Preparation method of high-hardness wear-resistant silicon nitride ceramic
Through the ball milling and discharge plasma sintering process of raw materials with specific ratios, the problem of mechanical strength decrease in silicon nitride ceramic tools when improving hardness and wear resistance is solved, and a silicon nitride ceramic material with high hardness, high wear resistance and high mechanical strength is achieved, reducing production costs.
Patent Information
- Application Number
- CN202510347545.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-24
- Publication Date
- 2025-06-20
AI Technical Summary
When existing silicon nitride ceramic tools improve hardness and wear resistance, their mechanical strength decreases and their production costs are higher.
The specific ratios of Si3N4 powder, MgO powder, MgF2 powder and ZrO2 powder are used for ball milling, drying, screening and discharge plasma sintering processes, and the sintering time, pressure and temperature are controlled to improve the hardness, wear resistance and mechanical strength of silicon nitride ceramics.
It significantly improves the hardness, wear resistance and mechanical strength of silicon nitride ceramics, reduces production costs, and has a relatively simple process, and is suitable for ceramic cutting tools.
Smart Images
Figure CN120172748A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of cutting tool materials, and particularly to a preparation method of high-hardness wear-resistant silicon nitride ceramics. Background Art
[0002] Silicon nitride ceramics are excellent wear-resistant materials. Due to their characteristics such as high hardness, high strength, corrosion resistance, low thermal expansion coefficient, and self-lubricity, they are widely used in fields such as mechanical engineering, automotive manufacturing, aerospace, and metallurgical engineering. The high hardness of silicon nitride means that it can more effectively resist friction and wear from other objects. Under the same friction conditions, a material with higher hardness can maintain a longer service life because its surface is more difficult to be worn. Therefore, improving the hardness of silicon nitride ceramics is an effective way to enhance their wear resistance.
[0003] For silicon nitride ceramic tools, their wear resistance is an important performance index. In the prior art, the research on silicon nitride ceramic tools mainly enhances the hardness of silicon nitride ceramics by refining grains and using a second phase (β phase).
[0004] However, the above methods for enhancing the hardness of silicon nitride ceramics have the following disadvantages:
[0005] First, it reduces the mechanical strength of silicon nitride;
[0006] Second, it increases the manufacturing cost of silicon nitride ceramics. Summary of the Invention
[0007] Aiming at the deficiencies of the prior art, the present invention provides a preparation method of high-hardness wear-resistant silicon nitride ceramics, which not only has a simple preparation process and low manufacturing cost, but also can obtain a silicon nitride ceramic material with good hardness, wear resistance, and mechanical strength.
[0008] To achieve the above object, a preparation method of high-hardness wear-resistant silicon nitride ceramics designed by the present invention is characterized in that it includes the following steps:
[0009] S1) Put the raw materials into a ball mill tank, add ZrO2 ball mills and ethanol solvent into the ball mill tank, and after ball milling, obtain a composite powder containing ethanol solvent;
[0010] The mass ratio of ZrO2 ball mills to the raw materials is 8 - 12:1;
[0011] The raw materials include Si3N4 powder, MgO powder, MgF2 powder, and ZrO2 powder, and the mass ratio of Si3N4 powder, MgO powder, MgF2 powder, and ZrO2 powder is 15 - 25:1:1:0.2 - 0.6;
[0012] S2) Dry the composite powder containing ethanol solvent to remove the ethanol solvent;
[0013] S3) Screen the dried composite powder;
[0014] S4) Prepare Si3N4 ceramic by spark plasma sintering the sieved composite powder under vacuum. The heating rate of spark plasma sintering is 80 - 120 °C / min, the sintering temperature is 1650 - 1800 °C, the sintering holding time is 8 - 18 min, and the pressure is 20 - 40 MPa.
[0015] Further, in S1), the purity of the Si3N4 powder is 99%, and the average particle size is less than 50 μm; the purity of the MgO powder is 98%, and the average particle size is less than 100 μm; the purity of the MgF2 powder is 99%, and the average particle size is less than 70 μm; the purity of the ZrO2 powder is 99%, and the average particle size is less than 30 μm.
[0016] Furthermore, in S1), the α-phase content in the Si3N4 powder is 85 - 90%, and the rest is β-phase.
[0017] Furthermore, in S1), the ball milling time is 10 - 14 h, and the rotation speed of the ball mill is 250 - 350 RPM.
[0018] Furthermore, in S1), the diameter of the ZrO2 milling balls is 6 - 10 mm.
[0019] Further, in S2), the drying temperature is 100 °C, and the drying time is 12 - 18 h.
[0020] Furthermore, in S2), dry the composite powder in an oven.
[0021] Further, in S3), screen through a 60-mesh sieve.
[0022] Furthermore, in S4), place the sieved composite powder in a graphite mold for spark plasma sintering.
[0023] Furthermore, in S4), the diameter of the graphite mold is 15 - 25 mm, and the mass of the raw materials used for one sintering is 15 - 20 g.
[0024] The principle of the present invention for improving the hardness, wear resistance, and mechanical strength of the silicon nitride ceramic material is as follows:
[0025] 1. Si3N4 ceramics belong to polycrystalline materials with a hexagonal crystal structure, generally divided into two crystal orientations, α and β. Among them, β-Si3N4 has a higher symmetry and a smaller molar volume, and is a thermodynamically stable phase at a certain temperature. While α-Si3N4 is more easily formed kinetically. At high temperatures of 1400 °C to 1800 °C, the α phase will undergo a phase transformation to become the β type, and this phase transformation is irreversible. Therefore, the α phase is beneficial to sintering. In this invention, MgO powder is used as a sintering aid for Si3N4 ceramics. MgO can form a liquid phase with SiO2 at 1543 °C and promote the densification and phase transformation of Si3N4 ceramics. The addition of MgF2 powder can significantly reduce the viscosity of the liquid phase and effectively lower the liquid phase formation temperature, further promoting the sintering of Si3N4 ceramics. ZrO2 powder is a very potential ceramic reinforcement phase at present, and can improve the fracture toughness of Si3N4 ceramics through mechanisms such as transformation toughening. Therefore, by changing the raw material ratio in this invention, the functions of each component during the sintering process can be effectively controlled, affecting the properties of Si3N4 ceramics.
[0026] 2. In this invention, the grain growth is affected by controlling the sintering time, pressure, and regime. For example, too short sintering time may result in incomplete grain growth, and too long time may lead to secondary recrystallization. Applying pressure can accelerate pore closure, but excessive pressure may cause grains to preferentially grow along the pressure direction. The heating and holding time and atmosphere during the sintering process will also affect the grain growth and ultimately affect the product performance. Therefore, each step of the process needs to be strictly controlled.
[0027] The advantages of this invention are as follows:
[0028] 1. In this invention, a small amount of MgO powder, MgF2 powder, and ZrO2 powder are mixed with Si3N4 powder, and then subjected to a process flow of ball milling, drying, sieving, and spark plasma sintering, significantly improving the densification of silicon nitride ceramic materials, making the components evenly distributed in the matrix, with a stable structure, obtaining high-hardness and high-wear-resistant silicon nitride ceramic materials, significantly enhancing the mechanical strength of silicon nitride ceramics, having good wear resistance and cutting performance, and can be applied to the field of ceramic cutting tools.
[0029] 2. In the process flow of this invention, the raw material cost is relatively low and it is relatively easy to obtain. Moreover, the spark plasma sintering process used belongs to a relatively fast process. The obtained silicon nitride ceramic materials are not only high in hardness and wear resistance, but also have strong mechanical strength.
[0030] 3. The Si3N4 ceramic materials prepared by this invention have at least the advantages of being pollution-free, high in purity of the prepared materials, long in service life, and strong in performance controllability.
[0031] The preparation method of the high-hardness wear-resistant silicon nitride ceramic of the present invention not only has a relatively low production cost and a simple preparation process, but also the prepared silicon nitride ceramic material has good hardness, wear resistance and mechanical strength, and can be applied to the field of ceramic cutting tools. Brief Description of the Drawings
[0032] Figure 1 It is a flowchart of the present invention. Detailed Embodiments
[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0034] As Figure 1 shown, a preparation method of a high-hardness wear-resistant silicon nitride ceramic of the present invention includes the following steps:
[0035] S1) Put the raw materials into a ball mill tank, add ZrO2 ball mills and ethanol solvent into the ball mill tank, and after ball milling, obtain a composite powder containing ethanol solvent.
[0036] The mass ratio of ZrO2 ball mills to the raw materials is 8-12:1.
[0037] The raw materials include Si3N4 powder, MgO powder, MgF2 powder and ZrO2 powder, and the mass ratio of Si3N4 powder, MgO powder, MgF2 powder and ZrO2 powder is 15-25:1:1:0.2-0.6.
[0038] Ethanol is the grinding medium for ball milling. Adding ethanol is to make the raw materials mix more evenly during ball milling. Subsequently, all ethanol will be evaporated during the drying stage, and finally only the raw material powder remains.
[0039] Specifically, the purity of the Si3N4 powder is 99%, and the average particle size is less than 50 μm; the purity of the MgO powder is 98%, and the average particle size is less than 100 μm; the purity of the MgF2 powder is 99%, and the average particle size is less than 70 μm; the purity of the ZrO2 powder is 99%, and the average particle size is less than 30 μm.
[0040] Specifically, the α-phase content in the Si3N4 powder is 85-90%, and the rest is the β-phase. Si3N4 ceramic is a polycrystalline material, and its crystal structure belongs to the hexagonal crystal system. Generally, it is divided into two crystal orientations, α and β. Among them, β-Si3N4 has a higher symmetry and a smaller molar volume, and is a thermodynamically stable phase at temperature. While α-Si3N4 is easier to generate kinetically. At high temperatures of 1400°C to 1800°C, the α-phase will undergo a phase change and become the β-type. This phase change is irreversible, so the α-phase is beneficial to sintering.
[0041] Specifically, the ball milling time is 10-14h, and the rotation speed of the ball mill is 250-350 RPM.
[0042] Specifically, the diameter of the ZrO2 ball mills is 6 - 10 mm.
[0043] S2) Dry the composite powder containing an ethanol solvent to remove the ethanol solvent.
[0044] Specifically, the drying temperature is 100 °C and the drying time is 12 - 18 h.
[0045] Preferably, dry the composite powder in an oven.
[0046] S3) Screen the dried composite powder.
[0047] Specifically, screen through a 60 - mesh sieve.
[0048] S4) Prepare Si3N4 ceramics by spark plasma sintering the sieved composite powder under a vacuum state. The heating rate of spark plasma sintering is 80 - 120 °C / min, the sintering temperature is 1650 - 1800 °C, the sintering holding time is 8 - 18 min, and the pressure is 20 - 40 MPa.
[0049] Preferably, place the sieved composite powder in a graphite mold for spark plasma sintering.
[0050] Specifically, the diameter of the graphite mold is 15 - 25 mm, and the mass of the raw materials used for one - time sintering is 15 - 20 g.
[0051] The principle adopted in the present invention is as follows:
[0052] Use MgO powder as a sintering aid for Si3N4 ceramics. MgO can form a liquid phase with SiO2 at 1543 °C and promote the sintering densification and phase transformation of Si3N4 ceramics; the addition of MgF2 powder can significantly reduce the viscosity of the liquid phase and effectively lower the liquid - phase formation temperature, further promoting the sintering of Si3N4 ceramics; ZrO2 powder is a very potential ceramic reinforcing phase at present, and can improve the fracture toughness of Si3N4 ceramics through mechanisms such as transformation toughening; therefore, by changing the raw material ratio in the present invention, the roles of each component during the sintering process can be effectively controlled, affecting the properties of Si3N4 ceramics;
[0053] In addition, the present invention controls the grain growth by controlling the sintering time, pressure, and regime, and finally affects the properties of the product.
[0054] The following is a detailed description of the embodiments.
[0055] Example 1
[0056] S1) Weigh 27.9 g of Si3N4 powder, 0.9 g of MgO powder, 0.9 g of MgF2, and 0.3 g of ZrO2 powder, put them into a ZrO2 ball milling tank, add 300 g of ZrO2 balls with a diameter of 6 mm, put them into a planetary ball mill for ball milling. The rotational speed of the ball mill is 300 RPM, and the ball milling time is 12 h to obtain a composite powder.
[0057] S2) Put the powder obtained in step S1) into an oven for drying. The holding temperature of the oven is 100 °C, and the holding time is 12 h.
[0058] S3) Take the dried powder, pass it through a 60-mesh sieve, and take 15 g of the sieved powder and pour it into a graphite mold.
[0059] S4) Put graphite pressure heads at both ends for pre-pressing and then put it into a spark plasma sintering furnace for sintering. First, perform vacuum pumping through a mechanical pump. Set the heating rate to 100 °C / min, the maximum temperature to 1750 °C, the holding time to 10 min, and the pressure to 25 MPa.
[0060] After testing, the Vickers hardness of the sintered silicon nitride ceramic material is 2101 H V , the flexural strength is 925 MPa, and the fracture toughness is 7.97 MPa / m 1 / 2 .
[0061] Example 2
[0062] S1) Weigh 26.4 g of Si3N4 powder, 1.5 g of MgO powder, 1.5 g of MgF2, and 0.6 g of ZrO2 powder, put them into a ZrO2 ball milling tank, add 300 g of ZrO2 balls with a diameter of 10 mm, put them into a planetary ball mill for ball milling. The rotational speed of the ball mill is 300 RPM, and the ball milling time is 12 h to obtain a composite powder.
[0063] S2) Put the powder obtained in step S1) into an oven for drying. The holding temperature of the oven is 100 °C, and the holding time is 12 h.
[0064] S3) Take the dried powder, pass it through a 60-mesh sieve, and take 20 g of the sieved powder and pour it into a graphite mold.
[0065] S4) Put graphite pressure heads at both ends for pre-pressing and then put it into a spark plasma sintering furnace for sintering. First, perform vacuum pumping through a mechanical pump. Set the heating rate to 100 °C / min, the maximum temperature to 1800 °C, the holding time to 15 min, and the pressure to 35 MPa.
[0066] After testing, the Vickers hardness of the sintered silicon nitride ceramic material is 2321 H V , the flexural strength is 1036 MPa, and the fracture toughness is 10.21 MPa / m 1 / 2 .
[0067] Example 3
[0068] S1) Weigh 27 g of Si3N4 powder, 1.2 g of MgO powder, 1.2 g of MgF2 and 0.6 g of ZrO2 powder, put them into a ZrO2 ball milling jar, add 300 g of ZrO2 balls with a diameter of 6 mm, put them into a planetary ball mill for ball milling. The rotational speed of the ball mill is 300 RPM, and the ball milling time is 12 h to obtain a composite powder.
[0069] S2) Put the powder obtained in step S1) into an oven for drying. The heat preservation temperature of the oven is 100 °C, and the heat preservation time is 12 h.
[0070] S3) Take the dried powder, pass it through a 60-mesh sieve, and pour 15 g of the sieved powder into a graphite mold.
[0071] S4) Put graphite pressure heads at both ends, pre-press and then put it into a spark plasma sintering furnace for sintering. First, perform vacuum pumping treatment with a mechanical pump. Set the heating rate to 100 °C / min, the highest temperature to 1750 °C, the heat preservation time to 10 min, and the pressure to 30 MPa.
[0072] After testing, the Vickers hardness of the sintered silicon nitride ceramic material is 2300 H V , the flexural strength is 940 MPa, and the fracture toughness is 9.37 MPa / m 1 / 2 .
[0073] The instruments and models involved in the experimental processes of Examples 1 to 3 are shown in Table 1 below.
[0074] Table 1 Instruments and models in the experimental process
[0075] Equipment Name Model Electrothermal Blast Drying Oven DHG-9245A Planetary Ball Mill XGB2 Microhardness Tester HVT-1000 Universal Testing Machine QJ211S-10KN Plasma Sintering Furnace DSP-510
[0076] The experimental raw material ratios and experimental process parameters involved in Examples 1 to 3 are shown in Table 2 below.
[0077] Table 2 Experimental raw material ratios and experimental process parameters
[0078]
[0079]
[0080] The properties of the silicon nitride ceramic materials obtained in Examples 1 to 3 are shown in Table 3 below.
[0081] Table 3 Properties of silicon nitride ceramic materials
[0082] Example 1 Example 2 Example 3 Vickers Hardness (Hv) 2101 2321 2300 Flexural Strength (MPa) 925 1036 940 <![CDATA[Fracture toughness (MPa / m 1 / 2 )]]> 7.97 10.21 9.37
[0083] It can be seen that the hardness of the silicon nitride ceramic materials prepared in Examples 1 to 3 is 2101 - 2321H V , the flexural strength is 925 - 1036 MPa, and the fracture toughness is 7.97 - 10.21 MPa / m 1 / 2 . Among them, the comparison between Example 2 and the silicon nitride ceramics prepared by other methods is shown in Table 4 below.
[0084] Table 4 Comparison of Silicon Nitride Ceramic Materials
[0085]
[0086] As can be seen from Table 4 above, by using MgO powder, MgF2 powder and ZrO2 powder and carrying out the technological process of ball milling, drying, sieving and spark plasma sintering, the prepared silicon nitride ceramic materials can significantly improve the flexural strength, hardness and fracture toughness of the materials.
[0087] The preparation method of the high-hardness wear-resistant silicon nitride ceramic of the present invention not only has a relatively low production cost and a simple preparation process, but also the prepared silicon nitride ceramic materials have good hardness, wear resistance and mechanical strength, and can be applied to the field of ceramic cutting tools.
[0088] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.
Claims
1. A method for preparing high-hardness wear-resistant silicon nitride ceramics, characterized in that: The steps include: S1) placing the raw materials into a ball mill, adding a ZrO2 ball mill and an ethanol solvent into the ball mill, and performing ball milling to obtain a composite powder containing the ethanol solvent; The mass ratio of ZrO2 ball mill to raw material is 8-12:1; The raw materials include Si3N4 powder, MgO powder, MgF2 powder and ZrO2 powder, and the mass ratio of Si3N4 powder, MgO powder, MgF2 powder and ZrO2 powder is 15-25:1:1:0.2-0.6; S2) drying the composite powder containing the ethanol solvent to remove the ethanol solvent; S3) sieving the dried composite powder; S4) preparing Si3N4 ceramics by spark plasma sintering the sieved composite powder under vacuum, the spark plasma sintering heating rate is 80-120°C / min, the sintering temperature is 1650-1800°C, the sintering holding time is 8-18min, and the pressure is 20-40MPa.
2. The method for preparing high-hardness wear-resistant silicon nitride ceramic according to claim 1, characterized in that: S1), the Si3N4 powder has a purity of 99% and an average particle size of less than 50 μm; the MgO powder has a purity of 98% and an average particle size of less than 100 μm; the MgF2 powder has a purity of 99% and an average particle size of less than 70 μm; the ZrO2 powder has a purity of 99% and an average particle size of less than 30 μm.
3. The method for preparing high hardness wear-resistant silicon nitride ceramic according to claim 2, characterized in that: S1), the α-phase content in the Si3N4 powder is 85-90%, and the rest is β-phase.
4. The method for preparing high-hardness wear-resistant silicon nitride ceramics according to claim 3, characterized in that: In S1), the ball milling time is 10 to 14 hours, and the ball mill speed is 250 to 350 RPM.
5. The method for preparing high-hardness wear-resistant silicon nitride ceramics according to claim 4, characterized in that: In S1), the diameter of the ZrO2 ball mill is 6 to 10 mm.
6. The method for preparing high-hardness wear-resistant silicon nitride ceramics according to claim 1, characterized in that: In S2), the drying temperature is 100° C. and the drying time is 12 to 18 hours.
7. The method for preparing high-hardness wear-resistant silicon nitride ceramics according to claim 6, characterized in that: In S2), the composite powder is dried in an oven.
8. The method for preparing high-hardness wear-resistant silicon nitride ceramics according to claim 1, characterized in that: In S3), the mixture is sieved through a 60-mesh sieve.
9. The method for preparing high-hardness wear-resistant silicon nitride ceramics according to claim 8, characterized in that: In S4), the sieved composite powder is placed in a graphite mold for spark plasma sintering.
10. The method for preparing high-hardness wear-resistant silicon nitride ceramics according to claim 9, characterized in that: In S4), the graphite mold has a diameter of 15 to 25 mm, and the mass of the raw material used in the first sintering is 15 to 20 g.