Gas Turbine Parts Research Articles

Rotordynamic analysis and leakage performance study of a hole diaphragm labyrinth seal using the CFD method

Improving rotor stability and reducing leakage at various working parts of gas turbines is an important topic that experts and scholars have always pursued. In this article, a new type of hole-diaphragm-labyrinth seal (HDLS) structure is obtained by introducing an additional damping source. The HDLS structure is built by the traditional diaphragm labyrinth seal (DLS) with a single hole added to the diaphragm. The simulation under different working conditions of three different seal structures is carried out by ANSYS Fluent. Subsequently, the tangential force under different whirl frequencies was obtained. Meanwhile, the empirical parameters in Childs’ model of the dynamic performance of rotor-seal structures were obtained. The results show that the HDLS achieved a 71.4% improvement in the direct stiffness coefficient and a 71.8% improvement in the direct damping coefficient of the traditional labyrinth seal. The leakages of HDLS at different rotation speeds were lower than those of DLS by 1.53% and LS by 3.64%. The HDLS can be comprehensively considered the most promising seals among LS, DLS, and HDLS not only by stability but also by mass flow leakage in the rotor system.

Degradation and lifetime of self-healing thermal barrier coatings containing MoSi2 as self-healing particles in thermo-cycling testing

Yttria-stabilized zirconia (YSZ) is the state-of-the-art top coat material for thermal barrier coatings (TBCs) applied on highly loaded gas turbine parts. During operation at high temperatures, stresses are induced by the thermal expansion coefficient mismatch between the ceramic TBC and the metallic substrate. As a consequence cracks can grow, propagate and finally lead to a spallation of the top coat. Using atmospheric plasma spraying (APS), so-called self-healing MoSi2 particles can be incorporated into the YSZ matrix to mitigate the propagation of cracks leading to a lifetime gain and possibly higher temperature capability of the TBC. In the present work, the healing process is realized by the oxidation of the self-healing particles, which introduces a volume expansion by a formation of reaction products, which can seal the cracks. The self-healing particles were introduced within the first 150 μm of the YSZ coating matrix immediately on top of the bond coat. The degradation and lifetime of such systems were studied in furnace cycling and in burner rig tests, in which a temperature gradient through the sample was applied. The lifetime of the self-healing coatings was then compared to the lifetime of an YSZ coating without self-healing particles. In burner rig tests a clear lifetime extension of the self-healing TBCs was observed. The origin of this different behavior was investigated by microstructural analysis in scanning electron microscopy. A further insight into the failure mechanisms was gained by the analysis of a self-healing TBC cycled in a furnace cycling test only for about 55% of its expected lifetime.

Thirty Years of Thermal Barrier Coatings (TBC), Photothermal and Thermographic Techniques: Best Practices and Lessons Learned

With the adoption of thermal barrier coatings (TBCs) to protect the hot parts of gas turbines at the end of the last century, the characterization of their thermophysical properties and the evaluation of their state of integrity has become necessary. That leads to the development and/or the adaptation of photothermal and thermographic techniques to meet the newly requirements that have emerged. Whereas this is not an all-encompassing review of all the literature on the subjects, this work summarizes the research and the development of techniques specifically aimed at measuring the thermophysical properties, the characterization of the microstructure and the identification of adhesion defects to the metal component of the TBCs. In the following, the best practices, the lessons learned, the successes and the defeats experienced along almost thirty years will be summarized.

A Perspective on Thermally Sprayed Thermal Barrier Coatings: Current Status and Trends

For more than 6 decades, thermal barrier coatings have been used to protect structural parts in both stationary and aviation gas turbines. These coatings allow the use of significant higher operation temperatures and hence increased efficiencies. In the 1970s, yttria-stabilized zirconia (YSZ) was identified as outstanding material for this application. As major deposition technologies both electron beam physical vapor deposition (EB-PVD) and atmospheric plasma spraying (APS) have been established. Although the topic is already rather old, there are still frequent activities ongoing to further improve the technology, both with respect to materials and microstructural issues also regarding the use of advanced coating technologies, especially in the field of thermal spray. The paper tries to summarize major developments in both fields, the materials and the processing focusing on thermal spray methods. The impact of both materials and processing are summarized by the results of burner rig tests for various systems. Furthermore, a short outlook on possible future directions of developments will be given.

Studying the effect of heat treatment modes on corrosion resistance of welded joints

Studying the effect of heat treatment modes on corrosion resistance of welded joints

Study into the effect of different energy sources on the structure and mechanical properties of EP693 nickel alloy weld joint

The paper provides the results of a study on the influence of welding types (laser, electron beam, and TIG welding) on the properties of a permanent connection made of an EP693 alloy of the Ni–Cr–W–Co–Mo system used in the production of gas turbine engine components and parts. EP367 filler wire of the Ni–Mo–Cr–Mn system was used to obtain a weld during laser and TIG welding. A comparative analysis of heating areas and power densities was performed for the welding types studied. It was established that TIG welding features by greater values of the heating area and power density in comparison with laser and electron beam welding. It was found that the type of welding affects the features of weld formation. For example, a weld is formed with the transition to knife fusion penetration in the weld root for electron beam welding, and in the form of an «hourglass» for laser welding. The analysis of the heat affected zone microstructure showed that the smallest grain size is formed during laser welding. The distribution of elements in the weld joint was analyzed. It was found that when welding with the use of filler wire, the Mo content increases and the W, Co, Al, and Ti content decreases in the weld and heat affected zone relative to the base metal. This determines the peculiarities of failure for samples obtained using the welding types studied. Samples obtained by TIG and laser welding broke along the heat affected zone on the weld reinforcement side. Samples obtained by electron beam welding broke along the weld. Mechanical tests of samples at room and elevated temperatures showed that samples obtained by laser and electron beam welding have the highest tensile strength.

A process modeling approach for micro drilling of aerospace alloys with a waterjet guided laser system

Laser drilling is a preferred method to make cooling holes on gas turbine parts. Although it is a fast process, there are some quality issues. Waterjet guided laser (WJGL) is a hybrid process, in which a laser beam is coupled with and guided through thin cylindrical waterjet. Pressurized water in this novel process provides focusing, cooling and cleaning of the machining zone, eliminating undesired side effects of the laser. The process can be conveniently used for micro drilling operations on aerospace jet engine parts. However, more research on the process is required to understand the effects of the variables on material removal rate. The drilling time varies for each material and geometry. Optimum parameters should be adjusted for each case. In this study, the material removal mechanism of WJGL is investigated and a holistic modeling approach is developed including the necessary parameters for drilling of different aerospace materials and hole geometries.

Microstructure and Mechanical Properties of Materials Formed by Diffusion Bonding of VT6 Alloy Parts Produced by Rolling and Selective Laser Melting

Nowadays, the rapid development of the new methods of assembling large-scale parts consisting of several materials elaborated by different manufacturing methods is observed. These materials are unique in terms of the mechanical and physical properties of the part. Diffusion welding is one of the most promising multipurpose assembling techniques allowing the formation of lowporous high-quality welding joints with stable mechanical properties and absence of oxide inclusions. This method is widely applied for assembling titanium alloy parts requiring the welding in a vacuum due to the high chemical activity of titanium in the normal atmosphere containing oxygen, nitrogen and hydrogen. In this work, the structure and properties of parts produced from Ti6Al4V titanium alloy by the combination of laser powder bed fusion, hot rolling and diffusion welding were studied. The diffusion welding was performed in an autoclave (at temperature T = 920 оC, pressure 4 MPa, holding time of 4 h) and hot isostatic pressing (at temperature T = 930 оC, pressure 100 MPa, holding time of 2 h). It was shown that the microstructure of the weld joint depended on the welding method (autoclave or HIP). No defects in the zone of diffusion joints were observed in both cases. The impact toughness of samples obtained during hot isostatic pressing is higher than for the samples obtained in an autoclave. Both types of welded samples had high mechanical properties and met the requirements of GOST 23755–79 standard for bulk titanium samples.The authors would like to thank V. V. Cheverikin, Candidate of Technical Sciences, MISiS, and P. V. Petrovskiy, Candidate of Technical Sciences, MISiS, for conducting metallography studies and discussing the results. This research was funded by the Ministry of Science and Higher Education of the Russian Federation. Within the framenork of the Government Resolution No. 218 based on the Agreement on subvention assignment No. 075-11-2019-058 dated 25.11.2019 “Establishing a production line for locally reinforced titanium alloy components designed to operate under high loads and temperatures as a part of innovative gas turbine engines“.

The Rehbinder effect in tests of superalloys in contact with molten salts

The results of the Rehbinder effect manifestation during testing of superalloys in contact with corrosive media containing Na2SO4 + NaCl are discussed. We present the experimental study of the effect of salts containing chlorine and sulfur on the mechanical properties and long-term strength of single crystal and powder nickel-based superalloys at high temperatures. The practical value of the work is associated with the possible operation of gas turbine parts in conditions of ingress of the particles containing chlorine, sulfur and sodium into the flow path. A simplified (compared to a previously used) procedure of testing wrought alloys for long-term strength in molten salts is developed. A comparative study of the mechanical properties and long-term strength of a single crystal superalloy in the initial state (previously damaged by corrosion of different duration) and being in contact with salts during testing is carried out. Due to the large scatter of experimental data, the method of lower envelopes has been proposed and implemented to determine the guaranteed values of the long-term strength. It is shown that the guaranteed values of the long-term strength at different temperatures and test durations can decrease by 2.5 – 5.0 times in the presence of salts. Metallographic studies of the nature of damage and destruction of samples are carried out. The revealed decrease in the long-term strength of heat-resistant alloys in contact with salts is interpreted as the Rehbinder effect and not as a manifestation of the effect of stress corrosion cracking. A methodology for using the obtained test results with a duration of up to several thousand hours in highly aggressive environments is proposed to predict the long-term strength in relation to long-term operation (tens of thousands of hours) under conditions of relatively low salt loads.

The new concept of thermal barrier coatings with Pt + Pd/Zr/Hf-modified aluminide bond coat and ceramic layer formed by PS-PVD method

AbstractThermal barrier coatings (TBCs) are widely used for protection of gas turbine parts from high temperature and corrosion. In the present study, the new concept of TBCs with three-element-modified aluminide coatings was presented. In the first stage, the Pt and Pd were electroplated on MAR M247 nickel superalloy. In the next stage, the low-activity CVD aluminizing process with Zr or Hf doping was conducted. The ceramic layer containing yttria-stabilized zirconia was obtained by the plasma spray physical vapour deposition (PS-PVD) method. The microscopic examination showed the formation of aluminide coating containing up to 5 at% of Pt and 10 at% of Pd in (Ni, Pt, Pd)Al solid solution. The small concentration of Hf and Zr in diffusion zone of aluminide bond coat was noted as well. The outer ceramic layer was characterized by columnar structure typically formed during the PS-PVD process. The obtained results showed that the new concept of TBCs formed using new processes might be an attractive alternative to conventional coatings produced using the expensive electron beam physical vapour deposition (EB-PVD) method.

Fractographic investigation of Low Cycle Fatigue behaviour of IN718 coated with NaCl at 550°C

Nickel base super alloys due to their superior properties are used in different parts of gas turbines, in jet engines, and as well as in marine application from 250°C to 650°C. At such high temperature sulphur and vanadium as impurities in fuel oil get oxidised in SO2 and V2O5. Further, sulphur oxide reacts with NaCl to form Na2SO4. These salts cause high temperature corrosion which causes stress corrosion cracking of engine components of marine gas turbine. Therefore, LCF resistance of the material becomes an important consideration in design of turbine. Fatigue samples both coated with NaCl salt and uncoated samples were tested in low cycle fatigue. The fatigue tested samples were analyzed under Scanning Electron Microscope (SEM). Since micrographs analysis is an important tool with the testing of materials to evaluate the various properties of the materials. In present study micrographs analysis helped to a great extent for evaluation the Low cycle fatigue behaviour of Nickel base super alloy INCONAL 718 (IN718) at high temperature which is 550°C.

Microstructure and Oxidation Resistance of Thermal Barrier Coatings with Different Ceramic Layer

Thermal barrier coatings are widely used for protection of gas turbine parts against high temperature oxidation and hot corrosion. In present work the microstructural assessment of TBCs produced by atmospheric plasma spray (APS) method was conducted. Three types of ceramic powders were used: magnesia- stabilized zirconia oxide (Metco 210), yttria stabilized zirconia oxide (YSZ -Metco 204) and fine-grained YSZ – Metco 6700. As a base material the Inconel 713 was used as well and CoNiCrAlY was plasma sprayed (APS) as a bond coat. The thickness of all ceramic layers was in range 80 – 110 μm. The elemental mapping of cross-section of magnesia-stabilized zirconia showed the presence of Mg, Zr and O in outer layer. In the YSZ ceramic layer the Y, Zr and O were observed during elemental mapping. The isothermal oxidation test was conducted at 1100 °C for 500 h in static laboratory air. On all samples the delamination and spallation of ceramic layers was observed. Chemical composition analysis of coatings showed the presence of two areas: the first one contained elements from bond coats: Ni, Cr, Al, Co and second area contained O, Cr Co and O that suggest the scale formation. The obtained results showed the total degradation of all ceramic layers as a result of internal stresses in bond-coat. Microscopic analysis showed the areas with complete degradation of bond coats and formation of thick oxides layer.

Modeling the influence of the composition of refractory elements on the heat resistance of nickel alloys by a deep learning artificial neural network

Nickel alloys are widely used in the manufacture of gas turbine parts. The alloys show resistance to mechanical and chemical degradation under prolonged loads and high temperatures. The properties of an alloy are determined by its composition and are subject to careful modeling. A set of basic refractory elements makes a special contribution to the parameters of the alloy. One of the main mechanical properties of the alloys is the high‐temperature tensile strength. Determining the influence of certain elements on certain properties of an alloy is a complex scientific and engineering problem that affects the time and cost of developing new materials. Simulation is a great chance to cut costs. In this article, we predict high temperature strength based on the composition of refractory elements in alloys using a specially designed deep learning artificial neural network. We build the model based on prior knowledge of alloy composition, information on the role of alloying elements, type of crystallization, test temperature and time, and tensile strength. Successful simulation results show the applicability of this method in practice.

Decarbonizing materials sourcing and machining in the gas turbine sector, through a cost-carbon footprint nexus analysis

The energy industry is committed to support sustainable development, balancing environmental, social and economic benefits. Turbomachinery products, in particular gas turbines, have not only to overcome the barriers imposed by: performance, lifetime and costs requirements, but to be more environmentally sustainable. The goal of this work is to integrate quantitative analysis of sustainability, based on Life Cycle Assessment (LCA), with company costs assessment methods, to provide a new multicriteria optimization methodology. This has been applied to the single components of the gas turbine and has shown that the Second Stage Low Pressure Turbine (LPT) Case can be sourced from different suppliers, reducing both: the costs of supply and the Greenhouse Gases (GHG) emissions. The LCA analysis provides also an environmental characterization of materials, machining operations and coating processes, which are necessary to realize the gas turbine parts. The findings allow to compare conceptual design alternatives of gas turbines, according to the Design for the Environment principles and can be extended also to other industrial sectors.

Heat Transfer Coefficient Augmentation for a Shaped Film Cooling Hole at a Range of Compound Angles

Abstract Film cooling holes with shaped diffusers are used to efficiently deliver coolant to the surface of a gas turbine part to keep metal temperatures low. Reducing the heat flux into a component, relative to a case with no coolant injection, is the ultimate goal of film cooling. This reduction in heat flux is primarily achieved via a lower driving temperature at the wall for convection, represented by the adiabatic effectiveness. Another important consideration, however, is how the disturbance to the flowfield and thermal field caused by the injection of coolant augments the heat transfer coefficient. The present study examines the spatially resolved heat transfer coefficient augmentation, measured using a constant heat flux foil and infrared (IR) thermography, for a shaped film cooling hole at a range of compound angles. Results show that the heat transfer coefficient increases with the compound angle and the blowing ratio. Due to the unique asymmetric flowfield of a compound angle hole, a significant amount of augmentation occurs to the side of the film cooling jet, where the very little coolant is present. This causes local regions of increased heat flux, which is counter to the goal of film cooling. Heat transfer results are compared with adiabatic effectiveness and flowfield measurements from a previous study.

Study of boriding surface treatment in the tribological behavior of an AISI 316L stainless steel

AISI 316L stainless steel possesses high tensile and rupture strength at low and high temperatures; therefore, it is employed in several industry fields like manufacturing gas turbine parts, automotive pieces, and prosthetic devices like joints prosthesis. However, the debris and oxide products resulting from wear lead to detrimental performance, particularly in medical applications like partial hip prosthesis, orthopedic screws, or bone plates. This liberation of metallic ions may cause aseptic implant loosening, granuloma formation, and demineralization of bone tissue. On the other hand, research in the last few years has focused on improving the tribological performance of the steel surface, including ceramic coatings and different engineering surface treatments. In this work, the tribological performance of boride layers synthesized on an AISI 316L was studied. As it was mentioned before, the AISI 316L steel is widely used for biomedical applications, so the improvement of their tribological properties is the particular interest in this field. Also, boriding treatment increases the corrosion resistance of the steel due to the boride layers acting as a barrier that reduces the pitting corrosion properly of the stainless steel. For this purpose, diffusional boriding treatments were performed at the following parameters: 850, 950, and 1050 °C over 2, 4, and 6 h for each temperature. Surfaces were characterized using scanning electron microscopy, X-ray diffraction, micro and nano-hardness testing, and roughness measurements. The tribological response was studied through a ball on disc tribometer under dry-sliding conditions with a distance of 10 km, tracking the coefficient of friction, mass loss, wear rate, and surface damage. All borided conditions decreased the wear rate in comparison with the untreated samples. The differences in wear performance among the borided surfaces were detailed discussed in this paper.

Технология получения композиционных конгломератных порошков для плазменного напыления высокотемпературных защитных покрытий

Introduction. For parts of gas turbines operating under conditions of corrosion-erosion and intense wear, the most acceptable are compositions containing Ni, Co, Cr, Al, B, Y both in pure form and in the composition of compounds applied on the contact surface during thermal spraying. Modern integrated complexes obtained by combining dissimilar substances in the form of a single composition are promising. Such powders are obtained either by cladding or by conglomeration of finely dispersed starting components into a larger particle. The problem of developing and manufacturing plants for conglomeration of powders is urgent and practically important, since it makes it possible to obtain material for thermal spraying of coatings for high-temperature purposes. The aim of the work is to develop a technological scheme for obtaining powders of the required chemical composition with a given particle shape and size, intended for spraying high-temperature protective coatings. Materials and research methods. A technology is developed for the production of integrated powders for spraying coatings using the method of spray drying and subsequent sintering in vacuum or in an argon-hydrogen atmosphere, which avoids the loss of feedstock due to the return of fine and coarse fractions. A technology for preparing materials for spray drying and granulation is proposed. A gravity type aerodynamic classifier is designed and manufactured, which makes it possible to select automatically the powder fraction necessary for spraying the coating, as well as return the unwanted fraction for recycling. The morphology of the granular powder is determined using a TESCAN scanning electron microscope. The chemical composition of the resulting integrated complexes is determined by X-ray microanalysis on an OXFORD attachment. Results and discussion. The technological conditions for obtaining powders of a given size (40…100 µm) are established. It is shown that the shape of the conglomerate particles after spray drying is close to spherical. On the basis of a multifactor experiment, the optimization of the technological process for obtaining powders Ni-17Cr-10Al-1Y and Ni-22Cr-16Al-1Y with sizes up to 100 µm is performed. It is shown that when conglomerating powders with increased aluminum content (Ni-22Cr-16Al-1Y), it is necessary to take into account the exothermic reaction of nickel aluminide formation and dilute the mixture of initial components before sintering with the finished sintered powder. The resulting integrated complexes are characterized by high heat resistance; therefore they are designed and successfully used for plasma spraying of protective coatings for high-temperature purposes. Conclusions. A technology is developed for obtaining composite conglomerated powders Ni-17C-10Al-1Y and Ni-22Cr-16Al-1Y with particle sizes up to 100 µm and a shape close to spherical. A distinctive feature of this technology is that it avoids the loss of feedstock by returning fine and coarse fractions.

Mathematical model of the axial compressor blade in system assessing technical condition of the industrial gas turbine

The paper presents the key stages of developing a geometric model of the axial compressor blade. The model is based on Bezier curves, which are used to design the parts of airfoil and allow making local changes to the airfoil and blade geometry. This model is designed to assess the technical condition of the axial compressor being a part of an industrial gas turbine or gas-turbine units, depending on the defects of axial compressor blade row (in the gas-flow channel) and the turbine as a whole. As a part of the study the algorithm, which describes the process of the blade formation, were presented. Although the study presents the main equations of the model based on the key geometric parameters of the airfoil, provides examples of airfoil, blade and stage modelling using the presented method, and shows the results of model verification using numerical simulation methods.

РАЗРАБОТКА ФУНКЦИОНАЛЬНЫХ ИОННО-ПЛАЗМЕННЫХ ПОКРЫТИЙ НА ОСНОВЕ МНОГОСЛОЙНЫХ ГЕТЕРОГЕННЫХ СТРУКТУР НИТРИДОВ МЕТАЛЛОВ

The article deals with the development of ion-plasma coating systems based on multilayer heterogeneous structures of the type (Me1)N/(Me2)N, (Me1–Me2)N/(Me3)N, (Me1–Me2–Me3)N/(Me4)N, where Me: Ti, Al, Cr, Mo. Tests for heat resistance and wear resistance, gas-abrasive resistance, metallographic and x-ray structural studies were carried out. It is shown that the ion-plasma coating (Ti–Al–Cr)N/CrN can be used to increase the heat resistance, wear resistance (including abrasive) of steel and titanium intermetallic parts of aircraft gas turbine engines operating in the temperature range up to 800 °C.

Design and Numerical Analysis of a Micro Gas Turbine Combustion Chamber

The interest in micro gas turbines has been steadily increasing. As a result, attention has been focused on obtaining optimal configurations for micro gas turbines depending on the applications in which they are used. This paper presents the CFD modeling results regarding an annular type combustion chamber, part of an 800N micro gas turbine, predestined to equip a small scale multifunctional airplane. Two configurations have been taken into consideration and 3D RANS numerical simulations have been conducted with the use of the commercial software ANSYS CFX. The liquid fuel droplets were modeled by the particle transport model, which tracks the particles in a Lagrangian way. An initial fuel droplet diameter of 500µm has been imposed. The numerical results obtained are encouraging. The flame was developed in the central area of the fire tube, its walls thus not being subjected to high temperatures. Also, the maximum temperatures were obtained in the primary zone of the fire tube. The temperature then decreased in the fire tube's secondary zone and dilution zone. The numerical results will be validated by conducting combustion tests on a testing rig which will be developed inside the institute's Combustion Chamber Laboratory.