CN101318839B - Preparation method of silicon carbide ceramic and diamond composite drawing die - Google Patents

Abstract

The invention relates to a method for preparing a silicon carbide ceramic and diamond composite drawing die in the field of coating technology. The silicon carbide ceramic is used as a substrate to perform multiple times of conventional diamond coating deposition→plasma polishing→nanometer diamond coating deposition→mechanical Polishing, so that the surface defects of the original inner hole of the ceramic mold disappear. In the CVD diamond deposition-polishing cycle process, the combination of conventional diamond coating and nano-diamond coating, plasma polishing and mechanical polishing is used. Deposition of conventional coating and Plasma polishing is inserted between nanocoatings, making it more suitable for mechanical polishing after growing nanocoatings. The mold prepared by the invention can replace traditional hard alloy products, not only can greatly extend the service life of traditional molds and devices, improve production efficiency, significantly improve the quality of related products, effectively save raw materials, and greatly reduce tungsten and cobalt resources It is of great significance to effectively solve the resource crisis faced by the cemented carbide industry.

Description

Preparation method of silicon carbide ceramic and diamond composite drawing die

technical field

The invention relates to a preparation method in the technical field of molds, in particular to a method for preparing a chemical vapor deposition (CVD) silicon carbide ceramic and diamond composite drawing mold.

Background technique

Drawing dies are usually made of wear-resistant materials, ideally diamond materials, followed by hard alloys to improve the life of the dies and ensure the dimensional accuracy and smoothness of the products. Considering cost and technical factors, most of the current manufacturing drawing dies use cemented carbide in the case of large aperture (d ≥ 5 mm), and diamond (polycrystalline or single crystal) is only used in small aperture occasions (d ≤ 3 mm). Mold, however, the traditional hard alloy mold wears very seriously during drawing and stranding, the working life is short, the accuracy of related products is difficult to guarantee, the surface quality is poor, the consumption of mold is large, especially the waste of raw materials such as copper is serious, resulting in production efficiency low, and the labor intensity of workers is high, which seriously restricts the further improvement of the benefits of related industries and product quality. On the other hand, the manufacture of cemented carbide consumes a large amount of tungsten. disappear, the cemented carbide industry will also face a resource crisis, and the safety of tungsten resources has become a bottleneck in the development of the cemented carbide industry.

Engineering ceramic materials have the characteristics of high temperature resistance, wear resistance, oxidation resistance, corrosion resistance and good high temperature strength, and are currently being used in many fields where cemented carbide was used in the past, such as cutting tools, wear-resistant devices, grinding balls, bearings, nozzles , key components of the engine, etc. As the impact strength and fracture toughness of advanced ceramics have been greatly improved, it is most likely to develop into an ideal substitute for hard alloy materials with resource constraints, especially non-oxide structural ceramics such as silicon carbide (SiC), which do not have resource problems. At the same time, it is a typical strong carbide-forming material with strong covalent bonds. It has a structure unit similar to diamond tetrahedron. On the SiC ceramic substrate, CVD diamond has a high nucleation density and has a good combination with the diamond coating. Compared with cemented carbide, ceramic materials have a smaller coefficient of thermal expansion and have no Co graphitization effect. Therefore, on SiC ceramic substrate materials, it is easy to obtain a diamond coating with significantly higher bonding strength than cemented carbide.

However, unlike cemented carbide materials, ceramic materials are mostly solid-phase sintered. There are a large number of structural defects in crystalline ceramics, which make the material not dense, and there are often many micropores inside. The inherent defects of ceramic materials have a great impact on its physical and mechanical properties, especially on the friction and wear characteristics, which directly affects its performance in the field of tribology instead of cemented carbide as wear-resistant materials. .

After searching the literature of the prior art, it was found that the Chinese patent "Preparation Method of Diamond Composite Coated Drawing Die" (Patent No. ZL01113027.X) proposes to use a large-aperture cemented carbide die as a substrate, and use a chemical vapor phase method on the surface of the inner hole Deposit a layer of conventional diamond and nano-diamond composite coating to make a diamond coating mold, which can increase the working life by 5-10 times, but the invention uses a WC-Co cemented carbide substrate material, composed of tungsten carbide particles and Binder (cobalt, nickel, etc.) The bonding strength with the base material needs to be improved, and the performance of the coating product is discrete, which limits the further improvement of the service life of the diamond composite coating mold. Since the substrate is still cemented carbide, there is also the consumption of tungsten and cobalt resources. and rising manufacturing costs. In further searches, silicon carbide ceramics and diamond-coated composite molds have not been found.

Contents of the invention

The object of the present invention is to solve the existing problems in the prior art, and provide a method for preparing a silicon carbide ceramic and diamond composite drawing mold, using silicon carbide ceramic as the mold substrate, and adopting a method of multiple deposition and polishing of the diamond coating, Overcome the surface defects of ceramics to obtain a composite mold of silicon carbide ceramics and diamond coating.

The present invention is achieved through the following technical solutions:

The present invention uses silicon carbide ceramics as the substrate to perform multiple processes of "conventional diamond coating deposition→plasma polishing→nano-diamond coating deposition→mechanical polishing", so that the original surface defects of the ceramic mold, such as trachoma (pit), disappear , not only improves the smoothness of the surface of the inner hole of the mold, but also increases the service life by more than 10 times due to the strengthening of the diamond coating. In the CVD diamond deposition-polishing cycle process, the combination of conventional diamond coating and nano-diamond coating, the combination of plasma polishing and mechanical polishing, plasma polishing is inserted between the deposition of conventional coating and nano-coating, so that the growth It is more suitable for mechanical polishing after nano-coating.

The inventive method comprises the following steps:

Step 1: After the silicon carbide ceramic mold is pretreated with a mixed solution of nitric acid and hydrofluoric acid, the surface of the mold hole is rotated and ground with diamond micropowder, and after ultrasonic cleaning, it is placed in a hot wire CVD reaction chamber, and a straight-drawing tantalum wire is used to pass through it. The die hole is straightened with a high temperature resistant spring, and the hot wire coincides with the axis of the die hole.

The nitric acid, hydrofluoric acid mixed liquid pretreatment refers to: placing in the nitric acid, hydrofluoric acid mixed liquid, wherein HNO ₃ : HF is 1: 3, to remove SiO ₂ and free Si on the outer surface.

The second step is to inject hydrogen and acetone to deposit a conventional diamond coating on the surface of the inner hole of the mold. The grains are coarse and uneven, and the surface is uneven.

The deposition time of the conventional diamond coating is 4 hours, and the thickness is controlled at 7 μm-9 μm.

The third step, carry out plasma polishing in situ, add argon gas (Ar/H ₂ is 1.0, volume ratio), because the hole diamond film in the mold has negative electron affinity, apply between the filament and the mould. The DC bias of the AC component will form a directional positive ion flow to bombard and remove the sharp corners of the coarse crystal grains on the coating surface.

The specific parameters of the plasma polishing are pressure 100Pa, voltage 200V, bias current 0.5A, and time 0.5 hour.

The fourth step is to continue to deposit the nano-diamond coating in situ.

Described deposition nano-diamond coating, its process parameter is: pressure 1KPa, acetone and hydrogen are 4%-6% (volume ratio), add Ar gas, Ar and H Be _1.0 (volume ratio), time 1 and a half hours , the thickness is controlled at 2μm-4μm;

The fifth step is to perform rotary grinding and mechanical polishing on the surface of the die hole with diamond micropowder.

The sixth step, repeating the second step to the fifth 2 to 3 times, alternate deposition and polishing of conventional and nano-diamond coatings, with a thickness of about 20-30 microns, to prepare silicon carbide ceramic and diamond composite drawing dies, ceramic substrates Significant reduction of surface defects (trachoma, etc.).

Compared with the prior art, the present invention uses silicon carbide ceramics instead of cemented carbide as the substrate, and performs multiple chemical vapor phase (referred to as CVD) diamond deposition and polishing cycles. On the one hand, the original defects on the surface of the inner hole of the ceramic mold, For example, the trachoma (pit) disappears, and the surface finish is significantly improved, which meets the requirements of the drawing die; on the other hand, the ceramic surface is strengthened with a diamond coating, and the service life of the die is extended by more than 10 times. The present invention is characterized by the combination of conventional diamond coating and nano-diamond coating, the combination of plasma polishing and mechanical polishing, and the insertion of plasma polishing process between the deposition of conventional coating and nano-coating, so that the growth of nano-coating is more suitable Mechanical polishing and plasma polishing can be carried out in situ in hot wire CVD deposition diamond equipment. The ceramic/diamond composite drawing die prepared by the present invention can be widely used in the drawing of metal wires and pipes, the twisting and pressing of conductive cores, Metal pipe wall butt welding and drawing, welding rod powder coating die, nozzle, sliding bearing, wear-resistant valve seat and other occasions, the working surface of ceramic material is coated with diamond film coating, which is used to replace traditional hard alloy products (tools and wear-resistant device) occasions, not only can greatly extend the service life of traditional molds and devices, improve production efficiency, significantly improve the quality of related products, effectively save raw materials, but also greatly reduce the consumption of tungsten and cobalt resources, effectively solve the problem of hard alloy industry Facing a resource crisis is significant.

Description of drawings

Fig. 1 is a schematic diagram of the disappearance process of trachoma on the mold surface;

Fig. 2 schematic diagram of diamond coating deposition polishing process;

Among them: Figure 2a is plasma polished, Figure 2.b removes the sharp corners of the coating surface, Figure 2c deposits a nano-diamond coating, and Figure 2d obtains a smooth diamond coating.

Detailed ways

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following the described embodiment.

Example

As shown in Figure 1, where a is the original surface of the ceramic, showing sand holes (pit); b. is the surface after a diamond film deposition by CVD method and polished. The drastic reduction in the size of the trachoma is the result of a combination of faster diamond growth in the pits and thinning of the outer surface by polishing. c is the surface after the second CVD diamond deposition and polishing, and the size of the sand holes is further greatly reduced. d: After the third deposition and polishing, the trachoma almost disappeared. In this way, two purposes are achieved: (1) The trachoma defects gradually disappear, and the surface finish is greatly improved, which meets the requirements of the mold; (2) The diamond surface replaces the ceramic surface, because diamond is the hardest substance in the world, its The hardness is much higher than that of ceramics (SiC, Si ₃ N ₄ , Al ₂ O _3, etc.), so the surface is ideally strengthened. The use of this ceramic/diamond composite mold not only saves the strategic resource tungsten, but also prolongs the life of the mold by more than 10 times, and the dimensional accuracy and smoothness of related products have also been greatly improved. It will become a cemented carbide diamond-coated drawing mold. Ideal for upgrading products.

The preparation process of this embodiment is to uniformly deposit a diamond coating on a silicon carbide SiC ceramic substrate by a chemical vapor phase method to form a smooth diamond surface, and obtain an ideal ceramic/diamond composite mold. One of the most critical techniques is the alternate deposition and polishing of diamond coatings. Generally speaking, due to the large surface energy of diamond, the surface of diamond coating is uneven, and the hardness is extremely high, so it is difficult to polish the coating. For this, the solution is shown in Figure 2, D: conventional diamond coating, ND: nano-diamond coating. The ceramic inner hole is pretreated, and after depositing a layer of conventional diamond coating with a thickness of about 7-9 μm by chemical vapor phase method (CVD method), plasma polishing is performed (Fig. 2.a, Ar ⁺ , H ⁺ ion beam polishing), To remove the sharp corners of the coating surface (Figure 2.b), then change the CVD process conditions to deposit a layer of nano-diamond coating of about 3-5 μm (Figure 2.c). After mechanical polishing (diamond powder is made abrasive), just can obtain one deck smooth diamond coating (Fig. →Mechanical polishing” cycle process can be understood as a combination of conventional diamond and nano-diamond coating, plasma polishing and mechanical polishing.

In this embodiment, the substrate is pressureless sintered SiC ceramics, the outer dimensions are φ50×25 mm, and the aperture is φ18.2 mm. The surface of the inner hole of the mold is trimmed and ground and placed in a mixed solution of nitric acid and hydrofluoric acid (HNO ₃ : HF is 1:3), to remove SiO ₂ and free Si on the outer surface, after neutralization and cleaning, the surface of the die hole is ground with diamond micropowder, ultrasonically cleaned, and then placed in the hot wire CVD reaction chamber after cleaning. The hot filament adopts a tantalum wire with a diameter of 1.0 mm. After the hot wire passes through the die hole, it is connected with the filament electrode. It is straightened by a high temperature resistant spring, and the hot wire coincides with the axis of the die hole.

Feed reaction gas (hydrogen and acetone) after reaction chamber is evacuated, start CVD deposition diamond coating after adjusting reaction chamber pressure, process parameter is pressure 5KPa, gas total flow 700 milliliters/min, acetone/hydrogen are 2% (volume ratio ), the temperature of the hot filament is about 2200°C, and the DC bias current is 4A. After 4 hours of deposition, the surface of the die hole is deposited to obtain a conventional diamond coating of about 8 microns.

On this basis, plasma polishing is performed in situ, adding argon gas (Ar/H ₂ is 1.0, volume ratio) to apply a DC bias voltage with AC components between the filament and the mold (no filtering after full-wave rectification), Bombard the substrate with Ar ⁺ and H ⁺ to remove the sharp corners on the surface of the diamond coating, and the coating thickness is also slightly reduced. The specific parameters are pressure 100Pa, voltage 200V, bias current 0.5A, and time 0.5 hours.

Then adjust the parameters, continue to deposit the nano-diamond coating in situ, the process conditions become: pressure 1KPa, the volume ratio of acetone and hydrogen is 4%, 5%, 6%, add Ar gas, the volume ratio of Ar and _H is 1.0 After one and a half hours, a nano-diamond coating of about 3 microns was obtained.

Take out the mold from the reaction chamber and perform mechanical polishing to obtain a smooth diamond composite coating with a thickness of about 8 μm.

Repeat the above process for two more times to obtain a ceramic and diamond composite mold, the defects (trachoma or pit) on the surface of the ceramic substrate are greatly reduced, the diamond coating of the mold is about 20-30 microns thick, and the surface finish Ra≤0.05 μm. The trachoma originally present on the ceramic substrate also disappears, and the mold is used for twisting and compacting the conductive core of a power cable with a cross ^- section of 240mm2, and its working life can be increased from 30km of the original cemented carbide mold to more than 600km (about 20 times), and the surface quality and dimensional accuracy of the core have also been greatly improved. Ceramic/diamond composite coating can be widely used in the drawing of metal wires, rods and tubes, the twisting and compacting of conductive cores, butt welding and shaping of tube walls, powder coating dies for welding electrodes, nozzles, etc., and can also be used in sliding bearings , wear-resistant valve seat and other occasions, it has the advantages of small friction coefficient, resistance to all acids and alkalis, extremely long service life, and no resource consumption problems.

The above-mentioned embodiment inserts the plasma polishing process after depositing the conventional diamond coating and before growing the nano-diamond coating to remove sharp corners on the surface of the conventional coating, improve the flatness of the coating, and make it easier to grow the nano-diamond coating. Suitable for mechanical polishing. Plasma polishing can be performed on an ion beam etcher or in situ in a hot-filament CVD deposition device. Because the surface temperature of the substrate can reach 800-900°C during the deposition of the diamond film, at such a high temperature, both the silicon carbide ceramic and the diamond coating change from the original insulator to a conductor, which can be used as an electrode. If a DC or AC voltage, or a biased AC voltage is applied between the filament and the ceramic substrate, plasma can be generated under a certain pressure, and the purpose of plasma polishing can be achieved. The remarkable feature of the above embodiments is that plasma polishing can be performed in situ, which effectively simplifies the CVD process.

Claims (6)

1. silicon carbide ceramics and method for manufacturing composite drawing mould of diamond is characterized in that, may further comprise the steps:

After the first step, silicon carbide ceramics mould pass through nitric acid, hydrofluoric acid mixed solution preliminary treatment, with diadust the nib surface is rotated grinding, in the ultrasonic clean rearmounted heated filament CVD reative cell, adopt the vertical pulling tantalum wire to pass nib, stretching with high temperature resistant spring, and heated filament and nib axis are matched;

Second step, feeding hydrogen and acetone deposit conventional diamond coatings at the mould bore area;

The 3rd step, original position are carried out plasma polishing, add argon gas, mould endoporus diamond thin has negative electron affinity, between filament and mould, apply a Dc bias that has Alternating Component, the cation stream that forms directed movement is bombarded the wedge angle of removing the coating surface coarse grain;

The 4th step, original position continue the depositing nano diamond coatings;

The 5th step, the nib surface is rotated grinding machinery polishing with diadust;

The 6th step, repetition second go on foot the 5th and go on foot 2 to 3 times, and conventional diamond coatings and nano diamond coating alternating deposit and polishing prepare silicon carbide ceramics and composite drawing mould of diamond.

2. silicon carbide ceramics according to claim 1 and method for manufacturing composite drawing mould of diamond is characterized in that, in second step, and the conventional diamond coatings of described deposition, 4 hours its time, THICKNESS CONTROL is at 7 μ m-9 μ m.

3. silicon carbide ceramics according to claim 1 and method for manufacturing composite drawing mould of diamond is characterized in that, in the 3rd step, the argon gas of interpolation is 1.0 with the hydrogen volume ratio.

4. according to claim 1 or 3 described silicon carbide ceramics and method for manufacturing composite drawing mould of diamond, it is characterized in that, in the 3rd step, described original position is carried out plasma polishing, and its concrete parameter is pressure 100Pa, voltage 200V, bias current 0.5A, the time is 0.5 hour.

5. silicon carbide ceramics according to claim 1 and method for manufacturing composite drawing mould of diamond is characterized in that, in the 4th step, described depositing nano diamond coatings, its technological parameter is: pressure 1KPa, the volume ratio of acetone and hydrogen is 4%-6%, add Ar gas, Ar gas and H ₂Volume ratio be 1.0,1 and a half hours time, THICKNESS CONTROL is at 2 μ m-4 μ m.

6. silicon carbide ceramics according to claim 1 and method for manufacturing composite drawing mould of diamond is characterized in that, in the 6th step, the total thickness of described conventional diamond coatings and nano diamond coating is the 20-30 micron.

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