What is physical vapor deposition (PVD)

Physical vapor deposition (PVD) is a technology that vaporizes the surface of materials (solid or liquid) into gaseous atoms, molecules or partially ionized into ions by physical methods (evaporation, sputtering, etc.) in vacuum, and deposits thin films with certain functions on the substrate surface through low-pressure gas (or plasma) process. The types of physical vapor deposition mainly include vacuum evaporation, sputtering, ion plating, etc. This process is widely used to prepare the coating of stainless steel bipolar plates because of its simple operation, environmental protection, no pollution, less consumables and excellent film performance. Two of these technologies are described below.

1. Vacuum sputtering coating

With the demand of industry and the development of surface technology, vacuum sputtering coating technology has been greatly developed and applied. According to different sputtering methods, vacuum sputtering can be divided into DC diode sputtering, magnetron sputtering and other methods. Magnetron sputtering is commonly used in vacuum sputtering coating. New magnetron sputtering, such as high-speed sputtering and self sputtering, has become a new development trend in the field of magnetron sputtering. Due to the size limitation of stainless steel, the targets of sputtering coating are basically bars or wires, and the deposited film materials are mostly metal films or alloys, and many coating methods use magnetic field assisted sputtering.

The tin film can be deposited in the stainless steel pipe by DC sputtering coating technology, that is, the discharge voltage range is 80 ~ 90 PA, and the substrate temperature of the plated pipe is 160 ~ 180 ℃. The high-quality, uniform and golden tin film can be obtained on the substrate of the stainless steel vacuum pipe. It can be completely applied to the industrial production and processing of the accelerator slender pipe vacuum chamber. In addition, aluminum oxide ceramics can be prepared by DC reactive magnetron sputtering on the surface of stainless steel substrate YBiO3, which is mainly used in the field of medical and surgical instruments. In order to prepare high activity and strong TiO2 films, the DC magnetron sputtering technology is also used to deposit TiO2 films on the surface of stainless steel.

2. Vacuum ion plating

The molecules of evaporated substances are ionized by electron impact and deposited on the solid surface with ions, which is called ion plating. This technology was proposed by D. matox in 1963. Ion plating is a combination of vacuum evaporation and cathode sputtering technology. Therefore, the ion plating process combines the characteristics of evaporation (high deposition rate) and sputtering (good film adhesion) processes, and has good diffraction. It can coat workpieces with complex shapes, and is widely used in the industrial production of wear-resistant, high-temperature oxidation resistant tool and die surface strengthening. A team prepared hard chromium film on the surface of stainless steel substrate by vacuum ion plating.

The experiment shows that the technology of ion plating hard chromium on stainless steel is environmentally friendly, and the prepared hard chromium layer has high hardness, excellent corrosion resistance, wear resistance and strong adhesion. It is an ideal alternative technology to the traditional chromium plating technology. In addition, multi arc ion plating technology can be used to prepare tic and tin films on stainless steel bipolar plates, which can meet the corrosion resistance requirements of bipolar plates, and the channel pressing has little effect on the corrosion resistance of bipolar plates.