 10 hours, and the ball-material mass ratio is (8-15): 1.
In the above production method, preferably, B obtained in the step (2)4C-MnNiCoCrFexHigh entropy alloy MnNiCoCrFe in mixed powderxThe volume fraction of (A) is 5-15%.
In the above production method, preferably, in the step (3), the pressure sintering is hot-press sintering or spark plasma sintering (SPS sintering).
In the preparation method, the sintering temperature is 1500-2000 ℃, the sintering pressure is 10-30MPa, and the heat preservation time is 1-10 min.
In the preparation method, the sintering temperature is 1500-.
The boron carbide ceramic of the invention has the component B4The C-MnNiCoCrFex and MnNiCoCrFex are high-entropy alloys, have excellent performances of high strength, high hardness, high-temperature creep resistance, high-temperature oxidation resistance, corrosion resistance and the like, Fe in the high-entropy alloys can react with boron carbide at high temperature (1273 ℃) to generate FeB and C in situ, and the toughness of B4C ceramic is well increased; ni in the high-entropy alloy can be used as an inhibitor for grain growth to control the grain growth; the high-entropy alloy has high mixing entropy and low melting point, forms a liquid phase at high temperature, and can fill gaps in the fully and uniformly mixed powder in the sintering process, so that the densification temperature of boron carbide is effectively reduced, the toughness of the boron carbide material is increased, the bending strength of the material is improved, the crystal boundary energy is reduced, and the growth of crystal grains is inhibited.
Compared with the prior art, the invention has the advantages that:
(1) according to the invention, MnNiCoCrFex high-entropy alloy powder is added into the boron carbide substrate, so that a liquid phase can be formed during high-temperature sintering to fill pores, the sintering densification temperature of the boron carbide ceramic material is effectively reduced, and the energy consumption is reduced; the boron carbide product with the density of more than 99 percent can be obtained by heat preservation for five minutes below 1900 ℃, the temperature is reduced by at least 200 ℃ compared with the prior sintering temperature, and the heat preservation time is greatly shortened.
(2) According to the invention, MnNiCoCrFex high-entropy alloy powder is added into the boron carbide matrix, and Ni in the MnNiCoCrFex high-entropy alloy powder can be used as a grain growth inhibitor to effectively inhibit the growth of grains, so that the boron carbide bearing material with fine grains can be prepared.
(3) According to the invention, MnNiCoCrFex high-entropy alloy powder is added into the boron carbide substrate, different Fe contents in a MnNiCoCrFex high-entropy alloy system have different influences on the compactness of the boron carbide material, Fe can react with boron carbide at high temperature (1273 ℃) to generate FeB and C in situ, and B is well increased4C, toughness of the ceramic; at the same time, within the adding range of the invention, the high entropyThe alloy does not reduce the hardness, corrosion resistance and wear resistance of the boron carbide material, and still maintains the inherent excellent mechanical properties of high hardness, corrosion resistance, wear resistance and the like.
Detailed Description
In order to facilitate an understanding of the present invention, the present invention will be described more fully and in detail with reference to the preferred embodiments, but the scope of the present invention is not limited to the specific embodiments below.
Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
Example 1:
the invention relates to a preparation method of a dense superfine crystal boron carbide ceramic material for reducing sintering temperature, which comprises the following steps:
(1) selecting 200g of boron carbide coarse powder with the average particle size of 20 mu m, weighing 2kg of carbon steel balls with the diameter of 6mm, ensuring the ball-material mass ratio of 10:1, and carrying out ball milling for 10 hours at the ball milling speed of 480 r/min;
(2) placing the boron carbide mixed solution after ball milling in a 5L big beaker, thoroughly pickling twice by using concentrated hydrochloric acid, and then washing by using deionized water until the boron carbide mixed solution is not easy to layer; placing the mixed solution washed by acid washing water in a transparent container with the height of 1m, adding deionized water to 90% of the volume of the container, uniformly stirring, after completely dispersing, taking the suspension with the upper layer of 20cm in 24h, 48h and 72h respectively, and dropwise adding a small amount of hydrochloric acid to promote the sedimentation of boron carbide fine particles; finally, pouring out supernatant liquor, and drying at 80 ℃ to obtain boron carbide fine powder with the average particle size of about 1 mu m;
(3) preparing MnNiCoCrFe high-entropy alloy powder by adopting a gas atomization method according to the volume ratio of Mn, Ni, Co, Cr, Fe =1:1:1:1:1, and sieving the prepared powder to obtain MnNiCoCrFe high-entropy alloy powder with the particle size less than 15 mu m;
(4) taking 60g of boron carbide fine powder and 10g of MnNiCoCrFe high-entropy alloy powder with the grain size less than 15 mu m obtained in the step (3) (the volume fraction of the high-entropy alloy powder is about 5%), taking alcohol as a ball milling medium, placing the ball milling medium on a planetary ball mill, and performing ball milling for 10 hours at the rotating speed of 160r/min, wherein the ball-material mass ratio is 10:1, drying to obtain B with the volume fraction of 5%4C-MnNiCoCrFe mixed powder;
(5) get B415g of C-MnNiCoCrFe mixed powder is sintered by adopting discharge plasma, the sintering temperature is 1900 ℃, the heating rate is 100K/min, the sintering pressure is 40MPa, the heat preservation time is 2min, and after a sample is completely cooled, the compact ultra-fine crystal boron carbide ceramic material with the relative density of more than 99 percent is obtained.
The hardness of the boron carbide ceramic material obtained in the embodiment is measured by a Vickers hardness tester, the test pressure is 200g, the measured Vickers hardness HV is 4603 (average value is taken for 10 times of measurement), the rotating speed during friction and wear measurement is 420r/min, the wear pressure is 15N, the test time is 30 minutes, the grinding material is a tungsten carbide ball, the wear loss of the material after the test is less than 0.1g, and the friction coefficient is 0.23.
Example 2:
the invention relates to a preparation method of a dense superfine crystal boron carbide ceramic material for reducing sintering temperature, which comprises the following steps:
(1) selecting 200g of boron carbide coarse powder with the average particle size of 20 mu m, weighing 2kg of carbon steel balls with the diameter of 6mm, ensuring the ball-material ratio of 10:1, and carrying out ball milling for 10 hours at the ball milling speed of 480 r/min;
(2) placing the boron carbide mixed solution after ball milling in a 5L big beaker, thoroughly pickling twice by using concentrated hydrochloric acid, and then washing by using deionized water until the boron carbide mixed solution is not easy to layer; placing the mixed solution washed by acid washing water in a transparent container with the height of 1m, adding deionized water to 90% of the volume of the container, uniformly stirring, after completely dispersing, taking the suspension with the upper layer of 20cm in 24h, 48h and 72h respectively, and dropwise adding a small amount of hydrochloric acid to promote the sedimentation of boron carbide fine particles; finally, pouring out supernatant liquor, and drying at 80 ℃ to obtain boron carbide fine powder with the average particle size of about 1 mu m;
(3) adding Mn, Ni, Co, Cr, Fe =1:1:1:1:2 (B)Volume ratio), preparing MnNiCoCrFe by adopting gas atomization method2High-entropy alloy powder, sieving the prepared powder to obtain MnNiCoCrFe with the particle size less than 15 mu m2High entropy alloy powder;
(4) 60g of boron carbide fine powder and MnNiCoCrFe are taken210g of high-entropy alloy powder (the volume fraction of the high-entropy alloy powder is about 5%), taking alcohol as a ball milling medium, and placing the high-entropy alloy powder on a planetary ball mill for ball milling at a speed of 160r/min for 10 hours, wherein the mass ratio of ball materials is 15: 1, drying to obtain B with the volume fraction of 5%4C-MnNiCoCrFe2Mixing the powder;
(5) get B4C-MnNiCoCrFe2And (2) mixing 15g of powder, sintering by adopting discharge plasma, wherein the sintering temperature is 1900 ℃, the heating rate is 100K/min, the sintering pressure is 40MPa, the heat preservation time is 2min, and after the sample is completely cooled, obtaining the compact superfine crystal boron carbide ceramic material with the relative density of more than 99%.
The hardness of the boron carbide ceramic material obtained in the embodiment is measured by a Vickers hardness tester, the test pressure is 200g, the measured Vickers hardness HV is 4562 (average value is obtained by measuring 10 times), the rotating speed during friction and wear measurement is 420r/min, the wear pressure is 15N, the test time is 30 minutes, the grinding material is a tungsten carbide ball, the wear loss of the material after the test is less than 0.1g, and the average friction coefficient is 0.24.
Example 3:
the invention relates to a preparation method of a dense superfine crystal boron carbide ceramic material for reducing sintering temperature, which comprises the following steps:
(1) 200g of boron carbide coarse powder with the average particle size of 20 mu m is selected, 2kg of carbon steel balls with the diameter of 6mm are weighed, the ball-material ratio of 10:1 is ensured, the ball milling speed is 480r/min, and the ball milling is carried out for 72 hours;
(2) placing the boron carbide mixed solution after ball milling in a 5L big beaker, thoroughly pickling twice by using concentrated hydrochloric acid, and then washing by using deionized water until the boron carbide mixed solution is not easy to layer; placing the mixed solution washed by acid washing water in a transparent container with the height of 1m, adding deionized water to 90% of the volume of the container, uniformly stirring, after completely dispersing, taking the suspension with the upper layer of 20cm in 24h, 48h and 72h respectively, and dropwise adding a small amount of hydrochloric acid to promote the sedimentation of boron carbide fine particles; finally, pouring out supernatant liquor, and drying at 80 ℃ to obtain boron carbide fine powder with the average particle size of about 1 mu m;
(3) preparing MnNiCoCrFe high-entropy alloy powder by adopting a gas atomization method according to the volume ratio of Mn, Ni, Co, Cr, Fe =1:1:1:1:1, and sieving the prepared powder to obtain MnNiCoCrFe high-entropy alloy powder with the particle size less than 15 mu m;
(4) taking 57g of boron carbide fine powder and 20g of MnNiCoCrFe high-entropy alloy powder with the grain size less than 15 mu m obtained in the step (3) (the volume fraction of the high-entropy alloy powder is about 10%), taking alcohol as a ball milling medium, placing the ball milling medium on a planetary ball mill, and performing ball milling for 10 hours at the rotating speed of 160r/min, wherein the ball-material mass ratio is 10:1, drying after ball milling to obtain B with the volume fraction of 10%4C-MnNiCoCrFe mixed powder;
(5) get B415g of C-MnNiCoCrFe mixed powder is sintered by adopting discharge plasma, the sintering temperature is 1900 ℃, the heating rate is 100K/min, the sintering pressure is 40MPa, the heat preservation time is 2min, and after a sample is completely cooled, the compact ultra-fine crystal boron carbide ceramic material with the relative density of more than 99 percent is obtained.
The hardness of the boron carbide ceramic material obtained in the embodiment is measured by a Vickers hardness tester, the test pressure is 200g, the measured Vickers hardness HV is 4867 (the average value is obtained by measuring 10 times), the rotating speed during friction and wear measurement is 420r/min, the wear pressure is 15N, the test time is 30 minutes, the grinding material is a tungsten carbide ball, the wear loss of the material after the test is less than 0.1g, and the friction coefficient is 0.22.
Example 4:
the invention relates to a preparation method of a dense superfine crystal boron carbide ceramic material for reducing sintering temperature, which comprises the following steps:
(1) 200g of boron carbide coarse powder with the average particle size of 20 mu m is selected, 2kg of carbon steel balls with the diameter of 6mm are weighed, the ball-material ratio of 10:1 is ensured, and the ball milling speed is 480r/min for ball milling for 72 hours;
(2) placing the boron carbide mixed solution after ball milling in a 5L big beaker, thoroughly pickling twice by using concentrated hydrochloric acid, and then washing by using deionized water until the boron carbide mixed solution is not easy to layer; placing the mixed solution washed by acid washing water in a transparent container with the height of 1m, adding deionized water to 90% of the volume of the container, uniformly stirring, after completely dispersing, taking the suspension with the upper layer of 20cm in 24h, 48h and 72h respectively, and dropwise adding a small amount of hydrochloric acid to promote the sedimentation of boron carbide fine particles; finally, pouring out supernatant liquor, and drying at 80 ℃ to obtain boron carbide fine powder with the average particle size of about 1 mu m;
(3) preparing MnNiCoCrFe high-entropy alloy powder by adopting a gas atomization method according to the volume ratio of Mn, Ni, Co, Cr, Fe =1:1:1:1:1, and sieving the prepared powder to obtain MnNiCoCrFe high-entropy alloy powder with the particle size less than 15 mu m;
(4) taking 60g of boron carbide fine powder and 10g of MnNiCoCrFe high-entropy alloy powder with the grain size of less than 15 mu m obtained in the step (3) (the volume fraction of the high-entropy alloy powder is about 5%), taking alcohol as a ball milling medium, placing the ball milling medium on a planetary ball mill at the rotating speed of 160r/min, wherein the ball-material mass ratio is 10:1, ball-milling for 10h, and drying to obtain B with volume fraction of 5%4C-MnNiCoCrFe mixed powder;
(5) get B4And (3) hot-pressing and sintering 15g of C-MnNiCoCrFe mixed powder at the sintering temperature of 2000 and the sintering pressure of 40MPa for 2min, and obtaining the compact ultra-fine crystal boron carbide ceramic material with the relative density of more than 99% after the sample is completely cooled.
The hardness of the boron carbide ceramic material obtained in the embodiment is measured by a Vickers hardness tester, the test pressure is 200g, the measured Vickers hardness HV is 5022 (average value is obtained by measuring 10 times), the rotating speed during friction and wear measurement is 420r/min, the wear pressure is 15N, the test time is 30 minutes, the grinding material is a tungsten carbide ball, the wear loss of the material after the test is less than 0.1g, and the average friction coefficient is 0.26.
Example 5:
the invention relates to a preparation method of a dense superfine crystal boron carbide ceramic material for reducing sintering temperature, which comprises the following steps:
(1) 200g of boron carbide coarse powder with the average particle size of 20 mu m is selected, 2kg of carbon steel balls with the diameter of 6mm are weighed, the ball-material ratio of 10:1 is ensured, the ball milling speed is 480r/min, and the ball milling is carried out for 72 hours;
(2) placing the boron carbide mixed solution after ball milling in a 5L big beaker, thoroughly pickling twice by using concentrated hydrochloric acid, and then washing by using deionized water until the boron carbide mixed solution is not easy to layer; placing the mixed solution washed by acid washing water in a transparent container with the height of 1m, adding deionized water to 90% of the volume of the container, uniformly stirring, completely dispersing, taking the suspension with the upper layer of 20cm for 24h, 48h and 72h respectively, and drying at 80 ℃ to obtain boron carbide fine powder with the average particle size of about 1 mu m;
(3) preparing MnNiCoCrFe high-entropy alloy powder by adopting a gas atomization method according to the volume ratio of Mn, Ni, Co, Cr, Fe =1:1:1:1:1, and sieving the prepared powder to obtain MnNiCoCrFe high-entropy alloy powder with the particle size less than 15 mu m;
(4) 60g of boron carbide fine powder and 10g (the volume fraction of the high-entropy alloy powder is about 5%) of MnNiCoCrFe high-entropy alloy powder with the grain size of less than 15 mu m obtained in the step (3) are taken, alcohol is taken as a ball milling medium, the ball milling medium is placed on a planetary ball mill at the rotating speed of 160r/min, the ball-material mass ratio is 10:1, after ball milling is carried out for 10 hours, drying is carried out, and B with the volume fraction of 5% is obtained4C-MnNiCoCrFe mixed powder;
(5) get B4And (2) hot-pressing and sintering 15g of C-MnNiCoCrFe mixed powder at 1900 ℃, 25MPa for 2min, and completely cooling to obtain the compact ultra-fine crystal boron carbide ceramic material with the relative density of more than 99 percent after the sample is completely cooled.
The hardness of the boron carbide ceramic material obtained in the embodiment is measured by a Vickers hardness tester, the test pressure is 200g, and the measured Vickers hardness HV is 4934 (the average value is obtained by measuring 10 times); the rotating speed is 420r/min, the abrasion pressure is 15N, the testing time is 30 minutes, the grinding material is a tungsten carbide ball, the abrasion loss of the material after testing is less than 0.1g, and the average friction coefficient is 0.22.
Example 6:
the invention relates to a preparation method of a dense superfine crystal boron carbide ceramic material for reducing sintering temperature, which comprises the following steps:
(1) 200g of boron carbide coarse powder with the average particle size of 20 mu m is selected, 2kg of carbon steel balls with the diameter of 6mm are weighed, the ball-material ratio of 10:1 is ensured, the ball milling speed is 480r/min, and the ball milling is carried out for 72 hours;
(2) placing the boron carbide mixed solution after ball milling in a 5L big beaker, thoroughly pickling twice by using concentrated hydrochloric acid, and then washing by using deionized water until the boron carbide mixed solution is not easy to layer; placing the mixed solution washed by acid washing water in a transparent container with the height of 1m, adding deionized water to 90% of the volume of the container, uniformly stirring, after completely dispersing, taking the suspension with the upper layer of 20cm in 24h, 48h and 72h respectively, and dropwise adding a small amount of hydrochloric acid to promote the sedimentation of boron carbide fine particles; finally, pouring out supernatant liquor, and drying at 80 ℃ to obtain boron carbide fine powder with the average particle size of about 1 mu m;
(3) preparing MnNiCoCrFe high-entropy alloy powder by adopting a gas atomization method according to the volume ratio of Mn, Ni, Co, Cr, Fe =1:1:1:1:1, and sieving the prepared powder to obtain MnNiCoCrFe high-entropy alloy powder with the particle size less than 15 mu m;
(4) 60g of boron carbide fine powder and 10g of MnNiCoCrFe high-entropy alloy powder with the grain diameter of less than 15 mu m obtained in the step (3) (the volume fraction of the high-entropy alloy powder is about 5 percent) are taken as ball milling media, the ball milling media are put on a planetary ball mill to be ball milled for 10 hours at the rotating speed of 160r/min (the ball-material mass ratio is 8: 1), and B with the volume fraction of 5 percent is obtained by drying4C-MnNiCoCrFe mixed powder;
(5) get B4And (3) 15g of C-MnNiCoCrFe mixed powder is sintered by hot pressing, the sintering temperature is 2000 ℃, the sintering pressure is 40MPa, the heat preservation time is 10min, and after the sample is completely cooled, the compact ultra-fine crystal boron carbide ceramic material with the relative density of more than 99 percent is obtained.
The hardness of the boron carbide ceramic material obtained in the embodiment is measured by a Vickers hardness tester, the test pressure is 200g, and the measured Vickers hardness HV is 5072 (10 measurements are taken as an average value); the rotating speed is 420r/min, the abrasion pressure is 15N, the testing time is 30 minutes, the grinding material is a tungsten carbide ball, the abrasion loss of the material after testing is less than 0.1g, and the average friction coefficient is 0.21.
Comparative example:
the preparation method of the compact superfine crystal pure boron carbide ceramic material of the comparative example comprises the following steps:
(1) 200g of boron carbide coarse powder with the average particle size of 20 mu m is selected, 2kg of carbon steel balls with the diameter of 6mm are weighed, the ball-material ratio of 10:1 is ensured, the ball milling speed is 480r/min, and the ball milling is carried out for 72 hours;
(2) placing the boron carbide mixed solution after ball milling in a 5L big beaker, thoroughly pickling twice by using concentrated hydrochloric acid, and then washing by using deionized water until the boron carbide mixed solution is not easy to layer; placing the mixed solution washed by acid washing water in a transparent container with the height of 1m, adding deionized water to 90% of the volume of the container, uniformly stirring, after completely dispersing, taking the suspension with the upper layer of 20cm in 24h, 48h and 72h respectively, and dropwise adding a small amount of hydrochloric acid to promote the sedimentation of boron carbide fine particles; finally, pouring out supernatant liquor, and drying at 80 ℃ to obtain boron carbide fine powder with the average particle size of about 1 mu m;
(3) taking B obtained in the step (2)4And (3) sintering 15g of C ultrafine powder by adopting SPS (spark plasma sintering), wherein the sintering temperature is 2100 ℃, the sintering pressure is 40MPa, the heat preservation time is 20min, and after the sample is completely cooled, obtaining the compact ultrafine crystal pure boron carbide ceramic material with the relative density of more than 99%.
The hardness of the material of the comparative example was measured using a vickers hardness tester at a test pressure of 200g, and the vickers hardness HV of 5172 (average value was taken for 10 measurements); the rotating speed is 420r/min, the abrasion pressure is 15N, the testing time is 30 minutes, the grinding material is a tungsten carbide ball, the abrasion loss of the tested material is less than 0.1g, and the average friction coefficient is 0.20.

Claims (5)

1. A preparation method of a dense superfine crystal boron carbide ceramic material for reducing sintering temperature is characterized by comprising the following steps:
(1) selecting coarse boron carbide powder with the average particle size of less than 20 mu m, and carrying out ball milling and sedimentation to obtain boron carbide superfine powder with the particle size of less than 1 mu m;
(2) mixing the boron carbide superfine powder obtained in the step (1) with MnNiCoCrFe with different iron contentsxMixing high-entropy alloy powder and ball-milling to obtain B4C-MnNiCoCrFexMixing the powder, wherein x is more than 0 and less than or equal to 2; b is4C-MnNiCoCrFexHigh entropy alloy MnNiCoCrFe in mixed powderxThe volume fraction of (A) is 5-15%; the ball milling speed is 160r/min, and the ball milling time is 10 h;
(3) b obtained in the step (2)4C-MnNiCoCrFexThe mixed powder is pressed and sintered to obtain a compact superfine crystal boron carbide ceramic material with reduced sintering temperature; the pressure sintering is hot-pressing sintering or discharge plasma sintering, wherein the sintering temperature is 1500-1900 ℃ during the hot-pressing sintering, the sintering pressure is 10-30MPa, and the heat preservation time is 2 min; the sintering temperature is 1500-1900 ℃ during the spark plasma sintering, the sintering pressure is 20-40MPa, and the heat preservation time is 2 min.
2. The method according to claim 1, wherein in the step (2), MnNiCoCrFexThe high-entropy alloy powder is prepared by adopting an air atomization method; the MnNiCoCrFexThe particle size of the high-entropy alloy powder is not higher than 15 mu m.
3. The preparation method of claim 1, wherein in the step (1), the ball milling process is carried out by using a planetary ball mill, the ball milling medium is deionized water, and the mass ratio of ball materials is (8-15):1, the rotating speed is 480-.
4. The method according to claim 1, wherein the boron carbide powder is subjected to acid washing with concentrated hydrochloric acid and then water washing with deionized water before the precipitation; settling in a glass container with the height of 1-2m, wherein the settling medium is deionized water, and after the boron carbide particles naturally settle in the deionized water completely and uniformly, taking the upper suspension, and dropwise adding hydrochloric acid to promote the settling of the boron carbide fine particles; finally, pouring out the supernatant, and drying at 80 ℃ to obtain boron carbide superfine powder with the average grain diameter less than 1 mu m.
5. The preparation method of claim 1, wherein in the step (2), the ball milling process adopts a planetary ball mill, the ball milling medium is alcohol, and the mass ratio of ball materials is (8-15): 1.
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