Gas Turbine Engine Components Research Articles

Novel oxide based anti-corrosion composite coating for gas turbines

In the present study glass-ceramic−8YSZ based multilayered functionally graded corrosion resistant coating was developed for gas turbine applications. Corrosion resistance property of developed coating was evaluated by exposing coating to molten mixture of 80 wt% Na2SO4 + 20 wt% NaCl in air at 1000 °C up to 100 h. It was found that coating morphology was gradually changed with respect to time at 1000 °C. No thermally grown oxide (TGO) layer was observed within different layers of TBC. However, thin reaction film was developed at substrate-coating interface, which helped to increase adherence of coating with substrate. Tetragonal zirconia to monoclinic zirconia phase transformation was not occurred in top coat even after long corrosive salt attack that strengthened TBC system. Developed coating showed good potential to be used as corrosion resistant coating for actual superalloy based gas turbine engine components.

Hot Deformation Behavior of Inconel 718 Alloy Using Regression-based Dynamic Material Model and Applications in Ring Rolling Manufacturing

Inconel 718 nickel-based alloy is extensively used in the aerospace industry (e.g., gas turbine engine components) because of its excellent corrosion resistance and high mechanical properties at elevated temperatures. However, there is a certain limit to manufacturing the alloy through plastic deformation due to its high deformation resistance and complicated deformation behaviors. In this study, the hot deformation behavior of Inconel 718 alloy was investigated to establish how processing conditions of flow stress-strain, at strain rates from 0.001 to 10 s<sup>-1</sup>, and temperatures from 850 to 1200<sup>o</sup>C, affected dynamic recrystallization. The regression-based material model was utilized to calculate the strain-rate sensitivity, and subsequently depict the efficiency of the power dissipation and instability criterion of hot deformation. The processing map and instability criterion predicted by the developed 3<sup>rd</sup>-order polynomial regression model corresponded with the experimental results and in particular, showed a better prediction for instability regime compared to the existing discrete derivative approach. Predicting the strain-rate sensitivity values on a continuous scale with regression analysis covered the additional instability region of the high strain rate near 10 s<sup>-1</sup>. The dynamic recrystallization deformation was also characterized by microstructural analysis along with the processing map. Consequently, ring-rolled aviation parts were manufactured with the optimum processing parameters, which conform to the AMS 5663 standard (Aerospace material specifications for Inconel 718).

Application of a Performance-Improvement Method for Small-Size Axial Flow Turbines

As a main component of most gas-turbine engines, the axial flow turbines have been in a process of continuous improvement, reaching high efficiencies and reliability. A well-known drawback of these systems is the rapid decrease in performance when operating at lower than nominal conditions. Thus, a novel performance-enhancement method for axial turbines operating at partial loads has been previously proposed and numerically characterized. In this paper, one applies the aforementioned method for a smaller size axial flow turbine, part of a gas-generator assembly for a microjet engine, to determine, by the use of CFD analysis, the influence of the system at different partial regimes across the working line. A logical scheme based on iterative steps and multiple numerical simulations is also used to determine the engine response to the injection of compressor bleed air into the turbine passages. The results show, as determined in the previous study, that the generated power can be increased for all partial regimes, with the influence being more noticeable at higher regimes, leading to a reduction in fuel consumption in order to achieve the same regimes.

Deep learning-based modeling method for probabilistic LCF life prediction of turbine blisk

Turbine blisk is one of the typical components of gas turbine engines. The fatigue life of turbine blisk directly affects the reliability and safety of both turbine blisk and aeroengine whole-body. To monitor the performance degradation of an aeroengine, an efficient deep learning-based modeling method called convolutional-deep neural network (C-DNN) method is proposed by absorbing the advantages of both convolutional neural network (CNN) and deep neural network (DNN), to perform the probabilistic low cycle fatigue (LCF) life prediction of turbine blisk regarding uncertain influencing parameters. In the C-DNN method, the CNN method is used to extract the useful features of LCF life data by adopting two convolutional layers, to ensure the precision of C-DNN modeling. The two close-connected layers in DNN are employed for the regression modeling of aeroengine turbine blisk LCF life, to keep the accuracy of LCF life prediction. Through the probabilistic analysis of turbine blisk and the comparison of methods (ANN, CNN, DNN and C-DNN), it is revealed that the proposed C-DNN method is an effective mean for turbine blisk LCF life prediction and major factors affecting the LCF life were gained, and the method holds high efficiency and accuracy in regression modeling and simulations. This study provides a promising LCF life prediction method for complex structures, which contribute to monitor health status for aeroengines operation.

Ytterbium Disilicate/Monosilicate Multilayer Environmental Barrier Coatings: Influence of Atmospheric Plasma Spray Parameters on Composition and Microstructure

SiC/SiC ceramic matrix composites (SiCf/SiC CMCs) are regarded as the new materials for the hot-section components of aircraft gas turbine engines, since they have one-third of the density of metallic superalloys, a higher temperature capability, good mechanical strength, and excellent thermal shock resistance. However, high-temperature water-vapor-rich combustion gases can induce severe surface recession phenomena in SiC/SiC leading to component failure. For this reason, it is necessary to design protective coatings, i.e., environmental barrier coatings (EBCs), able to protect the SiC/SiC surface in combustion environments. In the present work, ytterbium monosilicate (Yb2SiO5), stable when exposed to water vapor at high temperatures, and ytterbium disilicate (Yb2Si2O7), characterized by a thermal expansion coefficient closer to that of the substrate, were selected for a multilayer EBC system. EBCs were processed using the atmospheric plasma spray (APS) technique. A set of deposition parameters were tested, varying the power of the torch, and the composition and microstructure of the deposited coatings were studied in terms of porosity, crack density, and post-deposition phase retention by performing SEM, EDS, and XRD analysis. The results allow for the definition of the influence of deposition parameters on the final properties of multilayer EBC coatings.

Preparation of Highly Durable Columnar Suspension Plasma Spray (SPS) Coatings by Pre-Oxidation of the CoNiCrAlY Bondcoat

Columnar structured thermal barrier coatings (TBCs) have been intensively investigated due to their potential to enhance the durability and reliability of gas turbine engine components. These coatings consist of vertically aligned columns that provide excellent resistance to thermal cycling. In this study, the lifetime of columnar suspension-plasma-sprayed (SPS) TBCs was evaluated using burner rig tests. The tests were carried out under high-temperature conditions. Significantly, the pre-oxidation of the bondcoat during diffusion bonding treatment was found to have a substantial impact on the performance of the SPS TBCs. The optimized treatment resulted in columnar SPS TBCs demonstrating excellent thermal stability and resistance under the test conditions. The lifetime of the coatings was significantly extended compared to conventional TBCs by pre-oxidation of the CoNiCrAlY bondcoat in argon, which suggests that columnar SPS TBCs have great potential for use in gas turbine engines.

Effect of coating degradation on the hot corrosion behavior of yttria-stabilized zirconia (YSZ) and blast furnace slag (BFS) coatings

In order to provide thermal insulation thermal barrier coatings (TBCs) used in gas turbine engine components under conditions of impure fuels and high turbine inlet temperatures are expected to have hot corrosion resistance. Techniques and material combinations used in the production of TBCs are primarily effective in the progression of failure mechanisms as a result of hot corrosion. In this study, the hot corrosion damage mechanism, which is caused by the impurities of the fuels used in the industry and causes great damage to the TBC systems, was simulated and evaluated in the laboratory environment. For the creation of TBC systems, CoNiCrAlY metallic bond coating powders were deposited on Ni-based super alloy substrates by the detonation gun (D-gun) process. Commercial yttria-stabilized zirconia (YSZ) and blast furnace slag (BFS) powders were deposited on the bond coating by Atmospheric plasma spraying (APS) technique. Hot corrosion testing of TBCs was performed at 800 °C for 8, 24, 50, and 75 h in an environmental condition consisting of a 45 wt% Na2SO4 and 55 wt% V2O5 corrosive salt mixture. Blast furnace slag, which is completely cost-free and a waste product, provided excellent protection against hot corrosion damage without deteriorating its stability at high temperatures. In this way, it is open to be evaluated as a new type of coating material alternative to the traditional top coating material YSZ, which has a very high production and cost, and to be used in different areas.

Grain boundary microstructure-property relationships in the cast & wrought Ni-based superalloy René 41 with boron and carbon additions

Cast & wrought Ni-based superalloys are required for manufacturing high-performance components in gas turbine engines. Their excellent high-temperature properties and corrosion resistance are brought about by their complex microstructure of a γ-matrix, intra- and intergranular γ' precipitates, carbides, and borides. The most highly-alloyed superalloy grades provide the high-temperature strength required for the design of next generation gas turbine engines but their processability remains challenging due to grain boundary (GB) cracking. A common mitigation approach is the addition of B and C to improve GB cohesion and strength. However, their detailed roles in GB segregation and precipitation and the link to GB properties during processing remains largely unexplored.We provide a systematic study on decorated GBs in the cast & wrought Ni-based superalloy René 41 with B and C additions. Tensile testing reveals that B additions reduce its ductility due to GB cracking but slow down grain growth during heat treatments more effectively, than C additions. GB-M2B, M6C, M23C6, and GB-γ' precipitates decorating GBs are sequentially precipitated. Their structures and compositions are shown to be unaffected by B and C additions. However, significant differences in the interfacial segregation of solutes are revealed. B is captured by GB-M2B and therefore unavailable to improve GB cohesion. C depletion and enrichment of solutes at interphase boundaries are identified as origin for the reduced ductility and thus, GB cracking. The findings are summarized as microstructural model and advance the detailed understanding of the processing – microstructure – properties relationships of cast & wrought Ni-based superalloys.

Solid Particle Erosion Performance and Damage Mechanism of AlTiN Coating

Aircraft, when operating in a sandy environment, can experience severe solid particle erosion damage to gas turbine engine components, such as compressor rotor blades, vanes, and impeller blisks/wheels, due to sand particle ingestion into the engine. Material removal from these components as the result of erosion not only leads to significant aerodynamic losses, but also results in their structural weakening. Applying erosion-resistant coatings on airfoil surfaces has been proven effective in extending the serviceable life of engine components. In this study, cathodic arc evaporated AlTiN was explored for its potential as an erosion-resistant coating for the compressor blades and helicopter impellers applications. AlTiN coating, along with baseline TiN coating, was subjected to gas jet sand erosion testing under different particle impingement angles and velocities. The erosion rates of the AlTiN coating were found to be much lower than those of the TiN coating in the entire range of the tested conditions. While the TiN coating mainly suffered from severe brittle erosion damage through coating chipping, the AlTiN coating exhibited only mild erosion damage through microcutting by sand particles. To include the aerodynamic effect on airfoil erosion in the consideration, dynamic wind tunnel sand erosion testing was also performed on AlTiN- and TiN-coated propeller blades. The results of these tests also confirmed superior erosion resistance of the AlTiN coating over that of the TiN coating.

Application of fused refractories in smelting of mineral melts in electric furnaces

In conditions of growing loads and temperatures on engineering products, the problem of choosing efficient materials is relevant, especially in the realities of import substitution. One of such tasks for modern materials science is the production of high-temperature products of special engineering, including complex shapes. Metal and ceramic materials have a number of unique properties, which, on the one hand, determine the prospects for their use in the construction of special engineering products, and on the other hand, cause a number of technological problems, without which the operation of such products is extremely difficult. An analysis of advanced materials used for products of special high-temperature engineering, including the production of various components of gas turbine engines, is presented, as well as the results of research on the development of materials with improved characteristics.

Modern мaterials and тheir аpplication in the design of high-temperature products of special engineering

In conditions of growing loads and temperatures on engineering products, the problem of choosing efficient materials is relevant, especially in the realities of import substitution. One of such tasks for modern materials science is the production of high-temperature products of special engineering, including complex shapes. Metal and ceramic materials have a number of unique properties, which, on the one hand, determine the prospects for their use in the construction of special engineering products, and on the other hand, cause a number of technological problems, without which the operation of such products is extremely difficult. An analysis of advanced materials used for products of special high-temperature engineering, including the production of various components of gas turbine engines, is presented, as well as the results of research on the development of materials with improved characteristics.

Tool for automatic macrozone characterization from EBSD data sets of titanium alloys.

Microtexture heterogeneities are commonly found in titanium forgings because of the thermomechanical processing. Also known as macrozones, these regions can reach millimetres in length, with grains sharing a similar crystallographic orientation leading to less resistance to crack propagation. Since the link between macrozones and the reduction of cold-dwell-fatigue performance on rotative components in gas turbine engines was established, efforts have been put into macrozone definition and characterization. The electron backscatter diffraction (EBSD) technique, widely used for texture analysis, allows for a qualitative macrozone characterization; however, further processing is required to define the boundaries and disorientation spread of each macrozone. Current approaches often use c-axis misorientation criteria, but this can sometimes lead to a large disorientation spread within a macrozone. This article describes the development and application of a computational tool implemented in MATLAB for automatic macrozone identification from EBSD data sets on the basis of a more conservative approach where both the c-axis tilting and rotation are considered. The tool allows for detection of macrozones according to the disorientation angle and density-fraction criteria. The clustering efficiency is validated by pole-figure plots, and the effects of the key parameters defining the macrozone clustering (disorientation and fraction) are discussed. In addition, this tool was successfully applied to both fully equiaxed and bimodal microstructures of titanium forgings.

다양한 작동 조건에서의 마이크로 터보젯 엔진 성능 예측을 위한 통합 해석 모델 구현 연구

In this study, an integrated CFD analysis implementation were conducted for the commercial micro turbojet engine, JetCat P300-RX, which has a maximum thrust of 300 N. A three-dimensional integrated analysis model includes major components of the micro gas turbine engine. A steady-state RANS (Reynolds Averaged Navier-Stokes) analysis was performed using ANSYS CFX V20.2. For the turbulence model and combustion model, the k-ω SST (Shear Stress Transport) model and the EDM (Eddy Dissipation Model) model were applied, respectively. The analysis were performed for various engine speed (RPM) conditions from 30,000 RPM to 106,000 RPM and various altitude conditions from sea level to 3.0 km. And the analysis results were verified by comparing with the actual engine test results. The comparison results showed that most of the performance parameters, such as thrust, exhaust gas temperature (EGT), air flow rate, and compression ratio in all analysis conditions (RPM and altitude) are in good agreement with the ground test results of commercial engines.

Design rules for the thermal and elastic properties of rare-earth disilicates

Rare-earth silicates are the current standard material for use as environmental barrier coatings for SiC-based ceramic matrix composites as hot-section components in gas-turbine engines. Expanding the design space to all available rare-earth elements to facilitate optimizing functionality requires an understanding of systematic trends in RE2Si2O7 properties. In this work, we combine first-principles calculations with experimental measurements of Young’s modulus, coefficient of thermal expansion, and thermal conductivity for a range of different RE2Si2O7 compositions and phases. Clear trends are observed in these properties as a function of the radius of the rare-earth cation. In the case of Young’s modulus and thermal expansion, these trends also hold for multi-component systems; while the thermal conductivity of multi-component systems is noticeably lower, indicating the potential of such materials to also act as thermal barriers. These results provide design rules for developing new thermal and environmental barrier coatings with stiffness and thermal expansion engineered to match that of the substrate, while simultaneously having reduced thermal conductivity.

Research Progress of Laser Additive Manufacturing Nickel-Based Alloy Metal Matrix Composites

Nickel-based alloy metal matrix composite (NAMMC) is a new type of composite material which is expected to replace traditional Nickel-base superalloy used in the manufacture of important hot-end components in aerospace, naval ships and industrial gas turbine engines due to its excellent high temperature strength, superior thermal fatigue resistance, high oxidation resistance and thermal corrosion resistance. However, these outstanding properties make it hard to process these materials with conventional manufacturing methods such as forging and machining owing to posing problems of high cost and energy consumptions. Laser additive manufacturing (AM) with a high degree of machining freedom and a high-energy-density laser beam as heat source has been used for processing NAMMC hot-end components with superior performance and complicated structure. Nevertheless, some manufacturing defects of poor bonding, high residual stress, cracking, pore etc. still exist in laser AM NAMMC parts. Therefore, this paper reviews research progress of laser AM NAMMC at present. The control method of manufacturing defect and the effect of reinforcements on the microstructure and mechanical properties of NAMMC are summarized. In addition, the challenges and prospects of laser AM NAMMC in the future are also discussed.

NUMERICAL ANALYSIS OF THE DURABILITY OF STRUCTURAL ELEMENTS UNDER THERMAL CYCLIC LOADING

The methodological aspects of assessing the service life of new equipment (elements of gas turbine engines), the operating modes of which lead to non-stationary thermomechanical loads, are considered. The associated thermoviscoplastic processes of deformation and damage states of the degradable continuum are modeled. A model of thermal fatigue in polycrystalline structural alloys for arbitrary complex deformation trajectories is described, consisting of relationships that determine cyclic thermoviscoplastic deformation; evolutionary equations for damage accumulation and strength criteria for damaged material. Kinetic equations take into account the effects of nonlinear damage accumulation, are based on the introduction of a scalar damage parameter, and are based on energy principles. The related formulation of the kinetic equations for damage accumulation under low-cycle fatigue and long-term strength describes the nonlinear nature of damage accumulation. The criterion for the strength of damaged material is the condition that the damage reaches a critical value. Using the developed original methodological, algorithmic and software that allows for end-to-end numerical modeling of thermal cyclic processes, the problem of assessing the thermal cyclic durability of models of elements and components of gas turbine engines during thermal pulsations has been solved. The results of an analysis of the influence of the angle of inclination of cooling channels in a model of combustion chamber pipes on the thermal cyclic durability are presented. The issues of the influence of complex thermal cyclic deformation, accumulation of fatigue damage, plastic deformations and creep deformations on the thermal fatigue of structural elements are considered. A comparative analysis of numerical results with experimental data was carried out. The efficiency of the model for describing the process of thermal fatigue of materials and structures under multiaxial disproportionate paths of thermal cyclic loading has been confirmed.

Risk-based maintenance optimization of aircraft gas turbine engine component

The integrity of an aircraft gas turbine engine is critical for safety of flight. Although the reliability of engines has improved considerably, a large number of legacy engines continue to operate. The maintenance of legacy engines is a major burden for their operators owing to the high cost involved, and the engines pose a high risk to flight safety. In this study, we developed a comprehensive approach for risk-based maintenance optimization of aircraft engine components. The approach involved the use of a physics-informed data-driven model incorporated with the Weibayes model and a simple fatigue crack growth model. The crack length distribution and corresponding risks were evaluated using Bayesian updating and knowledge of nondestructive inspection reliability. The model was used for the computation of the fatigue reliability of the first-stage blisk of a CT7-9C turboprop engine. A single failure was used for the Weibayes analysis, and a master crack growth curve was obtained through quantitative-fractography-based crack growth analysis. Furthermore, an inspection model based on the evaluation of field inspectors was used to obtain the posterior crack length distribution, and through a sensitivity analysis, important factors were identified. Finally, optimal inspection and replacement plans were formulated using approximated objective and constraint functions. In particular, the life-cycle cost was minimized while maintaining the risks within strict limits.

Investigation on bi-layer coating with La2(Ti0.2Zr0.2Sn0.2Ce0.2Hf0.2)2O7/YSZ prepared by laser cladding

Thermal barrier coatings are an effective technology for improving the high-temperature performance of hot section components in gas turbine engine. Due to their excellent properties, high-entropy oxides are considered to be promising materials for thermal barrier coatings. Laser cladding is a coating preparation technology and the top coat prepared by laser cladding technology has an important application value for thermal barrier coatings. In this work, to improve the thermal cycling behavior of the La2(Ti0.2Zr0.2Sn0.2Ce0.2Hf0.2)2O7 high-entropy oxide coating, a bi-layer coating with the La2(Ti0.2Zr0.2Sn0.2Ce0.2Hf0.2)2O7 high-entropy oxide layer and the YSZ layer was designed and fabricated by laser cladding on the NiCoCrAlY alloy surface. The microstructure, phase and mechanical properties of the coating were analyzed by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and micro-hardness and nanoindentation tests, respectively. The results show that a bi-layer La2(Ti0.2Zr0.2Sn0.2Ce0.2Hf0.2)2O7/YSZ coating was successfully prepared by the laser cladding method, and shows good bonding at the interface between the layers. The high-entropy oxide layer maintains a relatively stable defective fluorite structure and its microstructure exists in the stable cellular and dendrite crystalline state after laser cladding. The high-entropy oxide layer prepared by laser cladding showed an average elastic modulus of 167 GPa and an average hardness of 1022.8HV in nanoindentation tests. Thermal cycling of the coating was carried out at 1050 °C. Failure of the bi-layer coating occurred after 60 thermal cycles at 1050 °C. Thermal stresses between different layers are calculated during thermal cycling. Due to its excellent mechanical properties, the bi-layer coating with the La2(Ti0.2Zr0.2Sn0.2Ce0.2Hf0.2)2O7 high-entropy oxide and YSZ layers is expected to become an effective high-entropy oxide thermal barrier coating.

Quantifying the dynamic spreading of a molten sand droplet using multiphase mesoscopic simulations

Molten sand droplets deposited on gas turbine engine components cause severe damage. To better understand the deposition process, we study the wetting dynamics of a highly viscous molten sand droplet on a smooth substrate. A universal contact line spreading, independent of the droplet size, is observed with the characteristic inertial and viscous spreading regimes. It is also shown that the dynamic contact angle is in excellent agreement with Cox's theory.

Electrolytic-Plasma Jet Polishing of Additively Manufactured Gas Turbine Engine Components

Electrolytic-Plasma Jet Polishing of Additively Manufactured Gas Turbine Engine Components