Principle and application of ion coating

- Mar 16, 2019-

Principle and application of ion coating


There are many kinds of coating methods used in modern aviation industry, such as electroplating, spraying, chemical plating, diffusion, rolling and coating. Many of these processes have been mastered and have played a significant role in production. However, the existing coating technology can not keep up with the rapid development of products, so that people explore new coating technology. "Ion plating" is a new vacuum coating technology developed in recent years.


1. Introduction

Ion plating, ion plating) ion plating under vacuum conditions, using the gas discharge make gas ionization or evaporate material part, and the gas ion or vaporized material under the bombardment of ions, the evaporation material or the way of the reactant deposition on the substrate. These include magnetron sputtering ion plating, reactive ion plating, hollow cathode discharge ion plating (hollow cathode evaporation method), multi-arc ion plating (cathode arc ion plating), etc.


2. The importance of

In the aviation and aerospace industry, the components of various aircraft, missiles, satellites and airships often work under complex and harmful conditions. Aircraft, for example, wings, fuselage skin and landing gear and other external parts, are directly affected by the atmosphere, moisture, dust and fuel combustion products contained in the chemical activity of the gas corrosion. The external parts of a seaplane, especially the airframe and buoy, are often eroded by sea water, lake water or river water. Combustion Chambers, turbine parts and cylinder piston parts of aero-engines are also frequently oxidized by high temperature gas flows containing acids and other active substances. There are also instrument components such as aerobearings, micro-transmission devices, precision gear, potentiometers, etc., which are often subjected to varying degrees of friction and wear. To make the above various parts can adapt to the temperature, corrosion, wear and other harsh requirements, simply from the parts of the structure or material to think, often is not enough. How to do? One of the most widely used methods is to use surface coating method to protect the parts of the matrix to meet the above requirements. This is just like people according to different environmental conditions put on different clothes, according to the need to the parts of the heat, corrosion or wear - resistant coating.


3. Development

There are many kinds of coating methods used in modern aviation industry, such as electroplating, spraying, chemical plating, diffusion, rolling, coating and so on. Many of these processes have been mastered and have played a significant role in production. However, the existing coating technology can not keep up with the rapid development of products, so that people explore new coating technology. "Ion plating" is a new vacuum coating technology developed in recent years.


4. Principle and process


Ion plating is a new development of vacuum coating technology. Ordinary vacuum coating (also known as vacuum evaporation), the workpiece clamped in the vacuum cover, when the high temperature evaporation source electric heating, promote to be plated material - evaporation material melting evaporation. Due to the temperature rise, the evaporator particles gain some kinetic energy, then rise slowly along the line of sight, and finally adhere to the surface of the workpiece accumulated into a film. The plating layer that forms with this kind of craft, neither have firm chemical union with the surface of the part, have without diffusion connection, adherent performance is very poor, the dust that falls like the desktop sometimes is same, touch with the hand also can erase. However, the ion plating process is different, although also in the vacuum cover, but then the coating process is in the form of charge transfer to achieve. In other words, particles of the evaporator, as high-energy ions with positive charge, are attracted by the high-pressure cathode (i.e. the workpiece) and injected into the workpiece surface at a high speed. Equivalent to a high-speed bullet shot from the barrel, it can penetrate deep into the target, forming a solid diffusion coating on the workpiece.

The process of ion plating is as follows: the evaporation source is connected to the anode, and the workpiece is connected to the cathode. A glow discharge is generated between the evaporation source and the workpiece after a high voltage direct current of three to five thousand volts is applied. As inert argon gas is filled in the vacuum cover, part of argon gas is ionized under the action of discharge electric field, thus forming a plasma dark area around the cathode workpiece. The positive argon ions, attracted by the negative high pressure of the cathode, violently bombarded the surface of the workpiece, causing particles and dirt on the surface of the workpiece to be splashed out, so that the surface of the workpiece to be plated was thoroughly cleaned by ion bombardment. The evaporator particles melt and evaporate, enter the glow discharge area and are ionized. Positively charged evaporator ions, attracted by the cathode, rushed to the workpiece together with argon ions. When the amount of evaporator ions on the workpiece surface exceeded the amount of ions spatter, they gradually accumulated to form a layer of coating that adhered firmly to the workpiece surface. This is the simple process of ion plating.


5. Characteristics

The coating has good adhesion

In ordinary vacuum coating, evaporator particles are only about one electron volt energy to the surface of the workpiece, in the workpiece surface and between the coating, the formation of interface diffusion depth is usually only a few hundred angstrom (10000 angstrom =1 micron =0.0001 cm). That's less than one percent of a human hair. It can be said that there is almost no connection between the two transition layer, as if completely separate. In ion plating, the evaporator particles ionize and have a kinetic energy of 3,000 to 5,000 electron volts. If ordinary vacuum coating particles is equivalent to a breathless runner, so ion plating are like passengers on the high-speed rocket, when its high-speed bombardment workpiece, deposit not only fast, but also can penetrate the workpiece 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. The tensile test of the sample after ion plating shows that the coating still extends plastically along with the base metal and no peeling or peeling occurs until the sample is about to break. It shows how strong the attachment is! In the case of ion plating with high plating capacity, the evaporator particles move in the electric field in the form of charged ions along the direction of the power line, so that all parts with electric field can obtain a good coating, which is much better than the ordinary vacuum coating can only be obtained in the direct direction. Therefore, this method is very suitable for plated parts on the inner hole, groove and narrow slot. Other methods difficult to plating parts. With ordinary vacuum coating can only be plated directly on the surface, evaporation material particles, such as climbing ladder, can only follow the ladder; Ion plating, on the other hand, can be evenly wound around the back of the part and into the inner hole, and charged ions can be transported to any place within the radius of its radius by following a prescribed route, as in a helicopter. The coating with good quality has compact structure, no pinhole, no bubble and uniform thickness. Even the edges and grooves can be plated evenly without forming metal nodules. Parts such as threads can also be plated, because this process can also repair the workpiece surface micro cracks and pitting defects, so it can effectively improve the surface quality and physical and mechanical properties of the plated parts. Fatigue tests show that, if properly handled, the fatigue life of the workpiece is 20 to 30 percent higher than that before plating.


Cleaning process simplification

Existing coating process, most of the requirements of prior to the workpiece for strict cleaning, both complex and trouble. However, the ion plating process itself has an ion bombardment cleaning effect, and this effect 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 cleaning before plating.


A wide range of plating materials


Ion plating is the use of high-energy ions bombarding the surface of the workpiece, so that a large amount of electrical energy on the surface of the workpiece into heat energy, thus promoting the surface tissue diffusion and chemical reaction. However, the whole workpiece, especially the core of the workpiece, was not affected by the high temperature. Therefore, this kind of coating process has a wide range of applications, but the limitations are small. In general, all kinds of metals, alloys and some synthetic materials, insulation materials, thermal materials and high melting point materials can be plated. Can be plated on the metal workpiece nonmetal or metal, also can be plated on the nonmetal or nonmetal, or even plastic, rubber, quartz, ceramics and so on.


6. Aerospace applications


Non-lubricating oil

In modern aircraft, aircraft engines or aircraft instruments, especially in the aerospace, such as spacecraft, satellites, there are a number of rotating parts are required to have good lubrication, but often due to seal up too long, the environment temperature is too high or space volatilization, the ordinary grease lubricant is no longer applicable, so as to put forward to solid lubricant instead. The experimental results show that it is better to make solid lubrication film by ion plating than other methods. Not only strong adhesion, thin and uniform coating, does not affect the parts of the dimensional accuracy and tolerance. Economy is also good, a little lubrication material can be plated a large area. The quality of lubrication film is also better, the friction coefficient is small, the service life is long. For example, there is a satellite on the precision bearings, not plated before the working life of only a few minutes, simply can not be used; However, the ion-plated solid lubrication film can reliably work for thousands of hours in flight. Ion plating can not only be plated many kinds of solid lubrication materials at room temperature, but also can be coated with a variety of high temperature solid lubrication materials, some even can be more than eight hundred degrees Celsius under the high temperature play a good role in lubrication. The solid lubricating materials that can be plated include silver, gold, copper, lead, lead-tin alloy, fluoride and so on.


True gold does not fear fire

Aircraft parts, especially many engine parts, often need to work at high temperatures. For example, the working temperature of turbine blades and guide blades is usually around 1,000 degrees centigrade, and some even reach 1,400 degrees centigrade. In the mythological novel journey to the west, when sun wukong was put into the furnace by the supreme Lord, he probably could not reach such a high temperature. Modern aero-engine parts work at such a high temperature, it is difficult to meet the requirements only depending on the performance of the part matrix material itself. So, how can the engine parts without high temperature ablation? At present in addition to the parts of the structure to take measures (such as the use of hollow cooling blades, divergent cooling blades, etc.), most of the need for heat resistance coating for protection. Ion plating has many advantages for the deposition of heat resistant films. It can be applied to a variety of high melting point materials, such as aluminum oxide, silicon oxide, beryllium oxide, hafnium alloy, etc. The composition of the alloy coating is also easier to control, suitable for the composition of the more complex heat resistant alloy, such as iron chromium aluminum yttrium, cobalt chromium aluminum yttrium or nickel chromium aluminum yttrium alloy.


At present, turbine blade is the main object of trying to use the heat-resistant coating of ion plating. It is reported that the high temperature working life of a kind of blade plated by this method with a nickel-chromium-aluminum yttrium alloy is three times higher than that of aluminum plated. Suitable for the use of ion plating heat - resistant engine parts and turbine disk, cylinder piston parts. After being treated with this advanced technology, some parts can work for thousands of hours at high temperature.


Metal does not rust

Metal parts are to rust, but if the parts are plated with a layer of corrosion prevention coating, it can prevent the parts from rust. As a result of the high density of ion plating coating, less pinhole, corrosion resistance, and can deposit many other processes can not deposit good corrosion coating. Therefore, ion plating is currently the most widely used in corrosion - resistant materials. Such as the seaplane wall and other external parts, this method can be used to prevent the corrosion of salt spray and sea water corrosion coating; Other material parts with aluminum alloy parts can be plated by this method to prevent potential corrosion. In addition, with the improvement of flight speed and altitude and the progress of space exploration, the application of titanium alloy is more and more. But if plated with alumina, it can completely meet the requirements. However, electroplating and other processes can not be plated this material. Ion plating, on the other hand, works wonders. So far, in addition to alumina, corrosion resistant materials suitable for ion plating include chromium, titanium, tantalum, stainless steel, etc. The plated aviation parts include screws, nuts, rivets, pins, pipes, joints, gyro rotors, precision gears, metal seal rings, etc.


In short, ion plating in the aviation industry and other sectors of the application potential is great, in addition to the above, there are many, such as conductive film plating, hardening film, decorative film and used for precision welding, precision sealing, surface repair. Ion plating process is a new technology which has been developed for more than ten years. It has some unique advantages and may solve some production keys which were difficult to overcome in the past. However, due to the emergence of the time is not long, there are many technical keys to be solved, such as coating thickness control, the workpiece non-plating surface shielding, etc. Secondly, the equipment capacity is small, large parts are difficult to plating, large investment. We believe that with the further study of this technology, ion plating will be gradually improved and developed, and will be fully applied and promoted in the aviation industry.


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