Chromium-aluminum-magnesium-silicon alloy target material and preparation method thereof
Through powder metallurgy and SPS spark plasma sintering process, chromium-aluminum-magnesium-silicon alloy targets are prepared, which solves the problem of hot isostatic pressing failure caused by Mg-Al reaction and achieves the preparation of targets with high density and excellent coating performance.
Patent Information
- Application Number
- CN202510871913.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-26
- Publication Date
- 2025-09-16
AI Technical Summary
It is difficult to effectively prepare chromium-aluminum-magnesium-silicon multi-element alloy targets with existing technologies, mainly because the Mg element has active chemical properties and undergoes a diffusion reaction with Al under normal pressure, resulting in the melting of the ingot during the hot isostatic pressing process and the failure of the preparation.
The powder metallurgy process is adopted, AlSix alloy powder is used instead of pure Si powder, and the SPS spark plasma sintering process is combined. The chromium-aluminum-magnesium-silicon alloy target is prepared through a two-stage temperature and pressure increase SPS sintering method to avoid the exothermic Mg-Al reaction and improve the density and alloying degree of the target.
The invention provides a chromium-aluminum-magnesium-silicon alloy target material with short process flow, high production efficiency, low cost and stable quality. The target material has high density, uniform structure, easy processing and forming, good thermal conductivity and excellent coating performance.
Smart Images
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Abstract
Description
Technical Field
[0001] The present application relates to the technical field of physical vapor deposition coating, and in particular to a chromium-aluminum-magnesium-silicon alloy target and a preparation method thereof. Background Art
[0002] Since the 1960s, physical vapor deposition (PVD) has been a key method for improving tool performance by depositing ultra-hard thin films on the surfaces of metal cutting tools. This technology significantly increases cutting speed, wear resistance, and tool life, extending tool life. In recent years, driven by the development of high-end equipment manufacturing, aerospace, and the automotive industry, the global manufacturing industry has made significant advances in technology and production efficiency, leading to an increasing demand for high-performance tools and molds. Target materials, as key source materials in PVD coating technology, are also experiencing increasing demand. Commonly used tool surface coatings include TiN, TiAlN, CrAlN, and TiSiN. As tool coatings expand into increasingly specialized sectors, tool coating modifications are increasingly tailored to the specific material being processed. For example, additional elements (such as boron, magnesium, silicon, tungsten, molybdenum, vanadium, tael, and ytterbium) are being introduced into conventional coatings to enhance the film's hardness, oxidation resistance, and reduce friction.
[0003] In PVD coatings, the addition of Mg can significantly improve the coating's oxidation resistance and corrosion resistance. At the same time, the synergistic effect of Mg with other elements such as Al and Si can further optimize the coating's performance. For example, the combination of Mg and Al can significantly improve corrosion resistance and heat resistance, while the addition of Si can refine the grains and improve the uniformity of the structure, which is of great significance for improving coating performance. However, it is very difficult to prepare Mg-containing targets using powder metallurgy technology. Because the chemical properties of Mg are active, it will diffuse and react with Al at relatively low temperatures (about 438-500°C) under normal pressure. When using hot isostatic pressing (HIP) technology to prepare magnesium-containing aluminum-based targets, the reaction between Mg and Al releases a large amount of heat, causing the ingot to melt, resulting in the failure of target preparation. Therefore, the current research on the preparation technology of chromium-aluminum-magnesium-silicon multi-element alloy targets is still blank. Summary of the Invention
[0004] In order to solve the above technical problems, the present application provides a chromium-aluminum-magnesium-silicon alloy target and a preparation method thereof.
[0005] On the one hand, the present application provides a chromium-aluminum-magnesium-silicon alloy target, which is composed of the following components in atomic percentage: Cr = 10-60at%, Al = 30-90at%, Mg = 0-20at% and not 0, Si = 0-20at% and not 0; the Si is introduced in the form of AlSix alloy powder.
[0006] Preferably, the chromium-aluminum-magnesium-silicon alloy target material is composed of the following components in atomic percentage: Cr = 10-50 at%, Al = 40-80 at%, Mg = 0-15 at% and not 0 at%, Si = 0-15 at% and not 0 at%.
[0007] Preferably, the Si is introduced in the form of AlSix alloy powder, wherein X=18-50at%.
[0008] Preferably, the Si is introduced in the form of AlSi80 / 20at% alloy powder.
[0009] Preferably, in the CraAlbMgcSid alloy target, the Al / Si atomic ratio b / d is ≥4.
[0010] Preferably, in the CraAlbMgcSid alloy target, the Al / Si atomic ratio b / d is 4-60.
[0011] Preferably, in the CraAlbMgcSid alloy target, the Al / Si atomic ratio b / d is 12-60.
[0012] In a specific embodiment, the chromium-aluminum-magnesium-silicon alloy target material is composed of the following components in atomic percentage: Cr=10at%, Al=88at%, Mg=1at%, Si=1at%.
[0013] In a specific embodiment, the chromium-aluminum-magnesium-silicon alloy target material is composed of the following components in atomic percentage: Cr=60at%, Al=30at%, Mg=5at%, and Si=5at%.
[0014] In a specific embodiment, the chromium-aluminum-magnesium-silicon alloy target material is composed of the following components in atomic percentage: Cr=10at%, Al=71at%, Mg=2at%, and Si=17at%.
[0015] In a specific embodiment, the chromium-aluminum-magnesium-silicon alloy target material is composed of the following components in atomic percentage: Cr=10at%, Al=80at%, Mg=8.7at%, Si=1.3at%.
[0016] In a specific embodiment, the chromium-aluminum-magnesium-silicon alloy target material is composed of the following components in atomic percentage: Cr=23at%, Al=60at%, Mg=15at%, Si=2at%.
[0017] In a specific embodiment, the chromium-aluminum-magnesium-silicon alloy target material is composed of the following components in atomic percentage: Cr=25at%, Al=60at%, Mg=10at%, and Si=5at%.
[0018] On the other hand, the present application provides a method for preparing the chromium-aluminum-magnesium-silicon alloy target, which specifically includes the following steps in sequence: powder mixing, mold filling, SPS sintering, and machining.
[0019] Preferably, the method for preparing the chromium-aluminum-magnesium-silicon alloy target material specifically comprises the following steps in sequence: S1: Under Ar gas protection, Cr powder, Al powder, AlSix alloy powder, and Mg powder are weighed in proportion and mixed uniformly to obtain CrAlMgSi alloy powder; S2: uniformly filling the CrAlMgSi alloy powder obtained in S1 into a graphite mold of corresponding size; S3: placing the graphite mold in an SPS spark plasma sintering furnace and performing SPS sintering and densification under vacuum conditions. After cooling, demoulding is performed to obtain a densely sintered CrAlMgSi compact. S4: machining the compact obtained in S3 to obtain the chromium-aluminum-magnesium-silicon alloy target product.
[0020] Preferably, the purity of the Cr powder is ≥99.8wt%, and the particle size is -200 mesh; the purity of the Al powder is ≥99.8wt%, and the laser particle size D50 is 5-10μm; the purity of the AlSix alloy powder is ≥99.8wt%, and the particle size is -300 mesh; the purity of the Mg powder is ≥99.8wt%, and the particle size is -150 mesh.
[0021] Preferably, the SPS sintering conditions are: the entire sintering process is vacuumed, with a vacuum degree of 10 -1 -10 -3 Pa; heating rate is 10-60℃ / min; The first stage: heating to 350-450℃, while linearly increasing the pressure to 20-40MPa, keeping the temperature for 0-10min and not to 0; The second stage: heating to 450-550℃, while linearly increasing the pressure to 30-50MPa, keeping the temperature for 0-10min and not to 0; The temperature of the second stage is higher than that of the first stage, and the pressure of the second stage is higher than that of the first stage.
[0022] Preferably, the SPS sintering conditions are as follows: first stage: heating to 350-450°C at a heating rate of 20-60°C / min, while linearly increasing the pressure to 25-35 MPa, and holding for 0-10 min and not 0; The second stage: heating to 450-550℃ at a heating rate of 10-30℃ / min, while linearly increasing the pressure to 35-45MPa, and keeping the temperature for 0-10min and not 0; The heating rate in the second stage is lower than that in the first stage.
[0023] In summary, the technical solution of this application has the following effects: The preparation method provided in this application overcomes the shortcomings of conventional hot isostatic pressing processes, providing a method for preparing CrAlMgSi alloy targets with a short process flow, high production efficiency, low production cost, and stable quality. The CrAlMgSi alloy targets prepared using the preparation method provided in this application have high density (relative density ≥ 100.2%), uniform structure, easy processing and forming, good thermal conductivity, low oxygen content, and excellent coating performance.
[0024] This application adopts a powder metallurgy process, replaces pure Si powder with AlSix alloy powder, and combines it with the SPS spark plasma sintering process to solve the problems of the current hot isostatic pressing (HIP) process for preparing chromium aluminum magnesium silicon targets, such as the easy melting of the Mg-Al reaction exothermic sheath, which can only be HIPed at a relatively low temperature, resulting in low target density and alloying degree, and poor coating performance; and this preparation process significantly improves the thermal conductivity of the target. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 This is the microstructure diagram of the chromium-aluminum-magnesium-silicon alloy target in Example 6 (metallographic photograph - 200 times). DETAILED DESCRIPTION
[0026] The present application is further described in detail below in conjunction with examples, comparative examples and performance testing experiments. These examples should not be construed as limiting the scope of protection claimed in this application. Example
[0027] Examples 1-6 Examples 1-6 respectively provide a chromium-aluminum-magnesium-silicon alloy target material and a preparation method thereof.
[0028] The difference between the above embodiments is that the components of the chromium-aluminum-magnesium-silicon alloy target are different, as shown in Table 1.
[0029] The preparation method of the chromium-aluminum-magnesium-silicon alloy target in the above embodiment is as follows: S1: Under Ar gas protection conditions, Cr powder, Al powder, AlSi80 / 20at% alloy powder, and Mg powder were weighed according to the proportion and mixed evenly in a three-dimensional mixer to obtain CrAlMgSi alloy powder; no stirring balls such as ZrO2, Al2O3, and alloy balls were added during the powder mixing process, and the mixing time was 6 hours.
[0030] S2: The CrAlMgSi alloy powder obtained in S1 is uniformly filled into a graphite mold of corresponding size; the graphite mold can be circular or rectangular, and in this embodiment, it is circular.
[0031] S3: The graphite mold is placed in an SPS spark plasma sintering furnace and subjected to SPS sintering and densification under vacuum conditions. After cooling, the mold is demoulded to obtain a densely sintered CrAlMgSi compact.
[0032] The SPS sintering conditions are as follows: first stage: heating to 400°C at a heating rate of 35°C / min, while linearly increasing the pressure to 30 MPa, and keeping warm for 5 min; second stage: heating to 535°C at a heating rate of 20°C / min, while linearly increasing the pressure to 40 MPa, and keeping warm for 3 min.
[0033] S4: Machining the compact obtained in S3 to obtain a target product that meets the drawing requirements and surface quality.
[0034] Table 1 Composition of chromium-aluminum-magnesium-silicon alloy targets in Examples 1-6 and Comparative Examples 1-3 Examples 7-14 Examples 7-14 respectively provide a chromium-aluminum-magnesium-silicon alloy target material and a preparation method thereof.
[0035] The difference between the above embodiment and embodiment 6 is that the SPS sintering conditions are different, as shown below.
[0036] In Example 7: The SPS sintering conditions are as follows: first stage: heating to 350°C at a heating rate of 35°C / min, while linearly increasing the pressure to 30 MPa, and keeping warm for 5 minutes; second stage: heating to 535°C at a heating rate of 20°C / min, while linearly increasing the pressure to 40 MPa, and keeping warm for 3 minutes.
[0037] In Example 8, the SPS sintering conditions are as follows: first stage: heating to 450°C at a heating rate of 35°C / min, while linearly increasing the pressure to 30 MPa, and keeping warm for 5 minutes; second stage: heating to 535°C at a heating rate of 20°C / min, while linearly increasing the pressure to 40 MPa, and keeping warm for 3 minutes.
[0038] In Example 9: The SPS sintering conditions are as follows: first stage: heating to 400°C at a heating rate of 35°C / min, while linearly increasing the pressure to 20 MPa, and keeping warm for 5 minutes; second stage: heating to 535°C at a heating rate of 20°C / min, while linearly increasing the pressure to 40 MPa, and keeping warm for 3 minutes.
[0039] In Example 10, the SPS sintering conditions are as follows: first stage: heating to 400°C at a heating rate of 35°C / min, while linearly increasing the pressure to 40 MPa, and keeping warm for 5 minutes; second stage: heating to 535°C at a heating rate of 20°C / min, pressure 40 MPa, and keeping warm for 3 minutes.
[0040] In Example 11, the SPS sintering conditions are as follows: first stage: heating to 400°C at a heating rate of 35°C / min, while linearly increasing the pressure to 30 MPa, and keeping warm for 5 minutes; second stage: heating to 450°C at a heating rate of 20°C / min, while linearly increasing the pressure to 40 MPa, and keeping warm for 10 minutes.
[0041] In Example 12, the SPS sintering conditions are as follows: first stage: heating to 400°C at a heating rate of 35°C / min, while linearly increasing the pressure to 30 MPa, and keeping warm for 5 minutes; second stage: heating to 550°C at a heating rate of 20°C / min, while linearly increasing the pressure to 40 MPa, and keeping warm for 2 minutes.
[0042] In Example 13, the SPS sintering conditions are as follows: first stage: heating to 400°C at a heating rate of 35°C / min, while linearly increasing the pressure to 30 MPa, and keeping warm for 5 minutes; second stage: heating to 535°C at a heating rate of 20°C / min, pressure of 30 MPa, and keeping warm for 3 minutes.
[0043] In Example 14, the SPS sintering conditions are as follows: first stage: heating to 400°C at a heating rate of 35°C / min, while linearly increasing the pressure to 30 MPa, and keeping warm for 5 minutes; second stage: heating to 535°C at a heating rate of 20°C / min, while linearly increasing the pressure to 50 MPa, and keeping warm for 2 minutes.
[0044] The other process parameters in the above embodiment are the same as those in Example 6.
[0045] Comparative Example Comparative Examples 1-3 Comparative Examples 1-3 respectively provide a chromium-aluminum-magnesium-silicon alloy target material and a preparation method thereof.
[0046] The difference between the comparative example and Example 6 is that the composition of the chromium-aluminum-magnesium-silicon alloy target is different, as shown in Table 1.
[0047] The other process parameters in the above comparative example are the same as those in Example 6.
[0048] Comparative Examples 4-9 Comparative Examples 4-9 respectively provide a chromium-aluminum-magnesium-silicon alloy target material and a preparation method thereof.
[0049] The difference between the comparative example and Example 6 is that the sintering process is different, as shown below.
[0050] In Comparative Example 4: a hot isostatic pressing process is adopted, as shown below.
[0051] S1: uniformly mix Cr powder, Al powder, Mg powder and Si powder in a three-dimensional mixer to obtain CrAlMgSi alloy powder; S2: pack the powder into a bag; S3: degas the bag at a degassing temperature of 320°C and a degassing vacuum of ≤10 -2 Pa, keep warm for 4h; S4: hot isostatic pressing sintering, sintering temperature 450℃, pressure 125MPa, keep warm and pressure for 2h.
[0052] After the hot isostatic pressing in this comparative example was completed and the ingot was taken out of the furnace, it was found that the ingot jacket was melted.
[0053] In Comparative Example 5: a hot isostatic pressing process was adopted.
[0054] The difference between this comparative example and comparative example 4 lies in the hot isostatic pressing sintering process parameters, specifically, the hot isostatic pressing sintering is as follows: sintering temperature 390° C., pressure 130 MPa, and heat and pressure holding for 2 hours.
[0055] The hot isostatically pressed ingot obtained in this comparative example did not exhibit sheath melting, but the density of the prepared CrAlMgSi target was relatively low, with a relative density of only 98.01%.
[0056] In Comparative Example 6, the SPS sintering conditions were as follows: heating to 535° C. at a heating rate of 20° C. / min, while linearly increasing the pressure to 40 MPa, and holding the temperature for 8 min.
[0057] In Comparative Example 7: The SPS sintering conditions are as follows: first stage: heating to 300°C at a heating rate of 35°C / min, while linearly increasing the pressure to 30 MPa, and keeping warm for 5 minutes; second stage: heating to 535°C at a heating rate of 20°C / min, while linearly increasing the pressure to 40 MPa, and keeping warm for 3 minutes.
[0058] In Comparative Example 8: The SPS sintering conditions are as follows: first stage: heating to 400°C at a heating rate of 35°C / min, while linearly increasing the pressure to 30 MPa, and keeping warm for 5 minutes; second stage: heating to 585°C at a heating rate of 20°C / min, while linearly increasing the pressure to 40 MPa, and keeping warm for 3 minutes.
[0059] In Comparative Example 9: The SPS sintering conditions are as follows: first stage: heating to 400°C at a heating rate of 35°C / min, while linearly increasing the pressure to 10 MPa, and keeping warm for 5 minutes; second stage: heating to 535°C at a heating rate of 20°C / min, while linearly increasing the pressure to 20 MPa, and keeping warm for 3 minutes.
[0060] The other process parameters in the above comparative example are the same as those in Example 1.
[0061] Performance testing (1) Microstructure like Figure 1 This is the microstructure diagram of the chromium-aluminum-magnesium-silicon alloy target in Example 7 (metallographic photograph - 200 times). The target structure is uniform and the product appearance has no segregation.
[0062] (2) Test results: as shown in Table 2.
[0063] Relative density: The measured density is measured by the Archimedes displacement method. The relative density is equal to the measured density divided by the theoretical density value.
[0064] Thermal conductivity: The thermal conductivity is measured using an LFA-457 laser thermal conductivity meter. The thermal diffusivity of the underlying material is tested in accordance with the national standard GB / T22588-2008 "Flash method for measuring thermal diffusivity or thermal conductivity."
[0065] O content: measured by inert gas fusion infrared thermal conductivity method.
[0066] Table 2 Performance test results of chromium-aluminum-magnesium-silicon alloy targets in Examples and Comparative Examples From the test results in the above table, it can be seen that the density of the CrAlMgSi alloy target prepared by using the technical solution provided by the present application is ≥100.20%, the product appearance has no segregation, the thermal diffusion coefficient is ≥60.895mm2 / s, and the oxygen content is ≤1125ppm; the above test results show that the present application has obtained a CrAlMgSi alloy target with high density, uniform structure, good thermal conductivity, and excellent coating performance, and the oxygen content in the target is relatively low.
[0067] By comparing the test results in Examples 1-7 and Comparative Examples 1-3, it can be seen that the atomic composition content in Comparative Examples 1-3 does not match. The CrAlMgSi alloy target prepared in Comparative Example 1 has a low density and a high oxygen content; the CrAlMgSi target product prepared in Comparative Example 2 has segregated appearance, poor thermal conductivity, and a high oxygen content; and the CrAlMgSi alloy target prepared in Comparative Example 3 has a low density, poor thermal conductivity, and a high oxygen content. In contrast, in Examples 1-7 of the present application, the comprehensive performance of the CrAlMgSi alloy target is effectively guaranteed by precisely controlling the composition content of each atom.
[0068] In the preparation method of CrAlMgSi alloy target material, the hot isostatic pressing process is adopted in Comparative Example 4, and the sintering temperature and pressure are relatively high. After the hot isostatic pressing is completed and taken out of the furnace, it is found that the ingot sheath is melted; in Comparative Example 5, the hot isostatic pressing sintering temperature is relatively low, and the prepared CrAlMgSi alloy target material has a lower density and a higher oxygen content.
[0069] In the SPS sintering conditions of Comparative Example 6, the temperature was directly raised to 535°C at a heating rate of 20°C / min, and the pressure was linearly increased to 40 MPa for insulation. The prepared CrAlMgSi alloy target had a low density and a high oxygen content. In addition, the Al-Mg reaction continued to release a large amount of heat, causing Cr and Al to also undergo alloying reaction, which further intensified the heat release. Ultimately, the degree of alloying inside the target was too high, the target became more brittle, and microcracks appeared inside.
[0070] In the SPS sintering conditions of Comparative Example 7, the first stage holding temperature is relatively low at 300° C., the prepared CrAlMgSi alloy target has a high oxygen content, and the microstructure shows slight alloying of Cr and Al.
[0071] In the SPS sintering conditions of Comparative Example 8, the second stage holding temperature is as high as 585° C. The temperature is too high, a liquid phase appears, and white spots are visible on the target surface, which are component segregation.
[0072] The SPS sintering conditions of Comparative Example 9 are as follows: the pressure in the first stage is relatively low, 10 MPa, and the pressure in the second stage is relatively low, 20 MPa. The prepared CrAlMgSi alloy target has a low density and a high oxygen content.
[0073] In contrast, Examples 7-14 of the present application adopt SPS for sintering, and adopt a two-stage temperature increase and pressure increase-temperature and pressure maintenance treatment to control the process parameters of the two stages, thereby effectively improving the comprehensive performance of the CrAlMgSi alloy target.
[0074] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.
Claims
1. A chromium-aluminum-magnesium-silicon alloy target, characterized in that: The chromium-aluminum-magnesium-silicon alloy target material is composed of the following components in atomic percentage: Cr=10-60at%, Al=30-90at%, Mg=0-20at% and not 0, Si=0-20at% and not 0; the Si is introduced in the form of AlSix alloy powder.
2. The chromium-aluminum-magnesium-silicon alloy target according to claim 1, characterized in that: The chromium-aluminum-magnesium-silicon alloy target material is composed of the following components in atomic percentage: Cr=10-50at%, Al=40-80at%, Mg=0-15at% and not 0at%, and Si=0-15at% and not 0at%.
3. The chromium-aluminum-magnesium-silicon alloy target according to claim 1, characterized in that: The Si is introduced in the form of AlSix alloy powder, wherein X=18-50at%.
4. The chromium-aluminum-magnesium-silicon alloy target according to claim 1, characterized in that The Al / Si atomic ratio is ≥4.
5. The chromium-aluminum-magnesium-silicon alloy target according to claim 4, characterized in that: The Al / Si atomic ratio is 4-60.
6. A method for preparing a chromium-aluminum-magnesium-silicon alloy target according to any one of claims 1 to 5, characterized in that: Specifically, the following steps are carried out in sequence: powder mixing, mold filling, SPS sintering, and machining.
7. The method for preparing a chromium-aluminum-magnesium-silicon alloy target according to claim 6, characterized in that: Specifically, the following steps are performed in sequence: S1: Under Ar gas protection, Cr powder, Al powder, AlSix alloy powder, and Mg powder are weighed in proportion and mixed uniformly to obtain CrAlMgSi alloy powder; S2: uniformly filling the CrAlMgSi alloy powder obtained in S1 into a graphite mold of corresponding size; S3: placing the graphite mold in an SPS spark plasma sintering furnace and performing SPS sintering and densification under vacuum conditions. After cooling, demoulding is performed to obtain a densely sintered CrAlMgSi compact. S4: machining the compact obtained in S3 to obtain the CrAlMgSi alloy target product.
8. The method for preparing a chromium-aluminum-magnesium-silicon alloy target according to claim 7, characterized in that: The purity of the Cr powder is ≥99.8wt%, and the particle size is -200 mesh; the purity of the Al powder is ≥99.8wt%, and the laser particle size D50 is 5-10μm; the purity of the AlSix alloy powder is ≥99.8wt%, and the particle size is -300 mesh; the purity of the Mg powder is ≥99.8wt%, and the particle size is -150 mesh.
9. The method for preparing a chromium-aluminum-magnesium-silicon alloy target according to claim 7, characterized in that: The SPS sintering conditions are as follows: the entire sintering process is vacuumed, with a vacuum degree of 10 -1 -10 -3 Pa; heating rate is 10-60℃ / min; The first stage: heating to 350-450℃, while linearly increasing the pressure to 20-40MPa, keeping the temperature for 0-10min and not to 0; The second stage: heating to 450-550℃, while linearly increasing the pressure to 30-50MPa, keeping the temperature for 0-10min and not to 0; The temperature of the second stage is higher than that of the first stage, and the pressure of the second stage is higher than that of the first stage.
10. The method for preparing a chromium-aluminum-magnesium-silicon alloy target according to claim 9, characterized in that: The SPS sintering conditions are as follows: first stage: heating to 350-450°C at a heating rate of 20-60°C / min, while linearly increasing the pressure to 25-35 MPa, and holding for 0-10 min and not to 0; The second stage: heating to 450-550℃ at a heating rate of 10-30℃ / min, while linearly increasing the pressure to 35-45MPa, and keeping the temperature for 0-10min and not 0; The heating rate in the second stage is lower than that in the first stage.