What is a PVD Coating?
Physical Vapor Deposition (PVD), also known as Vacuum Plating, emerged in the 1970s and produced thin films with high hardness, low coefficient of friction, good wear resistance and chemical stability. The initial successful application in the field of HSS tools has attracted a lot of attention from manufacturing industries all over the world, and people are developing high-performance and high-reliability coating equipment, while also conducting more in-depth research on coating applications in carbide and ceramic tools.
As of today, physical vapor deposition is the most sophisticated and highest-end type of exterior treatment process available.
What is the basic principle of PVD coating?
Physical vapor deposition is a physical vapor phase reaction growth method. The deposition process is carried out under vacuum or low-pressure gas discharge conditions, i.e. in a low-temperature isotropic body. The material source of the coating is a solid material that is evaporated or sputtered to produce a new coating of a material on the surface of the substrate with completely different properties from the substrate.
There are three main stages: evaporation or sputtering of the coating material, the material extraction, and the deposition of the evaporated or sputtered material to form the coating.
The principle of chemical vapor deposition is similar to its principle, and the main difference is in the solution, which is the technology of construction by chemical method.
Features of PVD Coating Products:
- The surface of the product is bright and noble, and can be plated with rich colors.
- Compared with water plating, the PVD film layer has greater bonding force, high hardness, friction resistance, corrosion resistance and more stable performance.
- No toxic or polluting substances are produced during the production process, which is friendly to the environment
- With two characteristics of low temperature and high energy, it can form a film on almost any substrate.
- Whe equipment used is usually more expensive, plus the process is more complex and more expensive the surface of the workpiece must be kept dry and smooth, otherwise the treatment effect will be affected
- Is the most common metal surface treatment technology.
Features of PVD Coating itself:
- The need to use a solid or molten substance as the source material for the deposition process.
- The source material is subjected to physical processes to enter the gas phase
- Requires a relatively low gas pressure environment.
- No chemical reactions occur in the gas phase and on the substrate surface.
PVD Coating Advantages:
- Low deposition temperatures, generally below 600°C, which have little effect on the flexural strength of the tool material.
- The stress state inside the coating is compressive stress, which is more suitable for the coating of carbide precision and complex tools.
- No pollution to the environment, in line with the current development trend of green processes and green manufacturing.
- With the emergence of nano-coating, the quality of coated tools is significantly improved, not only with the advantages of high bond strength, high hardness and good oxidation resistance, but also effectively control the shape and precision of precision tool edges.
PVD Coating Disadvantages:
- Complexity of coating equipment, high process requirements and long coating time, which makes the cost of tools increase.
- Production of tools with poorer impact resistance, hardness and uniformity, and shorter service life than technically produced tools.
- Single geometry of the coated product, which limits the field of use.
- Susceptibility to internal stresses and microcracks, due to the different shrinkage rates of the coating and the substrate during cooling.
PVD Coating Technology Category:
At present, there are many complicated classifications in the PVD technology industry, and there is no uniform classification standard. The classification we are talking about today is based on the different ways of ionization of the target material (the material to be treated). It mainly includes vacuum evaporation coating, sputtering coating and ion coating.
1. Vacuum Vapor Deposition (PVD)
PVD is often referred to as vapor deposition or evaporation deposition, which is the process of heating the target material under vacuum to make it vaporize and sublimate into atoms or molecules, which are deposited onto the surface of the workpiece to form a thin film. Vacuum vapor deposition is also the earliest PVD process, so many people will take it as the representative of the whole PVD process, so pay attention to the distinction.
2. Sputter Coating (MSD)
MSD is filled with certain inert gas argon Ar in vacuum environment, using glow discharge technology to ionize argon into ionic state, the argon ion accelerates and bombards the cathode under the action of electric field, so that the target at the cathode is sputtered down and deposited to the surface of the workpiece to form a film layer.
3. Ion Coating (IP)
IP is a vacuum environment, the use of various gas discharge technology, the target evaporated part of the atom ionization at the same time, but also generate a large number of high-energy neutral particles, deposited on the surface of the workpiece to form a film layer.
PVD Coating Process Category:
According to the difference of physical mechanism during deposition, physical vapor deposition is generally divided into vacuum evaporation coating technology, vacuum sputtering coating, ion coating and molecular beam epitaxy. In recent years, the development of thin-film technology and thin-film materials has progressed rapidly with remarkable achievements, and on the basis of the original, ion-beam enhanced deposition technology, EDM deposition technology, electron-beam physical vapor deposition technology and multilayer jet deposition technology have emerged one after another.
1. Ion beam enhanced deposition technology (IBED)
Ion beam enhanced deposition is a new technology for surface modification of materials that integrates ion injection and thin film deposition. It involves bombardment mixing with ion beams of certain energy while vapor depositing the coating to form monolithic or compound film layers. In addition to retaining the advantages of ion implantation, it allows the continuous growth of layers of arbitrary thickness at low bombardment energy and the synthesis of compound layers with ideal chemical ratios (including new layers that cannot be obtained at room temperature and pressure) at room temperature or near room temperature. This technology has the advantages of low process temperature (<200°C), strong bonding to all substrates, high-temperature phase, sub-temperature phase and amorphous alloy at room temperature, easy control of chemical composition, and convenient control of the growth process. The main disadvantage is that the ion beam is direct-emitting, so it is difficult to treat surfaces with complex shapes.
2. Electric spark deposition technology (ESD)
The EDM technology is to release the high energy electrical energy stored in the power supply between the metal electrode (anode) and the metal base material (cathode) instantaneously at high frequency, through the ionization of the air between the electrode material and the base material, forming a channel to produce instantaneous high temperature and high pressure micro-zone on the surface of the base material. At the same time, the ionized electrode material is melted and infiltrated into the base material under the action of micro electric field, forming a metallurgical bond. The EDM process is a process between welding and sputtering or element infiltration, the metal deposition layer treated by EDM technology has high hardness and good resistance to high temperature, corrosion and abrasion, and the equipment is simple and versatile, the bond between the deposition layer and the substrate is very strong and generally does not fall off, the workpiece will not be annealed or deformed after treatment, the thickness of the deposition layer is easy to control, and the operation method is easy to master. The main disadvantage is the lack of theoretical support, and the operation has not yet been mechanized and automated.
3. Electron beam physical vapor deposition technology (EB-PVD)
Electron beam physical vapor deposition technology is a technique that uses a high energy density electron beam to directly heat the evaporated material, which is deposited on the surface of the substrate at a lower temperature. This technology has the advantages of high deposition rate (10kg/h~15kg/h evaporation rate), dense coating, easy and precise control of chemical composition, columnar crystal organization, no pollution and high thermal efficiency. The disadvantages of this technology are expensive equipment and high processing costs. At present, this technology has become a hot spot for research in various countries.
4. Multi-layer spray deposition technology (MLSD)
Compared with the traditional jet deposition technology, an important feature of multilayer jet deposition is that the motion of the receiver system and crucible system can be adjusted so that the deposition process is uniform and the trajectory is not repeated, thus obtaining a flat deposited surface. The main features are: the cooling rate during deposition is higher than that of conventional jet deposition, and the cooling effect is better; large-size workpieces can be prepared without any influence on the cooling rate; the process is simple and easy to prepare workpieces with high dimensional accuracy and uniform surface; the droplet deposition rate is high; the material microstructure is uniform and fine, and there is no obvious interfacial reaction, and the material properties are better. However, the technology is still in the stage of research, development and perfection, so the regularity study of the trajectory of its deposition to the surface of the workpiece is still lacking theoretical basis.
PVD Coating Applicable materials:
In addition to natural materials, materials suitable for vacuum plating include: metals, hard and soft materials (ABS, ABS+PC, PC, etc.), composite materials, ceramics, glass, etc.
The most commonly used vacuum plating surface treatment is aluminum, followed by silver and copper.
Comparison of commonly used vapor deposition processes:
|Scope of application
|Vacuum evaporation coating
|Smooth, beautiful coating and high surface quality
|High temperature resistant materials
|Radio Frequency Sputtering
|RF source, high precision, rigid film
|Metallic/non-metallic, conductive/non-conductive films
|High speed and low temperature, high precision, high purity and high density
|Evaporation / Sputtering
|The target remains solid and can be placed at multiple angles and controlled individually to improve efficiency and film thickness consistency, with a wide range of targets, high density and high adhesion
|Thin films of metals/compounds/ceramics/semiconductors/superconductors, etc.
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