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Summary of Vacuum Ion Plating

Text: [Big] [middle][small] Release date: 2019-1-24  Views: 237

Ion plating is a method of partially ionizing gas or evaporated substance by gas discharge under vacuum conditions, and depositing evaporated substance or its reactants on substrates under the bombardment of gas ion or evaporated substance ion.

Ion plating is a new development of vacuum plating technology. When ordinary vacuum plating (also known as vacuum evaporation) is applied, the workpiece is clamped in the vacuum cover. When the high-temperature evaporation source is heated by electricity, the evaporator, the material to be plated, is melted and evaporated. As a result of temperature rise, evaporation particles get a certain kinetic energy, then gradually rise along the line of sight direction, and finally adhere to the surface of the workpiece to accumulate film. The coating formed by this process has neither strong chemical bonding nor diffusive bonding with the surface of parts, and its adhesion performance is very poor. Sometimes, like dust falling on the desktop, it can be wiped off with a touch of the hand. However, the ion plating process is different, although it is also carried out in the vacuum cover, but at this time the coating process is realized in the form of charge transfer. That is to say, the evaporated particles, as positive charged high-energy ions, are injected into the surface of the workpiece at a high speed under the attraction of the high-pressure cathode (i.e. workpiece). It is equivalent to a high-speed warhead fired from the barrel, which can penetrate deep into the matrix and form a solid diffusion coating on the workpiece.

The process of ion plating is as follows: the evaporation source is connected with the anode, and the workpiece is connected with the cathode. When three to five kilovolt high voltage direct current is applied, arc discharge occurs between the evaporation source and the workpiece. Because inert argon is filled in the vacuum cover, some argon is ionized under the action of electric field, thus forming a plasma dark area around the cathode workpiece. The positive charged argon ion is attracted by the negative cathode pressure and bombards the workpiece surface violently, which causes the particles and dirt on the workpiece surface to be bombarded and thrown out, so that the workpiece surface to be plated can be fully cleaned by ion bombardment. Subsequently, the evaporator power supply is switched on, and the evaporator particles melt and evaporate into the glow discharge area and are ionized. Under the cathode attraction, positive charged evaporator ions rush to the workpiece together with argon ions. When the amount of evaporator ions thrown on the workpiece surface exceeds the amount of sputtered ions, a layer of coatings firmly adhered to the workpiece surface gradually accumulates. This is the simple process of ion plating.

In ordinary vacuum coating, evaporated particles are evaporated to the workpiece surface with only one electron volt of energy. The interface diffusion depth between the workpiece surface and the coating is usually only several hundred AE (10 000 AE = 1 micron = 0.0001 cm). That's less than one percent of a hair. It can be said that there are almost no connected transition layers between the two, as if they were completely separated. In ion plating, evaporated particles have kinetic energy of 3,000 to 5,000 electron volts after ionization. If the particles coated by ordinary vacuum are equivalent to a gasping long distance runner, then the particles coated by ion are like passengers riding on a high-speed rocket. When they bombard the workpiece at high speed, they not only deposit fast, but also penetrate the surface of the workpiece, forming a very deep diffusion layer implanted into the substrate. The diffusion depth of the ion-plated interface can reach four to five microns, that is to say, the diffusion depth of the ion-plated interface can reach four to five microns. The diffusion depth is tens or even hundreds of times deeper than that of ordinary vacuum plating, so they adhere to each other very firmly. Tensile tests on ion plated specimens show that the coating extends plastically with the base metal until it is about to break, and no peeling or spalling occurs. It can be seen how firmly attached it is.

Strong winding plating ability
In ion plating, evaporation particles move along the power line in the form of charged ions in the electric field. Therefore, good coatings can be obtained in all parts where the electric field exists, which is much superior to the conventional vacuum coating only in the direct direction. Therefore, this method is very suitable for inner holes, grooves and narrow seams on plated parts. The parts that are difficult to plating by other methods. With ordinary vacuum coating, only direct surface can be coated, evaporation particles can only climb up the ladder, especially like climbing a ladder; while ion plating can evenly circumvent the back and inner hole of the parts, and charged ions can fly anywhere within the range of their active radius along the prescribed flight path as if they were in a helicopter.
Good coating quality
Ion plating coating has compact structure, no pinholes, no bubbles and uniform thickness. Even prisms and grooves can be coated evenly without forming metal tumors. Components such as threads can also be plated. Because this process can also repair micro-cracks and pits on the surface of the workpiece, it can effectively improve the surface quality and physical and mechanical properties of the plated parts. Fatigue tests show that if properly treated, the fatigue life of the workpiece can be 2% or 30% higher than that before plating.
Simplification of cleaning process
Most of the existing coating processes require strict cleaning of the workpiece beforehand, which is complex and laborious. However, the ion plating process itself has an ion bombardment cleaning effect, and this effect has continued throughout the coating process. The cleaning effect is excellent, which can make the coating directly close to the substrate, effectively enhance the adhesion, and simplify a lot of cleaning work before plating.

Wide range of plating materials

Ion plating uses high-energy ions to bombard the workpiece surface, so that a large amount of electric energy can be converted into heat energy on the workpiece surface, which promotes the diffusion and chemical reaction of the surface structure. However, the whole workpiece, especially the core of the workpiece, is not affected by high temperature. Therefore, this coating process has a wide range of applications and less limitations. Usually, all kinds of metals and alloys are made of