Gas-tight PVD coatings
Market for gas-tight coatings
Nanostructured gas-tight coating are in demand, primarily in the manufacture of parts for gas turbine engines. The trend in development of up-to-date gas turbines is the increasing of the temperature of the working gas and, consequently, bigger heating of turbine impellers, blades and other parts of the nozzle block. Under high thermal and mechanical loads in corrosive environments these items are easily damaged, which leads to the destruction of expensive aggregates and serious accidents.
Obtaining of nanostructured gas-tight coatings
The most demanded technologies of coating are magnetron sputtering and vapor deposition. The disadvantages of the first are low productivity and high cost, the disadvantages of the second are instability of properties of the coating due to the inhomogeneities (dendrites) that cannot provide a gas impermeability, the use of highly toxic substances, and high cost.
To eliminate these drawbacks the studies were conducted and the process of obtaining of thick-film gas-tight composite nanostructured coatings using a separation of plasma flow was developed. The technology consists in obtaining of the plasma flow based on the composition of the four nitrides of metals CoN-NiN-CrN-AlN using the electric arc method. Magnetic stabilization of the flow in the plasma source eliminates the heterogeneity of the coating, providing a high adhesion with the substrate, on which the coating is applied. Due to the use of nickel alloys, the coating has high thermal stability. The combination of dense nanostructured composition and thickness (up to 500 μm) of coating provides high performance of parts in corrosive environments and at high temperatures.
The technological process consists of preliminary treatment of the surfaces using ion flows, heating and coating. The processing time is from 30 to 70 hours. Both equipment and technology meet all the requirements of modern production, including environmental.
The ideas behind the technology are protected by patents of the Russian Federation and the EU (International patent application PCT/R497/00106).
Equipment for PVD coating
by electric arc method
For the implementation of the technology special equipment was created, the chamber of which has a cylindrical shape with a top cover to loading. Loading is performed with the use of lifting mechanisms. A special mechanism allows the rotation of the product in the chamber in two planes, vertical and horizontal. The maximum size of the processed products is 800 mm.
Vacuum system of the equipment includes fore pump and diffusion pump with a pumping speed of 7000 l/s. The device is equipped with six high-performance electric arc plasma sources with magnetic system of arc discharge stabilization and of plasma flow focusing for coating. For surface pre-treatment by ion flux uses wide-aperture gas plasma source based on the thermionic discharge. Also the device is equipped with gas supply system with automatic maintenance of pressure in the chamber, temperature control system, automation systems.
Prospects of the new technology
New technology allows to replace other methods of physical vapor deposition. The structure of the coatings obtained with the use of the developed technology, is much more homogenous (no “dendrites”), the continuity of the coating is better, the boundary coating-substrate is poorly expressed due to the high adhesion to the monolithic material of the substrate base. High process stability ensures high yield.
In the project the Russian technologies are used. The new process allows to increase the resource of turbopump units of power plants. Assessing the prospects, we can predict that the solution of the problem of increasing the service life of turbopumps of power plants with the possibility of forced operation provides the overall competitiveness of domestic production of such equipment. Thus, the further commercialization of this development and creation of technological equipment for hardening will allow the production of powerful domestic power plants and will increase the export potential of engineering in the segments of power generation units and equipment for hardening.