Abstract
One of the possible ways to improve passive methods of the steam turbine blade material protection from water droplet erosion is to create “smart”-surface that combines the properties and characteristics that could not be implemented simultaneously when using one or another proven method of protection. To solve the problem of developing such surface, this article presents the metallographic researches results of the blade steel 20kH13 samples with various already used and promising passive methods of protection, consisting in the use of ion-plasma and polyurethane coatings, surface modification by means of diffusion saturation with nitrogen ions, creation of the structured surface relief by laser ablation. The results of the carried out researches have allowed to reveal both morphology of a possible “smart”-surface, and influence on a microstructure and characteristics of a near-surface layer of samples after treatments considered.
Highlights
IntroductionThere are different methods to combat water droplet erosion, which are based on the use of various separation devices (active methods) located on the periphery of the nozzle blades and removing part of the moisture from the two-phase flow, as well as the formation of different types of coatings or modifications of functional surfaces (passive methods), which allow to increase the erosion resistance of the blade material, which perceives the impact of drops not captured by separation devices [1,2,3,4,5]
There are different methods to combat water droplet erosion, which are based on the use of various separation devices located on the periphery of the nozzle blades and removing part of the moisture from the two-phase flow, as well as the formation of different types of coatings or modifications of functional surfaces, which allow to increase the erosion resistance of the blade material, which perceives the impact of drops not captured by separation devices [1,2,3,4,5]
The application of the laser surface structuring method may be relevant for the improvement of wear-resistant properties of such highly loaded and operated under severe conditions objects as steam turbine blades
Summary
There are different methods to combat water droplet erosion, which are based on the use of various separation devices (active methods) located on the periphery of the nozzle blades and removing part of the moisture from the two-phase flow, as well as the formation of different types of coatings or modifications of functional surfaces (passive methods), which allow to increase the erosion resistance of the blade material, which perceives the impact of drops not captured by separation devices [1,2,3,4,5]. Processes with the use of ion-plasma technologies of protective coatings formation in vacuum on the basis of nitrides, carbides, carbo-nitrides of refractory chemical elements or modification of the protected surface due to its diffusion of single- and multi-component saturation with metals and nonmetals are very promising methods. Effective and proven for various applications are coatings based on chromium Cr and it’s carbide CrC, superhard diamond-like DLC coatings, as well as processes of surface saturation with nitrogen ions (nitriding) [10,11,12,13,14]. The use of laser structuring for the creation of different-scale ordered surface relief and changes in it’s properties is one of the most promising methods due to the potentially high rates of creation of such surfaces, as well as the possibility of obtaining given geometric parameters of the topography with high accuracy. Creation of relief with known and specific required geometric parameters can potentially increase the ability of the blade material to withstand various types of destructions [15, 16]
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