Steam Degradation of Ytterbium Disilicate Environmental Barrier Coatings: Effect of Composition, Microstructure and Temperature

Recession of environmental barrier coatings (EBC) in environments containing steam is a pressing concern that requires further research before their implementation in gas turbine engines can be realized. In this work, free-standing plasma sprayed Yb2Si2O7 coatings were exposed to flowing steam at 1350 °C and 1400 °C for 96 h. Three samples were investigated, one coating with a low porosity level (< 3 %) and 1 wt.% Al2O3 representing traditional EBCs; and two coatings with higher porosity levels (~20 %) representing abradable EBCs. Phase composition and microstructural evolution were studied in order to reveal the underlying mechanism for the interaction between high temperature steam and ytterbium disilicate. The results show depletion of Yb2SiO5 near the surface and formation of ytterbium garnet (Yb3Al5O12) on top of all three coatings due to the reaction with gaseous Al-containing impurities coming from the alumina furnace tubes. The 1 wt.% Al2O3 added to the EBC sample exacerbated the formation of garnet at 1400 °C compared to the abradable samples, which presented lower quantities of garnet. Additionally, inter-splat boundaries were visible after exposure, indicating preferential ingress of gaseous Al-containing impurities through the splat boundaries.

TECHNOLOGY FOR RESTORATION AND REPAIR OF AIRCRAFT ENGINE PARTS

Problems of increasing the service life of compressor blades of aircraft gas turbine engines using detonation spraying technology are considered. The simulation of the parameters of the velocity and temperature of the particles of the sprayed material in the barrel of the detonation unit and in the flooded space to the substrate was carried out, followed by the choice of the optimal technological parameters of the spraying process. The control system of the detonation unit has been modernized. An experiment was carried out on the deposition of the Al2O3 coatings on the samples of a substrate made of titanium alloy VT3-1. Based on the results of the experiment, technological recommendations were developed concerning both the parameters of the spraying process and the parameters of the preparation of the substrate surface before spraying. The equipment for brazing the blades of the guide vanes is described and a device for spraying coatings on the end surfaces of the compressor blades is proposed. Thus, a complex technology has been developed for restoring the end surfaces of titanium alloy compressor blades by deposition of Al2O3 coatings.

MULTIPARAMETRIC DIAGNOSTICS OF GAS TURBINE ENGINES

This article addresses the issue of diagnostics and maintenance of Gas Turbine Engines which are located in high Speed Ferries, Cruisers, Frigates, Corvettes, etc. Assurance of reliable operation can be performed only by using correct diagnostic methods and procedures of monitoring the condition of the devices and by selecting the correct strategy of maintenance. The issue of monitoring the technical condition of Gas Turbine Engines is treated through multiparametric methods of technical diagnostics incorporated into predictive maintenance, which is a part of proactive maintenance. There are methods of vibrodiagnostics, thermography, tribology, borescopy and emissions measurement. Each of these methods has lots of advantages and disadvantages; therefore it is very important to ensure their correct combination for trouble-free operation of those important facilities. Their suitability at work is discussed in the matrix of diagnostic methods application and the PF chart. The output of the work is a proposal of a suitable model of maintenance control which uses multiparametric diagnostic methods for small and big Gas Turbine Engines and optimizes maintenance costs.

Introduction to the problem of calculating the parameters of the mixing chamber of an afterburning bypass engine

The article considers the problem of calculation accuracy when using mathematical models of gas-turbine engines of the second level of complexity, using the example of a device for mixing the flows of the core engine and the bypass duct of a gas turbine engine, and suggests methods for solving it. The processes taking place in mixing chambers of air-breather engines are considered to be difficult for mathematical modeling since the exchange of kinetic and thermal energies of the flows characterized by different velocities, pressures, temperatures and chemical composition occurs in them simultaneously. The mixer does not only ensure mixing of flows from different engine ducts, but also acts as a kind of throttle. It regulates the pressure downstream of the fan and, consequently, air consumption in the bypass duct, thus affecting directly the fan characteristics and the distribution of flows over the engine ducts. The paper presents the dependencies of the workflow parameters that allow for more accurate verification of mixer models of the second level of complexity.

The eddy-current and ultrasonic investigations of the nickel-base superalloy the gas turbine engine blades after exploitation

The work carried out microstructural, eddy-current and ultrasonic studies of the material of spent blades of gas turbine engines made of nickel-base superalloy. To determine the degree of damage to the material of the spent blades, studies of the microstructure were carried out on a scanning electron microscope. It was found that γ' coagulation occurred in some specimens, which corresponds to overheated material. Acoustic studies of the material were carried out using the ultrasonic pulse echo method. Comparative analysis showed that in such specimens there is a significant decrease in the velocity of propagation and attenuation of longitudinal ultrasonic waves. It is found that the readings of the eddy-current flaw detector in overheated specimens differ more than twice in comparison with non-overheated specimens. This fact can be used for operational non-destructive testing of the actual state of the metal structure by the eddy current method with the aim of further safe operation of gas turbine engines.

Application of the vacuum casting technology in the production of small-size gas turbine engine blade machines

The application of casting technologies in the production of parts and assemblies of small-size gas turbine engines is justified in the paper. The technology of vacuum casting in gypsum molds was tested during the production of an experimental centrifugal compressor of a small-size gas turbine engine. On the basis of a 3D model of the designed centrifugal compressor, computational studies of vacuum casting were carried out and rational parameters of the technological process were determined. Prototypes of the developed centrifugal compressor of a small-size gas turbine engine were made. The results of calculations and the performed technological experiment confirmed the fill rate of the gating form and the absence of short pour. The distribution of shrinkage porosity and cavities corresponds to the design values and is concentrated in the central part of the casting that is subjected to subsequent machining. The area of the blades, disc and sleeve is formed without defects. The use of casting technologies in the production of parts and assemblies of small-size gas turbine engines assures the required quality with a comparatively low price of the finished product, making it possible to achieve the balance between the cost of the technology and the quality of the product made according to this technology.