CN112142469A - Graphite-based oxidation-resistant section bar, preparation method and application - Google Patents
Graphite-based oxidation-resistant section bar, preparation method and application Download PDFInfo
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Abstract
The invention provides a graphite-based oxidation-resistant section bar, a preparation method and application thereof. The graphite-based oxidation-resistant section is prepared from 75-85 parts of graphite powder, 15-30 parts of boron nitride powder, 5-10 parts of water-based carbon black and 2-5 parts of boric acid; the preparation method comprises the following steps: adding water into carbon black and boric acid, heating, dissolving, dispersing uniformly, spraying and granulating, crushing to average diameter below 2 μm, mixing with graphite powder and boron nitride powder, ball milling, and hot pressing at temperature of 1900-2100 ℃ under vacuum of 100 Pa; in the obtained graphite-based oxidation-resistant section, boron nitride is completely converted, and a large amount of boron carbide which does not have acute angles and is more than 90 percent of which the size is 0.3-0.5 mu m is dispersed among graphite grains; the aluminum alloy can be ground to 1.6 mu m surface finish, has low resistivity, high thermal conductivity, oxidation resistance, thermal shock resistance and stable performance, does not adhere to the contact surface of metal aluminum, is easy to demould, has low reduction of the finish of the contact surface and light abrasion, and can be used as a die material for induction diffusion welding hot-pressing forming of a metal aluminum sheet material.
Description
Technical Field
The invention belongs to the technical field of graphite-based novel composite materials, and particularly relates to a graphite-based oxidation-resistant section bar, a preparation method and application thereof.
Background
The graphite-based hot-pressed section has better electric conductivity, heat conductivity and thermal shock resistance, does not soak metal materials, can generate heat through medium-frequency induction, and is used for hot-press forming of 500-650 ℃ induction diffusion welding of metal aluminum layer materials; however, the strength, wear resistance and oxidation resistance of the alloy are often contradictory to the electric conduction, heat conduction and metal adhesion resistance, and are not easy to balance.
CN110563465A provides a mold material for hot press molding and a preparation method thereof, wherein the mold material comprises graphite, silicon carbide, pitch, and zirconia; the weight percentage content is as follows: 1-3% of silicon carbide, 5-15% of asphalt, 0.1-1% of zirconia and the balance of graphite. The preparation method comprises the following steps: (1) adding graphite and asphalt into a kneading machine, kneading for 30-60min, and cooling to obtain a mixed material; (2) putting the mixed material into a mold, compacting and vacuumizing, then sending into an isostatic press for static pressure forming, and demolding to obtain a raw blank; (3) roasting the green blank under the protection of inert gas at the roasting temperature of 900-1100 ℃ to obtain graphite blocks; (4) putting the roasted graphite block into an antioxidant impregnant for pressure impregnation treatment for 3-6h, wherein the antioxidant impregnant comprises the following raw materials: aluminum dihydrogen phosphate, sodium pyrophosphate, sodium tungstate, barium oxide, strontium carbonate, sodium fluoride, triethanolamine and water; (5) heating the graphite block after the dipping treatment to 400-500 ℃, keeping the temperature and roasting for 0.5-1.5h, then heating to 850-950 ℃, keeping the temperature for 0.5-1.0h, and cooling to room temperature; (6) and (4) coating the surface of the graphite module roasted in the step (5) with the silicon carbide and zirconium oxide mixed slurry, airing, placing into a graphite furnace, heating to 1300-.
CN110563464A discloses a high-temperature-resistant and oxidation-resistant graphite mold and a preparation method thereof, wherein the mold material comprises, by weight, 15-25% of asphalt, 3-5% of silicon nitride, 0.3-0.8% of titanium nitride, 0.1-0.5% of yttrium and 0.1-0.5% of erbium; the balance being graphite. The preparation method comprises the following steps: the preparation method comprises the following steps of (1) adding graphite and asphalt into a kneading machine, kneading for 30-60min, cooling to obtain a mixed material, (2) placing the mixed material into a mold, compacting and vacuumizing, then sending into an isostatic press for static pressure forming, demolding to obtain a raw blank, (3) roasting the raw blank for 1-2h under the protection of inert gas, wherein the roasting temperature is 900-, preserving the heat for 0.5 to 1.0 hour, and cooling to room temperature; (6) and (3) coating the surface of the graphite module roasted in the step (5) with mixed slurry containing silicon nitride, titanium nitride, yttrium and erbium, airing, putting into a graphite furnace, heating to 1500-.
The graphite mold prepared by the two processes of CN110563465A and CN110563464A has certain oxidation resistance, compressive strength and electric conductivity under the conditions of 500-650 ℃, but the preparation process is more complex, the density is lower than 90 percent, the service life is shorter in the application of 500-650 ℃ induction diffusion welding of the metal aluminum sheet material, and the use cost is higher; the anti-oxidation impregnant, the mixed slurry containing silicon carbide and zirconium oxide and the mixed slurry containing silicon nitride, titanium nitride, yttrium and erbium, which are used in the preparation steps (4) to (6), are basically coated on the surface layer and the surface of the graphite module, and the coating formed after high-temperature treatment in a graphite furnace is still mainly on the surface layer and the surface of the graphite module, less enters the interior of the graphite module, and the loss is large or the precision mechanical grinding treatment is inconvenient after the further precision mechanical grinding treatment. In the two processes (6), the graphite furnace has more volatile amount of impregnant in the high-temperature treatment process, which causes the heating of the graphite furnace and the faster corrosion of heat-insulating materials; the non-volatile part of the impregnant or the conversion product thereof is easy to adhere to the metal aluminum sheet material in the hot pressing process of the induction diffusion welding, so that the demolding speed is reduced, and the surface layer of the graphite mold can be adhered and separated sometimes.
CN101550004A provides a graphite-zirconium carbide oxidation-resistant ablation-resistant material and a preparation method thereof; the material is prepared from 10-30% of zirconia powder and 90-70% of graphite powder by volume ratio; wherein the purity of the zirconium oxide powder is more than 98 percent, and the particle size is 1 mu m; the purity of the graphite powder is more than 98%, the diameter is 10-20 mu m, and the thickness is 1-2 mu m. The preparation method comprises the following steps: firstly, ball-milling and wet-mixing raw material powder to obtain slurry; evaporating and drying the slurry on a rotary evaporator, and then grinding to obtain mixed powder; and thirdly, placing the mixed powder under the vacuum condition that the temperature is 1900-2100 ℃ and the pressure is 20-40 MPa, carrying out heat preservation sintering for 30-90 min, cooling along with the furnace, and taking out to obtain the graphite-zirconium carbide oxidation-resistant ablation type material. The high-strength zirconium carbide in the graphite-zirconium carbide oxidation and ablation resistant material is generated by chemical reaction, the zirconium carbide is better contacted with graphite, and the final density of the material is more than 90%. As described in page 5, second last line, etc., of the specification, white fine zirconium carbide particles are seen to be distributed in the graphite matrix in the observation of the microstructure of the material.
The graphite-zirconium carbide oxidation-resistant ablation-resistant material prepared by CN101550004A, such as the material prepared by the fourteen methods of the embodiment, and the mold further processed, has short service life in the application of 500-650 ℃ induction diffusion welding of the metal aluminum sheet material, because the wear-resistant performance is not enough, mainly because the zirconium carbide particles generated in the microstructure are too small to reach the required size of 0.3-0.5 μm.
CN1235941 provides a preparation method of a high-temperature oxidation-resistant carbon-based composite material, which comprises the following steps: (1) mixing calcined coke powder, asphalt powder, graphite powder and B4C, uniformly mixing the raw materials according to the weight ratio of (20-40) to (1-10) to 1 to (1-5), ball-milling the mixture for 0.5 to 2 hours, and carrying out hot pressing on the mixture at the temperature of 2300 ℃ under the pressure of 20MPa and 2000-; (2) adopting SiO to the surface of the graphite base material obtained in the step (1)2Chemical vapor infiltration diffusion of vapor to produce gradient SiC coatings with SiO2And carbon powder or silicon powder as raw material according to SiO2And the weight ratio of C or Si = 1: 1, siliconizing the graphite matrix material for 1 hour at 1500-1600 ℃ under the vacuum condition, and obtaining the product.
The CN1235941 does not disclose the physical and chemical indexes of the used boron carbide powder. The available boron carbide powder in the market includes industrial powder and nanometer powder. The industrial boron carbide powder is produced into lump materials by an electric arc furnace method, and then is crushed and smashed into the powder, the powder has large particles and sharp corners, the overall dimension of the particles is generally more than 10 mu m, most of the particles are reserved in the prepared carbon-based composite material product, the appearance and the dimension of the particles are basically unchanged, so that the prepared carbon-based composite material can not be used as a die material for the induction diffusion welding of the metal aluminum sheet material, and the reason is that the carbon-based composite material has sharp corners and boron carbide particles with the overall dimension of more than 10 mu m are dispersed in graphite, so that the carbon-based composite material is difficult to obtain the surface finish within 1.6 mu m required by the metal aluminum sheet material induction diffusion welding die material through. The surface finish within 1.6 mu m of the die material is required to avoid the improvement of the surface roughness of the metal and the reduction of the oxidation resistance. Some nano boron carbide powder particles are close to spherical in appearance, the appearance size is about 50nm, the price is high, the nano boron carbide powder particles are difficult to be uniformly mixed with carbon raw materials such as calcined coke powder, asphalt powder, graphite powder and the like, the nano boron carbide powder particles are difficult to grow to the required size of more than 0.3 mu m in the preparation process disclosed in CN1235941, and the effect of improving the wear resistance of the obtained carbon-based composite material is not easy to play.
Disclosure of Invention
In order to solve the technical problems, the invention provides a graphite-based oxidation-resistant section, a preparation method and application in an induction diffusion welding die for a metal aluminum sheet material.
The graphite-based oxidation-resistant section comprises, by mass, 75-85 parts of graphite powder, 15-30 parts of boron nitride powder, 5-10 parts of water-based carbon black and 2-5 parts of boric acid; the graphite powder has a mass purity of more than or equal to 99.9%, a volume average particle size of 12-30 μm, and a specific surface area of 15-35m2(ii)/g; the boron nitride powder has a volume average particle diameter of 1-3 μm and a specific surface area of 20-40m2The mass content of BN is more than or equal to 99 percent, and the mass content of elements except nitrogen, boron, oxygen and carbon is less than or equal to 0.1 percent; the mass content of C in the water-based carbon black is more than or equal to 96 percent, the average particle size is 15-30nm, and the specific surface area is 100-2The mass content of elements except carbon, oxygen, nitrogen and sulfur is less than or equal to 0.1 percent.
The invention discloses a preparation method of a graphite-based oxidation-resistant section, which comprises the following steps:
(1) putting the water-based carbon black and boric acid into a container with a stirring device, adding 40-80 parts of water, heating to 40-60 ℃, stirring until the boric acid is completely dissolved and the water-soluble carbon black is uniformly dispersed, and then carrying out spray granulation to obtain carbon black-boric acid granulated powder with the average diameter of 25-150 mu m; the inlet temperature of hot air for spray granulation is 150-180 ℃, and the exhaust temperature is 80-90 ℃;
(2) crushing the carbon black-boric acid granulated powder until the average diameter is less than 2 mu m to obtain carbon black-boric acid micro powder;
(3) uniformly mixing graphite powder, boron nitride powder and carbon black-boric acid micro powder, then ball-milling, loading into a hot-pressing furnace, vacuumizing to below 100Pa, pressurizing to 20-30MPa, heating to 1200-1300 ℃ at the speed of 20-30 ℃/min, heating to 1900-2000 ℃ at the speed of 10-15 ℃/min, preserving heat for 2-4h, heating to 2100 ℃ at the speed of 2000-20 ℃/min, preserving heat for 1-3h, stopping heating, cooling to below 150 ℃, discharging, and maintaining the vacuum below 100Pa and the pressure of 20-30MPa before discharging;
(4) and (3) cutting the discharged furnace lump material to remove the surface layer to obtain the graphite-based oxidation-resistant section.
Detecting that boron nitride is completely converted in the obtained graphite-based oxidation-resistant section, and a large amount of boron carbide, namely B, is dispersed among graphite grains4C crystal grains; the edges of the boron carbide crystal grains have certain roundness without acute angles or sharp angles; the boron carbide grains have a size of 0.3 to 0.5 μm in 90% or more and a size of less than 3% in 0.7 μm or more, and boron carbide particles having a size of 1.0 μm or more are found as a base.
Other test results for the graphite-based oxidation resistant shapes obtained are listed in table 1 below. The thermal conductivity testing method is a laser flash method. The thermal shock circulation at 500-650 ℃ is carried out by heating a 200x100x10mm test block ground to 1.6 mu m surface finish with about 1000W induction heating power in air atmosphere, keeping the temperature at 500-650 ℃ for 2-3min respectively, and cooling from 650-500 ℃ through covering a 250x130x30mm metal aluminum plate at room temperature-300 ℃; or heating with 60x10mm test block with surface smoothness of 1.6 μm under air atmosphere with induction power of about 200W, maintaining at 500 deg.C and 650 deg.C for 2-3min, and cooling from 650 deg.C to 500 deg.C by covering with 100x100x20mm aluminum metal plate at room temperature-300 deg.C.
Table 1 partial test results for graphite-based oxidation resistant shapes
The test results in table 1 show that the obtained graphite-based oxidation-resistant section has very high oxidation resistance and very stable electric and heat conductivity at 500 ℃ and 650 ℃ in air atmosphere, and that the surface of graphite grains or particles which can contact air is tightly covered with the boron carbide dense layer, and the boron carbide dense layer and the boron carbide grains are very stable and do not oxidize at the temperature of below 650 ℃ in air, which is the root cause of the oxidation resistance of the graphite-based section of the invention. This is also different from the situation that some documents report that the industrial boron carbide powder produced by the electric arc furnace-grinding method is significantly oxidized and weighted under the air condition of 600 ℃, and the reasons for the non-oxidation of the industrial boron carbide powder include short/fast high-temperature preparation reaction process (using boron oxide and high-specific-surface-area and high-activity carbon material as raw materials, supplying heat by electric arc, reacting to the boron carbide melting temperature of more than 2350 ℃), high impurity content (the purity of boron carbide is generally less than 98%), and cracks and defects caused by high-strength grinding; in the graphite-based oxidation-resistant section, the boron carbide dense layer and the boron carbide submicron crystal grains are mainly volatilized at a very low rate under the temperature of 1900-2000 ℃, and then slowly generate boron carbide with carbon materials such as graphite with a relatively low specific surface area and relatively low activity, and then the boron carbide is subjected to an aging process at the temperature of 2000-2100 ℃, so that the obtained boron carbide coating is dense, the graphite crystal grains or particles are completely coated, the impurity content is very low, the obtained submicron boron carbide crystal grains are perfect and sufficient, and the impurity content is very low, therefore, the oxidation basically does not occur after the heat treatment of 650 ℃ air atmosphere for 500h and the 100 times of thermal shock circulation at the temperature of 500-650 ℃, and the performance of the graphite-based section is prevented from being basically stable and not changing.
The main functions or reactions of the steps in the preparation process of the graphite-based oxidation-resistant section comprise: in the carbon black-boric acid micropowder of the step (1), boric acid or a preliminary thermal decomposition dehydrate thereof is dispersed among carbon black particles and on the surfaces of the carbon black particles; uniformly mixing and ball-milling graphite powder, boron nitride powder and carbon black-boric acid micro powder, completely dehydrating boric acid or a preliminary thermal decomposition dehydrate of the carbon black-boric acid micro powder in the temperature rising process to generate boron oxide melt, absorbing and coating the boron oxide melt in and on the carbon black crystal grains, generating more boron carbide crystal seeds after the temperature is 1600 ℃, slowly volatilizing a part of boron nitride and slowly depositing the boron carbide generated by the carbon black on the boron carbide crystal seeds and continuously growing the boron carbide crystal seeds into crystal grains at the temperature of 1800 ℃ and 2000 ℃, slowly volatilizing a part of boron nitride and slowly depositing the boron carbide generated by the graphite on the inner part and the surface of the graphite crystal grains until the boron oxide and the boron nitride completely react with the carbon material; in the heat preservation process of 2000-2100 ℃, the previously generated boron carbide is subjected to slow volatilization, internal recrystallization, impurity discharge and/or volatilization to densify the coating and completely coat graphite grains or particles, and the obtained boron carbide grains reach the size of 0.3-0.5 mu m and have no acute angles or sharp angles.
In the heating process of the hot pressing furnace in the step (3) of the preparation process of the graphite-based oxidation-resistant section, a higher heating rate is adopted, and one of the purposes is to avoid the problems that the number of boron carbide crystal seeds generated at the outer edge of a hot pressing block is less due to volatilization loss of boron oxide obtained by thermal decomposition of boric acid in the slow heating process, so that the number of boron carbide crystal grains generated at the outer edge of the hot pressing block is less and the grain size is overlarge, wherein the boron carbide crystal grains are 0.3-0.5 mu m; the second purpose is to reduce the problems of excessive growth, recrystallization and too fast reduction of specific surface area of graphite grains, carbon black grains and boron nitride grains in the slow temperature rise process, which leads to the fast reduction of reaction and volatilization activities of the graphite, the carbon black and the boron nitride, and further leads to the problems of less quantity of the generated 0.3-0.5 mu m boron carbide grains and too large grain size.
In the heating process of the hot pressing furnace in the step (3) of the preparation process of the graphite-based oxidation-resistant section, after the temperature is raised to 1200 ℃, if the temperature is not subjected to the 1900-2000 ℃ heat preservation reaction stage, and the temperature is directly raised from 1200 ℃ to 2050-2100 ℃ for example, and after the temperature is preserved for 3 hours, the heating is stopped, and in the obtained graphite-based section, boron carbide dispersed among graphite grains, namely B4The number of C grains is significantly reduced, with the boron carbide grains mostly being 1.0 μm or more in size and much exceeding 2.0 μm, making the resulting graphite-based profile incapable of being mechanically ground to a 1.6 μm surface finish. This is achieved byIt shows that boron oxide and carbon black produce boron carbide seed crystal with less quantity due to volatilization and recrystallization, and boron nitride volatilizes too fast and boron carbide crystal grain grows too fast, which results in obviously less quantity and over-large size of boron carbide crystal grain.
The graphite-base oxidation-resistant section bar of the invention can be used as a die material for induction diffusion welding hot-press forming of a metal aluminum layer material, after mechanical grinding processing, the surface finish degree of 1.6 mu m, the required structure, the required size and necessary accessories are achieved, and the obtained single set of die has low resistivity, high thermal conductivity, oxidation resistance, thermal shock resistance and stable performance, does not adhere to the contact surface of metal aluminum, is easy to demould, has very slow reduction of the finish degree of the contact surface and extremely light abrasion in the application of the induction diffusion welding hot-press forming of the metal aluminum layer material at the temperature of 500 ℃ and 650 ℃, can have the hot-press forming processing amount of more than 20000 times and the service life of more than 3 months, reduces the finish degree of the contact surface with the metal aluminum during use, and can be subjected to multiple grinding treatments after abrasion without reduction of the performance basically. The contact surface of the graphite-based section bar mold and the metal aluminum is not adhered to each other and is easy to demould, and the reasons are that the graphite and the metal aluminum are not soaked and a coating layer of the metal aluminum is not easy to adhere to each other; the reason why the contact surface can be given a surface finish of, for example, 1.6 μm, is mainly that the graphite grains or intergranular boron carbide grains have substantially a size of 0.3 to 0.5 μm and no sharp or pointed corners; the reason why the smoothness of the contact surface is reduced slowly and the abrasion is light is mainly that the boron carbide crystal grains with the size of 0.3-0.5 mu m and no sharp angle or sharp angle are dispersed in the graphite more uniformly and form good combination with the graphite, wherein the compact boron carbide coating which completely coats the graphite crystal grains or particles also greatly contributes to the combination of the boron carbide crystal grains with the size of 0.3-0.5 mu m and the stone mill crystal grains or particles; the characteristics can ensure that the graphite-based section bar of the invention obtains better overall performance in the application of the metal aluminum sheet material induction diffusion welding hot-press molding die material.
Detailed Description
The technical solution of the present invention will be specifically described and illustrated with reference to the following examples, but the present invention is not limited thereto.
Graphite powder used in the following examples and comparative examples99.9% mass purity, 19 μm volume average particle diameter, and 22m specific surface area2(ii)/g; the boron nitride powder used has a volume average particle diameter of 1.8 μm and a specific surface area of 27m2The mass content of BN is 99.2 percent, and the mass content of elements except nitrogen, boron, oxygen and carbon is less than or equal to 0.1 percent; the mass content of C in the used water-based carbon black is more than or equal to 96 percent, the average particle size is 20nm, and the specific surface area is 118m2The mass content of elements except carbon, oxygen, nitrogen and sulfur is less than or equal to 0.1 percent.
Example 1
The invention discloses a preparation method of a graphite-based oxidation-resistant section, which comprises the following steps:
(1) placing 80g of the water-soluble carbon black and 30g of boric acid in a container with a stirrer, adding 600g of water, heating to 50 ℃, stirring until the boric acid is completely dissolved and the water-soluble carbon black is uniformly dispersed, and then carrying out spray granulation to obtain carbon black-boric acid granulated powder with the average diameter of 60 mu m; the inlet temperature of hot air for spray granulation is 170 ℃, and the exhaust temperature is 85 ℃;
(2) crushing the carbon black-boric acid granulated powder until the average diameter is 1.3 mu m to obtain carbon black-boric acid micro powder;
(3) uniformly mixing 800g of graphite powder, 200g of boron nitride powder and all carbon black-boric acid micro powder, then ball-milling, putting about 120g of graphite powder into a hot-pressing experimental furnace, vacuumizing to about 50Pa, pressurizing to 25MPa, heating to 1200 ℃ at the speed of 25 ℃/min, heating to 1950 ℃ at the speed of 15 ℃/min, preserving heat for 3h, heating to 2050 ℃ at the speed of 12 ℃/min, preserving heat for 2h, stopping heating, cooling to below 150 ℃, discharging, and maintaining the vacuum below 50Pa and the pressure of 25MPa before discharging;
(4) and (3) cutting the discharged furnace lump material to remove the surface layer to obtain the graphite-based oxidation-resistant section.
The hot-pressing in the experimental furnace of the step (3) and the step (4) are repeated 6 times to obtain enough graphite-based profile samples for testing.
Detecting that boron nitride is completely converted in the obtained graphite-based sectional material, and a large amount of boron carbide, namely B, is dispersed among graphite crystal grains4C crystal grains; the edges of the boron carbide crystal grains have certain roundness without acute angles or sharp angles; more than 92% of the boron carbide crystal grains have a size of 0.3-0.5 μm, and less than 3% of the size of 0.7 μmBoron carbide particles having a size of 1.0 μm or more were found; microscopic analysis shows that the surface of graphite crystal grains or particles is covered with a boron carbide dense layer. The obtained graphite-based sectional material is easy to mechanically grind to 1.6 mu m surface smoothness; firstly, processing to the size phi of 60x10mm, and then grinding one surface to the surface smoothness of 1.6 mu m to prepare a graphite-based profile test block; the test surface with the surface finish of 1.6 microns is pressed on a fixed metal aluminum grinding block with the surface finish of 1.6 microns under the conditions of room temperature and air at the pressure of 0.1MPa, and the graphite-based section bar test block is moved at the speed of 30mm/min for 200mm in total, so that the surface finish of the test surface of the graphite-based section bar test block is reduced, which indicates that the wear resistance of the test surface is better and meets the wear resistance requirement of a hot-press forming die material for induction diffusion welding of a metal aluminum sheet material.
Other test results for the graphite-based oxidation resistant shapes obtained are listed in table 2 below. Wherein the thermal conductivity test method is a laser flash method; the thermal shock circulation at 500-650 deg.C is carried out by heating test block with surface smoothness of 1.6 μm and size phi 60x10mm with induction power of about 200W in air atmosphere, maintaining at 500 deg.C and 650 deg.C for 2-3min, and cooling from 650 deg.C to 500 deg.C by covering with 100x100x20mm aluminum metal plate at room temperature-300 deg.C.
Table 2 partial test results for graphite-based oxidation resistant shapes
Comparative example 1
The operations of steps (1) to (4) of example 1 were substantially repeated except that the aqueous carbon black was not used.
The result was that the graphite-based material obtained had been completely converted from boron nitride and much less boron carbide, B, had dispersed among the graphite grains than in example 14C crystal grains, wherein about 45% of the boron carbide crystal grains have a size of 0.3 to 0.5 μm, and about 40% of the boron carbide crystal grains have a size of 0.7 μm or more, and a large number of boron carbide particles having a size of 1.0 μm or more are present. The graphite-based profile obtained is more difficult to mechanically grind to a surface finish of 1.6 μm.
Comparative example 2
The operations of steps (1) to (4) of carrying out 1 were substantially repeated except that boric acid was not used.
The result is that the boron nitride in the obtained graphite-based section bar is completely converted, and only a small amount of boron carbide, namely B, is dispersed among graphite crystal grains4C crystal grains, and boron carbide crystal grains having a majority size of 1.0 μm or more, and a majority of them having a size of 1.5 μm or more. The resulting graphite-based profile was not mechanically ground to a 1.6 μm surface finish.
Comparative example 3
The operations of steps (1) to (4) of carrying out 1 are substantially repeated except that boron nitride powder is not used. And (4) repeating the experimental furnace hot pressing in the step (3) and the step (4) for 3 times to obtain the required test sample of the graphite-based profile.
One of the test results is that the boron oxide in the obtained graphite-based sectional material is completely converted, and a small amount of boron carbide, namely B, is dispersed among graphite crystal grains4C crystal grains, but most of the boron carbide crystal grains have a size of 0.2 μm or less. The obtained graphite-based section is easy to mechanically grind to a surface finish of 1.6 microns, but the result of the wear resistance test performed according to the embodiment 1 and the fixed metal aluminum grinding block with the surface finish of 1.6 microns is that the surface finish of the test surface of the graphite-based section test block is obviously reduced, which indicates that the wear resistance of the test surface is not good and does not meet the wear resistance requirement of the metal aluminum sheet material induction diffusion welding hot-pressing forming die material.
The second test result is that the oxidation resistance of the obtained graphite-based profile is significantly reduced. In an air atmosphere oxidation test at 650 ℃, the weight loss is 0.1% in 12h and 0.3% in 20h, which indicates that the graphite crystal grains or the graphite particle powder can be completely coated with the compact boron carbide coating or the boron carbide coating is not compact. After the 20-hour 650 ℃ air atmosphere oxidation test, the resistivity of the test sample is improved by 16%, and the bending strength is reduced by 8%.
Comparative example 4
The operations of steps (3) to (4) of step (1) are substantially repeated except that each temperature increase rate is halved during the temperature increase of the autoclave of step (3).
The test result of the obtained graphite-based sectional material shows that the boron oxide is not completely converted, and the boron carbide dispersed among graphite crystal grains is B4The number of C crystal grains is obviously reduced, the majority of the boron carbide crystal grains have the size of more than 0.8 mu m,and much more than 1.5 μm, especially the outer edge part of the hot-press block; the graphite-based profile obtained is more difficult to mechanically grind to a surface finish of 1.6 μm.
Comparative example 5
Basically repeating the operations of the steps (3) to (4) in the step (1), wherein the difference is that in the heating process of the autoclave in the step (3), the temperature is increased to 1200 ℃, then the temperature is directly increased to 2050 ℃ at the speed of 15 ℃/min, the heating is stopped after the heat preservation is carried out for 3h, and the heat preservation is not carried out for 3h at the temperature of 1950 ℃.
The test result of the obtained graphite-based section bar shows that the boron carbide dispersed among graphite crystal grains is B4The number of C crystal grains is obviously reduced, and most of the boron carbide crystal grains have the size of more than 1.0 mu m and much more than 2.0 mu m; the resulting graphite-based profile was not mechanically ground to a 1.6 μm surface finish.
Example 2
About 20kg of a graphite-based oxidation-resistant shape was prepared by using industrial equipment substantially in accordance with the methods of steps (1) to (4) of example 1 and the charge ratio. The difference is that the average diameter of the carbon black-boric acid granulated powder obtained in the step (1) is 78 mu m; step (2) crushing the carbon black-boric acid granulated powder until the average diameter is 1.5 mu m; and (3) keeping about 10Pa vacuum in the operation of the industrial hot-pressing furnace.
A plurality of small test blocks are cut out of the obtained graphite-based section for detection, a plurality of large test blocks are cut out, and a die material is made for an application test of induction diffusion welding hot-press forming of the metal aluminum sheet material.
In the obtained graphite-based section detection block, boron nitride is completely converted, and a large amount of boron carbide, namely B, is dispersed among graphite crystal grains4C crystal grains; the edges of the boron carbide crystal grains have certain roundness without acute angles or sharp angles; the boron carbide grains have a size of 0.3 to 0.5 μm in 90% or more and a size of less than 2% in 0.7 μm or more, and boron carbide particles having a size of 1.0 μm or more are found as a base. The obtained graphite-based sectional material is easy to mechanically grind to 1.6 mu m surface smoothness; firstly, processing to the size phi of 60x10mm, and then grinding one surface to the surface smoothness of 1.6 mu m to prepare a graphite-based profile test block; the obtained test surface with a surface finish of 1.6 μm was pressed against a fixed metal with a surface finish of 1.6 μm under a pressure of 0.1MPa at room temperature in airAnd moving the graphite-based section test block at the speed of 30mm/min for 200mm on the aluminum grinding block, so that the surface finish of the test surface of the graphite-based section test block is reduced, which indicates that the graphite-based section test block has better wear resistance and meets the wear resistance requirement of the metal aluminum sheet material induction diffusion welding hot-press forming die material.
Other test results for the graphite-based oxidation resistant shapes obtained are listed in table 3 below. Wherein the thermal conductivity test method is a laser flash method; the thermal shock cycle at 500-650 deg.C is carried out by heating a 200X100X10mm test block ground to 1.6 μm surface finish with about 1000W induction power in an air atmosphere, maintaining the temperature at 500 deg.C and 650 deg.C for 2-3min, and cooling from 650 deg.C to 500 deg.C by covering a 250X130X30mm aluminum metal plate at room temperature-300 deg.C.
Table 3 partial test results for graphite-based oxidation resistant shapes
The application surface of the manufactured die has 1.6 mu m surface finish, and in a user application test of induction diffusion welding hot press molding of the metal aluminum sheet material, the typical die temperature range condition is 500-650 ℃, the pressure is 10MPa, the thickness of the aluminum foil is 0.12mm, and 25 layers are laminated. The graphite-based section of the die has the advantages of low resistivity, high thermal conductivity, oxidation resistance, thermal shock resistance, stable performance, no adhesion with the contact surface of metal aluminum, easy die release, slow reduction of the finish degree of the contact surface, extremely light abrasion and the like, the processing amount of the single die set for hot press molding exceeds 20000 times, the service life is more than 3 months, the finish degree of the contact surface with the metal aluminum is reduced during the use, the performance is not reduced basically after 5 times of grinding treatment after abrasion, and the application surface of the die can reach the finish degree of 1.6 mu m after each grinding treatment.
Claims (8)
1. A graphite-based oxidation-resistant section is prepared from 75-85 parts of graphite powder, 15-30 parts of boron nitride powder, 5-10 parts of water-based carbon black and 2-5 parts of boric acid by mass; the graphite powder has the mass purity of more than or equal to 99.9 percent, the volume average particle size of 12-30 mu m and the specific surface area of 15-35m2(ii)/g; the boron nitride powder has a volume average particle diameter of 1-3 μm and a specific surface area of 20-40m2The mass content of BN is more than or equal to 99 percent, and the mass content of elements except nitrogen, boron, oxygen and carbon is less than or equal to 0.1 percent; the mass content of C in the water-based carbon black is more than or equal to 96 percent, the average particle size is 15-30nm, and the specific surface area is 100-2The mass content of elements except carbon, oxygen, nitrogen and sulfur is less than or equal to 0.1 percent.
2. The graphite-based oxidation-resistant profile according to claim 1, wherein the raw materials for preparing the graphite-based oxidation-resistant profile comprise 80 parts of graphite powder, 20 parts of boron nitride powder, 8 parts of water-based carbon black and 3 parts of boric acid.
3. A method of making the graphite-based oxidation resistant shape of claim 1, comprising the steps of:
(1) putting the water-based carbon black and boric acid into a container with a stirring device, adding 40-80 parts of water, heating to 40-60 ℃, stirring until the boric acid is completely dissolved and the water-soluble carbon black is uniformly dispersed, and then carrying out spray granulation to obtain carbon black-boric acid granulated powder with the average diameter of 25-150 mu m; the inlet temperature of hot air for spray granulation is 150-180 ℃, and the exhaust temperature is 80-90 ℃;
(2) crushing the carbon black-boric acid granulated powder until the average diameter is less than 2 mu m to obtain carbon black-boric acid micro powder;
(3) uniformly mixing graphite powder, boron nitride powder and carbon black-boric acid micro powder, then ball-milling, loading into a hot-pressing furnace, vacuumizing to below 100Pa, pressurizing to 20-30MPa, heating to 1200-1300 ℃ at the speed of 20-30 ℃/min, heating to 1900-2000 ℃ at the speed of 10-15 ℃/min, preserving heat for 2-4h, heating to 2100 ℃ at the speed of 2000-20 ℃/min, preserving heat for 1-3h, stopping heating, cooling to below 150 ℃, discharging, and maintaining the vacuum below 100Pa and the pressure of 20-30MPa before discharging;
(4) and (3) cutting the discharged furnace lump material to remove the surface layer to obtain the graphite-based oxidation-resistant section.
4. The method for preparing the graphite-based oxidation-resistant shape according to claim 3, wherein in the obtained graphite-based oxidation-resistant shape, boron carbide grains are dispersed among graphite grains; the edge of the boron carbide crystal grain has no acute angle or sharp angle; more than 90% of the boron carbide crystal grains have a size of 0.3-0.5 μm.
5. The method for producing an oxidation-resistant graphite-based molding according to claim 3 or 4, wherein the graphite-based oxidation-resistant molding obtained is coated with a dense layer of boron carbide on the surface of graphite crystal grains or particles.
6. The use of the graphite-based oxidation resistant shape as defined in claim 1 as a material for an induction diffusion welding hot-press forming die for a metal aluminum laminate material.
7. The use of the graphite-based oxidation-resistant material as the material of the hot-press forming die for the induction diffusion welding of the aluminum foil material as set forth in claim 6, wherein the application surface of the hot-press forming die for the induction diffusion welding of the aluminum foil material is prepared to have a surface finish of 1.6 μm.
8. The use of the graphite-based oxidation resistant shape as a hot-press molding die material for metal aluminum laminate material induction diffusion welding as claimed in claim 6, wherein the operation conditions of the graphite-based oxidation resistant shape in the die are air atmosphere and temperature of 500-650 ℃.
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