Common vacuum coating processes are divided into four categories: vacuum evaporation coating, vacuum sputtering coating, vacuum ion coating, and chemical vapor deposition.
1. Vacuum evaporation coating
Vacuum evaporation coating is a vacuum coating method of heating and evaporating the material under vacuum conditions to sublime the evaporated particle stream directly to the substrate, and deposit a solid film on the substrate.
Advantages: simple equipment and easy operation; high film purity and accurate thickness control; fast film formation rate and high efficiency.
Disadvantages: poor density (only 95% of theoretical density); film adhesion is small.
At present, vacuum evaporation coating is more used in the surface treatment of architectural engineering hardware, bathroom hardware, clocks, hardware, and even wheels, stainless steel profiles, furniture, lighting equipment, hotel supplies, and decorations.
2. Vacuum sputtering coating
The surface of the material is bombarded with energetic particles with tens of electron volts or higher kinetic energy so that its atoms get high enough energy to sputter into the gas phase. This sputtered and complex particle scattering process is called sputtering. Vacuum sputtering coating is the use of the sputtering phenomenon to achieve the preparation of various thin films.
Advantages: good controllability and repeatability of film thickness; strong adhesion to the substrate; high purity and high quality of the film layer; material films different from those of the target can be prepared.
Disadvantages: The film forming speed is lower than that of evaporation coating; the substrate temperature is high; it is easily affected by impurity gas; the device structure is more complicated.
The most commonly used sputtering coating technology is magnetron sputtering coating technology. This technique increases the chance of collision with the gas, increasing the sputtering rate of the target and ultimately the deposition rate. Therefore, it is more suitable for functional films, decoration fields, and microelectronics fields with functions such as absorption, transmission, reflection, refraction, and polarization.
3. Vacuum ion coating
Vacuum ion coating is a new coating technology developed on the basis of vacuum evaporation coating and sputtering coating. By carrying out the entire vapor deposition process in plasma, the vacuum ion plating process greatly improves the particle energy of the film layer, and can obtain a film layer with better performance, which expands the application field of "thin film".
Advantages: strong adhesion, not easy to fall off; improved film coverage; high coating quality; fast film forming speed; high density and small grain size.
Disadvantage: The substrate must be a conductive material.
Due to its excellent coating performance, vacuum ion coating has a wider range of applications. Currently, it is mainly used in mechanical parts, aircraft, ships, automobiles, exhaust pipes, aircraft engines, high-speed rotating parts, tools, superhard tooling, molds, etc.
4. Chemical vapor deposition (CVD)
CVD technology utilizes gaseous compounds or mixtures of compounds to chemically react on the heated surface of a substrate to form a non-volatile coating on the surface of the substrate.
Advantages: simple operation, strong flexibility, suitable for single or composite film layer and composite film layer; wide applicability; deposition rate can reach several microns to hundreds of microns per minute, high production efficiency; suitable for coating substrates with complex shapes; The coating has good compactness.
Disadvantages: The deposition temperature is high, which is easy to cause the performance of the substrate to decline; the reaction gas and reaction tail gas may have certain corrosiveness, flammability, and toxicity; the coating is very thin.
The CVD method is mainly used in two directions:
a. Prepare a coating layer, improve the surface properties of materials, improve the oxidation resistance, wear resistance, corrosion resistance, and certain electrical, optical, and tribological properties of materials or parts.
b. Develop new structural materials. At present, CVD technology has been widely used in many aspects such as protective film layer, microelectronic technology, solar energy utilization, optical fiber communication, superconducting technology, and preparation of new materials.
In addition, in the preparation of powder materials, the use of efficient and stable catalysts to promote the CVD pulverization process, or combined with physical methods, to prepare powder materials under low temperature and high vacuum conditions has also become the future direction of chemical vapor deposition technology development.