Chemical Vapor Deposition – Process, Advantages, Materials

Sequence of the CVD process

There are different types of chemical vapor deposition, such as plasma CVD and thermal CVD. In principle, however, the treatment is carried out in similar steps. Firstly, the substrate is heated to the reaction temperature. This can be carried out by thermal radiation, laser (light), induction or the passage of current.

The coating material is supplied as a gaseous compound (precursor). The activation, i.e. the chemical decomposition, of the precursor is usually brought about thermally, although plasma activation is also possible. The layer is formed on the surface by the chemical reaction of the substrate and the precursor, which takes place at high temperatures. This utilizes the fact that volatile compounds condense as a layer when heat is applied, as they react chemically. In addition to the solid layer, at least one waste gas is also produced as a by-product. The layer thickness and quality can be controlled by various parameters such as temperature, pressure, gas flow rate and reaction time. The layer structure can also be influenced by the choice of precursor and the process conditions.

Advantages and disadvantages of the CVD process

CVD coatings have particularly good adhesion. Depending on the coating material and precursor, different surface properties can be changed. Common coatings for steel materials consist of titanium carbide and nitride, which give the substrate surface high hardness and good corrosion protection. The coating has high chemical resistance and offers high temperature resistance. In contrast to physical processes, components with complicated contours can also be treated evenly.

The high coating temperature can have a detrimental effect on the substrate, as it can reach up to 1000°C. Another disadvantage of the CVD process is the relatively long process duration compared to other coating methods.

Suitable materials

A number of steel grades are suitable for the CVD process, including:

• High-speed steels
• Cold work steels
• Hot work tool steels

Due to the high chemical versatility, not only metallic materials are suitable for the CVD process. Other applications are on glass, ceramics, semiconductors or plastics.

Differentiation from PVD

A related process is physical vapor deposition, or PVD for short. Similar to CVD, coating materials are transferred into the vapor phase and form a solid layer on the surface of the substrate. While CVD uses the volatile compounds of the coating components to form a solid layer, PVD processes use physical forces to form a target layer. Common PVD variants are evaporation processes (including vapor deposition, electron beam evaporation and laser beam evaporation) in a vacuum. Coating materials are brought into a gaseous state and then condense on the substrate. In terms of adhesion, PVD coating is inferior to CVD coating. PVD coatings generally have a higher hardness and wear resistance than CVD coatings. In addition, PVD processes are generally more environmentally friendly as they do not require any chemical reactions and do not release any toxic gases. The choice between CVD and PVD therefore depends on the specific requirements of the application.

Hardening of stainless steel with the BORINOX® process

Chemical vapor deposition is just one way to harden your steel materials. With the BORINOX® process for stainless steel hardenining, you not only increase the hardness of your materials, but also maintain their corrosion resistance. Our materials specialists will be pleased to advise you as soon as you contact us.