CN104892005A - Preparation method of silicon nitride-based self-lubricating ceramic cutter material containing alumina-coated hexagonal boron nitride composite powder - Google Patents

Abstract

The invention relates to a method for preparing a silicon nitride-based self-lubricating ceramic tool material with aluminum oxide-coated hexagonal boron nitride composite powder. The volume percentage of the raw material components is: micron silicon nitride 57-70%, nano silicon nitride 5-15%, micron titanium carbide 5-15%, alumina 3.2%, yttrium oxide 4.8%, alumina-coated hexagonal boron nitride 2-15%; including the steps: first prepare the alumina coating with a particle size of 4-12μm Hexagonal boron nitride-coated composite powder; weigh micron silicon nitride, nano silicon nitride, and micron titanium carbide, respectively make suspensions, ultrasonically disperse, mix, then add alumina and yttrium oxide, and ultrasonically disperse for 15-20 minutes; Composite suspension; ball milling the composite suspension, then adding aluminum oxide-coated hexagonal boron nitride composite powder to continue ball milling, vacuum drying to obtain a mixed powder; vacuum hot-pressing sintering. The silicon nitride-based self-lubricating ceramic cutter material prepared by adding alumina-coated hexagonal boron nitride composite powder can not only improve the mechanical properties of the ceramic cutter, but also take into account the self-lubricating performance.

Description

Preparation method of silicon nitride-based self-lubricating ceramic tool material with alumina-coated hexagonal boron nitride composite powder added

technical field

The invention relates to a method for preparing a silicon nitride-based self-lubricating ceramic tool material, especially a method for preparing a silicon nitride-based self-lubricating ceramic tool material with alumina-coated hexagonal boron nitride composite powder, which belongs to the technology of self-lubricating tool materials field.

Background technique

In the process of metal cutting, the negative effects brought by the use of cutting fluid are becoming more and more obvious, such as polluting the environment, endangering the health of workers, and increasing the production cost of enterprises due to the processing of cutting fluid. Therefore, it is necessary to cancel cutting fluid and replace it with dry Type cutting can well solve the above problems. Therefore, people put forward the concept of self-lubricating tools, which is to add solid lubricants to the tools, so that the solid lubricants can be dispersed in the tools, so that the tools have self-lubricating properties, reduce the friction coefficient, reduce the wear of the tools, and improve the tool life. service life. The study found that the composite self-lubricating tool materials containing solid lubricants were prepared. With the increase of solid lubricant content, the mechanical properties of self-lubricating tool materials generally decreased with the increase of lubricant content.

Hexagonal boron nitride (h-BN) has very excellent chemical stability, it is still very stable at a temperature of 2800°C in an inert atmosphere, and it also has good lubricating properties, and is an excellent solid lubricant. Adding h-BN to ceramic tool materials can effectively improve the lubricating performance and thermal shock resistance of ceramic materials, realize the effect of reducing friction and antiwear, and avoid the environmental and cost problems caused by the use of lubricating fluid. However, the mechanical properties of h-BN are low, and the dispersed distribution in the tool may make the mechanical properties of the tool worse. To overcome this shortcoming, people have developed micro-pool self-lubricating tools, coated self-lubricating tools and in-situ reaction self-lubricating tools. However, none of these three methods can fundamentally solve the problem that directly adding solid lubricants to the cutting tool leads to the reduction of the mechanical properties of the cutting tool. CN102502535A discloses a method for preparing carbon-coated hexagonal boron nitride, which uses boric acid and urea as raw materials to prepare hexagonal boron nitride, and then uses maleic anhydride ethylene octene graft copolymer as a carbon source, through stirring, extraction, Suction filtration, drying and high-temperature carbonization steps to obtain carbon-coated hexagonal boron nitride with a core-shell structure; it shows good dispersion when added to base oil or polymer resin, and can still perform in extreme environments such as high temperature and high pressure. Good mechanical properties and good wear resistance. However, this carbon-coated hexagonal boron nitride method is not suitable for silicon nitride-based self-lubricating ceramic tool materials.

Contents of the invention

In order to make up for the deficiencies of the existing technology, a method for preparing silicon nitride-based self-lubricating ceramic tool materials with alumina-coated hexagonal boron nitride composite powder is provided, which not only ensures the mechanical properties of self-lubricating tools but also takes into account its self-lubricating properties , so that the Vickers hardness, fracture toughness, and bending strength of the tool material are improved, and the wear-reducing and wear-resisting properties are better.

Technical scheme of the present invention is as follows:

A method for preparing a silicon nitride-based self-lubricating ceramic tool material with alumina-coated hexagonal boron nitride composite powder, the raw material component volume percentage is: micron silicon nitride (α-Si ₃ N ₄ ) 57-70% , nano silicon nitride (α-Si ₃ N ₄ ) 5-15%, micron titanium carbide 5-15%, aluminum oxide 3.2%, yttrium oxide 4.8%, aluminum oxide coated hexagonal boron nitride 2-15%;

Including the following steps:

(1) Mix hexagonal boron nitride powder with a particle size of 3-10 μm and dispersant polyethylene glycol in distilled water to form a 3-8g/L hexagonal boron nitride suspension. The amount of dispersant added is the mass of hexagonal boron nitride 3-5%. Add acetic acid-sodium acetate buffer solution with a pH value of 4.5, ultrasonically disperse and heat to 30°C-40°C with stirring, slowly add aluminum nitrate solution with an Al3 ⁺ concentration of 0.1-0.2mol/L dropwise, the aluminum nitrate solution The amount to be added is based on the molar ratio BN:Al=1:0.5-1, then slowly add ammonia water dropwise until the pH value of the reaction solution is 7.0-7.5, after the addition, keep the temperature at 30°C-40°C for 1.5-2.5h, and then let it stand Aging, sedimentation, filtration, cleaning, centrifugation, and vacuum drying to obtain hexagonal boron nitride composite powder coated with aluminum hydroxide on the surface, and vacuum calcination to obtain alumina-coated hexagonal boron nitride composite powder with a particle size of 4-12 μm;

(2) Proportionally weigh micron silicon nitride, nano silicon nitride, and micron titanium carbide, and use an appropriate amount of absolute ethanol as the dispersion medium to prepare micron silicon nitride, micron titanium carbide suspension and nano silicon nitride respectively. Suspension, fully stirred while ultrasonically dispersed for 15-20min; mixed the dispersed micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension, and then added the aluminum oxide and yttrium oxide in proportion, fully Stir and ultrasonically disperse for 15-20 minutes; obtain a multi-phase suspension;

(3) Pour the above-mentioned multi-phase suspension into a ball milling tank, fill with argon or nitrogen as a protective gas, add balls for ball milling, and mill for 36-48 hours to obtain the mixture after ball milling, and weigh the aluminum oxide in step (1) in proportion Coat the hexagonal boron nitride composite powder, use absolute ethanol as the dispersion medium, make a suspension, and disperse it ultrasonically for 10 minutes; add the obtained suspension to the mixture after ball milling, fill with argon or nitrogen as a protective gas, and add ball milling balls , continue ball milling for 8-12h. Then take out the ball milling liquid and place it in a drying box, and dry it in vacuum at 100-120°C for 24-36 hours; after the drying is complete, pass the obtained mixed powder through a 200-mesh sieve to obtain the mixed powder, which is sealed for later use;

(4) Vacuum hot pressing sintering process is adopted to sinter the mixed powder obtained in step (3) into a compression mold.

Preferably according to the present invention, the volume percentage of the raw material components is 62-67% of micron silicon nitride, 10% of nano silicon nitride, 10% of micron titanium carbide, 3.2% of aluminum oxide, 4.8% of yttrium oxide, aluminum oxide coated Coated with hexagonal boron nitride 5-10%. The tool material prepared with this ratio has the best comprehensive mechanical properties and anti-friction and wear-resisting properties.

Preferably according to the present invention, the stirring and heating described in step (1) is magnetically stirred and heated in a digital display heat-collecting magnetic stirrer, so that the suspension is uniformly dispersed.

Preferably according to the present invention, the aluminum nitrate solution described in the step (1) is prepared by adding water to aluminum nitrate nonahydrate; the most preferred Al3 ⁺ concentration is the aluminum nitrate solution of 0.15mol/L.

Preferably according to the present invention, the added amount of the pH buffer solution in step (1) is 8-15mL/100mL distilled water, more preferably the added amount of the pH buffer solution is 10-11mL/100mL distilled water.

Preferably according to the present invention, the ammonia water described in the step (1) is diluted 5-10 times with distilled water with 28% concentrated ammonia water by mass percentage to obtain an ammonia solution with a pH value of 6.5-8.5.

Preferably according to the present invention, the suspension described in step (1) is left to stand for 10-12 hours to allow the reactant to fully precipitate; the washing is to wash with distilled water 2-3 times respectively , Wash with absolute ethanol 2-3 times.

Preferably according to the present invention, the vacuum calcination described in step (1) is to place the completely dried aluminum hydroxide-coated hexagonal boron nitride composite powder in an alumina crucible, vacuum calcine in a vacuum hot-press sintering furnace, and heat up The speed is 8-12° C./min, the sintering temperature is 1100-1200° C., and the holding time is 1.5-2.5 hours, so as to prepare alumina-coated hexagonal boron nitride composite powder.

Preferably according to the present invention, in the step (2), the average particle size (D50) of micron silicon nitride is 0.5 μm, the average particle size (D50) of nanometer silicon nitride is 50 nm, and the average particle size (D50) of micron titanium carbide is 0.5 μm , the average particle size (D50) of alumina is 1 μm, the average particle size (D50) of yttrium oxide is 1 μm, and the raw materials are all commercially available products.

Preferably according to the present invention, the ball milling ball described in step (3) is a cemented carbide (YG8) ball. The added amount of ball milling balls is 10 times of the total mass of raw materials of each component. The oven described in step (3) is an electric vacuum oven.

Preferably according to the present invention, the vacuum hot-pressing sintering process in the step (4) is to first put the powder into a graphite mold, cold-press molding for 15 minutes, and then perform hot-pressing sintering. Further preferred hot pressing sintering parameters are: hot pressing sintering temperature 1650-1700°C, holding time 45-75min, pressure 25-30MPa, heating rate 10-20°C/min.

The ceramic green body prepared by hot pressing and sintering in the step (4) is prepared into a ceramic sample bar of 3mm×4mm×30mm through the steps of cutting-rough grinding-finishing-grinding-polishing.

The invention adopts a non-uniform nucleation method, first coating aluminum hydroxide on the surface of hexagonal boron nitride particles to make aluminum hydroxide-coated hexagonal boron nitride composite powder, and then preparing aluminum oxide-coated hexagonal boron nitride composite powder by vacuum calcination. Boron composite powder. The aluminum oxide-coated hexagonal boron nitride composite powder is added to the silicon nitride-based self-lubricating ceramic tool material, with micron silicon nitride as the matrix, micron titanium carbide and nano-silicon nitride as the reinforcing phase, and micron alumina And micron yttrium oxide as a sintering aid, aluminum oxide coated hexagonal boron nitride composite powder as a self-lubricating phase, and vacuum hot-pressed sintering to make a self-lubricating ceramic tool material, which can not only improve the mechanical properties of ceramic tools, but also take into account its Self-lubricating effect. Compared with the silicon nitride-based self-lubricating tool material added with h-BN without surface coating treatment, the silicon nitride-based self-lubricating ceramic tool material with 10vol.% coated solid lubricant h-BN has a better performance in Vickers The hardness, fracture toughness and flexural strength increased by 27%, 22.2% and 5.9% respectively, and the mechanical properties were significantly improved.

Description of drawings

Fig. 1 is a SEM surface morphology image of the surface of alumina-coated hexagonal boron nitride powder particles.

Fig. 2 is the SEM topography diagram of the surface corrosion of the test sample of the self-lubricating tool material added with coated hexagonal boron nitride composite powder in Example 1.

Fig. 3 is the SEM morphology diagram of the fracture surface of the test sample of the self-lubricating tool material added with coated hexagonal boron nitride composite powder in Example 1.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The methods are conventional methods unless otherwise specified.

The aluminum oxide-coated hexagonal boron nitride composite powder used in the components of each embodiment is prepared as follows:

Weigh 0.5 g of hexagonal boron nitride powder and polyethylene glycol 6000, a dispersant accounting for 4% by mass of the hexagonal boron nitride powder, and mix them with 100 ml of distilled water to form a suspension. Add 10 mL of a buffer solution with a pH of 4.5 to the suspension, ultrasonically disperse for 10 min, and magnetically stir in a digital display heat-collecting magnetic stirrer and heat to 35°C. Weigh an appropriate amount of aluminum nitrate nonahydrate, configure it into an aluminum nitrate solution with a concentration of 0.15mol/L, drop it into the hexagonal boron nitride suspension, and then slowly drop ammonia water diluted to a concentration of 2.5% into the suspension, the reaction temperature Continue stirring for 2 hours at 35 °C until the pH of the suspension reaches 7.5. The prepared suspension was left to stand for 12 hours, the precipitate was filtered, washed twice with distilled water and absolute ethanol, centrifuged with a high-speed centrifuge at 2000r/min for 10min, then placed in a drying oven and dried at 80°C for 24h. Aluminum hydroxide-coated hexagonal boron nitride composite powder was prepared. The completely dried aluminum hydroxide-coated hexagonal boron nitride composite powder is placed in a crucible, and vacuum calcined in a vacuum hot-pressing sintering furnace. The temperature of vacuum calcination is 1200°C, the heating rate is 10°C/min, and the temperature is kept for 2h. Finally, alumina-coated hexagonal boron nitride composite powder is obtained. The morphology is shown in Figure 1, with an average particle size of 5 μm.

The micron silicon nitride average particle size (D50) used in the embodiment is 0.5 μm, the nanometer silicon nitride average particle size (D50) is 50nm, the micron titanium carbide average particle size (D50) is 0.5 μm, the aluminum oxide average particle size (D50) is 1 μm, and the average particle size (D50) of yttrium oxide is 1 μm, and the raw materials are all commercially available products.

The milling balls used in the examples are cemented carbide (YG8) balls. The oven used is an electric vacuum oven.

Example 1

The silicon nitride-based self-lubricating ceramic tool material with aluminum oxide-coated hexagonal boron nitride composite powder is added. The volume percentage of each raw material component is 62% of micron silicon nitride (α-Si ₃ N ₄ ), nano-silicon nitride (α- Si ₃ N ₄ ) 10%, micron titanium carbide 10%, alumina 3.2%, yttrium oxide 4.8%, alumina-coated hexagonal boron nitride 10%.

In proportion, micron silicon nitride (α-Si ₃ N ₄ ), nanon silicon nitride (α-Si ₃ N ₄ ), micron titanium carbide, aluminum oxide, and yttrium oxide were respectively weighed. Use an appropriate amount of absolute ethanol as the dispersion medium, respectively configure micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension, and ultrasonically disperse for 15 minutes while fully stirring. The obtained micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension were mixed, then aluminum oxide and yttrium oxide were added to prepare a mixed suspension, fully stirred and ultrasonically dispersed for 15 minutes.

Pour the above-mentioned multi-phase suspension into a ball mill jar, fill it with nitrogen as a protective gas, add ball milling balls with a ratio of the total mass of raw materials of each component to the weight of ball milling balls at a ratio of 1:10, and mill for 36 hours to obtain a milled mixture. Weigh the aluminum oxide-coated hexagonal boron nitride composite powder in proportion, add an appropriate amount of absolute ethanol as a dispersion medium to prepare a suspension, and disperse it ultrasonically for 10 minutes. Add the suspension obtained above to the mixture obtained after ball milling, fill with nitrogen as a protective gas, add ball milling balls with a weight ratio of the total amount of raw materials of each component to ball milling balls at a weight ratio of 1:10, and continue ball milling for 12 hours. After taking it out, put it in a drying oven, and dry it under vacuum for 36 hours at 100-120°C. After the drying is complete, pass the mixed powder through a 200-mesh sieve, put the mixed powder into a graphite mold, and cold-press for 15 minutes to perform vacuum hot-press sintering. The hot pressing sintering parameters are: hot pressing sintering temperature 1700°C, holding time 60min, pressure 30MPa, heating rate 20°C/min. A silicon nitride-based self-lubricating ceramic tool material is prepared.

The ceramic body prepared by hot pressing and sintering is prepared into a ceramic sample bar of 3mm×4mm×30mm through the steps of cutting—rough grinding—fine grinding—grinding—polishing. The measured mechanical performance parameters are: Vickers hardness 14.1GPa, fracture toughness 7.2MPa·m ^1/2 , bending strength 732MPa. When paired with 45 steel, the friction coefficient is 0.31.

The SEM morphology of the silicon nitride-based self-lubricating ceramic tool material processed by adding alumina-coated hexagonal boron nitride composite powder after corrosion is shown in Figure 2. α-Si ₃ N ₄ is transformed by hot pressing It is β-Si ₃ N ₄ . The β-Si ₃ N ₄ in the material are criss-crossed, forming a long columnar interlocking structure nested with each other, and the ratio of length to diameter is large (about 3-8). According to the observation of the SEM morphology of the sample cross-section in Figure 3, there are holes left after the grains are pulled out at the fracture, the coarse grains are evenly distributed among the grains of the columnar matrix, and the microstructure of the material is relatively dense.

Example 2

Silicon nitride-based self-lubricating ceramic tools with aluminum oxide-coated hexagonal boron nitride powder added, the volume percentage of each raw material component is micron silicon nitride (α-Si ₃ N ₄ ) 67%, nano-silicon nitride (α-Si ₃ N ₄ ) 10%, micron titanium carbide 10%, alumina 3.2%, yttrium oxide 4.8%, alumina-coated hexagonal boron nitride 5%.

In proportion, micron silicon nitride (α-Si ₃ N ₄ ), nanon silicon nitride (α-Si ₃ N ₄ ), micron titanium carbide, aluminum oxide, and yttrium oxide were respectively weighed. Use an appropriate amount of absolute ethanol as the dispersion medium, respectively configure micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension, and ultrasonically disperse for 15 minutes while fully stirring. The obtained micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension were mixed, then aluminum oxide and yttrium oxide were added to prepare a mixed suspension, fully stirred and ultrasonically dispersed for 15 minutes.

Pour the above-mentioned multi-phase suspension into a ball mill jar, fill it with nitrogen as a protective gas, add ball milling balls with a ratio of the total mass of raw materials of each component to the weight of ball milling balls at a ratio of 1:10, and mill for 36 hours to obtain a milled mixture. Weigh the aluminum oxide-coated hexagonal boron nitride composite powder in proportion, add an appropriate amount of absolute ethanol as a dispersion medium to prepare a suspension, and disperse it ultrasonically for 10 minutes. Add the suspension obtained above to the mixture obtained after ball milling, fill with nitrogen as a protective gas, add ball milling balls with a weight ratio of the total amount of raw materials of each component to ball milling balls at a weight ratio of 1:10, and continue ball milling for 12 hours. After taking it out, put it in a drying oven, and dry it under vacuum for 36 hours at 100-120°C. After the drying is complete, pass the mixed powder through a 200-mesh sieve, put the mixed powder into a graphite mold, and cold-press for 15 minutes to perform vacuum hot-press sintering. The hot pressing sintering parameters are: hot pressing sintering temperature 1700°C, holding time 60min, pressure 30MPa, heating rate 20°C/min. A silicon nitride-based self-lubricating ceramic tool material is prepared.

The ceramic body prepared by hot pressing and sintering is prepared into a ceramic sample bar of 3mm×4mm×30mm through the steps of cutting—rough grinding—fine grinding—grinding—polishing. The measured mechanical performance parameters are: Vickers hardness 13.3GPa, fracture toughness 7.53MPa·m ^1/2 , bending strength 839MPa. When paired with 45 steel, the friction coefficient is 0.37.

Example 3

Adding alumina-coated hexagonal boron nitride powder to the silicon nitride-based self-lubricating ceramic tool, the volume percentage of each raw material component is micron silicon nitride (α-Si ₃ N ₄ ) 57%, nano-silicon nitride (α-Si ₃ N ₄ ) 10%, micron titanium carbide 10%, alumina 3.2%, yttrium oxide 4.8%, alumina-coated hexagonal boron nitride 15%.

In proportion, micron silicon nitride (α-Si ₃ N ₄ ), nanon silicon nitride (α-Si ₃ N ₄ ), micron titanium carbide, aluminum oxide, and yttrium oxide were respectively weighed. Use an appropriate amount of absolute ethanol as the dispersion medium, respectively configure micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension, and ultrasonically disperse for 15 minutes while fully stirring. The obtained micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension were mixed, then aluminum oxide and yttrium oxide were added to prepare a mixed suspension, fully stirred and ultrasonically dispersed for 15 minutes.

Pour the above-mentioned multi-phase suspension into a ball mill jar, fill it with nitrogen as a protective gas, add ball milling balls with a ratio of the total mass of raw materials of each component to the weight of ball milling balls at a ratio of 1:10, and mill for 36 hours to obtain a milled mixture. Weigh the aluminum oxide-coated hexagonal boron nitride composite powder in proportion, add an appropriate amount of absolute ethanol as a dispersion medium to prepare a suspension, and disperse it ultrasonically for 10 minutes. Add the suspension obtained above to the mixture obtained after ball milling, fill with nitrogen as a protective gas, add ball milling balls with a weight ratio of the total amount of raw materials of each component to ball milling balls at a weight ratio of 1:10, and continue ball milling for 12 hours. After taking it out, put it in a drying oven, and dry it under vacuum for 36 hours at 100-120°C. After the drying is complete, pass the mixed powder through a 200-mesh sieve, put the mixed powder into a graphite mold, and cold-press for 15 minutes to perform vacuum hot-press sintering. The hot pressing sintering parameters are: hot pressing sintering temperature 1700°C, holding time 60min, pressure 30MPa, heating rate 20°C/min. A silicon nitride-based self-lubricating ceramic tool material is prepared.

The ceramic body prepared by hot pressing and sintering is prepared into a ceramic sample bar of 3mm×4mm×30mm through the steps of cutting—rough grinding—fine grinding—grinding—polishing. The measured mechanical performance parameters are: Vickers hardness 10.3GPa, fracture toughness 6.2MPa·m ^1/2 , bending strength 637MPa. When paired with 45 steel, the friction coefficient is 0.42.

Embodiment 4: comparative example

The volume percentage of each raw material component of the silicon nitride-based self-lubricating ceramic tool with uncoated hexagonal boron nitride powder is 62% of micron silicon nitride (α-Si ₃ N ₄ ), nano-silicon nitride (α-Si ₃ N ₄ ) 10%, micron titanium carbide 10%, aluminum oxide 3.2%, yttrium oxide 4.8%, surface uncoated hexagonal boron nitride 10%.

In proportion, micron silicon nitride (α-Si ₃ N ₄ ), nanon silicon nitride (α-Si ₃ N ₄ ), micron titanium carbide, aluminum oxide, and yttrium oxide were respectively weighed. Use an appropriate amount of absolute ethanol as the dispersion medium, respectively configure micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension, and ultrasonically disperse for 15 minutes while fully stirring. The obtained micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension were mixed, then aluminum oxide and yttrium oxide were added to prepare a mixed suspension, fully stirred and ultrasonically dispersed for 15 minutes.

Pour the above-mentioned multi-phase suspension into a ball mill tank, fill it with nitrogen as a protective gas, add ball mill balls with a weight ratio of the total amount of raw materials of each component to ball mill balls at a weight ratio of 1:10, and take out after ball milling for 36 hours. Weigh the hexagonal boron nitride powder (with an average particle size of 5 μm) that is not coated on the surface in proportion, add an appropriate amount of absolute ethanol as a dispersion medium to prepare a suspension, ultrasonically disperse for 10 minutes, and mix well. Add the suspension obtained above to the mixture obtained after ball milling, fill with nitrogen as a protective gas, add ball milling balls with a weight ratio of the total amount of raw materials of each component to ball milling balls at a weight ratio of 1:10, and continue ball milling for 12 hours. After taking it out, put it in a drying oven, and dry it under vacuum for 36 hours at 100-120°C. After the drying is complete, pass the mixed powder through a 200-mesh sieve, put the mixed powder into a graphite mold, and cold-press for 15 minutes to perform vacuum hot-press sintering. The hot pressing sintering parameters are: hot pressing sintering temperature 1700°C, holding time 60min, pressure 30MPa, heating rate 20°C/min. A silicon nitride-based self-lubricating ceramic tool material added with uncoated hexagonal boron nitride powder is prepared. The prepared ceramic body is prepared into a ceramic sample strip of 3 mm×4 mm×30 mm through the steps of cutting—rough grinding—finish grinding—grinding—polishing. The measured mechanical performance parameters are: Vickers hardness 11.1GPa, fracture toughness 6.8MPa·m ^1/2 , bending strength 599MPa. When paired with 45 steel, the friction coefficient is 0.35.

Claims (10)

1. A method for preparing a silicon nitride-based self-lubricating ceramic tool material with alumina-coated hexagonal boron nitride composite powder. The volume percentage of raw material components is: micron silicon nitride 57-70%, nano silicon nitride 5% -15%, micron titanium carbide 5-15%, alumina 3.2%, yttrium oxide 4.8%, alumina-coated hexagonal boron nitride 2-15%; Including the following steps: (1) Mix hexagonal boron nitride powder with a particle size of 3-10 μm and dispersant polyethylene glycol in distilled water to form a 3-8g/L hexagonal boron nitride suspension. The amount of dispersant added is the mass of hexagonal boron nitride 3-5%. Add acetic acid-sodium acetate buffer solution with a pH value of 4.5, ultrasonically disperse and heat to 30°C-40°C with stirring, slowly add aluminum nitrate solution with an Al3 ⁺ concentration of 0.1-0.2mol/L dropwise, the aluminum nitrate solution The amount to be added is based on the molar ratio BN:Al=1:0.5-1, then slowly add ammonia water dropwise until the pH value of the reaction solution is 7.0-7.5, after the addition, keep the temperature at 30°C-40°C for 1.5-2.5h, and then let it stand Aging, sedimentation, filtration, cleaning, centrifugation, and vacuum drying to obtain hexagonal boron nitride composite powder coated with aluminum hydroxide on the surface, and vacuum calcination to obtain alumina-coated hexagonal boron nitride composite powder with a particle size of 4-12 μm; (2) Proportionally weigh micron silicon nitride, nano silicon nitride, and micron titanium carbide, and use an appropriate amount of absolute ethanol as the dispersion medium to prepare micron silicon nitride, micron titanium carbide suspension and nano silicon nitride respectively. Suspension, fully stirred while ultrasonically dispersed for 15-20min; mixed the dispersed micron silicon nitride, micron titanium carbide suspension and nano silicon nitride suspension, and then added the aluminum oxide and yttrium oxide in proportion, fully Stir and ultrasonically disperse for 15-20 minutes; get a complex suspension (3) Pour the above-mentioned multi-phase suspension into a ball milling tank, fill with argon or nitrogen as a protective gas, add balls for ball milling, and mill for 36-48 hours to obtain the mixture after ball milling, and weigh the aluminum oxide in step (1) in proportion Coat the hexagonal boron nitride composite powder, use absolute ethanol as the dispersion medium, make a suspension, and disperse it ultrasonically for 10 minutes; add the obtained suspension to the mixture after ball milling, fill with argon or nitrogen as a protective gas, and add ball milling balls , continue ball milling for 8-12h. Then take out the ball milling liquid and place it in a drying box, and dry it in vacuum at 100-120°C for 24-36 hours; after the drying is complete, pass the obtained mixed powder through a 200-mesh sieve to obtain the mixed powder, which is sealed for later use; (4) Vacuum hot pressing sintering process is adopted to sinter the mixed powder obtained in step (3) into a compression mold. 2. the preparation method of the silicon nitride-based self-lubricating ceramic cutter material that adds aluminum oxide coating hexagonal boron nitride composite powder as claimed in claim 1, it is characterized in that the volume percent of described raw material component is micron silicon nitride 62 -67%, nano silicon nitride 10%, micron titanium carbide 10%, alumina 3.2%, yttrium oxide 4.8%, alumina coated hexagonal boron nitride 5-10%. 3. the preparation method of the silicon nitride-based self-lubricating ceramic cutter material that adds aluminum oxide coating hexagonal boron nitride composite powder as claimed in claim 1, it is characterized in that the stirring heating described in step (1) is in several Magnetically stir and heat in a heat-collecting magnetic stirrer. 4. the preparation method of the silicon nitride-based self-lubricating ceramic cutter material that adds aluminum oxide coating hexagonal boron nitride composite powder as claimed in claim 1, it is characterized in that described in step (1) pH buffer solution addition is 8-15mL/100mL distilled water, more preferably the added amount of pH buffer solution is 10-11mL/100mL distilled water; preferably the pH value of the pH buffer solution is 4.5. 5. the preparation method of the silicon nitride-based self-lubricating ceramic cutter material that adds aluminum oxide coating hexagonal boron nitride composite powder as claimed in claim 1, is characterized in that the ammoniacal liquor described in step (1) is with mass The concentrated ammonia water with a percentage of 28% is diluted 5-10 times with distilled water to obtain an ammonia solution with a pH value of 6.5-8.5. 6. the preparation method of the silicon nitride-based self-lubricating ceramic cutter material that adds aluminum oxide coating hexagonal boron nitride composite powder as claimed in claim 1, is characterized in that the static aging described in step (1), is The suspension is left to stand for 10-12 hours to allow the reactant to fully precipitate; the washing is 2-3 times with distilled water and 2-3 times with absolute ethanol. 7. the preparation method of the silicon nitride-based self-lubricating ceramic tool material that adds aluminum oxide coating hexagonal boron nitride composite powder as claimed in claim 1, it is characterized in that the vacuum calcining described in step (1) is to dry The complete aluminum hydroxide-coated hexagonal boron nitride composite powder is placed in an alumina crucible and vacuum calcined in a vacuum hot-pressing sintering furnace. The heating rate is 8-12°C/min, the sintering temperature is 1100-1200°C, and the holding time is It takes 1.5-2.5 hours to prepare alumina-coated hexagonal boron nitride composite powder. 8. the preparation method of the silicon nitride-based self-lubricating ceramic cutter material that adds aluminum oxide coating hexagonal boron nitride composite powder as claimed in claim 1, is characterized in that the ball milling ball described in step (3) is hard For alloy (YG8) balls, the amount of ball milling balls added is 10 times the total mass of the raw materials of each component. 9. the preparation method of the silicon nitride-based self-lubricating ceramic cutter material that adds aluminum oxide coating hexagonal boron nitride composite powder as claimed in claim 1, it is characterized in that in the described step (4) vacuum hot pressing sintering process, The powder is put into the graphite mold first, cold pressed for 15 minutes and then hot pressed and sintered. 10. the preparation method of the silicon nitride-based self-lubricating ceramic cutting tool material that adds aluminum oxide coating hexagonal boron nitride composite powder as claimed in claim 1, is characterized in that in described step (4), hot-pressing sintering parameter is: The hot pressing sintering temperature is 1650-1700°C, the holding time is 45-75min, the pressure is 25-30MPa, and the heating rate is 10-20°C/min.