CN111825458A - High-density boron carbide ceramic material and pressureless sintering preparation method thereof - Google Patents
High-density boron carbide ceramic material and pressureless sintering preparation method thereof Download PDFInfo
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Abstract
The invention discloses a high-density boron carbide ceramic material and a pressureless sintering preparation method thereof, wherein the high-density boron carbide ceramic material comprises the following raw materials in percentage by mass: 2-8% of chromium disilicide, 4-10% of silicon carbide, 0-2% of aluminum, 3-8% of polyimide powder, 0.5-2.5% of carbon black and the balance of boron carbide. In order to improve the density of the boron carbide ceramic, a metal simple substance or a compound thereof with good wettability with boron carbide is often added. The invention adopts chromium disilicide and silicon carbide as sintering aids to improve the mechanical property of the alloy. The chromium disilicide can form an eutectic liquid phase with the boron carbide to realize liquid phase sintering, and the density of the boron carbide can be remarkably improved. The silicon carbide can be pinned at the boron carbide crystal boundary to prevent the crystal grains from growing, and the mechanical property of the silicon carbide is improved. The two sintering aids as second-phase particles are well mixed with the boron carbide matrix, have good wettability and can improve the strength of the ceramic material bonding surface.
Description
Technical Field
The invention belongs to the technical field of boron carbide ceramic materials, and particularly relates to a high-density boron carbide ceramic material and a pressureless sintering preparation method thereof.
Background
Boron carbide has been the focus of research since its discovery in the 19 th century as a by-product of metal boride research due to its high hardness, high melting point, high elastic modulus, low density, and the like. Meanwhile, the boron carbide ceramic has good chemical stability and neutron absorptivity, so that the boron carbide ceramic is widely applied to the fields of wear-resistant materials, nuclear industry, bulletproof materials and the like. Although boron carbide materials have a plurality of advantages, boron carbide as covalent bond ceramics has very low self-diffusion coefficient, so that the boron carbide ceramics are extremely difficult to sinter and compact; meanwhile, boron carbide is a brittle material, and has low fracture toughness, which is not beneficial to practical application. In actual production, a hot-pressing sintering method is often adopted, so that plastic deformation, grain boundary slippage, grain rearrangement and the like are generated in the sintering process of the ceramic, and the densification of the boron carbide ceramic is promoted. However, the hot-pressing sintering equipment is complex, the sintering temperature is high in the sintering process, continuous pressurization is needed, and the energy consumption is high, so that the hot-pressing sintering of the boron carbide ceramic is expensive. Because the sintering temperature is high, crystal grains are easy to grow in the sintering process, the production efficiency is low, and only products with simple shapes can be produced.
The pressureless sintering process can be used for preparing a blank with a complex shape, has high single-furnace yield, is suitable for large-scale batch production, and greatly widens the application field of the boron carbide ceramic. But the pressureless sintered boron carbide ceramic is difficult to sinter compactly, so that the boron carbide ceramic has lower density and toughness; in order to improve the properties of pressureless sintered products of boron carbide ceramics, researchers have attempted to add sintering aids during sintering. For example, by adding metal oxide, the densification is realized by increasing the activation of grain boundary and volume diffusion by increasing the density of point defects or dislocation; or adding transition metal boride and carbide to generate pinning effect and prevent the growth of crystal grains. However, the toughening metal is very easy to chemically react with boron carbide during high-temperature sintering, and the addition of the sintering aid also damages the hardness and high-temperature performance of the boron carbide ceramic, so that a metal material capable of well bonding boron carbide is not found at present, and the popularization and application of the pressureless sintered boron carbide ceramic are restricted by the factors.
Disclosure of Invention
The invention aims to provide a high-density boron carbide ceramic material and a pressureless sintering preparation method thereof, and solves the problem that the conventional sintering aid cannot effectively bond boron carbide in pressureless sintering.
The high-density boron carbide ceramic material comprises the following raw materials in percentage by mass: 2-8% of chromium disilicide, 3-10% of silicon carbide, 0-2% of aluminum, 3-8% of polyimide powder, 0.5-2.5% of carbon black and the balance of boron carbide.
Preferably, the high-density boron carbide ceramic material comprises the following raw materials in percentage by mass: 3-6% of chromium disilicide, 3-8% of silicon carbide, 0.5-2% of aluminum, 3-7% of polyimide powder, 0.5-2% of carbon black and the balance of boron carbide.
The preparation method of the high-density boron carbide ceramic material comprises the following steps:
1) mixing the materials except the polyimide, and then putting the mixture into a planetary ball mill for ball milling to obtain ball-milled materials;
2) adding polyimide into the ball-milled material in the step 1), uniformly mixing, drying, sieving and drying to obtain mixture micro powder;
3) pressing and molding the mixture micro powder in the step 2) to obtain a blank, and then carrying out pressureless vacuum sintering on the blank to obtain the boron carbide substrate.
4) Fully coating the boron carbide substrate in the step 3) by using an aluminum silicon foil, and sintering at low temperature in an argon atmosphere by adopting a reaction infiltration method to obtain the boron carbide ceramic.
In the step (1), a ball milling medium is absolute ethyl alcohol, the liquid-material ratio is 1: 1-2.5 g/L, the ball-material ratio is 3-8: 1, and the ball milling rotating speed is 400-600 r/min; the ball milling time is 15-50 h.
In the step (2), the aperture of the sieved screen is 50-80 meshes; the molding pressure is 180-250 MPa, and the density of the biscuit is controlled to be 1.65-2.00 g/cm3。
In the step (3), the vacuum sintering process comprises the following specific steps: firstly, heating to 1000-1200 ℃ at the speed of 8-16 ℃/min, and preserving heat for 1-2 h; then heating to 2100-2200 ℃ at a speed of 10-12 ℃/min, and preserving heat for 1.5-2.5 h; and then cooling along with the furnace, and finally completing sintering to obtain the boron carbide matrix.
In the step (4), before the infiltration process, the boron carbide substrate coated with sufficient aluminum-silicon foil is placed in a small graphite crucible with a cover, and then the small graphite crucible is placed in a large crucible to form a semi-closed system so as to prevent Al and Si from volatilizing into a furnace chamber; during infiltration, the vacuum is firstly pumped, and then argon is introduced to the micro positive pressure.
And (4) heating the obtained boron carbide substrate to 1150-1250 ℃ at a speed of 10-12 ℃/min in the infiltration process, preserving heat for 1h, and then cooling along with the furnace to obtain the boron carbide ceramic.
The invention has the beneficial effects that:
in order to improve the density of the boron carbide ceramic, a metal simple substance or a compound thereof with good wettability with boron carbide is often added. The invention adopts chromium disilicide and silicon carbide as sintering aids to improve the mechanical property of the alloy. The chromium disilicide can form an eutectic liquid phase with the boron carbide to realize liquid phase sintering, and the density of the boron carbide can be remarkably improved. The silicon carbide can be pinned at the boron carbide crystal boundary to prevent the crystal grains from growing, and the mechanical property of the silicon carbide is improved. The two sintering aids as second-phase particles are well mixed with the boron carbide matrix, have good wettability and can improve the strength of the ceramic material bonding surface. In addition, the low-melting-point Al has an activating effect on the sintering of the boron carbide, and the volume diffusion rate of the boron carbide ceramic can be improved; since Al is already contained in the reaction infiltration, the Al content in the mixed fine powder is reduced. Al is easy to react with boron carbide and silicon carbide in the sintering aid, thereby promoting the densification process of the boron carbide ceramic and improving the densification process of the boron carbide ceramicMechanical properties. Si can completely spread and wet the boron carbide matrix at 1600 ℃, and can rapidly react with boron carbide to form SiC, which is beneficial to the strength of the composite material. The polyimide and the carbon black can form CO and CO at high temperature2When gas is released, the gas reacts with the ceramic sintering to form a plurality of fine particles with high activity, and the small particle phase can inhibit abnormal growth of crystal grains in the sintering process, indirectly promotes solid phase sintering in the later stage of the reaction, and is favorable for improving the density of the boron carbide ceramic. The method combines the advantages of Al and Si, and the Al-Si alloy is infiltrated into the boron carbide matrix at low temperature to prepare the high-density boron carbide composite material.
Drawings
Figure 1 gold phase diagram for example 1 preparation of boron carbide composite material.
Figure 2 gold phase diagram of example 5 preparation of boron carbide composite.
Figure 3 gold phase diagram of pure boron carbide material prepared in comparative example 2.
Detailed Description
In order to make the technical solutions of the present invention better understood by those skilled in the art, the present invention is further described in detail with reference to the following examples. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention.
Example 1
The embodiment provides a method for preparing high-density boron carbide ceramic through pressureless sintering, which comprises the following steps of: 86% of boron carbide, 3% of chromium disilicide, 3% of silicon carbide, 1% of aluminum, 7% of polyimide and 1% of carbon black;
mixing the materials except the polyimide, and then putting the mixture into a planetary ball mill for ball milling for 40 hours; wherein the material-liquid ratio is 1:1, the ball material ratio is 6:1, and the rotating speed of the ball mill is 600 r/min. After ball milling is finished, adding polyimide into the materials, uniformly mixing, drying, sieving by a 50-mesh screen, and drying in a drying box of an air blower at low temperature to obtain mixture micro powder.
Pressing and molding the mixture micro powder under the molding pressure of 200MPa, then carrying out green body, carrying out pressureless vacuum sintering on the green body, heating to 1150 ℃ at the speed of 8 ℃/min in the sintering process, and preserving heat for 1.5 h; then heating to 2150 ℃ at a speed of 10 ℃/min, and keeping the temperature for 2 h; cooling along with the furnace after sintering to obtain a boron carbide matrix;
after trimming and cleaning the boron carbide substrate, coating the boron carbide substrate with sufficient aluminum-silicon foil, then placing the boron carbide substrate in a small graphite crucible with a cover, and then placing the boron carbide substrate in a large crucible to form a semi-closed system so as to prevent Al and Si from volatilizing into a furnace chamber; during infiltration, vacuumizing is firstly carried out, and then argon is introduced to micro positive pressure; and finally, carrying out reaction infiltration in a semi-closed system, heating to 1200 ℃ at the speed of 12 min/DEG C in the infiltration process, preserving heat for 1h, and then cooling along with the furnace to obtain the boron carbide ceramic.
The relative density of the boron carbide ceramic obtained in the embodiment is 98.8%, the Vickers hardness is 32.0GPa, and the fracture toughness is 4.1 MPa.m1/2Bending strength is 542.3 MPa; the gold phase diagram is shown in figure 1, the white part is sintering aid and infiltration metal which are uniformly distributed in the boron carbide ceramic; the method has the advantages that the size of the holes in the matrix is small, and the porosity is low, so that the method is beneficial to improving the strength and the toughness of the boron carbide ceramic while improving the relative density of the boron carbide ceramic.
Example 2
The embodiment provides a method for preparing high-density boron carbide ceramic through pressureless sintering, which comprises the following steps of: 84% of boron carbide, 4% of chromium disilicide, 6% of silicon carbide, 1.5% of aluminum, 3% of polyimide and 1.5% of carbon black;
mixing the materials except the polyimide, and then putting the mixture into a planetary ball mill for ball milling for 25 hours; wherein the material-liquid ratio is 1:2, the ball material ratio is 6:1, and the rotating speed of the ball mill is 500 r/min. And after ball milling is finished, adding polyimide into the material, uniformly mixing, drying, sieving by using a 70-mesh screen, and drying in a drying box of an air blower at low temperature to obtain mixture micro powder.
Pressing and forming the mixture at the forming pressure of 190MPa to obtain a biscuit, carrying out pressureless vacuum sintering on the biscuit, heating to 1150 ℃ at the speed of 12 ℃/min in the sintering process, and preserving heat for 1.5 h; then heating to 2150 ℃ at a speed of 12 ℃/min, and keeping the temperature for 2 h; obtaining a boron carbide matrix;
after trimming and cleaning the boron carbide substrate, coating the boron carbide substrate with sufficient aluminum-silicon foil, then placing the boron carbide substrate in a small graphite crucible with a cover, and then placing the boron carbide substrate in a large crucible to form a semi-closed system so as to prevent Al and Si from volatilizing into a furnace chamber; during infiltration, vacuumizing is firstly carried out, and then argon is introduced to micro positive pressure; and finally, carrying out reaction infiltration in a semi-closed system, heating to 1200 ℃ at the speed of 10 min/DEG C in the infiltration process, preserving heat for 1h, and then cooling along with the furnace to obtain the boron carbide ceramic.
The boron carbide ceramic prepared by the embodiment has the relative density of 97.6 percent, the Vickers hardness of 30.3GPa and the fracture toughness of 3.9 MPa.m1/2The bending strength is 470.1 MPa.
Example 3
The embodiment provides a method for preparing high-density boron carbide ceramic through pressureless sintering, which comprises the following steps of: 82% of boron carbide, 5% of chromium disilicide, 7% of silicon carbide, 0.5% of aluminum, 5% of polyimide and 0.5% of carbon black;
mixing the materials except the polyimide, and then putting the mixture into a planetary ball mill for ball milling for 30 hours; wherein the material-liquid ratio is 1:1, the ball-material ratio is 3:1, and the rotating speed of the ball mill is 500 r/min. And after ball milling is finished, adding polyimide into the material, uniformly mixing, drying, sieving by using a 70-mesh screen, and drying in a drying box of an air blower at low temperature to obtain mixture micro powder.
Pressing and molding the mixture micro powder at the molding pressure of 220MPa to obtain a biscuit, then carrying out pressureless vacuum sintering on the biscuit, heating to 1100 ℃ at the speed of 10 ℃/min in the sintering process, and preserving heat for 1 h; then heating to 2100 ℃ at a speed of 12 ℃/min, and preserving heat for 2 h; obtaining the boron carbide matrix.
After trimming and cleaning the boron carbide substrate, coating the boron carbide substrate with sufficient aluminum-silicon foil, then placing the boron carbide substrate in a small graphite crucible with a cover, and then placing the boron carbide substrate in a large crucible to form a semi-closed system so as to prevent Al and Si from volatilizing into a furnace chamber; during infiltration, vacuumizing is firstly carried out, and then argon is introduced to micro positive pressure; and finally, carrying out reaction infiltration in a semi-closed system, heating to 1150 ℃ at the speed of 12 min/DEG C in the infiltration process, preserving heat for 1h, and then cooling along with the furnace to obtain the boron carbide ceramic.
The carbonisation prepared in this exampleThe relative density of the boron ceramic is 98.9 percent, the Vickers hardness is 28GPa, and the fracture toughness is 4.7 MPa.m1/2Bending strength is 490.1 MPa.
Example 4
The embodiment provides a method for preparing high-density boron carbide ceramic through pressureless sintering, which comprises the following steps of: 79% of boron carbide, 6% of chromium disilicide, 8% of silicon carbide, 2% of aluminum, 3% of polyimide and 2% of carbon black;
mixing the materials except the polyimide, and then putting the mixture into a planetary ball mill for ball milling for 20 hours; wherein the material-liquid ratio is 1:1, the ball material ratio is 3:1, and the rotating speed of the ball mill is 400 r/min; after ball milling is finished, adding polyimide into the materials, uniformly mixing, drying, sieving by a 50-mesh sieve, and drying in a drying box of an air blower at low temperature to obtain mixture micro powder.
Pressing and molding the mixture micro powder under the molding pressure of 200MPa to obtain a biscuit, and then carrying out pressureless vacuum sintering on the biscuit, wherein the temperature is increased to 1100 ℃ at the speed of 12 ℃/min in the sintering process, and the temperature is kept for 1 h; then heating to 2100 ℃ at a speed of 10 ℃/min, and preserving heat for 2 h; obtaining the boron carbide matrix.
After trimming and cleaning the boron carbide substrate, coating the boron carbide substrate with sufficient aluminum-silicon foil, then placing the boron carbide substrate in a small graphite crucible with a cover, and then placing the boron carbide substrate in a large crucible to form a semi-closed system so as to prevent Al and Si from volatilizing into a furnace chamber; during infiltration, vacuumizing is firstly carried out, and then argon is introduced to micro positive pressure; and finally, carrying out reaction infiltration in a semi-closed system, heating to 1150 ℃ at the speed of 10 min/DEG C in the infiltration process, preserving heat for 1h, and then cooling along with the furnace to obtain the boron carbide ceramic.
The boron carbide ceramic obtained in the embodiment has the relative density of 96.0 percent, the Vickers hardness of 29.3GPa and the fracture toughness of 5.3 MPa-m1/2Bending strength 440.6 MPa.
Examples 5 to 6
Example 5 differs from example 1 in that the ball milling time in the preparation process was 15h, as in example 1; example 6 differs from example 1 in that the ball milling time in the preparation process was 50h, as in example 1.
Example 5 boron carbide ceramic comparativeThe density is 98.0 percent, the Vickers hardness is 30GPa, and the fracture toughness is 3.9 MPa.m1/2Bending strength 511.1 MPa; the gold phase diagram is shown in fig. 2, and the mixed powder particles are larger due to the reduction of the milling time. The porosity of the finished product is higher, the size of the holes is increased, and all the mechanical properties are reduced compared with those of the product in the embodiment 1.
The boron carbide ceramic obtained in example 6 had a relative density of 98.6%, a Vickers hardness of 31GPa, and a fracture toughness of 4.4 MPa-m1/2Bending strength 526.6 MPa.
Examples 7 to 8
Example 7 differs from example 3 in that the molding pressure of the green body during the production process was 180MPa, and the rest is the same as example 3; example 8 differs from example 3 in that the green body forming pressure during the production process was 250MPa, and the rest is the same as example 3.
The boron carbide ceramic obtained in example 7 had a relative density of 95.6%, a Vickers hardness of 30GPa, and a fracture toughness of 4.7MPa m1/2Bending strength 403.1 MPa.
The boron carbide ceramic obtained in example 8 had a relative density of 99.1%, a Vickers hardness of 38GPa, and a fracture toughness of 5.3MPa m1/2Bending strength 521.3 MPa.
Comparative example 1
The difference between the comparative example and the example 1 is that the reaction infiltration process is not carried out, and the boron carbide ceramic finished product is directly obtained after the presintering is finished, and the rest is the same as the example 1.
The relative density of the boron carbide ceramic prepared by the comparative example is 94.2 percent, the Vickers hardness is 30.4GPa, the fracture toughness is 3.6 MPa.m 1/2, and the bending strength is 501.2 MPa.
Comparative example 2
This comparative example differs from example 1 in that only boron carbide powder was contained in the raw material in the pre-sintering process, and the rest is the same as example 1.
The relative density of the boron carbide ceramic prepared by the comparative example is 93.3%, the Vickers hardness is 30.6GPa, the fracture toughness is 3.2 MPa.m 1/2, the bending strength is 460.2MPa, and a metallographic diagram is shown in figure 3, so that the size of holes in a matrix is increased, and the porosity is obviously improved. This is because the pre-sintering process contained only boron carbide powder, which was difficult to sinter and densify, and the density was significantly reduced compared to example 1. Meanwhile, because the sintering aid is not used as a toughening phase in the pre-sintering process, the fracture toughness and the bending strength are obviously deteriorated.
According to the invention, chromium disilicide and silicon carbide are introduced as dense phases at the same time, Al and polyimide are used as sintering aids to prepare the boron carbide ceramic, the boron carbide ceramic is sieved by a 50-80-mesh screen during preparation, the mixed powder obtained after drying is less in agglomeration and good in dispersion, and a more fine and uniform internal structure can be formed after pressing into a blank. And the molding pressure of 180-250 MPa is adopted, so that the inner part of the blank body is uniformly distributed, and the phenomena of cracking and the like are not easy to occur in the sintering process. And then, the aluminum-silicon foil is used for carrying out reaction infiltration in a mode of coating the boron carbide matrix, so that the compactness of the boron carbide ceramic prepared by a pressureless sintering method is obviously improved, and the method is also beneficial to improving the toughness of the material. The boron carbide ceramic prepared by the method has the relative density of more than 95 percent and the fracture toughness of 3.9 MPa-m1/2Above, the bending strength can reach 542.3 MPa.
It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
Claims (8)
1. The high-density boron carbide ceramic material is characterized by comprising the following raw materials in percentage by mass: 2-8% of chromium disilicide, 3-10% of silicon carbide, 0-2% of aluminum, 3-8% of polyimide powder, 0.5-2.5% of carbon black and the balance of boron carbide.
2. The high-density boron carbide ceramic material as claimed in claim 1, wherein the raw materials comprise the following components by mass percent: 3-6% of chromium disilicide, 3-8% of silicon carbide, 0.5-2% of aluminum, 3-7% of polyimide powder, 0.5-2% of carbon black and the balance of boron carbide.
3. A method for preparing a highly dense boron carbide ceramic material according to claim 1 or 2, comprising the steps of:
1) mixing the materials except the polyimide, and then putting the mixture into a planetary ball mill for ball milling to obtain ball-milled materials;
2) adding polyimide into the ball-milled material in the step 1), uniformly mixing, and then drying, sieving and drying to obtain mixture micro powder;
3) pressing and forming the mixture micro powder in the step 2) to obtain a blank, and then carrying out pressureless vacuum sintering on the blank to obtain a boron carbide substrate;
4) fully coating the boron carbide substrate in the step 3) by using an aluminum silicon foil, and sintering at low temperature in an argon atmosphere by adopting a reaction infiltration method to obtain the boron carbide ceramic.
4. The preparation method of the high-density boron carbide ceramic material according to claim 3, wherein in the step (1), the ball milling medium is absolute ethyl alcohol, the liquid-material ratio is 1: 1-2.5 g/L, the ball-material ratio is 3-8: 1, and the ball milling speed is 400-600 r/min; the ball milling time is 15-50 h.
5. The preparation method of the high-density boron carbide ceramic material according to claim 3, wherein in the step (2), the size of the sieved mesh is 50-80 meshes; the molding pressure is 180-250 MPa, and the density of the biscuit is controlled to be 1.65-2.00 g/cm3。
6. The method for preparing the high-density boron carbide ceramic material according to claim 3, wherein in the step (3), the vacuum sintering comprises the following specific steps: firstly, heating to 1000-1200 ℃ at the speed of 8-16 ℃/min, and preserving heat for 1-2 h; then heating to 2100-2200 ℃ at a speed of 10-12 ℃/min, and preserving heat for 1.5-2.5 h; and then cooling along with the furnace, and finally completing sintering to obtain the boron carbide matrix.
7. The method for preparing a highly densified boron carbide ceramic material according to claim 3, wherein in the step (4), before the infiltration process, the boron carbide substrate coated with a sufficient amount of aluminum-silicon foil is placed in a small graphite crucible with a cover and then placed in a large crucible to form a semi-closed system so as to prevent Al and Si from volatilizing into a furnace chamber; during infiltration, the vacuum is firstly pumped, and then argon is introduced to the micro positive pressure.
8. The preparation method of the high-density boron carbide ceramic material according to claim 3 or 7, wherein in the step (4), the temperature of the obtained boron carbide substrate is raised to 1150-1250 ℃ at a rate of 10-12 ℃/min in the infiltration process, the temperature is maintained for 1h, and then the boron carbide ceramic is obtained after furnace cooling.
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