A diamond / silicon carbide composite material and a method for producing the same

Abstract

The present application relates to a kind of diamond / silicon carbide composite material and its preparation method.The preparation method of the diamond / silicon carbide composite material includes the following steps: (1) diamond powder, carbon fiber and binder solution are mixed, to obtain raw material mixed slurry;(2) the raw material mixed slurry is granulated to obtain raw material mixed powder and is formed into shape, to obtain green body;(3) the green body is subjected to debinding treatment, to obtain preform;(4) the preform is subjected to silicon infiltration treatment, to obtain the diamond / silicon carbide composite material;In step (1), the diameter of the carbon fiber is 0.5-10 μm, the length is 10-80 μm, and the carbon fiber includes long-cut carbon fiber and short-cut carbon fiber;Preferably, the diameter of long-cut carbon fiber is 3-4 μm, the length is 70-80 μm;The diameter of short-cut carbon fiber is 2-2.5 μm, and the length is 10-20 μm.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide composite material preparation technology, specifically relating to a diamond / silicon carbide composite material and its preparation method. Background Technology

[0002] Diamond / silicon carbide composites have been widely used in electronic packaging and high-performance heat dissipation due to their excellent thermal conductivity, low coefficient of thermal expansion, and superior mechanical properties. However, diamond / silicon carbide composites prepared by traditional methods often have certain limitations in their microstructure, resulting in poor bonding strength and coefficient of thermal expansion, which cannot meet the requirements for higher performance.

[0003] Carbon fibers possess a highly ordered crystalline structure, which can significantly improve the bonding strength and thermal stability of composite materials. Especially in terms of dimensional control, carbon fibers of different diameters and lengths can be selected and customized according to requirements, and the combination of long and short cuts can optimize the mechanical and thermal properties of composite materials. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a diamond / silicon carbide composite material and its preparation method.

[0005] In a first aspect, the present invention provides a method for preparing a diamond / silicon carbide composite material, the method comprising the following steps: (1) Diamond powder, carbon fiber and binder solution are mixed to obtain raw material mixture slurry; (2) The raw material mixture slurry is granulated to obtain raw material mixture powder and then molded to obtain a green body; (3) The blank is degreased to obtain a preform; (4) The preform is subjected to silicon infiltration treatment to obtain the diamond / silicon carbide composite material; In step (1), the carbon fiber has a diameter of 0.5-10 μm and a length of 10-80 μm, and the carbon fiber includes long-cut carbon fiber and short-cut carbon fiber; preferably, the long-cut carbon fiber has a diameter of 3-4 μm and a length of 70-80 μm; the short-cut carbon fiber has a diameter of 2-2.5 μm and a length of 10-20 μm.

[0006] Preferably, in step (1), the particle size of the diamond powder is 10-600 μm.

[0007] Preferably, in step (1), the solute binder in the binder solution is phenolic resin; preferably, the mass percentage of solute binder and solvent in the binder solution is 35-50%: 50-65%, calculated with the total mass of solute binder and solvent as 100%.

[0008] Preferably, in step (1), based on the total mass of the diamond powder, long-cut carbon fiber, short-cut carbon fiber and binder solution as 100%, the mass percentage of the diamond powder, long-cut carbon fiber, short-cut carbon fiber and binder solution is 70-85%:3.5-10.5%:1.5-4.5%:5-15%, more preferably 80%:7%:3%:10%.

[0009] Preferably, in step (2), the compression molding is carried out in a steel mold, and the compression molding pressure is 45-60 MPa.

[0010] Preferably, in step (3), the degreasing process is carried out in a vacuum environment, the temperature of the degreasing process is 600-1200℃, preferably 700-1200℃, and the holding time is 0.5-2h.

[0011] Preferably, in step (4), the silicon infiltration process is carried out in a vacuum environment with a vacuum degree of 1-3 MPa, a temperature of 1500-1700℃, and a time of 1-3 h.

[0012] Secondly, the present invention provides a diamond / silicon carbide composite material obtained according to the above preparation method.

[0013] Preferably, the diamond / silicon carbide composite material has a thermal conductivity ≥600 W / m·K at 25℃ and a coefficient of thermal expansion of 2.4-2.6 × 10⁻⁶ at 50-400℃. -6 K -1 Flexural strength ≥400MPa.

[0014] Beneficial effects The preparation method provided by this invention innovatively introduces carbon fibers of different sizes. Through a liquid-phase melting and infiltration reaction sintering process of silicon, the thermal conductivity, mechanical properties, and coefficient of thermal expansion of the composite material are significantly improved. The carbon fibers form a continuous silicon carbide network structure in the material, enhancing the strength and thermal conductivity of the material, while also improving the density and stability. The final product is a composite material with excellent thermal conductivity and high flexural strength, suitable for high-performance heat dissipation devices and electronic packaging. This invention provides a new approach to the preparation of high-performance composite materials through the optimization of carbon fiber size and proportion. Detailed Implementation

[0015] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0016] The following is an exemplary description of a method for preparing the diamond / silicon carbide composite material provided by the present invention. The preparation method may include the following steps: (1) Diamond powder, carbon fiber and binder solution are mixed to obtain raw material mixture slurry; (2) The raw material mixture slurry is granulated to obtain raw material mixture powder and then molded to obtain a blank; (3) The blank is degreased to obtain a preform; (4) The preform is subjected to silicon infiltration treatment to obtain the diamond / silicon carbide composite material.

[0017] In some embodiments, in step (1), the particle size of the diamond powder can be 10-600 μm. If the particle size is too large, the contact area between particles will decrease, the heat conduction path will be discontinuous, and the overall thermal conductivity of the composite material will be affected. Simultaneously, the interface area between the composite material particles prepared from large-diameter diamond particles and the silicon carbide matrix will be small, reducing the interfacial bonding force and affecting the overall strength and toughness of the material. If the particle size is too small, the specific surface area of ​​the diamond particles will increase, leading to more interfaces in the composite material and increased interfacial thermal resistance, thus affecting the thermal and mechanical properties of the composite material.

[0018] In some embodiments, in step (1), the diameter of the carbon fiber can be 0.5-10 μm and the length can be 10-80 μm. The carbon fiber can include chopped carbon fibers and short-chopped carbon fibers; the diameter of the chopped carbon fibers can be 3-4 μm, preferably 3 μm, and the length can be 70-80 μm, preferably 70 μm; the diameter of the short-chopped carbon fibers can be 2-2.5 μm, preferably 2.5 μm, and the length can be 10-20 μm, preferably 15 μm.

[0019] The selection of long-cut and short-cut carbon fibers with specific diameters is based on their impact on the silicon carbide network structure and the performance of the composite material. Choosing long-cut carbon fibers helps enhance the mechanical properties of the composite, while choosing short-cut carbon fibers facilitates fiber dispersion during the composite preparation process, reducing the difficulty of preparation. If the carbon fiber diameter is too large, the bond between the fiber and the matrix will be loose during sintering, forming pores and leading to a decrease in the mechanical properties of the composite. It will also affect the effective heat conduction path, reducing thermal conductivity. If the diameter is too small, the thin carbon fibers cannot provide sufficient support, further reducing the mechanical properties of the composite. If the carbon fiber length is too long, long carbon fibers will cause stress concentration, making them prone to breakage at high temperatures, affecting the long-term stability of the composite. If the length is too short, the contact area increases, leading to increased interfacial friction, affecting the bond between the fiber and the matrix, and reducing the mechanical properties of the composite.

[0020] By controlling the length and diameter of the long-cut carbon fibers within the aforementioned range, optimal mechanical and thermal conductivity of the composite material can be ensured. Conversely, by controlling the length and diameter of the short-cut carbon fibers within the aforementioned range, good dispersibility and filling properties of the carbon fibers in the raw material mixture slurry can be ensured. Furthermore, the carbon fibers used in this invention have a low coefficient of thermal expansion (0.3-1×10⁻⁶). -6 K -1 This can help improve the stability of composite materials in high-temperature environments.

[0021] This invention significantly improves the thermal conductivity, mechanical properties, and coefficient of thermal expansion of composite materials by introducing carbon fibers of different sizes and forms. This method specifically selects long-cut and short-cut carbon fibers, fully utilizing their complementary properties. Long-cut carbon fibers form a continuous network structure in the composite material, improving overall strength and thermal conductivity; short-cut carbon fibers fill the micropores of the matrix, increasing the material's density and stability.

[0022] In some embodiments, in step (1), the solute binder in the binder solution can be phenolic resin; preferably, the mass percentage of solute binder and solvent in the binder solution can be 35-50%: 50-65%, calculated with the total mass of solute binder and solvent as 100%.

[0023] In some embodiments, in step (1), based on the total mass of the diamond powder, long-cut carbon fibers, short-cut carbon fibers, and binder solution as 100%, the mass percentage of the diamond powder, long-cut carbon fibers, short-cut carbon fibers, and binder solution can be 70-85%:3.5-10.5%:1.5-4.5%:5-15%, preferably 80%:7%:3%:10%.

[0024] In this process, an excessively high proportion of diamond powder leads to difficulties in molding and processing; an excessively low proportion results in reduced thermal and mechanical properties of the composite material. Similarly, an excessively high proportion of long-cut carbon fiber leads to processing difficulties, as the uneven distribution of long-cut carbon fibers causes inconsistent thermal expansion properties; an excessively low proportion fails to fully utilize its role in enhancing the flexural strength of the composite material. An excessively high proportion of short-cut carbon fiber leads to reduced flexural strength and elastic modulus of the composite material; an excessively low proportion fails to adequately fill voids, resulting in reduced density and affecting the mechanical and thermal properties of the composite material. An excessively high proportion of binder results in poor flowability of the granulated composite powder, making it difficult to mold; an excessively low proportion results in low viscosity of the granulated composite powder, also making it difficult to mold.

[0025] Furthermore, long-cut carbon fibers are responsible for forming a continuous network. If they are too short, the network will be discontinuous, reducing the material's thermal conductivity and mechanical strength. Too many short-cut carbon fibers result in weak inter-fiber connections, affecting structural stability. Long-cut carbon fibers offer better continuity and conductivity. A high proportion of short-cut fibers disrupts the internal heat conduction channels of the composite material, reducing its thermal conductivity. An excessively high proportion of long-cut carbon fibers worsens the composite material's plasticity, affecting its toughness. An excessively high proportion of short-cut carbon fibers reduces flexural strength.

[0026] In some implementations, the mixing process in step (1) can be carried out in a ball mill for 8-10 hours.

[0027] In some embodiments, in step (2), the compression molding can be performed in a steel mold, and the compression molding pressure can be 45-60 MPa.

[0028] In some embodiments, in step (3), the degreasing process can be carried out in a vacuum environment, the temperature of the degreasing process can be 600-1200℃, preferably 700-1200℃, and the holding time can be 0.5-2h.

[0029] In some embodiments, in step (4), the silicon infiltration process can be carried out in a vacuum environment, with a vacuum degree of 1-3 MPa, a temperature of 1500-1700°C, and a time of 1-3 hours; preferably, the purity of the silicon particles used in the silicon infiltration process can be ≥90%.

[0030] Silicon particles are placed above and below the multiphase ceramic preform for silicon infiltration. During the silicon infiltration process, the silicon particles melt into molten silicon and enter the multiphase ceramic preform under the action of capillary force and gravity. This promotes the full reaction between the molten silicon and carbon fibers to generate fibrous silicon carbide, thereby effectively reducing the residual silicon content inside the diamond / silicon carbide composite material and improving the mechanical and thermal properties of the diamond / silicon carbide composite material.

[0031] This invention optimizes the size and proportion of carbon fibers and the uniform dispersion of diamond particles to ultimately form a composite material with excellent thermal conductivity, low coefficient of thermal expansion, and high mechanical strength, suitable for high-performance heat dissipation materials in demanding electronic packaging. The diamond / silicon carbide composite material obtained by the above-mentioned preparation method provided by this invention exhibits excellent thermal conductivity and good mechanical and thermal properties.

[0032] It should also be noted that the absence of silicon carbide powder in the raw materials used in this invention is intended to maximize the diamond content while ensuring the composite material can be molded, thereby obtaining a high-performance composite material and improving its density. This invention, entirely through a silicon infiltration process, can prepare composite materials with a density as high as 99%, ensuring sufficient strength. Conversely, the addition of silicon carbide may affect the density of the composite material, and the volume content of diamond particles will decrease, leading to a decline in the thermal and mechanical properties of the composite material.

[0033] In some embodiments, the diamond / silicon carbide composite material has a thermal conductivity ≥600 W / m·K at 25°C and a coefficient of thermal expansion of 2.4-2.6 × 10⁻⁶ at 50-400°C. -6 K -1 It has a flexural strength ≥400MPa. It significantly outperforms similar materials in existing technologies in terms of thermal properties and mechanical strength, and maintains good stability during use.

[0034] This invention innovatively introduces carbon fibers of different sizes into the preparation method, significantly improving the thermal conductivity, mechanical properties, and coefficient of thermal expansion of the composite material through a liquid-phase melt infiltration reaction sintering process with silicon. The carbon fibers form a continuous silicon carbide network structure within the material, enhancing its strength and thermal conductivity while simultaneously increasing its density and stability. The final product is a composite material with excellent thermal conductivity (650 W / mK) and high flexural strength (greater than 400 MPa), suitable for high-performance heat dissipation devices and electronic packaging. This invention provides a new approach to the preparation of high-performance composite materials through the optimization of carbon fiber size and proportion.

[0035] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0036] The following examples illustrate the testing methods: (1) Bending strength test refers to "GBT6569-2006-Test Method for Bending Strength of Fine Ceramics"; (2) Thermal expansion coefficient test refers to "QBT 1321-1991 Method for Determining Average Linear Thermal Expansion Coefficient of Ceramic Materials"; (3) Thermal conductivity test refers to "GB / T 22588-2008 Measurement of Thermal Diffusion Coefficient or Thermal Conductivity by Flash Method" to measure the thermal conductivity, then use the drainage method to measure the material density, calculate the corresponding theoretical specific heat capacity, and finally calculate the material thermal conductivity using the formula.

[0037] Example 1

[0038] The method for preparing the diamond / silicon carbide composite material provided in this embodiment includes the following steps: (1) Diamond powder, long-cut carbon fiber (3μm in diameter and 70μm in length), short-cut carbon fiber (2.5μm in diameter and 15μm in length), and phenolic resin solution were wet-mixed in a ball mill for 8 hours to obtain a raw material mixture slurry. The phenolic resin solution contains phenolic resin and solvent in a mass percentage ratio of 50%:50%. The mass percentage of the diamond powder, long-cut carbon fiber, short-cut carbon fiber, and phenolic resin solution can be 80%:7%:3%:10%. (2) The raw material mixed powder obtained by granulation of the raw material mixed slurry is placed into a mold and pressed at 50 MPa to obtain a green body; (3) The billet is degreased in a vacuum environment at 1100°C for 1.5 hours and then cooled in the furnace to obtain the preform; (4) Place the preform in a graphite crucible, place silicon particles on the top and bottom, place the crucible in a vacuum sintering furnace for silicon infiltration treatment, the silicon infiltration temperature is 1600℃, the vacuum degree is 3Mpa, and after silicon infiltration is completed, cool with the furnace to obtain the diamond / silicon carbide composite material.

[0039] Testing showed that the thermal conductivity of the diamond / silicon carbide composite material prepared in this embodiment was 650 W / m·K at 25℃, which is 20% higher than that of traditional materials; the coefficient of thermal expansion at 50-400℃ was 2.496 × 10⁻⁶. -6 K -1 Its flexural strength is 425 MPa.

[0040] The composite material samples prepared in this embodiment underwent durability testing in a high-temperature furnace at 800°C for 100 hours. After the high-temperature durability test, the following tests were performed on the material: (1) Thermal conductivity: The thermal conductivity of the composite material remains at 648 W / m·K, showing good thermal stability; (2) Mechanical properties: The flexural strength of the composite material remained at 420 MPa, without significant attenuation, showing good mechanical properties.

[0041] This embodiment demonstrates that diamond-silicon carbide composite materials prepared using long-cut and short-cut carbon fibers have excellent high-temperature durability and are suitable for use in high-temperature applications.

[0042] Example 2

[0043] The preparation method of the diamond / silicon carbide composite material provided in this embodiment is the same as that in Example 1, with the main difference being: In step (1), the diameter of the short-cut carbon fiber is 2μm and the length is 10μm.

[0044] Example 3

[0045] The preparation method of the diamond / silicon carbide composite material provided in this embodiment is the same as that in Example 1, with the main difference being: In step (1), the diameter of the short-cut carbon fiber is 2μm and the length is 20μm.

[0046] Example 4

[0047] The preparation method of the diamond / silicon carbide composite material provided in this embodiment is the same as that in Example 1. The main difference is that in step (1), the length of the long-cut carbon fiber is 80 μm; the diameter of the short-cut carbon fiber is 2 μm and the length is 10 μm.

[0048] Example 5

[0049] The preparation method of the diamond / silicon carbide composite material provided in this embodiment is the same as that in Example 1. The main difference is that in step (1), the length of the long-cut carbon fiber is 80 μm; the diameter of the short-cut carbon fiber is 2 μm and the length is 20 μm.

[0050] The performance of the diamond / silicon carbide composite materials prepared in Examples 2-5 was tested, and the results showed that: (1) Mechanical properties: the flexural strength of Example 2 was 400 MPa, the flexural strength of Example 3 was 420 MPa, the flexural strength of Example 4 was 400 MPa, and the flexural strength of Example 5 reached 460 MPa; (2) Thermal conductivity test: the thermal conductivity of Example 2 was 600 W / m·K, the thermal conductivity of Example 3 was 630 W / m·K, the thermal conductivity of Example 4 was 620 W / m·K, and the thermal conductivity of Example 5 was 650 W / m·K.

[0051] Example 6

[0052] The preparation method of the diamond / silicon carbide composite material provided in this embodiment is the same as that in Example 1. The main difference is that in step (1), the mass percentage of diamond powder, long chopped carbon fiber, short chopped carbon fiber and phenolic resin solution can be 85%:3.5%:1.5%:10%.

[0053] Example 7

[0054] The preparation method of the diamond / silicon carbide composite material provided in this embodiment is the same as that in Example 1. The main difference is that in step (1), the mass percentage of diamond powder, long-cut carbon fiber, short-cut carbon fiber and phenolic resin solution can be 75%:10.5%:4.5%:10%.

[0055] The composite materials with different carbon fiber contents prepared in Examples 1, 6, and 7 were subjected to the following tests and comparisons. The results show that: (1) Thermal conductivity: When the carbon fiber content is 10%, the composite material exhibits the highest thermal conductivity, which is 650 W / m·K; (2) Mechanical properties: When the carbon fiber content is 15%, the composite material exhibits the highest bending strength, which is 458 MPa.

[0056] Comparative Example 1

[0057] The method for preparing the composite material provided in this comparative example is the same as in Example 1, with the main difference being: In step (1), the long-cut carbon fiber has a diameter of 6 μm and a length of 100 μm, and the short-cut carbon fiber has a diameter of 1 μm and a length of 50 μm.

[0058] Tests showed that the composite material sample prepared in Comparative Example 1 had a thermal conductivity of 480 W / m·K at 25℃ and a coefficient of thermal expansion of 2.989 × 10⁻⁶ at 50-400℃. -6 K -1 Its flexural strength is 335 MPa.

[0059] Comparative Example 2

[0060] The method for preparing the composite material provided in this comparative example is the same as in Example 1, with the main difference being: In step (1), the mass ratio of diamond, long-cut carbon fiber, short-cut carbon fiber, and binder solution is 80%:5%:5%:10%.

[0061] Comparative Example 3

[0062] The method for preparing the composite material provided in this comparative example is the same as in Example 1, with the main difference being: In step (1), the mass ratio of diamond, long-cut carbon fiber, short-cut carbon fiber, and binder solution is 80%:4%:6%:10%.

[0063] Comparative Example 4

[0064] The method for preparing the composite material provided in this comparative example is the same as in Example 1, with the main difference being: In step (1), the mass ratio of diamond, long-cut carbon fiber, short-cut carbon fiber, and binder solution is 80%:3%:7%:10%.

[0065] The performance of the composite materials prepared in Comparative Examples 2-4 was tested, and the results showed that: (1) Mechanical properties: the flexural strength of the sample prepared in Comparative Example 2 was 300 MPa, the flexural strength of the sample prepared in Comparative Example 3 was 350 MPa, and the flexural strength of the sample prepared in Comparative Example 4 was 345 MPa; (2) Thermal conductivity: the thermal conductivity of the sample prepared in Comparative Example 2 was 580 W / m·K, the thermal conductivity of the sample prepared in Comparative Example 3 was 560 W / m·K, and the thermal conductivity of the sample prepared in Comparative Example 4 was 575 W / m·K; (3) Coefficient of thermal expansion: the coefficient of thermal expansion of the sample prepared in Comparative Example 2 at 50-400℃ was 2.785 × 10⁻⁶. -6 K -1 The coefficient of thermal expansion of the sample prepared in Comparative Example 3 at 50-400℃ was 2.867×10⁻⁶. -6 K -1 The coefficient of thermal expansion of the sample prepared in Comparative Example 4 at 50-400℃ was 2.998 × 10⁻⁶. -6 K -1 .

[0066] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a diamond / silicon carbide composite material, characterized in that, The preparation method includes the following steps: (1) Diamond powder, carbon fiber and binder solution are mixed to obtain raw material mixture slurry; (2) The raw material mixture slurry is granulated to obtain raw material mixture powder and then molded to obtain a blank; (3) The blank is degreased to obtain a preform; (4) The preform is subjected to silicon infiltration treatment to obtain the diamond / silicon carbide composite material; In step (1), the carbon fiber has a diameter of 0.5-10 μm and a length of 10-80 μm, and the carbon fiber includes long-cut carbon fiber and short-cut carbon fiber; preferably, the long-cut carbon fiber has a diameter of 3-4 μm and a length of 70-80 μm; the short-cut carbon fiber has a diameter of 2-2.5 μm and a length of 10-20 μm.

2. The preparation method according to claim 1, characterized in that, In step (1), the particle size of the diamond powder is 10-600 μm.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the solute binder in the binder solution is phenolic resin; preferably, the mass percentage of solute binder and solvent in the binder solution is 35-50%: 50-65%, calculated with the total mass of solute binder and solvent as 100%.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (1), based on the total mass of the diamond powder, long-cut carbon fibers, short-cut carbon fibers, and binder solution being 100%, the mass percentage of the diamond powder, long-cut carbon fibers, short-cut carbon fibers, and binder solution is 70-85%. 3.5-10.5%:1.5-4.5%:5-15%, preferably 80%:7%:3%:10%.

5. The preparation method according to any one of claims 1-4, characterized in that, In step (2), the compression molding is carried out in a steel mold, and the compression molding pressure is 45-60 MPa.

6. The preparation method according to any one of claims 1-5, characterized in that, In step (3), the degreasing process is carried out in a vacuum environment, the temperature of the degreasing process is 600-1200℃, preferably 700-1200℃, and the holding time is 0.5-2h.

7. The preparation method according to any one of claims 1-6, characterized in that, In step (4), the silicon infiltration process is carried out in a vacuum environment with a vacuum degree of 1-3 MPa, a temperature of 1500-1700℃, and a time of 1-3 h.

8. A diamond / silicon carbide composite material obtained by the preparation method according to any one of claims 1-7.

9. The diamond / silicon carbide composite material according to claim 8, characterized in that, The diamond / silicon carbide composite material has a thermal conductivity ≥600 W / m·K at 25℃ and a coefficient of thermal expansion of 2.4-2.6×10⁻⁶ at 50-400℃. -6 K -1 Flexural strength ≥400MPa.