Processable silicon nitride ceramic and preparation method thereof
By introducing Yb2O3 and SiO2 as sintering aids and controlling the transformation of the grain boundary phase of silicon nitride ceramics into the Yb2SiO5/Yb2Si2O7 phase through hot pressing sintering and annealing heat treatment, the problem of difficult processing of silicon nitride ceramics was solved, and the synergistic improvement of high strength and good machinability was achieved.
Patent Information
- Application Number
- CN202511480197.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-16
- Publication Date
- 2026-01-09
AI Technical Summary
The high hardness and brittleness of silicon nitride ceramics make them difficult to process. Existing technologies have neglected the influence of grain boundaries formed by sintering aids on the relative machinability, which limits their application.
Yb2O3 and SiO2 are used as composite sintering aids. Through hot pressing sintering and annealing heat treatment, the grain boundary phase is controlled to transform into Yb2SiO5/Yb2Si2O7 phase, which combines with h-BN phase to form a grain boundary structure with weak bonding surface, thereby improving machinability and high-temperature mechanical properties.
The silicon nitride ceramic exhibits good machinability, high room temperature mechanical strength, and high temperature stability. Its flexural strength, elastic modulus, fracture toughness, and Vickers hardness are significantly improved, and it maintains high strength even at high temperatures.
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of silicon nitride ceramic preparation, and particularly relates to a machinable silicon nitride ceramic and a preparation method thereof. BACKGROUND
[0002] As an important structural ceramic, silicon nitride (Si3N4) has excellent properties such as high strength and high thermal conductivity, and dense silicon nitride ceramics have important applications in the semiconductor industry. However, the inherent high hardness and brittleness of Si3N4 ceramics make them difficult to machine, limiting their more extensive application.
[0003] The main factors affecting the machinability of silicon nitride ceramics include density, phase composition and machinable phase content. Due to its strong covalent bond characteristics, the intrinsic sintering activity of silicon nitride is extremely low. Regardless of the sintering process, such as reaction sintering, hot-pressing sintering, gas-pressure sintering or normal-pressure sintering, sintering aids (such as MgO, Al2O3, rare earth oxides, etc.) need to be introduced to promote densification. The sintering aids react with SiO2 on the surface of Si3N4 to form a liquid phase at high temperatures, and densification is achieved through liquid-phase mass transfer. Generally, the residual grain boundary phase after cooling is mostly amorphous or high-hardness crystalline phase, which cannot effectively deflect / absorb cracks due to its high modulus and low toughness characteristics, and the amorphous grain boundary phase will soften at high temperatures, greatly reducing the high-temperature mechanical strength.
[0004] In order to improve the machinability of Si3N4 ceramics, usually only a single weak interfacial phase such as h-BN or porosity is introduced, while the influence of the grain boundary phase formed by the sintering aid on the machinability is ignored; single-phase rare earth silicate (such as Yb2SiO5) exhibits certain machinability due to its weak bonding surface within the crystal. It can be introduced into silicon nitride ceramics as a functional grain boundary phase. Generally, the grain boundary phase of Si3N4 ceramics with Yb2O3 as a sintering aid is mainly composed of amorphous and Yb4Si2O7N2 phases with poor machinability. Therefore, how to achieve controllable adjustment of the grain boundary phase still needs to be studied. SUMMARY
[0005] In view of the above technical problems, the purpose of the present application is to provide a machinable silicon nitride ceramic and a preparation method thereof.
[0006] In a first aspect, the present application provides a machinable silicon nitride ceramic, which comprises a silicon nitride crystalline phase, an h-BN crystalline phase and a Yb2SiO5 / Yb2Si2O7 grain boundary phase.
[0007] Preferably, the silicon nitride crystalline phase accounts for 76-91 wt% of the machinable silicon nitride ceramic, and the Yb2SiO5 / Yb2Si2O7 grain boundary phase accounts for 9-10 wt% of the machinable silicon nitride ceramic.
[0008] In a second aspect, the present application provides a preparation method of the processable silicon nitride ceramic, comprising the following steps: mixing silicon nitride raw material powder, composite sintering aid Yb2O3 powder / SiO2 powder and second phase h-BN powder and forming a green body, and then performing hot-pressing sintering and annealing heat treatment to obtain the processable silicon nitride ceramic.
[0009] Preferably, the median particle size of the silicon nitride raw material powder is 0.3-0.6 μm, the particle size of the Yb2O3 powder is 3-5 μm, the particle size of the SiO2 powder is 0.1-0.3 μm, and the median particle size of the h-BN powder is 0.1-0.3 μm.
[0010] Preferably, the content of the silicon nitride raw material powder and the composite sintering aid is 85-100 vol% and the content of the h-BN is 0-15 vol%, based on 100 vol% of the total volume percentage of the components. Preferably, the molar ratio of Si3N4:Yb2O3:SiO2 is 87-94:6-12:6-12.
[0011] Preferably, the mixing method is ball milling, and the ball milling parameters include a ball-to-material ratio of 1: (1-3), a ball milling rotation speed of 100-300 rpm, and a ball milling time of 4-6 hours. After ball milling, drying and sieving are performed; preferably, the drying temperature is 80-100℃, the drying time is 8-12 hours, and the sieving mesh size is 100-200 mesh.
[0012] Preferably, the hot-pressing sintering process includes: increasing the temperature to 1100-1200℃ at a rate of 5-10℃ / min under a nitrogen atmosphere of 1-2 atm in a hot-pressing furnace, and then increasing the temperature to 1700-1800℃ at a rate of 3-5℃ / min, and maintaining the temperature for 2-3 h under a pressure of 20-30 MPa.
[0013] Preferably, the hot-pressing sintering process includes: increasing the temperature to 1100℃ at a rate of 10℃ / min under a nitrogen atmosphere of 1 atm in a hot-pressing furnace, and then increasing the temperature to 1800℃ at a rate of 5℃ / min, and maintaining the temperature for 2 h under a pressure of 20 MPa.
[0014] Preferably, the annealing heat treatment process includes: increasing the temperature to 1500-1700℃ at a rate of 5-10℃ / min under a nitrogen atmosphere of 1-2 atm and maintaining the temperature for 6-8 h.
[0015] Advantages The application can effectively absorb crack energy by residual stress generated in the process of the grain boundary phase transformation, and can ensure high strength of the Si3N4 ceramic and good machinability by the combined action of the second phase h-BN; in addition, the crystallized ytterbium silicate phase has a high melting temperature and complete grain development, and still has high mechanical strength at 1400°C. BRIEF DESCRIPTION OF DRAWINGS
[0016] Figure 1 Machinability of Si3N4 ceramic prepared for Examples 2-5; Figure 2 Polished surface morphology of the Si3N4 ceramic prepared for Example 4; Figure 3 XRD phase analysis diagram of the Si3N4 ceramic prepared for Examples 4, 6, 7 and Comparative Example 1. DETAILED DESCRIPTION
[0017] The application will be further described by the following examples, which should be understood as merely illustrative of the application, but not limiting the application.
[0018] Firstly, the application provides a machinable silicon nitride ceramic. The machinable silicon nitride ceramic can include a silicon nitride crystalline phase, an h-BN crystalline phase and a Yb2SiO5 / Yb2Si2O7 grain boundary phase.
[0019] In some embodiments, the silicon nitride crystalline phase accounts for 76-91wt% of the machinable silicon nitride ceramic, and the Yb2SiO5 / Yb2Si2O7 grain boundary phase accounts for 9-10wt% of the machinable silicon nitride ceramic. If the content of the grain boundary phase is too low, the Vickers hardness and the bending strength will decrease slightly, and the machinability will be improved limitedly; if the content of the grain boundary phase is too high, the mechanical properties of the silicon nitride ceramic will be greatly reduced, but the machinability will be improved limitedly, and it is difficult for the grain boundary phase to be crystallized after annealing heat treatment, and it is difficult to be completely converted into the required grain boundary phase.
[0020] The single-phase rare earth silicate Yb2SiO5 / Yb2Si2O7 has a weak bonding surface and low cleavage energy, can effectively reduce hardness and promote crack branching / deflection, and can construct a grain boundary phase mainly composed of Yb2SiO5 / Yb2Si2O7 in Si3N4 ceramic, so as to synergistically improve the machinability and high-temperature mechanical strength of the Si3N4 ceramic.
[0021] The processable silicon nitride ceramic provided by the present application has good processability, high room temperature mechanical strength and high temperature stability. In some embodiments, the bending strength of the processable silicon nitride ceramic can be 642.1-866.1 MPa, the elastic modulus can be 246.4-308.1 GPa, the fracture toughness can be 6.13-8.42 MPa·m 1 / 2 , the Vickers hardness can be 8.6-13.7 GPa, and the high temperature bending strength at 1400℃ can be 466.2-564.9 MPa.
[0022] Hereinafter, the preparation method of the processable silicon nitride ceramic provided by the present application is exemplarily described. The preparation method can include the following steps: mixing silicon nitride raw material powder, composite sintering aid Yb2O3 powder / SiO2 powder and second phase h-BN powder and forming a green body, and then performing hot-pressing sintering and annealing heat treatment to obtain the processable silicon nitride ceramic.
[0023] In some embodiments, the median particle size of the silicon nitride raw material powder can be 0.3-0.6 μm, the particle size of the Yb2O3 powder can be 3-5 μm, the particle size of the SiO2 powder can be 0.1-0.3 μm, and the median particle size of the h-BN powder can be 0.1-0.3 μm. If the particle size of h-BN is too large, the mechanical strength of the silicon nitride ceramic will be greatly reduced.
[0024] In some embodiments, the content of the silicon nitride raw material powder and the composite sintering aid can be 85-100 vol% based on 100 vol% of the total volume percentage of each component, and the content of h-BN can be 0-15 vol%; wherein the molar ratio of Si3N4:Yb2O3:SiO2 is 87-94:6-12:6-12, and preferably 90.8:9.2:9.2.
[0025] By introducing a small amount of h-BN as an added phase, the Si3N4 ceramic has good processability, and too high h-BN content will greatly reduce the mechanical properties of the composite ceramic.
[0026] In some embodiments, the mixing method can be ball milling; preferably, the ball milling parameters can include a ball-to-material ratio of 1: (1-3), a ball milling speed of 100-300 rpm, and a ball milling time of 4-6 hours; after ball milling, drying and sieving can be performed before forming, the drying temperature can be 80-100℃, the drying time can be 8-12 hours, and the sieving mesh size can be 100-200 mesh.
[0027] In some embodiments, the forming method can be dry pressing, and the dry pressing pressure can be 10-20 MPa.
[0028] In some embodiments, the process of hot-press sintering can include: in a graphite mold, under 1-2 atm nitrogen atmosphere, in a hot-press furnace, increasing to 1100-1200 °C at a rate of 5-10 °C / min, then increasing to 1700-1800 °C at a rate of 3-5 °C / min, and holding for 2-3 h under a pressure of 20-30 MPa; preferably, under 1 atm nitrogen atmosphere, in a hot-press furnace, increasing to 1100 °C at a rate of 10 °C / min, then increasing to 1800 °C at a rate of 5 °C / min, and holding for 2 h under a pressure of 20 MPa.
[0029] The hot-press sintering densifies the material. Too low sintering temperature can result in incomplete phase transformation of β-Si3N4, and low toughness; too high sintering temperature can result in abnormal grain growth and reduced bending strength.
[0030] In some embodiments, the process of annealing heat treatment can include: in a BN crucible, carbon tube furnace, under 1-2 atm nitrogen atmosphere, increasing to 1500-1700 °C at a rate of 5-10 °C / min and holding for 6-8 h.
[0031] The annealing heat treatment can make the grain boundary phase transform into a processable phase, i.e., promote the grain boundary phase formed after hot-press sintering to form a well-crystallized layered Yb2SiO5 / Yb2Si2O7 phase, which can reduce hardness and absorb cracks, and the well-crystallized ytterbia phase can also improve high-temperature mechanical properties. It should be noted that, due to the high melting point of Yb2O3 and high sintering shrinkage temperature, the grain boundary phase transformation efficiency is low at a low heat treatment temperature, the grain development is incomplete, and the residual thermal stress introduced is less, which has limited effect on the improvement of processability; while at a high heat treatment temperature, the Si3N4 grains can grow again, and the excessive large-size Si3N4 grains can significantly reduce the mechanical strength.
[0032] That is, too low annealing heat treatment temperature can result in low softening degree of the grain boundary phase, and the grain boundary phase is difficult to crystallize into the required Yb2SiO5 phase; too short heat treatment time can result in incomplete reaction, and too long heat treatment time can result in the formation of other impurity phases.
[0033] In summary, the application adopts Yb2O3 and SiO2 as a composite sintering aid, and through annealing heat treatment process for long time heat preservation, the grain boundary phase can be accurately driven to convert into the required Yb2SiO5 / Yb2Si2O7 phase, and the grain growth thereof is promoted, the crystallization conversion process is accompanied by volume shrinkage effect, and a local residual compressive stress field is induced in the material. Therefore, the crystalline ytterbia phase induced by heat treatment, the derived residual compressive stress field and the small amount of h-BN introduced produce a multi-level synergistic effect, and the machinability of silicon nitride ceramic is improved. In addition, the annealing heat treatment makes the grain growth of the grain boundary phase more complete, and the high temperature stability is improved, and the strength retention rate thereof at 1400 DEG C high temperature can reach 80%, which is better than conventional Si3N4 ceramic.
[0034] It should be noted that silicon nitride is a strong covalent compound, and needs to be densified by liquid phase sintering, and the grain boundary phase is a necessary product after liquid phase cooling, and the crystallization thereof is a subsequent independent heat treatment step, and the commonly used sintering method usually obtains a grain boundary phase composed of Yb4Si2O7N2 phase and amorphous state, and it is difficult to obtain the target grain boundary phase, and the change of the grain boundary phase after annealing heat treatment is accompanied by an increase in residual thermal stress, which is also beneficial to the improvement of machinability. Unlike silicon carbide matrix, silicon carbide can be sintered by solid phase sintering or liquid phase sintering, and densification and grain boundary phase design are directly realized in the sintering process. The technical scheme provided by the application ensures the densification sintering of Si3N4, controls the content of liquid phase, and after sintering, the independent heat treatment process directionally converts the unfavorable grain boundary phase into the beneficial crystalline phase, and at the same time avoids the abnormal growth of the Si3N4 matrix.
[0035] The following further examples are provided to further illustrate the application. It should be understood that these examples are intended to be further illustrative only and should not be construed as limiting the scope of the application. Any modification and adjustment made by those skilled in the art based on the above description of the application are within the scope of the application. The specific process parameters in the following examples are only one example in the appropriate range, that is, those skilled in the art can select within the appropriate range according to the description herein, and are not limited to the specific values in the following examples. If not specified, the technical means used in the examples is the conventional means known to those skilled in the art.
[0036] Example 1 The preparation method of the machinable silicon nitride ceramic provided in this embodiment comprises the following steps: Take Si3N4 powder 100 g, according to the molar ratio of Si3N4: Yb2O3: SiO2=90.8:9.2:9.2, add composite sintering aid Yb2O3 and SiO2 powder, mix with Si3N4 powder and sintering aid to prepare a slurry with a solid content of 50 wt% with alcohol as solvent; mix with Si3N4 as a ball milling medium (ball to material ratio 1:1) at 300 rpm for 4 h; the slurry is dried in a constant temperature oven at 80℃, and the dried powder is ground through a 100 mesh screen; the obtained powder is dry pressed under a pressure of 10 MPa; then put into a graphite mold, with 1 atm nitrogen as the atmosphere, in a hot pressing furnace, at a rate of 10℃ / min to 1100℃, then at a rate of 5℃ / min to 1800℃, under a pressure of 20 MPa for 2 h; then the sample is placed in a BN crucible and annealed in a carbon tube furnace, with the specific parameters being 1700℃ for 6 h, 1 atm nitrogen atmosphere, and a heating rate of 10℃ / min, to obtain the processable silicon nitride ceramic.
[0037] Example 2 The preparation method of the processable silicon nitride ceramic provided in this example refers to Example 1, the main difference being that: 5 vol% of h-BN of the total volume of each component is added to the raw materials, and the h-BN powder is first ultrasonically dispersed in alcohol, and then mixed with Si3N4 powder and sintering aid to prepare a slurry.
[0038] Example 3 The preparation method of the processable silicon nitride ceramic provided in this example refers to Example 1, the main difference being that: 7.5 vol% of h-BN of the total volume of each component is added to the raw materials, and the h-BN powder is first ultrasonically dispersed in alcohol, and then mixed with Si3N4 powder and sintering aid to prepare a slurry.
[0039] Example 4 The preparation method of the processable silicon nitride ceramic provided in this example refers to Example 1, the main difference being that: 10 vol% of h-BN of the total volume of each component is added to the raw materials, and the h-BN powder is first ultrasonically dispersed in alcohol, and then mixed with Si3N4 powder and sintering aid to prepare a slurry.
[0040] Example 5 The preparation method of the processable silicon nitride ceramic provided in this example refers to Example 1, the main difference being that: 15 vol% of h-BN of the total volume of each component is added to the raw materials, and the h-BN powder is first ultrasonically dispersed in alcohol, and then mixed with Si3N4 powder and sintering aid to prepare a slurry.
[0041] Example 6 The preparation method of the processable silicon nitride ceramic material provided in this embodiment refers to that in Embodiment 4, and the main difference lies in that: The annealing heat treatment temperature is 1600℃.
[0042] Embodiment 7 The preparation method of the processable silicon nitride ceramic material provided in this embodiment refers to that in Embodiment 4, and the main difference lies in that: The annealing heat treatment temperature is 1500℃.
[0043] Comparative Example 1 The preparation method of the ceramic material provided in this comparative example refers to that in Embodiment 4, and the main difference lies in that: No annealing heat treatment is performed.
[0044] Comparative Example 2 The preparation method of the ceramic material provided in this comparative example refers to that in Embodiment 1, and the main difference lies in that Si3N4:Yb2O3:SiO2=87.7:12.3:12.3.
[0045] The process and performance parameters of the silicon nitride ceramic provided in the present application are shown in Table 1: h-BN (vol%) Annealing temperature Bending strength / MPa Elastic modulus / GPa Fracture toughness / MPa x m 1 / 2 ]] Vickers hardness / GPa High temperature bending strength - 1400°C (MPa) Example 1 0 1700℃ 866.1 308.1 8.42 13.7 564.9 Example 2 5 1700℃ 725.0 290.2 7.59 11.0 540.8 Example 3 7.5 1700℃ 715.7 279.3 7.53 10.3 543.6 Example 4 10 1700℃ 659.7 263.1 6.86 9.3 530.4 Example 5 15 1700℃ 642.1 246.4 6.13 8.6 508.2 Example 6 10 1600℃ 705.1 263.7 7.64 9.7 504.7 Example 7 10 1500℃ 701.4 261.9 7.64 9.4 489.3 Comparative Example 1 10 Untreated 785.3 268.0 7.60 9.8 466.2 Comparative Example 2 0 1700℃ 783.5 310.6 7.82 14.0 525.1
[0046] Figure 1 The machining performance of the Si3N4 ceramic prepared in Embodiments 2-5 is shown in the figure. As can be seen from the figure, the machinability is greatly improved due to the ytterbium silicate (Yb2SiO5 / Yb2Si2O7) formed after heat treatment as a weak interfacial phase, and the sample with only 10 vol% h-BN can be machined using a common hard alloy drill bit, while the conventional Si3N4 ceramic needs to introduce more than 20 vol% h-BN to achieve similar machining effect.
[0047] Figure 2 The polished surface morphology of the silicon nitride ceramic prepared in Embodiment 4 is shown in the figure. As can be seen from the indentation figure of the polished surface, the grain boundary phase is uniformly distributed, the cracks propagate along the h-BN interlayer and the grain boundary phase, and crack deflection is observed.
[0048] Figure 3 The XRD phase analysis figure of the silicon nitride ceramic prepared in Embodiments 4, 6, 7 and Comparative Example 1 is shown in the figure. As can be seen from the figure, the grain boundary phase of Comparative Example 1 without annealing heat treatment is mainly composed of Yb4Si2O7N2 phase, while the grain boundary phase of Embodiment 4 after 1700℃ annealing heat treatment is mainly composed of Yb2SiO5 and Yb2Si2O7. After long-time annealing heat treatment, the grain boundary phase is converted into the required processable phase, the crystallinity is improved, and the machinability and high-temperature mechanical strength are more excellent.
[0049] As can be seen from the above examples, the present application realizes the synergistic improvement of multiple performances by the active crystallization design of the grain boundary phase. Specifically, with Yb2O3 and SiO2 as sintering aids, after hot-pressing sintering, the crystallization transformation of the grain boundary phase is actively induced by the key annealing heat treatment process, generating Yb2SiO5 / Yb2Si2O7 intergranular phase with weak interface characteristics, and the grain phase transformation process is the key to realize performance breakthrough. Not only through the synergistic effect with a small amount of h-BN introduced, but also the grain boundary phase with more complete grain development improves the high-temperature stability of the material, so that it can still maintain excellent mechanical strength at high temperature.
[0050] Although the content of the present application has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present application. After reading the above content, various modifications and alternatives of the present application will be apparent to those skilled in the art. Therefore, the protection scope of the present application should be defined by the appended claims.
Claims
1. A processable silicon nitride ceramic, characterized by, The processable silicon nitride ceramic comprises a silicon nitride crystalline phase, a h-BN crystalline phase and a Yb2SiO5 / Yb2Si2O7 grain boundary phase.
2. The processable silicon nitride ceramic according to claim 1, wherein The silicon nitride crystalline phase accounts for 76-91 wt% of the processable silicon nitride ceramic, and the Yb2SiO5 / Yb2Si2O7 grain boundary phase accounts for 9-10 wt% of the processable silicon nitride ceramic.
3. A method of producing the processable silicon nitride ceramic according to claim 1 or 2, characterized in that The preparation method comprises the following steps: mixing silicon nitride raw material powder, composite sintering aid Yb2O3 powder / SiO2 powder and second phase h-BN powder, and forming a green body, and then performing hot-pressing sintering and annealing heat treatment to obtain the processable silicon nitride ceramic.
4. The production method according to claim 3, characterized by, The median particle size of the silicon nitride raw material powder is 0.3-0.6 μm, the particle size of the Yb2O3 powder is 3-5 μm, the particle size of the SiO2 powder is 0.1-0.3 μm, and the median particle size of the h-BN powder is 0.1-0.3 μm.
5. The production method according to claim 3 or 4, characterized by, The content of the silicon nitride raw material powder and the composite sintering aid is 85-100 vol% and the content of h-BN is 0-15 vol%, based on 100 vol% of the total volume percentage of each component. Preferably, the molar ratio of Si3N4:Yb2O3:SiO2 is 87-94:6-12:6-12.
6. The production method according to any one of claims 3 to 5, characterized by, The mixing method is ball milling, and the parameters of the ball milling include a ball-to-material ratio of 1: (1-3), a ball milling rotation speed of 100-300 rpm and a ball milling time of 4-6 hours. Drying and sieving are performed after the ball milling, and preferably, the drying temperature is 80-100℃, the drying time is 8-12 hours, and the sieving mesh size is 100-200 mesh.
7. The production method according to any one of claims 3 to 6, characterized by, The hot-pressing sintering process comprises the following steps: increasing the temperature to 1100-1200℃ at a rate of 5-10℃ / min under a nitrogen atmosphere of 1-2 atm in a hot-pressing furnace, and then increasing the temperature to 1700-1800℃ at a rate of 3-5℃ / min, and maintaining the temperature for 2-3 h under a pressure of 20-30 MPa.
8. The production method according to any one of claims 3 to 7, characterized by, The hot-pressing sintering process comprises the following steps: increasing the temperature to 1100℃ at a rate of 10℃ / min under a nitrogen atmosphere of 1 atm in a hot-pressing furnace, and then increasing the temperature to 1800℃ at a rate of 5℃ / min, and maintaining the temperature for 2 h under a pressure of 20 MPa.
9. The production method according to any one of claims 3 to 8, characterized by, The annealing heat treatment process comprises the following steps: increasing the temperature to 1500-1700℃ at a rate of 5-10℃ / min under a nitrogen atmosphere of 1-2 atm, and maintaining the temperature for 6-8 h.