One of the most promising directions in the field of obtaining coatings with specified physical, chemical and mechanical properties is the introduction of "chemical vapor deposition" of metals (Chemicikal Vapor Deposition - CVD) into the production cycle. This method makes it possible to obtain a wide range of nano-, micro- and macro- coatings of different chemical composition, structure and properties.

Gas-phase deposition methods are based on pyrolysis of metal-containing compounds in gaseous state. In other words, it is a method of material synthesis in which volatile components of the gas phase form a solid film on the substrate surface through chemical reactions (decomposition of organometallic compounds (MOCs).

 

 

In comparison with other methods of surface modification such as galvanic deposition, diffusion metallization, gas-flame and plasma spraying, laser and gas-powder surfacing, the following advantages of CVD process can be noted:

high coating speed, up to 10 µm/min;
high density (porosity-free) of coatings;
possibility of applying uniform high-quality coatings on complex profiles, including internal surfaces;
microhardness of coatings up to 32000 MPa;
adhesion strength of coatings with substrate material up to 260 MPa;
temperature intervals of the process from 70 to 650℃;
metallization of metals and non-metallic materials (ceramics/plastics/rubber/etc.);
the process is environmentally friendly;
the process is carried out in a closed cycle;
relative simplicity of realization of technological processes - it can be easily automated;
absence of high vacuum requirements (often processes are carried out at atmospheric pressure);
wide range of organometallic compounds (MOCs) produced on an industrial scale.

 

This technology is used to enhance the functional properties of parts through the use of protective coatings and is a very common technological tool today. Strengthening, wear-resistant, corrosion-resistant and other functional coatings are widely used in industry. The problem of creating new high-performance wear-resistant materials is especially acute for modern branches of machine building - aircraft construction, aggregate construction, shipbuilding, rocket and space technology, as well as for the production of high-quality layers for commercial power devices.

 

At the same time, along with cost reduction, it is necessary to ensure improvement of product quality and reduction of harmful impact of production factors on the environment. The application of such processes will allow to reduce the cost of production due to the reduction of high-alloy steels and improve the quality due to the formation of coatings with predetermined physical, chemical and mechanical properties on the working surfaces of parts.

The essence of the CVD process is as follows: the initial organometallic compound (MOC) is converted into a gaseous state by vaporization or sublimation. The resulting gas mixture is fed into a reaction chamber where it reacts with a substrate heated to the decomposition temperature of the compound used and forms a metal coating. Deposition of coatings can be carried out both in vacuum and in the environment of transporting gases.

 

Figure 2: Schematic diagram of the plant

 

Example of hardware design of CVD-process:

1 - reactor;
2 - sublimator;
3 - filter;
4 - vacuum pump;
5 - thermostat;
6,7 - tanks with liquid MOS;
8 - flow meter;
9 - IR lamps.