Vacuum coating (PVD technology)
1. Development of vacuum coating technology
Vacuum coating technology does not start for a long time. In the 1960s, CVD (chemical vapor deposition) technology was applied to carbide cutting tools. As the technology needs to be carried out at high temperature (the process temperature is higher than 1000 ° C), the coating type is single and has great limitations, so it was not popularized at first. At the end of 1970s, PVD (physical vapor deposition) technology began to appear, and PVD coating technology developed rapidly in a short period of 20 to 30 years. The reasons are as follows:
(1) it forms a membrane in the vacuum-sealed cavity, and there is almost no environmental pollution problem, which is conducive to environmental protection;
(2) it can obtain a bright and luxurious surface. In color, there are mature seven-color, silver, transparent, golden, black and any color from golden to black, which can meet various decorative needs;
(3) ceramic coatings and composite coatings with high hardness and wear resistance that are difficult to obtain by other methods can be easily obtained. When applied to tooling and molds, the service life can be doubled and the effect of low cost and high income can be achieved.
(4) in addition, PVD coating technology has two characteristics of low temperature and high energy, and can form film on almost any substrate. Therefore, it is not surprising that PVD coating technology has a wide range of applications and rapid development.
With the development of vacuum coating technology, PCVD (physicochemical vapor deposition), mt-cvd (medium temperature chemical vapor deposition) and other new technologies have emerged. Various coating equipment and coating processes have emerged in an endless fashion. At present, there are two mature PVD methods: multiarc plating and magnetron sputtering. Multi-arc plating equipment is simple in structure and easy to operate. The disadvantage of multi-arc plating is that when the coating thickness reaches 0.3um, the deposition rate is close to the reflectivity under the condition of low temperature coating with traditional DC power supply, and the film formation becomes very difficult. Moreover, the membrane surface becomes hazy. Another disadvantage of multi-arc plating is that the metal evaporates after melting, so the deposition particles are larger, the density is lower, and the wear resistance is worse than that of magnetron sputtering. It can be seen that multi-arc coating and magnetron sputtering coating have advantages and disadvantages respectively. In order to give full play to their advantages and complement each other as much as possible, the coating machine integrating multi-arc technology and magnetron technology came into being. In the process, a new method of multi-arc plating is presented, and then the coating is thickened by magnetron sputtering, and finally the color of the surface coating is stabilized by multi-arc plating.
2. Technical principles
PVD (Physical Vapor Deposition) is divided into vacuum evaporation Deposition, vacuum sputtering Deposition and vacuum ion Deposition. We usually say that the PVD coating, refers to vacuum ion coating and vacuum sputtering; Usually said NCVM coating, refers to vacuum evaporation coating.
Basic principles of vacuum evaporation: under vacuum conditions, metal and metal alloys are vaporized, and then deposited on the surface of the substrate. The method of evaporation is commonly used for resistance heating, and electron beam bombards the plating material to vaporize into gas phase, and then deposited on the surface of the substrate. Historically, vacuum evaporation is the earliest technology used in PVD method.
Basic principle of sputtering coating: under the vacuum condition of argon (Ar) gas, argon will be glow discharged. At this time, argon (Ar) atoms will ionize into argon ions (Ar). Under the action of electric field force, argon ions will accelerate the bombardment of the cathode target made of plating material, which will be sputtered out and deposited on the surface of the workpiece. The incident ions in sputtering coating are generally obtained by glow discharge in the range of l0-2 Pa ~ 10Pa. Therefore, during the flight to the substrate, the sputtered particles tend to collide with the gas molecules in the vacuum chamber, making the motion direction random and the deposited film easy to be uniform.
Ion plating basic principle: under vacuum conditions, using some kind of plasma ionization technology, so that the plating atom part of the ionization into ions, at the same time produce many high energy neutral atoms, in the plating substrate plus negative bias. In this way, under the action of deep negative bias, ions are deposited on the surface of the substrate to form a thin film.
Process steps of PVD technology
1. Workpiece cleaning: argon is used for glow discharge when dc power is connected and argon is bombarded with argon ions, which will splash particles and dirt on the surface of the workpiece.
2. Gasification of plating: that is, after ac, the plating evaporates.
3. Migration of plating ions: atoms, molecules or ions supplied by gasification source rush to the workpiece at high speed after collision and high-voltage electric field;
4. Deposition of plating atoms, molecules or ions on the substrate: when the amount of evaporation ions on the surface of the workpiece exceeds the amount of splashed ions, it gradually accumulates to form a layer of coating firmly adhering to the surface of the workpiece.
After particle ionization of ion plating, the evaporation material has three thousand to the kinetic energy of five thousand electron volts, high-speed bombardment artifacts, not only deposit speed is fast, and able to penetrate the surface, forming a deep into matrix diffusion layer, interface diffusion depth of ion plating would be four to five microns, that is to say, than the ordinary vacuum coating diffusion depth deep dozens of times, even one hundred times, and adhered to each other so fast.
Product performance advantages
1. Technical features
(1) PVD film can be directly plated on stainless steel and hard alloy. For relatively soft die castings such as zinc alloy, copper and iron, chemical chromium plating should be carried out first, and then PVD plating is suitable. However, PVD plating after water plating is easy to bubble, and the defect rate is high.
(2) typical PVD coating processing temperature ranges from 250 ℃ to 450 ℃;
(3) coating type and thickness determine the process time, the general process time is 3~6 hours;
(4) PVD coating layer thickness of micron grade, thickness of the thinner, the average of 0.3 mu m ~ 5 microns, the decorative coating membrane layer thickness is commonly 0.3 mu m ~ 1 mu m, so it can be almost does not affect the original size of the workpiece raise all kinds of physical properties and chemical properties on the surface of the workpiece, and can maintain the workpiece size, need not again after plating processing;
(5) PVD technology not only improves the bonding strength between coating film and substrate material, but also develops the coating components from the first generation of TiN into TiC, TiCN, ZrN, CrN, MoS2, TiAlN, TiAlCN, tin-aln, CNx, DLC and ta-c composite coatings, forming the surface effect of different colors.
(6) at present, the colors of the film layer can be made are dark gold, light gold, coffee, bronze, gray, black, grey-black, seven-color, etc. The color of plating can be controlled by controlling the parameters in the coating process. After coating, the color value can be measured with relevant instruments, so that the color can be quantified to determine whether the plated color meets the requirements.
2. Technical advantages
(1) coating adhesion performance is good
In ordinary vacuum coating, there is almost no connection between the surface of the workpiece and the coating, as if completely separated. Ion plating, ion bombardment high-speed artifacts, able to penetrate the surface, forming a deep into matrix diffusion layer, interface diffusion depth of ion plating would be four to five microns, after ion plating of the specimen for tensile test showed that all the way to going to fracture, plating with matrix metal plastic elongation, without peeling or flaking off, visible how strong adhesion, membrane layer uniform, dense.
(2) strong winding and plating capacity
During ion plating, the evaporator particles move along the direction of the electric field in the form of charged ions. Therefore, wherever there is an electric field, good coating can be obtained, which is much better than the ordinary vacuum coating which can only be obtained in the direct direction. Therefore, this method is very suitable for internal holes, grooves and narrow joints of plated parts. Other methods difficult to plating parts. With ordinary vacuum coating can only plating direct surface, evaporation particles like climbing ladder, can only go up the ladder; And ion plating can be uniformly around the back of the plating parts and the inner hole, charged ions are like a helicopter, can fly along the prescribed route to any place within the radius of its activity.
(2) good coating quality
The coating of ion plating is compact, without pinhole, bubble and even thickness. Even edge surface and groove can be even plated, do not form metal tumor. Parts like thread can also be plated, with high hardness, high wear resistance (low friction coefficient), good corrosion resistance and chemical stability, film life longer; At the same time the film can greatly improve the appearance of the workpiece decorative properties.
(4) simplified cleaning process
Most existing coating processes require strict cleaning of the workpiece in advance. However, ion plating process itself has an ion bombardment cleaning role, and this role has been continued throughout the coating process. Excellent cleaning effect, can make the coating directly close to the substrate, effectively enhance the adhesion, simplify a lot of pre-plating cleaning work.
(5) a wide range of plating materials
Ion plating is to use high-energy ions to bombard the surface of the workpiece, so that a large amount of electrical energy on the surface of the workpiece into heat energy, so as to promote the diffusion of surface tissue and chemical reactions. However, the whole workpiece, especially the workpiece center, is not affected by the high temperature. Therefore, this coating process has a wide range of applications and a small limitation. Generally, various metals, alloys and some synthetic materials, insulation materials, thermosensitive materials and high melting point materials can be plated. Can be plated on the metal work piece nonmetal or metal, also can be plated on the nonmetal or nonmetal, even can be plated plastic, rubber, quartz, ceramics and so on.
Market prospect and application
The application of PVD coating technology is mainly divided into two categories: decorative plating and tool plating.
1. Decorative plating
The purpose of decorative plating: mainly to improve the appearance of the workpiece decorative performance and color, at the same time to make the workpiece more wear-resistant corrosion and extend its service life; This aspect mainly applies the hardware profession each domain, like the door and window hardware, locks, the sanitary ware hardware and so on profession.
Tool plating purpose: mainly in order to improve the surface hardness and wear resistance of the workpiece, reduce the friction coefficient of the surface, improve the service life of the workpiece; This aspect is mainly used in various cutting tools, turning tools (such as turning tools, planer, milling cutter, drill and so on) and other products.
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