CN103343326B - Nanocrystalline ultrahard composite coating and preparation method thereof - Google Patents

Abstract

The invention provides a nanocrystalline ultrahard composite coating and preparation method thereof. The nanocrystalline ultrahard composite coating orderly composed of a combination layer, a transition layer, a supporting layer and a lubricating layer is generated by using arc discharge method and hollow cathode arc discharge carbon source combination method. The preparation method provided by the invention has the features of high ionization rate, simple coating device structure and fast deposition speed. The prepared C3N4-MoCn composite coating material is good in coating hardness, strong in adhesive force, good in self-lubricating performance, fast in coating growth speed, high in production efficiency, low in production cost, low in friction coefficient and good in coating tenacity, and capable of greatly improving the wear-resisting and lubricating performance of the processing tool, die and mechanical parts; furthermore, the preparation method is simple, the industrial production is easy to realize, and the good application prospect is realized.

Description

A kind of nanocrystalline superhard composite coating and preparation method thereof

technical field

The invention belongs to the field of materials, and relates to a nanocrystalline superhard composite coating and a preparation method thereof.

Background technique

The high-end manufacturing industry represented by aircraft manufacturing widely adopts high-speed and efficient CNC machining technology, and new materials such as titanium alloys (TC4, TC18, TC21), high-strength steel (300M), carbon fiber composite materials, and aluminum-lithium alloys replace traditional silicon-aluminum alloys. Alloy and structural steel put forward higher requirements on the performance of cutting tools. Ultra-fine-grained cemented carbide is a kind of cemented carbide with high hardness, high strength and high wear resistance. It has little adsorption or diffusion effect with the processed material, and can be used to process materials such as titanium alloy and high-strength steel. However, during high-speed cutting, due to the poor heat conduction of the processed material, the surface temperature of the tool is high, which seriously affects the processing performance.

Nano hard coating is an effective surface modification technology. Superhard coating is a coating material with a hardness greater than 40GPa. Carbide superhard coating tools integrate the advantages of strength, toughness and hardness, which can greatly improve the cutting efficiency and quality, and meet the new needs of high-speed and efficient CNC cutting. Representative of a new generation of high-end knives. The development of superhard coatings has important practical significance for improving the application level of my country's CNC machining technology and improving my country's basic manufacturing capabilities.

Transition metal carbides and nitrides have many attractive properties such as high hardness, perfect wear resistance, low friction coefficient and strong catalytic activity. The formation of transition metal carbides and nitrides is a very important contribution to hardness. So far, very high hardness values have not been obtained in these transition metal carbides and nitrides. However, high hardness can be obtained by forming nanostructured coatings in ternary nitrides. These film layers not only have high hardness but also have low coefficient of friction and high wear resistance.

Theoretical studies show that MoCN is likely to exhibit high hardness close to that of TiCN, CrCN and TiSiN. In Mo metal carbonitride, the nanocrystals of MoC and MoN embedded in the amorphous film can lead to high hardness of the film.

Carbon nitride (C ₃ N ₄ ) film has the characteristics of high hardness, low friction coefficient and high thermal stability. It is a new type of superhard material. Its theoretical hardness is close to diamond, and it is expected to replace diamond material in some occasions. Studies have shown that carbon nitride has obvious advantages when cutting hard and difficult materials. At present, there are many methods for preparing CNx thin films. The commonly used preparation methods include oscillatory wave compression, high-pressure pyrolysis, ion implantation, low-energy ion radiation, ion beam deposition, reactive sputtering, chemical vapor deposition, laser ablation, pulsed laser induction, and electrochemical deposition. and arc discharge. At present, a lot of research has been done on carbon nitride coating at home and abroad. However, due to the large stress of CN coating, it is easy to peel off from the substrate, and it has not been applied in large-scale industry.

Contents of the invention

    The technical problem to be solved by the present invention is to provide a nanocrystalline superhard composite coating and a preparation method thereof.

The composite coating of the present invention is composed of a bonding layer, a transition layer, a supporting layer and a lubricating layer in sequence from the inside to the outside on the substrate surface; wherein, the material of the bonding layer is transition metal Mo, the material of the transition layer is MoN, and the material of the supporting layer The material is the graded carbonitride MoCxN of Mo, where 0≤x≤1; the material of the lubricating layer is Mo containing carbon nitride (C ₃ N ₄ ), molybdenum nitride (MoN) and molybdenum carbide (MoC) nanocrystals. Carbonitride, that is, C ₃ N ₄ -MoCN.

The substrate is cemented carbide, stainless steel, high-speed steel, carbon steel or mold steel.

C ₃ N ₄ , MoC and MoN in the lubricating layer are nano crystals with a grain size of 5-10 nm.

For further improving the cost performance of product of the present invention:

The thickness of the bonding layer is 50-100 nanometers; the thickness of the transition layer is 100-200 nanometers; the thickness of the support layer is 100-500 nanometers; the thickness of the lubricating layer is 1-5 microns.

The preparation method of nanocrystalline superhard composite coating of the present invention, comprises the following steps successively:

1) Plasma cleaning the surface of the substrate, the cleaning conditions are: temperature 250-400°C, air pressure 0.1-0.5Pa, voltage -800V to -1000V bias;

2) Plasma vapor deposition bonding layer on the surface of the substrate, the deposition conditions are: temperature 200-400°C, air pressure 0.5-1.5Pa, voltage -100V to -200V bias;

3) Plasma vapor deposition transition layer on the bonding layer obtained in the previous step, the deposition conditions are: nitrogen environment, pressure 1-2Pa, voltage -100V to -200V bias;

4) Plasma vapor deposition of the support layer on the transition layer obtained in the previous step, the deposition conditions are: acetylene is fed under the condition of maintaining the flow rate of nitrogen gas, and the flow rate of acetylene is gradually increased until the volume flow ratio of acetylene and nitrogen is 3:4, and the pressure is 1-1.2Pa, voltage -100V to -200V bias;

5) Plasma vapor deposition of lubricating layer on the support layer obtained in the previous step, the deposition conditions are: the volume flow ratio of nitrogen and acetylene is kept at 3:4, the voltage is -100V to -200V, the pressure is 1-1.2Pa, Then cool naturally to get the nanocrystalline superhard composite coating.

The substrate is cemented carbide, stainless steel, high-speed steel, carbon steel or mold steel.

It can be known from the above technical scheme that the present invention uses the combined method of arc discharge method and hollow cathode arc discharge carbon source to prepare superhard C ₃ N ₄ -MoCN composite coating. In the conventional MoCN preparation process, the grain size of the coating is generally in the micron order, and the hardness of the coating is 25-30GPa. It is difficult to further increase the hardness of the coating. Nano-structured coating technology is a new coating technology developed rapidly in recent years, which is divided into nano-multilayer coating and nano-crystalline-amorphous composite coating. The high hardness of nano-multilayer coatings is mainly due to the difficulty of movement of dislocations within or between layers. Different from the nano-multilayer film, in the nanocrystalline-amorphous composite superhard coating, the high hardness of the coating is mainly related to the structure of the crystalline phase and the amorphous phase in the coating, and the size of the crystalline phase particles directly determines The hardness of the coating. Nanocrystalline composite superhard materials have aroused great interest of researchers all over the world due to their excellent properties, such as ultra-high hardness, high toughness and low friction coefficient.

The present invention utilizes the high hardness characteristic of C ₃ N ₄ to further increase the hardness of the MoCN coating; utilizes the dispersion effect of MoCN to reduce the internal stress of the C ₃ N ₄ coating. Use the amorphous characteristics of CN coating to limit the grain growth of MoCN coating, obtain MoCN in nanocrystalline state, make MoCN coating have good toughness, and form CN-MCN nanocrystalline composite coating, which is suitable for cutting high hardness and difficult-to-machine materials Provide new options.

Under normal conditions, MoCN is prepared mainly by arc discharge of a metal arc target in an environment where acetylene and nitrogen coexist. However, due to the limited ionization rate, the prepared MCN coating has low hardness and poor adhesion, which cannot meet the requirements well. Industrial practical application. Arc discharge uses the high ionization rate of the hollow cathode ion source to dissociate acetylene gas to generate a carbon source, and nitrogen gas is introduced to generate high concentrations of carbon ions and nitrogen ions. The nitrogen and carbon react to form carbon nitride on the workpiece. In addition, the metal arc is used to The target produces a high concentration of metal ions, and MoCN is formed under the condition of the coexistence of metal ions, carbon ions and nitrogen ions.

In the present invention, the high hardness of C ₃ N ₄ is used to increase the hardness of MoCN coating, and finally a new type of C ₃ N ₄ -MCN composite coating is developed. In order to improve the bonding force between the coating and the substrate, this patent first uses a high-power circular arc source to ionize the Mo metal, and applies a negative high voltage to the workpiece, and the Mo ions clean and remove the surface of the workpiece under bias bombardment The oxide layer on the surface, followed by lowering the workpiece bias, deposits a pure Mo bonding layer on the workpiece. After the preparation of the bonding layer, the composition of the matrix material has changed from a complex multi-component to a single Mo material. The hardness of the Mo coating is 20-23GPa. On this basis, nitrogen gas is gradually introduced to react with Mo to form MoN. MoN is a ceramic phase. , and the expansion coefficient of steel is relatively close, MoN and Mo are prepared in situ, and they are metallurgically combined with each other. The hardness of MoN is 25-28GPa, and the hardness of the steel matrix is 5-6GPa. In order to further increase the hardness of the substrate and reduce the stress, acetylene is gradually introduced on the basis of MoN to prepare a MoCxN support coating with higher hardness. The hardness of the MoCxN (0<x ≤ 1) coating is 25-30GPa. In the MoCxN support layer, in order to achieve gradual changes in composition and hardness, the flow of acetylene and nitrogen is controlled, and acetylene is gradually introduced under the condition of ensuring the flow of nitrogen. The gradual increase in the flow of acetylene makes the MoCN material undergo a gradual change in composition, and low carbon content. In the MoCxN coating, its composition is relatively close to that of the underlying MoN, so that the expansion coefficient is relatively close, and the hardness is also relatively close, which is conducive to reducing the internal stress of the coating; then gradually increase the flow of acetylene, and finally the acetylene and nitrogen reach 3 : The ratio of 4, to achieve a higher hardness value. On the basis of the MoCxN coating, the hollow cathode ion source is turned on, the acetylene gas is introduced from the tail of the hollow cathode ion source, and the nitrogen gas enters the vacuum chamber from other inlets. When the acetylene gas passes through the hollow cathode ion source, it is arc-discharged into the plasma Ionized into carbon ions, due to the pressure difference between the hollow cathode ion source and the vacuum chamber, the carbon ions are ejected from the hollow cathode ion source at high speed under pressure, when the workpiece rotates to the outlet of the hollow cathode ion source, the carbon ions and the vacuum chamber The nitrogen ions in the reaction form C ₃ N ₄ . At the same time, a metal arc target is arranged in the vacuum chamber. When the workpiece moves to the front end of the metal target, the metal ions react with carbon ions and nitrogen ions to form MoCN.

Therefore, the present invention has the following technical advantages: First, compared with the conventional MoCN coating (25-30GPa), the present invention uses C ₃ N ₄ to strengthen the MoCN coating with higher hardness (30-35GPa); second, the hollow cathode carbon The use of the source overcomes the large particles produced when the graphite target is filtered to prepare carbon nitride, and greatly simplifies the equipment; third, the coating structure of the present invention is designed reasonably, from the bottom bonding layer to the top superhard lubricating layer, not only has Gradual changes in composition and structural adjustments can greatly reduce the stress of the coating; fourth, the preparation equipment is similar to the current coating equipment, and the coating equipment is simple in structure, easy to control, and has a good industrial application prospect; Preparation of C ₃ N ₄ -MoCN composite coatings with different thicknesses on various workpieces such as cemented carbide, stainless steel, high-speed steel, carbon steel, and die steel.

In a word, the preparation method of the present invention has the characteristics of high ionization rate, simple structure of coating equipment, fast deposition rate and the like. The prepared C ₃ N ₄ -MoCN composite coating material has high coating hardness, strong adhesion, good self-lubricating performance, fast coating growth rate, high production efficiency, low production cost, low friction coefficient, and good coating toughness. The wear-resisting and lubricating properties of processing cutters, molds and mechanical parts can be greatly improved. In addition, the preparation method is simple, easy to realize industrial production, and has good application prospects.

Description of drawings

Fig. 1. is the schematic diagram of coating device adopted among the present invention;

Figure 2. Schematic diagram of the structure of the C ₃ N ₄ -MoCN composite coating prepared for the present invention;

Figure 3 is a scanning electron micrograph of the surface of the C ₃ N ₄ -MoCN composite coating prepared in the example;

Figure 4. The cross-sectional morphology of the C ₃ N ₄ -TiCN composite coating prepared for the embodiment;

In Figure 1: 1. Central heater; 2. 1# metal arc target; 3. Workpiece holder; 4. Hollow cathode arc discharge carbon source; 5. Furnace door; 6. 2# metal arc target; 7. Air extraction port;

In Fig. 2: 1. substrate; 2. bonding layer Mo; 3. transition layer MoN; 4. support layer MoCxN; 5. lubricating layer C ₃ N ₄ -MoCN.

Detailed ways

The device for implementing the method of the present invention is shown in Figure 1. The vacuum chamber of the device is surrounded by furnace walls, the height of the vacuum chamber is 50cm, and the volume is 50x50x50cm ³ . There is a furnace door on the side of the vacuum chamber to facilitate loading and unloading of workpieces. The vacuum chamber is equipped with a vacuum port, through which the vacuum pumping unit vacuumizes the vacuum chamber. The vacuum pumping unit is composed of a mechanical pump and a molecular pump, and the ultimate vacuum can reach 10-4Pa. A hollow cathode ion source is installed on the furnace door to increase the ionization rate of acetylene gas. Two arc Ti targets are respectively installed on both sides of the vacuum chamber. The diameter of the circular arc target is 100mm. The arc target is equipped with a strong magnet for binding The shape of the target arc. A heater is installed in the furnace, which can easily adjust the temperature in the vacuum chamber. The sample holder is located in the center of the furnace, and the sample is suspended on the sample holder, which can perform revolution and rotation, and the speed of the sample holder is adjustable. Such a layout can make

The plasma density in the vacuum chamber is greatly increased, and the workpiece is completely immersed in the plasma. The coating deposition rate, hardness and adhesion are greatly improved. Due to the optimization of the target structure, the distribution of the magnetic field is more uniform, so that the arc burns evenly on the target surface, which improves the uniformity of the coating and reduces the consumption of the target.

Example 1: Clean the substrate with a Mo target at 250°C, 0.1Pa, -800V for 10min; then deposit a 50nm-thick transition metal Mo layer at 250°C, 0.5Pa, -200V; 1Pa, -100V conditions to deposit a 150nm thick transition layer MoN; then under the conditions of 1.0Pa, -100V, acetylene is gradually introduced under the condition of nitrogen flow, and the flow of acetylene is gradually increased until the ratio of acetylene to nitrogen is 3:4. Deposit a 200 nm-thick support layer MoCxN; then deposit a 1 micron C ₃ N ₄ -MoCN superhard self-lubricating coating under the condition of a nitrogen and acetylene ratio of 3:4, a bias of -100V, and a pressure of 1.0Pa; The layer hardness is controlled at 30GPa, the friction coefficient is lower than 0.20, and the total coating thickness is 1.40 microns. After the preparation, it is naturally cooled to obtain a C ₃ N ₄ -MoCN nanocrystalline superhard self-lubricating nanocomposite coating. The crystal grains of C ₃ N ₄ , MoN and MoC in the lubricating layer are nano crystals with a grain size of 3nm.

Example 2: Clean the substrate with a Mo target at 350°C, 0.5Pa, -1000V for 10 minutes; then deposit a 50nm-thick transition metal Mo layer at 1Pa, -200V, and 300°C; Deposit a 100nm-thick transition layer MoN under the condition of 1.2Pa and -200V; then under the condition of 1.0Pa and -100V, gradually feed acetylene under the condition of nitrogen flow, and gradually increase the flow of acetylene until the ratio of acetylene to nitrogen is 3:4 , deposit a 100 nm thick support layer MoCxN; then deposit a 1 micron C3N4-MoCN superhard self-lubricating coating under the condition of nitrogen and acetylene ratio of 3:4, -100V bias, and 1.0Pa pressure; the coating The hardness is controlled at 35GPa, the coefficient of friction is lower than 0.20, and the total thickness of the coating is 1.21 microns. Cool naturally after preparation to obtain a C3N4-MoCN nanocrystalline superhard self-lubricating nanocomposite coating. The crystal grains of C ₃ N ₄ , MoN and MoC in the lubricating layer are nano crystals with a grain size of 5nm.

Example 3: At 400°C, under the conditions of 0.5Pa, -1000V, the substrate was cleaned with a Mo target for 10min; then at 1.5Pa, -100V, and 400°C, a transition metal Mo layer with a thickness of 100 nanometers was deposited; under a nitrogen environment, Deposit a transition layer MoN with a thickness of 200 nanometers at 2 Pa and -200V; then under the condition of 1.2Pa and -200V, acetylene is gradually introduced under the condition of nitrogen flow, and the flow of acetylene is gradually increased until the ratio of acetylene to nitrogen is 3: 4. Deposit a 500 nanometer thick support layer MoCxN; then deposit 1 micron C3N4-MoCN superhard self-lubricating coating under the condition of nitrogen and acetylene ratio of 3:4, -200V bias, and 1.2Pa pressure; The hardness of the layer is controlled at 32GPa, the coefficient of friction is lower than 0.20, and the total thickness of the coating is 1.81 microns. Cool naturally after preparation to obtain C3N4-MoCN nanocrystalline superhard self-lubricating nanocomposite coating. The C3N4, MoN, and MoC grains in the lubricating layer are nanocrystalline, and the grain size is 5-8nm.

Figure 2 is a schematic diagram of the structure of the C ₃ N ₄ -MoCN composite coating designed by the present invention. The coating transitions from a pure metal Mo layer to a MoN layer, then gradually becomes a MoCxN layer, and finally reaches a C ₃ N ₄ -MoCN composite coating , There is a gradual change in the composition of the coating, and a gradual change in the hardness at the same time. Reasonable design makes the internal stress of the coating small and the adhesion strong.

Figure 3 is the surface morphology of the C ₃ N ₄ -MoCN composite coating prepared in Example 2. It can be seen from the figure that there are a small amount of small particles on the surface of the coating, which is caused by a small amount of particles in the arc discharge process. Contamination, mainly Mo metal droplets.

Figure 4 is the transmission electron diffraction pattern of the C ₃ N ₄ -MoCN composite coating prepared in the example. From the figure, it can be seen that the diffraction rings of C ₃ N ₄ , MoN, and MoC grains indicate that the grains are disordered embedded in the MoCN coating. The obvious crystal diffraction ring of C ₃ N ₄ in it shows that the coating contains a considerable amount of C ₃ N ₄ grains, and it is precisely because of the high hardness of C ₃ N ₄ grains that the hardness of the MoCN coating is improved.

Claims (5)

1. A nanocrystalline superhard composite coating is characterized in that, from the inside to the outside on the substrate surface, it is formed successively by bonding layer, transition layer, support layer and lubricating layer; Wherein, the material of bonding layer is transition metal Mo, transition The material of the layer is MoN, the material of the supporting layer is the graded carbonitride MoCxN of Mo, where 0≤x≤1; the material of the lubricating layer is the carbonitride of Mo containing carbon nitride, molybdenum nitride and molybdenum carbide nanocrystals C ₃ N ₄ -MoCN, C ₃ N ₄ , MoC and MoN in the lubricating layer are nano crystals with a grain size of 5-10 nm. 2. The nanocrystalline superhard composite coating according to claim 1, wherein the substrate is cemented carbide, stainless steel, high-speed steel, carbon steel or die steel. 3. nanocrystalline superhard composite coating according to claim 1, is characterized in that, bonding layer thickness is 50-100 nanometer; Transition layer thickness is 100-200 nanometer; Support layer thickness is 100-500 nanometer; Lubricating layer The thickness is 1-5 microns. 4. the preparation method of nanocrystalline superhard composite coating as claimed in claim 1, is characterized in that, comprises the following steps successively: 1) Plasma cleaning the surface of the substrate, the cleaning conditions are: temperature 250-400°C, air pressure 0.1-0.5Pa, voltage -800V to -1000V bias; 2) Plasma vapor deposition bonding layer on the surface of the substrate, the deposition conditions are: temperature 200-400°C, air pressure 0.5-1.5Pa, voltage -100V to -200V bias; 3) Plasma vapor deposition transition layer on the bonding layer obtained in the previous step, the deposition conditions are: nitrogen environment, pressure 1-2Pa, voltage -100V to -200V bias; 4) Plasma vapor deposition of the support layer on the transition layer obtained in the previous step, the deposition conditions are: acetylene is fed under the condition of maintaining the flow rate of nitrogen gas, and the flow rate of acetylene is gradually increased until the volume flow ratio of acetylene and nitrogen is 3:4, and the pressure is 1-1.2Pa, voltage -100V to -200V bias; 5) Plasma vapor deposition of lubricating layer on the support layer obtained in the previous step, the deposition conditions are: the volume flow ratio of nitrogen and acetylene is kept at 3:4, the voltage is -100V to -200V, the pressure is 1-1.2Pa, Then cool naturally to get the nanocrystalline superhard composite coating. 5. The preparation method according to claim 4, characterized in that, the substrate is cemented carbide, stainless steel, high-speed steel, carbon steel or mold steel.