Metal-Ceramic Composite Material for Shroud Seals in the Steam Path of Steam Turbines
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Vol. 54, No. 4, November, 2020
METAL-CERAMIC COMPOSITE MATERIAL FOR SHROUD SEALS IN THE STEAM PATH OF STEAM TURBINES B. O. Bol’shakov,1 R. F. Galiakbarov,2 A. M. Smyslov,3 A. S. Kuleshov,4 and K. M. Usachev4 Translated from Élektricheskie Stantsii, No. 5, May 2020, pp. 25 – 30.
The results of the development of a new ceramic-metal composite material for seals of the steam path of steam turbines are presented. The concept of the new material and a model of its performance when rubbing against blade fins are developed. Data on its structure, physical and mechanical properties, and pilot operation as part of shroud seals of an experimental steam turbine, as well as commercial turbines of different capacity, are presented. Keywords: seals; steam path; steam turbine; metal-ceramic composite material; microstructure; mechanical properties; abradability.
— be made of a continuous material with minimum porosity. The classical approaches of materials engineering to the formation of the physical and mechanical properties of materials, such as thermomechanical, deformation, and thermal processing, fail to combine strength and abradability. To design new materials for seals, there is a need for alternative manufacturing methods, among which powder metallurgy [13] holds a special place. It offers a highly efficient process, allows varying the constituents of the material and, thus, controlling the properties of the final product, producing finished products, minimizing the cost of finishing machining. In [14 – 18], the required abrasive wear resistance of powder materials is proposed to achieve by adding a socalled solid lubricant (synthetic or natural crystalline material of graphite-like structure) to the starting charge. Such combinations of constituents are actively used in abradable (seal) coatings in the gas-turbine industry. However, the research and engineering literature provides no information on the application of such compositions in solid-phase sintering. The development of a powder metallurgy technique for producing a ceramic-metal composite material of certain structure and physical and mechanical properties for seals of steam turbines is a high-technology challenge. Given high temperatures and corrosive-erosive medium in the steam path of steam turbines, the designed material is based on PKh13M2 corrosion-resistant steel powder (GOST 13084–84) as the primary constituent and fine boron nitride BN powder (specifications U26.8-00222226-007–2003),
The efficiency and operating reliability of steam turbines are determined by, among other factors, the effectiveness, design, and material of the seals in the steam path, flow, dynamic, and other characteristics [1]. Contemporary turbine manufacturers apply seals of various design in the steam paths of steam turbines: thermalspray powder coated seals [2 – 4], honeycomb seals [5 – 7], brush seals [8 – 12], etc. The seal designs have both advantages and disadvantages. How much steam leaks through seals depends on their radial clearances. Reducing the clearance much can r
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