Preparation method of boron carbide-based composite ceramic with low sintering temperature

Abstract

The invention discloses a preparation method of boron carbide-based multiphase ceramic with low sintering temperature, which comprises the following steps: firstly, activating boron carbide powder in an activating etching solution, and removing surface oxides to form etching defects to improve the surface catalytic activity; then putting the activated boron carbide powder into a solution containing metal cations, adjusting the temperature and the pH value, and carrying out chemical plating treatment to form boron carbide ceramic powder wrapped by a metal layer; then, the powder is subjected to cold pressing on a cold press to form a green body, then the green body is put into a graphite mold, and in the hot pressing sintering process, the boron carbide-based composite ceramic is prepared at a relatively low temperature by utilizing the characteristic that the metal melting point is relatively low. The boron carbide-based composite ceramic prepared by sintering is high in density and uniform in composition and structure, and the problems that the boron carbide sintering temperature still cannot be greatly reduced by adding a traditional sintering aid, and adverse effects are possibly caused on the density, hardness and other mechanical properties are successfully avoided.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic preparation, in particular to a method for preparing boron carbide-based composite ceramics with a low sintering temperature. Background Art

[0002] Boron carbide is an excellent ceramic material with many excellent properties such as low density, high hardness, high strength, stable chemical properties, etc. However, due to its high internal covalent bond content (93.9%), its melting point is very high (2350℃), its plasticity is relatively poor, its sintering activation energy is relatively low, and its diffusion rate is very low, which makes the sintering and densification of boron carbide ceramics very difficult. In addition, the surface of boron carbide will generally oxidize to form a dense B2O3 film, which further hinders the densification of boron carbide. Therefore, improving the densification of boron carbide and achieving low-temperature sintering has always been the focus of current research. This results in boron carbide generally being sintered at a temperature greater than 2100°C. However, during the sintering process at a higher temperature, rapid grain growth is inevitable. Adding a sintering aid second phase for doping sintering is an effective way to reduce the densification temperature of boron carbide. For example, a carbonaceous precursor can remove the boron oxide (such as B2O3) on the surface of B4C at a low temperature, causing a reduction reaction, and can form a eutectic liquid phase at the grain boundary at a high temperature, thereby enhancing the density of B4C. The addition of oxides may react with B4C to form low-melting-point substances (such as the addition of aluminum oxide may form AlB 12 C2 phase), these substances will produce liquid phase sintering, promote the sliding, rotation and rearrangement of particles, and are beneficial to the densification of ceramics. Transition metal carbides can react with B4C in situ to generate carbon and transition metal borides to promote the sintering process and hinder the growth of grains. The addition of transition metal borides may form a eutectic liquid phase to promote the sintering of B4C (such as the addition of CrB2). Metal additives can promote the liquid phase sintering of B4C ceramics, but it is necessary to ensure good wettability between the two. The metal additives currently used mainly include Al, Ti, Fe, Mg, Cu, etc., which are beneficial to sintering by forming a liquid phase at high temperature and greatly reduce the porosity (such as the addition of Fe). However, the introduction of a large amount of other impurity elements will not only lead to a decrease in the hardness of the material, but also increase the density of the material. Therefore, under the premise of maintaining its low density and high hardness, how to promote the low-temperature sintering of boron carbide through reasonable design is a key issue currently studied. Summary of the invention

[0003] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0004] Therefore, the purpose of the present invention is to provide a method for preparing a boron carbide-based composite ceramic with a low sintering temperature, by performing surface chemical plating on boron carbide to wrap a metal layer on the surface of the boron carbide particles, taking advantage of the low melting point of the metal layer, and then performing low-temperature hot pressing sintering to form a boron carbide-based composite ceramic with a low melting point phase distributed along the grains.

[0005] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0006] A method for preparing a boron carbide-based composite ceramic with a low sintering temperature, comprising the following steps:

[0007] S1. Weigh the boron carbide powder, put the powder into 30-50 ml / L of activation etching solution, remove the boron oxide on the surface of the boron carbide, and form step-shaped defects on the surface of the boron carbide, then mechanically stir for 5-20 minutes at room temperature, then wash with deionized water 5 times to remove the etching solution and the etching product residue, and then dry it at 80 ° C for 10-12 hours to obtain dry activated boron carbide powder for subsequent chemical plating treatment;

[0008] S2, placing the activated boron carbide powder in step S1 into a chemical plating solution containing metal ions, adjusting the temperature and pH value to form a metal layer on the surface of the boron carbide, mechanically stirring at a speed of 50-100 r / min for 5-40 min, then washing with deionized water for 5 times to remove the residue of the chemical plating solution and some weakly bonded titanium particles, and then drying it at 80° C. for 10-12 h to finally obtain a dry metal-coated boron carbide ceramic powder for subsequent hot pressing sintering;

[0009] S3, placing the metal-coated boron carbide ceramic powder obtained in step S2 into a sintering mold made of graphite, and pressing it in a cold press to obtain a boron carbide-based composite ceramic body;

[0010] S4. The boron carbide-based composite ceramic green body obtained in step S3 is loaded into a graphite mold covered with graphite paper, and hot-pressed sintered in an argon atmosphere, with the sintering temperature controlled to be 1600-1700° C., the holding time to be 60-120 min, and the sintering pressure applied to be 20-60 MPa to obtain a boron carbide-based composite ceramic material.

[0011] As a preferred solution of the method for preparing a low sintering temperature boron carbide-based composite ceramic described in the present invention, the activation etching solution in step S1 is a hydrofluoric acid solution, an aqua regia solution, or SnCl2 and HCl that promote sensitization.

[0012] As a preferred solution of the method for preparing a low sintering temperature boron carbide-based composite ceramic according to the present invention, the concentration of the activation etching solution in step S1 is 30-50 ml / L, and the etching conditions of the boron carbide powder can be varied.

[0013] As a preferred embodiment of the method for preparing a low sintering temperature boron carbide-based composite ceramic described in the present invention, the rotation speed of the mechanical stirring in step S1 and step S2 is 50-100 r / min, the stirring time in step S1 is 5-20 min, and the stirring time in step S2 is 5-40 min.

[0014] As a preferred solution of the method for preparing a boron carbide-based composite ceramic with a low sintering temperature according to the present invention, the deionized water washing is performed 5 times in step S1 and step S2.

[0015] As a preferred embodiment of the method for preparing a low sintering temperature boron carbide-based composite ceramic according to the present invention, the powder drying process of the activation treatment and chemical plating treatment in step S1 and step S2 is to bake in a vacuum drying oven at 70-85°C for 8-12 hours.

[0016] As a preferred embodiment of the method for preparing a low sintering temperature boron carbide-based composite ceramic described in the present invention, the chemical plating solution in step S2 is a solution containing metal ions, such as a nickel ion solution or a copper ion solution, and the complexing agent in the chemical plating solution is generally an ethylenediamine solution.

[0017] As a preferred embodiment of the method for preparing a low sintering temperature boron carbide-based composite ceramic according to the present invention, the temperature of the chemical plating solution in step S2 is 75-85°C, the pH is 12-14, and the pH is adjusted with a sodium hydroxide solution.

[0018] As a preferred embodiment of the method for preparing a low sintering temperature boron carbide-based composite ceramic described in the present invention, the thickness of the metal layer in the metal-encapsulated boron carbide ceramic powder obtained in step S3 is variable, and boron carbide ceramic powders with different metal layer thicknesses can be obtained by adjusting the parameters of step S2.

[0019] As a preferred embodiment of the method for preparing a low sintering temperature boron carbide-based composite ceramic according to the present invention, in step S3, the heating is carried out in an argon / hydrogen atmosphere to 1600-1700°C according to a step-by-step heating method, and the heating rate is: 0-800°C heating rate is 10-15°C / minute, 800-1500°C heating rate is 7-8°C / minute, and above 1500°C heating rate is 5°C / minute. During the cooling process, the cooling rate is 5°C / minute above 1500°C. For the Cu metal layer, a hydrogen atmosphere is generally selected to prevent oxidation, and the same process steps are used.

[0020] As a preferred embodiment of the method for preparing a low sintering temperature boron carbide-based composite ceramic described in the present invention, the heating and pressurizing process in step S3 is pressurized according to a step-by-step pressurization method, firstly a pre-pressing pressure of 1 MPa is performed, and when the temperature is 0-300°C, the pressure of 1 MPa is maintained unchanged, and then when the temperature rises from 300°C to 800°C, the pressure is gradually increased to the set pressure, and finally the pressure remains unchanged until the end of the insulation stage, and then the pressure gradually drops to 1 MPa in the process of cooling to 1500°C, and the subsequent pressure is gradually reduced to 0 MPa.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention first activates boron carbide powder in an activated etching solution to remove surface oxides to form etching defects and improve surface catalytic activity; then the activated boron carbide powder is placed in a solution containing metal cations, the temperature and pH are adjusted, and chemical plating is performed to form a boron carbide ceramic powder wrapped in a metal layer; then the powder is cold-pressed on a cold press to form a green body, and then placed in a graphite mold. During the hot pressing sintering process, the boron carbide-based composite ceramic is prepared at a relatively low temperature by utilizing the characteristics of the low melting point of the metal. The boron carbide-based composite ceramic prepared by sintering has high density, uniform composition and structure, and successfully avoids the problem that the addition of traditional sintering aids still cannot significantly reduce the sintering temperature of boron carbide, and may have an adverse effect on mechanical properties such as density and hardness. Therefore, the present invention provides a process method for reducing the sintering temperature of boron carbide by surface modification of boron carbide particles, realizing the sintering preparation of boron carbide ceramics at a relatively low temperature, and has broad application prospects.

[0023] 2. The chemical plating treatment of the boron carbide surface makes full use of the characteristics of controllable thickness and low melting point of the chemically plated metal layer. On the one hand, only a thin layer of metal layer can be coated on the surface of the boron carbide particles, rather than a large amount of mixed powder addition, which has little effect on the overall density and mechanical properties; on the other hand, the melting point of the metal is low, and the purpose of promoting the sintering process is achieved by melting the metal first, thereby forming a boron carbide-based composite ceramic with high density, uniform composition and structure.

[0024] 3. The sintering temperature of the boron carbide-based composite ceramics prepared by the present invention is significantly reduced, and a boron carbide-based ceramic sample with a density of 98.9% can be obtained at a sintering temperature of 1700°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below in combination with the accompanying drawings and detailed embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0026] Figure 1 The present invention is a flow chart of a method for preparing a boron carbide-based composite ceramic with a low sintering temperature. DETAILED DESCRIPTION

[0027] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0028] The present invention provides a method for preparing a boron carbide-based composite ceramic with a low sintering temperature. The method comprises the following steps: performing a surface chemical plating treatment on boron carbide to wrap a metal layer on the surface of boron carbide particles, taking advantage of the low melting point of the metal layer, and then performing low-temperature hot pressing sintering to form a boron carbide-based composite ceramic with a low melting point phase distributed along the grains.

[0029] Embodiment 1:

[0030] S1. Activation treatment of boron carbide powder: Weigh a certain amount of boron carbide powder, put the powder into 50ml / L hydrofluoric acid activation etching solution to remove the boron oxide on the surface of boron carbide, and at the same time form step-shaped defects on the surface of boron carbide to make it have good catalytic activity, which is conducive to the adsorption, nucleation and growth of metal particles on the surface of boron carbide during chemical plating; mechanically stir for 30min at a speed of 100r / min at room temperature, and stirring is mainly to promote the activation process, on the one hand to avoid the sedimentation and agglomeration of boron carbide powder, on the other hand to accelerate the shedding and dissolution of etching products; then wash with deionized water 5 times to remove the etching solution and etching product residues, and then dry it in a vacuum drying oven at 80℃ for 12h, pass through a 100-mesh sieve to prevent the particle powder from agglomerating, and obtain dry activated boron carbide powder for subsequent chemical plating treatment;

[0031] S2, chemical plating treatment of boron carbide powder: put the activated boron carbide powder in step S1 into a chemical plating solution containing nickel ions, adjust the temperature to 85°C and the pH value to 12, so that a metal layer is formed on the surface of the boron carbide to promote sintering and reduce the sintering temperature of the ceramic powder; mechanically stir at a speed of 100r / min at room temperature for 40min, stirring is mainly to promote the chemical plating process, on the one hand to avoid the sedimentation and agglomeration of the boron carbide powder, on the other hand, it also plays a role in increasing the contact between the solution and the boron carbide powder, which is conducive to promoting the deposition process of chemical nickel plating powder, thereby obtaining a nickel plating layer with a more uniform thickness on the surface of the boron carbide; then wash it with deionized water 5 times to remove the residue of the chemical plating solution and some weakly bonded titanium particles, and then dry it in a vacuum drying oven at 80°C for 12h, pass it through a 100-mesh sieve to prevent the particle powder from agglomerating, and finally obtain a dry metal-coated boron carbide ceramic powder for subsequent hot pressing sintering;

[0032] S3, cold pressing of composite ceramic materials: placing the metal-coated boron carbide ceramic powder obtained in step S2 into a graphite sintering mold, and pressing the powder in a cold press at 60 MPa to obtain a boron carbide-based composite ceramic body;

[0033] S4. Sintering preparation of composite ceramic material: The boron carbide-based composite ceramic green body obtained in step S3 is loaded into a graphite mold (with a diameter of 32 mm) covered with graphite paper, and hot-pressed sintering is performed under an argon atmosphere. The sintering temperature is controlled to be 1700°C, the holding time is 120 min, and the sintering pressure is 50 MPa to obtain a boron carbide-based composite ceramic material. The temperature is heated according to a step-by-step heating method, and the heating rate is as follows: 0-800°C heating rate is 10-15°C / min, 800-1500°C heating rate is 7-8°C / min, 1500°C-1700°C heating rate is 5°C / min, and during the cooling process, the cooling rate is 5°C / min above 1700°C-1500°C, and then the material is cooled with the furnace. Sintering in an argon atmosphere prevents the formation of oxidation products. The heating and cooling rates above 1500°C are slow, all to prevent sintering too quickly and cracking. The heating and pressurizing process also follows the step-by-step pressurization method. First, pre-press 1MPa pressure is applied. When the temperature is 0-300°C, the pressure is kept constant at 1MPa. Then, when the temperature rises from 300°C to 800°C, the pressure is gradually increased to the set pressure. Finally, the pressure remains unchanged until the end of the insulation stage. Then, the pressure gradually drops to 1MPa during the cooling process to 1500°C, and then the pressure gradually decreases to 0MPa. Applying pressure during the sintering process helps to promote the sintering process and obtain a higher density sample.

[0034] Among them, the B4C powder is produced by Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of ≥99.9%, the hydrofluoric acid solution is produced by Sinopharm Chemical Reagent Co., Ltd., AR (Shanghai test), ≥40.0%, the vacuum drying oven is DZF-6050 type produced by Shanghai Yiheng Scientific Instrument Co., Ltd., the 100-mesh screen is a 304 stainless steel screen produced by Jiufeng Metal Wire Mesh Manufacturing Co., Ltd., the chemical plating solution containing metal ions is mainly NiSO4, the graphite mold is produced by Liaoyang Xingwang Graphite Products Co., Ltd., the hot pressing sintering furnace is a vacuum hot pressing sintering furnace produced by Shanghai Chenhua Technology Co., Ltd., and the argon gas is produced by Liquid Air (Shanghai) Compressed Gas Co., Ltd., with a purity of ≥99.99%.

[0035] Embodiment 2:

[0036] S1. Activation treatment of boron carbide powder: Weigh a certain amount of boron carbide powder, put the powder into 50ml / L hydrofluoric acid activation etching solution to remove the boron oxide on the surface of boron carbide, and at the same time form step-shaped defects on the surface of boron carbide to make it have good catalytic activity, which is conducive to the adsorption, nucleation and growth of metal particles on the surface of boron carbide during chemical plating; mechanically stir for 20min at a speed of 100r / min at room temperature. Stirring is mainly to promote the activation process, on the one hand to avoid the sedimentation and agglomeration of boron carbide powder, and on the other hand to accelerate the shedding and dissolution of etching products; then wash with deionized water 5 times to remove the etching solution and etching product residues, and then dry it in a vacuum drying oven at 80℃ for 12h, pass through a 100-mesh sieve to prevent the particle powder from agglomerating, and obtain dry activated boron carbide powder for subsequent chemical plating treatment;

[0037] S2, chemical plating treatment of boron carbide powder: put the activated boron carbide powder in step S1 into a chemical plating solution containing nickel ions, adjust the temperature to 85°C and the pH value to 12, so that a metal layer is formed on the surface of the boron carbide to promote sintering and reduce the sintering temperature of the ceramic powder; at room temperature, the speed is 50r / min and mechanical stirring is performed for 15min. The stirring is mainly to promote the chemical plating process. On the one hand, it prevents the boron carbide powder from settling and agglomerating. On the other hand, it also plays a role in increasing the contact between the solution and the boron carbide powder, which is conducive to promoting the deposition process of chemical nickel plating powder, thereby obtaining a nickel plating layer with a more uniform thickness on the surface of the boron carbide; then wash it with deionized water 5 times to remove the residue of the chemical plating solution and some weakly bonded titanium particles, and then dry it in a vacuum drying oven at 80°C for 12h, pass it through a 100-mesh sieve to prevent the particle powder from agglomerating, and finally obtain a dry metal-coated boron carbide ceramic powder for subsequent hot pressing sintering;

[0038] S3, cold pressing of composite ceramic materials: placing the metal-coated boron carbide ceramic powder obtained in step S2 into a graphite sintering mold, and pressing the powder in a cold press at 60 MPa to obtain a boron carbide-based composite ceramic body;

[0039] S4. Sintering preparation of composite ceramic material: The boron carbide-based composite ceramic green body obtained in step S3 is loaded into a graphite mold (with a diameter of 32 mm) covered with graphite paper, and hot-pressed sintering is performed under an argon atmosphere. The sintering temperature is controlled to be 1700°C, the holding time is 120 min, and the sintering pressure is 50 MPa to obtain a boron carbide-based composite ceramic material. The temperature is heated according to a step-by-step heating method, and the heating rate is as follows: 0-800°C heating rate is 10-15°C / min, 800-1500°C heating rate is 7-8°C / min, 1500°C-1700°C heating rate is 5°C / min, and during the cooling process, the cooling rate is 5°C / min above 1700°C-1500°C, and then the material is cooled with the furnace. Sintering in an argon atmosphere prevents the formation of oxidation products. The heating and cooling rates above 1500°C are slow, all to prevent sintering too quickly and cracking. The heating and pressurizing process also follows the step-by-step pressurization method. First, pre-press 1MPa pressure is applied. When the temperature is 0-300°C, the pressure is kept constant at 1MPa. Then, when the temperature rises from 300°C to 800°C, the pressure is gradually increased to the set pressure. Finally, the pressure remains unchanged until the end of the insulation stage. Then, the pressure gradually drops to 1MPa during the cooling process to 1500°C, and then the pressure gradually decreases to 0MPa. Applying pressure during the sintering process helps to promote the sintering process and obtain a higher density sample.

[0040] Among them, the B4C powder is produced by Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of ≥99.9%, the hydrofluoric acid solution is produced by Sinopharm Chemical Reagent Co., Ltd., AR (Shanghai test), ≥40.0%, the vacuum drying oven is DZF-6050 type produced by Shanghai Yiheng Scientific Instrument Co., Ltd., the 100-mesh screen is a 304 stainless steel screen produced by Jiufeng Metal Wire Mesh Manufacturing Co., Ltd., the chemical plating solution containing metal ions is mainly NiSO4, the graphite mold is produced by Liaoyang Xingwang Graphite Products Co., Ltd., the hot pressing sintering furnace is a vacuum hot pressing sintering furnace produced by Shanghai Chenhua Technology Co., Ltd., and the argon gas is produced by Liquid Air (Shanghai) Compressed Gas Co., Ltd., with a purity of ≥99.99%.

[0041] Embodiment 3:

[0042] S1. Activation treatment of boron carbide powder: Weigh a certain amount of boron carbide powder, put the powder into 50ml / L hydrofluoric acid activation etching solution to remove the boron oxide on the surface of boron carbide, and at the same time form step-shaped defects on the surface of boron carbide to make it have good catalytic activity, which is conducive to the adsorption, nucleation and growth of metal particles on the surface of boron carbide during chemical plating; mechanically stir for 20min at a speed of 100r / min at room temperature. Stirring is mainly to promote the activation process, on the one hand to avoid the sedimentation and agglomeration of boron carbide powder, and on the other hand to accelerate the shedding and dissolution of etching products; then wash with deionized water 5 times to remove the etching solution and etching product residues, and then dry it in a vacuum drying oven at 80℃ for 12h, pass through a 100-mesh sieve to prevent the particle powder from agglomerating, and obtain dry activated boron carbide powder for subsequent chemical plating treatment;

[0043] S2, chemical plating treatment of boron carbide powder: put the activated boron carbide powder in step S1 into a chemical plating solution containing copper ions, adjust the temperature to 85°C and the pH value to 12, so that a metal layer is formed on the surface of the boron carbide to promote sintering and reduce the sintering temperature of the ceramic powder; mechanically stir at a speed of 100r / min at room temperature for 40min, stirring is mainly to promote the chemical plating process, on the one hand to avoid the sedimentation and agglomeration of the boron carbide powder, on the other hand, it also plays a role in increasing the contact between the solution and the boron carbide powder, which is conducive to promoting the deposition process of chemical copper plating powder, thereby obtaining a copper plating layer with more uniform thickness on the surface of the boron carbide; then wash it with deionized water 5 times to remove the residue of the chemical plating solution and some weakly bonded titanium particles, and then dry it in a vacuum drying oven at 80°C for 12h, pass it through a 100-mesh sieve to prevent the particle powder from agglomerating, and finally obtain a dry metal-coated boron carbide ceramic powder for subsequent hot pressing sintering;

[0044] S3, cold pressing of composite ceramic materials: placing the metal-coated boron carbide ceramic powder obtained in step S2 into a graphite sintering mold, and pressing the powder in a cold press at 60 MPa to obtain a boron carbide-based composite ceramic body;

[0045] S4. Sintering preparation of composite ceramic material: The boron carbide-based composite ceramic green body obtained in step S3 is loaded into a graphite mold (with a diameter of 32 mm) covered with graphite paper, and hot-pressed sintering is performed under a hydrogen atmosphere. The sintering temperature is controlled to be 1700°C, the holding time is 120 min, and the sintering pressure is 50 MPa to obtain a boron carbide-based composite ceramic material. The temperature is heated according to a step-by-step heating method, and the heating rate is as follows: 0-800°C heating rate is 10-15°C / min, 800-1500°C heating rate is 7-8°C / min, 1500°C-1700°C heating rate is 5°C / min, and during the cooling process, the cooling rate is 5°C / min above 1700°C-1500°C, and then the material is cooled with the furnace. Sintering in a hydrogen atmosphere plays a reducing role to prevent the formation of oxidation products. The heating and cooling rates above 1500°C are slow, all to prevent sintering too fast and cracking. The heating and pressurizing process also follows the step-by-step pressurization method. First, pre-press 1MPa pressure is applied. When the temperature is 0-300°C, the pressure is kept constant at 1MPa. Then, when the temperature rises from 300°C to 800°C, the pressure is gradually increased to the set pressure. Finally, the pressure remains unchanged until the end of the insulation stage. Then, the pressure gradually drops to 1MPa during the cooling process to 1500°C, and then the pressure gradually decreases to 0MPa. Applying pressure during sintering helps to promote the sintering process and obtain a higher density sample.

[0046] Among them, the B4C powder is produced by Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of ≥99.9%, the hydrofluoric acid solution is produced by Sinopharm Chemical Reagent Co., Ltd., AR (Shanghai test), ≥40.0%, the vacuum drying oven is DZF-6050 type produced by Shanghai Yiheng Scientific Instrument Co., Ltd., the 100-mesh screen is a 304 stainless steel screen produced by Jiufeng Metal Wire Mesh Manufacturing Co., Ltd., the chemical plating solution containing metal ions is mainly NiSO4, the graphite mold is produced by Liaoyang Xingwang Graphite Products Co., Ltd., the hot pressing sintering furnace is a vacuum hot pressing sintering furnace produced by Shanghai Chenhua Technology Co., Ltd., and the hydrogen is produced by Shanghai Haoqi Gas Co., Ltd.

[0047] Although the present invention has been described above with reference to the embodiments, various modifications may be made thereto and parts thereof may be replaced by equivalents without departing from the scope of the present invention. In particular, as long as there is no structural conflict, the various features in the embodiments disclosed in the present invention may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a boron carbide-based composite ceramic with a low sintering temperature, characterized in that: Here are the steps: S1. Weigh the boron carbide powder, put the powder into 30-50 ml / L of activation etching solution, remove the boron oxide on the surface of the boron carbide, and form step-shaped defects on the surface of the boron carbide, then mechanically stir for 5-20 minutes at room temperature, then wash with deionized water 5 times to remove the etching solution and the etching product residue, and then dry it at 80 ° C for 10-12 hours to obtain dry activated boron carbide powder for subsequent chemical plating treatment; S2, placing the activated boron carbide powder in step S1 into a chemical plating solution containing metal ions, adjusting the temperature and pH value to form a metal layer on the surface of the boron carbide, mechanically stirring at a speed of 50-100 r / min for 5-40 min, then washing with deionized water for 5 times to remove the residue of the chemical plating solution and some weakly bonded titanium particles, and then drying it at 80° C. for 10-12 h to finally obtain a dry metal-coated boron carbide ceramic powder for subsequent hot pressing sintering; S3, placing the metal-coated boron carbide ceramic powder obtained in step S2 into a sintering mold made of graphite, and pressing it in a cold press to obtain a boron carbide-based composite ceramic body; S4. The boron carbide-based composite ceramic green body obtained in step S3 is loaded into a graphite mold covered with graphite paper, and hot-pressed sintered in an argon atmosphere, with the sintering temperature controlled to be 1600-1700° C., the holding time to be 60-120 min, and the sintering pressure applied to be 20-60 MPa to obtain a boron carbide-based composite ceramic material.

2. The method for preparing a low sintering temperature boron carbide-based composite ceramic according to claim 1, characterized in that: The activation etching solution in step S1 is a hydrofluoric acid solution, an aqua regia solution, or SnCl2 and HCl that promote sensitization.

3. The method for preparing a low sintering temperature boron carbide-based composite ceramic according to claim 1, characterized in that: The concentration of the activation etching solution in step S1 is 30-50 ml / L, and the etching conditions of the boron carbide powder can be varied.

4. The method for preparing a low sintering temperature boron carbide-based composite ceramic according to claim 1, characterized in that: The rotation speed of the mechanical stirring in step S1 and step S2 is 50-100 r / min, the stirring time in step S1 is 5-20 min, and the stirring time in step S2 is 5-40 min.

5. The method for preparing a boron carbide-based composite ceramic with a low sintering temperature according to claim 1, characterized in that: In the steps S1 and S2, the washing is performed with deionized water for 5 times.

6. The method for preparing a low sintering temperature boron carbide-based composite ceramic according to claim 1, characterized in that: The powder drying process of the activation treatment and chemical plating treatment in step S1 and step S2 is to dry the powder in a vacuum drying oven at 70-85° C. for 8-12 hours.

7. The method for preparing a low sintering temperature boron carbide-based composite ceramic according to claim 1, characterized in that: The chemical plating solution in step S2 is a solution containing metal ions, such as a nickel ion solution or a copper ion solution, and the complexing agent in the chemical plating solution is generally an ethylenediamine solution.

8. The method for preparing a low sintering temperature boron carbide-based composite ceramic according to claim 1, characterized in that: The solution temperature of the chemical plating solution in step S2 is 75-85° C., the pH is 12-14, and the pH is adjusted with sodium hydroxide solution.

9. The method for preparing a boron carbide-based composite ceramic with a low sintering temperature according to claim 1, characterized in that: The thickness of the metal layer in the metal-encapsulated boron carbide ceramic powder obtained in step S3 is variable, and boron carbide ceramic powders with different metal layer thicknesses can be obtained by adjusting the parameters of step S2.

10. The method for preparing a boron carbide-based composite ceramic with a low sintering temperature according to claim 1, characterized in that: In the step S3, the material is heated to 1600-1700°C in an argon atmosphere according to a step-by-step heating method, and the heating rate is: 0-800°C heating rate is 10-15°C / minute, 800-1500°C heating rate is 7-8°C / minute, and above 1500°C the heating rate is 5°C / minute. During the cooling process, the cooling rate above 1500°C is 5°C / minute. The heating and pressurizing process is pressurized according to a step-by-step pressurization method. First, a pre-pressing pressure of 1MPa is performed. When the temperature is 0-300°C, the pressure of 1MPa is maintained unchanged. Then, when the temperature is increased from 300°C to 800°C, the pressure is gradually increased to the set pressure. Finally, the pressure remains unchanged until the end of the insulation stage. Then, in the process of cooling to 1500°C, the pressure gradually drops to 1MPa, and the subsequent pressure gradually decreases to 0MPa. For the Cu metal layer, a hydrogen atmosphere is generally selected to prevent oxidation, and the same process steps are used.

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