Aircraft Engine Turbine Blades Research Articles

Fatigue notch strengthening effect of nickel-based single crystal superalloys under different stress ratios

Nickel-based single crystal superalloys (Ni-SXs) are widely used in turbine blades of aircraft engines. With the increasing demand for higher temperature-bearing capacity, the introduction of film cooling holes, impingement holes, and trailing edge slots for cooling induces stress concentration, which compromises the structural integrity of the blades, generates complex multiaxial stress states, and adversely affects their operational performance. In this study, Ni-SXs, DD6, was utilized to investigate the influence of stress ratios on fatigue performance under complex stress states. Low cycle fatigue (LCF) tests were carried out at different stress ratios with stress concentration coefficient Kt = 1.0, 2.0 and 3.0. The results indicate that the notched specimens exhibit a significant fatigue notch strengthening effect under high stress ratios. The fracture surface and microstructure also indicate that under high stress ratios loading, the notches exhibit significant creep failure characteristics. This means that the main cause of fatigue notch strengthening is similar to creep notch strengthening effect. A macroscopic anisotropic constitutive model coupled with damage was developed and applied to finite element analysis of notched specimens. The results demonstrate that as the stress ratio rises, the stress relaxation effect at the notch becomes more pronounced, yet the level of damage diminishes. Additionally, a stress-equivalent model based on Bridgman stress was proposed, which effectively unifies the lifetime trends of notched and smooth specimens, predicting lifetimes within a threefold error band.

Numerical simulation of the creep of a turbine blade made of a monocrystalline alloy

The article is devoted to the creep model of a monocrystalline alloy and the development of a methodology for identifying material parameters based on the results of physical experiments. A finite element analysis of the creep of a gas turbine engine blade was performed. Creep is one of the most dangerous types of deformation in the operating conditions of turbine blades. In the process of studying the problems of assessing the strength of turbine blades of aircraft engines and power plants, special attention should be paid to the study of stress redistribution during creep. The characteristics of the crystallographic structures of modern turbine blades have a very significant influence on the progress of the crack development process during engine operation. To date, turbine blades are manufactured by the method of single-crystal casting. This type of blade material structure is characterized by orthotropic mechanical properties. This study considers the steady-state creep model of an anisotropic heat-resistant single-crystal alloy with cubic symmetry. The authors carried out a numerical simulation of the material parameters using the well-known literary creep properties of single crystals. An algorithm is described that allows you to determine some creep characteristics of single crystals. The parameters of the given ratios can be obtained after conducting direct experiments, or based on micromechanical analysis, using the example of composite materials. The authors calculated the creep constants of a typical heat-resistant monocrystalline alloy as a result of the approximation of its creep curves, which were obtained experimentally. Based on the Norton-Bailey equation and using the Maple Release 2021.0 calculation complex, a graph of the dependence of the rate of creep deformation on the level of load applied to the material was plotted, and the minimum rate of deformation and creep constants were also determined. The results of the calculations were used for finite-element simulation of creep on the example of a solid-state model of a high-pressure turbine blade. Several series of calculations were carried out on the basis of the ANSYS Workbench complex, in particular, the calculation of the elastic problem when the blade is loaded by centrifugal forces, as well as the accumulation of creep deformations at different exposure times. Graphs of the change in equivalent stresses and creep deformations as a function of time are plotted.

Resource-efficient regeneration by generating a digital component image based on different NDT techniques

Manufacturing of components that are subjected to high stress levels during operation, such as aircraft engine turbine blades and battery calender rollers, is resource intensive and costly. These components are often designed not as a mono-material, but as a layered system. If operational stresses initiate crack-like defects or changes in the microstructure in the coating and/or base material, this can lead to premature component failure. To prevent this, the component’s condition is assessed during maintenance by inspections. Based on the data obtained, a decision is made whether the component can remain in operation, must be replaced or needs to be repaired. This decision is based on safety, economic and environmental considerations. In order to repair or regenerate such capital goods in a targeted and resource-efficient manner, a differentiated assessment of surface defects and material changes in the coating as well as in the base material is required. This can be achieved by an intelligent combination of different non-destructive testing techniques. In this paper, the differentiated assessment of the condition of the individual layers and the base material is presented using the example of a high-pressure turbine blade. The test results of the non-destructive testing techniques used are combined in a digital image of the component from which suitable repair measures can be derived. The transfer of the findings from the turbine blade to the layered system of a calender roller is also discussed.

Simultaneous improving high temperature oxidation resistance and room temperature toughness of Nb[sbnd]Si based alloy via appropriate Ta content addition strategy

NbSi based alloys are expected to become the application materials for high pressure turbine blades of aircraft engines. This paper investigates the impact of Ta addition on room temperature fracture toughness and isothermal oxidation behavior at 1250 °C of four NbSi based alloys with compositions of Nb-16Si-20Ti-8Zr-4Hf-1.5Al-xTa (x = 0, 1, 2, and 4 at.%) fabricated through vacuum non-consumable arc-melting. The results show that the room temperature fracture toughness and 1250 °C oxidation resistance of the alloys increase first and then decrease with the addition of Ta element. The room temperature fracture toughness of 1Ta alloy is the best, reaching 17.1 MPa·m1/2. Adding a moderate amount of Ta (1 at.%) significantly enhances the alloy's oxidation resistance, but an excessive Ta content diminishes this enhancement. This research has obtained a Nb-16Si-20Ti-8Zr-4Hf-1.5Al-1Ta alloy with high room temperature fracture toughness and excellent high temperature oxidation resistance simultaneously, which provide an ideal path for designing NbSi alloys with superior comprehensive properties.

Investigation of coatings with in-situ TiX reinforcements fabricated by additive-subtractive manufacturing: Hardness, microstructure and machinability

Wear resistance is essential for the long lifespan of critical components such as turbine blades in aircraft engines. Coatings reinforced by hard particles provide a highly effective means to enhance the anti-friction characteristics of these vital parts. Additive manufacturing presents a promising alternative for the fabrication of particle reinforced coatings. Nonetheless, it remains crucial to employ finishing processes on additively-manufactured parts to meet stringent quality and dimensional precision requirements before assembly. In this study, new findings on the additive-subtractive manufacturing of the coatings reinforced by in-situ TiC, TiB and TiB2 was comprehensively analyzed. The coupled influence of the fraction of WC and the laser power on the quality and properties of the coatings were explored, and the machinability of the coatings were evaluated via the finish milling. It was found that the fraction of WC was dominant on the morphology, phases, hardness, and microstructure of the laser-clad coatings; the difference in the properties of the coatings caused variance on the cutting force, surface quality and work hardening of the machined surface.

Effect of Gd doping on phase evolution, mechanical and thermal characteristics of 1La-xGd-2Yb-3.5YSZ solid solutions

Thermal barrier coatings (TBCs) are critical for the reliability and lifespan of aircraft engine turbine blades. In this study, a novel quaternary rare-earth oxide (La2O3, Gd2O3, Yb2O3, and Y2O3) co-doped ZrO2 solid solution, referred to as 1La-xGd-2Yb-3.5YSZ, was synthesized by varying the doping amount of Gd2O3 from 0 to 6 mol. %. The impact of co-doping-induced lattice distortion on the phase composition, high-temperature phase stability, sintering resistance, and mechanical and thermal properties of the solid solution has been explored. It is found that the addition of Gd2O3 stabilizer effectively increased the lattice distortion of the solid solution, which led to improved phase stability and sintering resistance, enhanced mechanical properties, and low thermal conductivity. Our findings highlight the promising properties of the 1La-xGd-2Yb-3.5YSZ solid solution, making it an attractive candidate for TBC materials.

Effects of the Seal Wire on the Nonlinear Dynamics of the Aircraft Engine Turbine Blades

Abstract Complicated systems made of multiple components are known to be difficult to model, considering their solutions can change dramatically even with the slightest variations in conditions. Aircraft engines contain such complicated systems, and some components in aircraft engines' turbines can cause significant changes in the system's overall response. Hence, this study is focused on investigating the behavior of a turbine blade of an aircraft engine and the effects of the contact between the blade and the seal wire on the dynamics of the blade-disk system. The investigation is performed via various numerical simulations in time and frequency domains. One sector of the bladed disk is modeled using the finite element method with the lock plate and the seal wire imposing cyclic symmetry boundary conditions in the static, modal, and frequency domain forced response analyses. In time domain analyses, the cyclic symmetry is replaced with simplified displacement restricting boundary conditions. The time domain analysis contains steady-state forced responses of the system. The results show that contact with the seal wire is not a major source of nonlinearity and damping. The contacts with the lock plate contribute more to the vibration damping than the seal wire. However, compared to the contacts at the root of the blade, both components remain less significant with regard to frictional damping and nonlinearity.

Методика оцінки залежності власних частот коливань лопаток газових турбін від анізотропії монокристалу

The subject of study of this article is one of the key tasks that arises during the development and operation of aviation gas turbine engines, namely ensuring the strength of their parts. The turbine blade is one of the most heavily loaded parts of an aircraft engine. Therefore, at the stage of designing these blades, it is necessary to be able to identify and avoid possible resonance modes that appear during the flight cycle of an aircraft gas turbine engine. Such resonant oscillations of gas turbine blades can occur due to time-varying gas-dynamic forces from the action of the gas flow and are periodic in nature, as they are determined by the frequency of rotation of the rotor. In order to regulate the frequency characteristics of the blades to prevent dangerous resonant forms of oscillations that arise under the action of various harmonics of the exciting force during variable modes of operation of the aircraft engine, it is necessary to carry out a complex of various technological or structural changes. At the current stage, turbine blades of aircraft engines are manufactured by the method of single-crystal casting. As is known, single crystals have anisotropic properties, namely they manifest themselves as materials with the characteristics of cubic symmetry. A very urgent task is to investigate the effect of the anisotropy of the elastic characteristics of monocrystalline blades on their natural frequencies and forms of oscillations. In this research, the authors developed a method for determining the elastic characteristics of a single crystal, namely Young's modulus of elasticity, Poisson's ratio and pure shear modulus, which is based on available experimental data for typical heat-resistant alloys. With the help of finite element analysis on the example of a typical model of a cooled blade of a gas turbine, its modal analysis was carried out and its resonance diagram was constructed. The trend of changing the natural frequencies and forms of blade oscillations when the elastic constants of the single crystal change due to the rotation of the crystallographic system of directions was also investigated. The three-dimensional model of the blade was built using the capabilities of the NX graphics complex, all calculations were performed in the Maple computing complex, and the capabilities of the ANSYS software complex were used for finite element analysis.

The creep behaviors of single crystal Ni-based superalloys with slant film cooling holes

The film cooling holes system is an indispensable structure for advanced turbine blades of aircraft engines. The film cooling holes with different slant angles have a significant impact on the service life of the blade. In the work, the effects of film cooling holes with different slant angles on creep rapture behaviors of single crystal Ni-based superalloys were systematically studied by experimental and numerical methods. The creep tests of the samples with different slant film cooling holes were carried out under 260 MPa and 980 °C. The experimental results showed that the creep fracture life first decreases and then increases with the increased slant angle of the film cooling holes. Furthermore, the creep fracture mode, path and mechanism also change significantly, which was related to the difference of stress distribution caused by distinct slant angles of film cooling hole. Based on the stress distribution characteristics obtained by finite element method, the crystal plasticity theory and “skeletal point” method were used to predict the creep life of the flat samples with film cooling holes at different slant angles. The predicted life were in good agreement with the test results.

Review on Creep Phenomenon and Its Model in Aircraft Engines

The aircraft is subjected to high-temperature and high-pressure conditions during flight, which renders it susceptible to the occurrence of creep phenomenon. Several academics have conducted extensive research on this issue. This research paper provides a comprehensive overview of the existing literature on creep phenomena in aircraft engines. First, several classical creep calculation models are enumerated and categorized as creep life calculation, creep-fatigue life calculation, and creep deformation calculation. Studies on creep phenomena are conducted in various components of aircraft engines, such as the engine’s turbine blades, turbine disks, and combustion chambers. The creep behavior of turbine blades in aircraft engines has been extensively researched. Furthermore, the protective measures aimed at mitigating creep are presented. Materials with high creep resistance can be used, and alternative fuels could be implemented. This paper provides an in-depth analysis of the advantages of creep in aircraft, presented in a favorable perspective. Finally, the prospective future research direction is discussed.

Deformation mechanisms of low cycle fatigue of a fourth generation Ni-based single crystal superalloy

Ni-based single-crystal superalloys are extensively employed in turbine blades for aircraft and industrial gas engines. The blades are subjected to complex thermal and stress impacts during service, which may cause sudden low-cycle fatigue damage and subsequent flight accidents. To investigate the relationship between the microstructure and mechanical properties, fatigue-damaged microstructures are compared under cyclic deformation at 800 and 900 °C using combined electron microscope characterizations. With an increase in temperature, the deformation is more concentrated in the γ matrix channels and the cyclic deformation behaviors stabilizes, whereas cutting the γ′ phase becomes difficult with decreasing slip bands. In addition, the significance of interfacial dislocation networks in enhancing cyclic stability and hindering cyclic tension–compression asymmetry is discussed.

Infrared Thermal Imaging-Based Turbine Blade Crack Classification Using Deep Learning

Non-destructive testing is widely applied for the detection and identification of defects in turbine blades of modern aircraft engines. Cracks in turbine blades can affect the turbine performance and pose a risk to safety and service life. For Original Equipment Manufacturers it is, therefore, essential to be able to identify all defects. Heat flow thermography offers, compared to the often used penetrant testing, the potential to improve the detection of defects in turbine blades and is contact-free, reproducible, quick to apply, and can be automated. With induction (heat flow) thermography, it is even possible to detect cracks that lie below the surface and therefore are not externally visible. However, manual inspection of thermography images is very time-consuming. By automating the image classification procedure with a deep learning technique, the speed and accuracy of the classification can be improved over a manually performed classification. The development objective of this AI application is expected to support and assist the highly skilled and experienced inspection specialists in the medium term. Our solution is based on convolutional neural networks. Several challenges of the AI training process, including data imbalance, a small dataset, and extremely small cracks in large images are addressed.

Методика визначення характеристик сталої повзучості монокристалічного сплаву

The subject of this article is the phenomenon of material destruction during creep, as one of the most dangerous and damaging effects on turbine blades in the conditions of their operation. Considering the strength of the turbine blades of aircraft engines and power plants, note that the mechanism of cracks in the creep process is largely due to the peculiarities of the crystal structures of the blades and the properties of these structures. At this stage of development of world technologies, turbine blades are made by single crystal casting and directional solidification. These types of crystal structures are characterized by the anisotropy of their properties. The reason for the anisotropy of crystals is that the ordered arrangement of atoms, molecules, or ions in the interaction between them and the interatomic distances (as well as some unrelated direct relations, such as polarization or electrical conductivity) differ in different directions. The article pays special attention to the consideration of the creep model of an anisotropic alloy with a monocrystalline structure. The natural way to determine the material parameters of the theoretical material model is to conduct the required number of basic experiments. Numerical modeling using the known creep properties of single crystals is an alternative possibility to determine the parameters of the material. The algorithm described in this article allows us to determine all the average creep properties of a single crystal. The parameters of the described ratios can be obtained either because of direct experiments, or on the basis of micromechanical analysis, as in the case of composite materials. This article considers an example of obtaining some characteristics of the single-crystal alloy ZhS-32 because of the approximation of its creep curves, obtained experimentally. Based on Norton-Bailey's law and using the modern calculation system Maple Release 2021.0, the minimum creep deformation rate and creep constants are determined, and a graph of the creep deformation rate dependence on the material load level is plotted.

Heat Transfer Performance Optimization of Rectangular Channel with Truncated-root Ribs

Cooling designs inside the gas turbine blades of aircraft engines are aimed to solve a problem that has existed since the very beginning of the aerospace industry. Since the working environment of turbine blades is extremely harsh when the temperature can rise to 2000K, which is considered a huge challenge for any materials. Therefore, cooling designs such as rib turbulators have always been researched and optimized for better heat transfer enhancement in the cooling mechanism of turbine blades. In this study, a geometric optimization of the rib turbulators inside a rectangular channel was performed with the aim to maximize heat transfer performance. This study investigated the effect of four rib configurations on the heat transfer efficiency of the channel, which include square, truncated-root, convergent truncated-root, and divergent truncated-root rib. Thereby, a module of coupling Python and OpenFOAM was developed to automatically perform the optimization of truncated-root rib design at Reynolds number of 37,000 with design variables are the upstream and downstream height with Powell optimization method. The aim is to figure out the point where the maximum heat transfer performance of the channel is achieved. The study presented in a specific, productive, and accurate way the factors that directly and indirectly affect the heat transfer performance of the channel, thereby giving the optimal results that the channel has the highest heat transfer performance of the presented designs. The results show that the highest heat transfer performance of the optimized design is 12.45% higher than the standard square ribs case.

COMPUTATIONAL STUDIES OF AEROELASTICITY OF AIRCRAFT ENGINE TURBINE BLADE

Transient blade loading limits the lifetime of aircraft engine turbine blades. Thus, accurate prediction of the unsteady aerodynamic loading and coupled fluid-structure interactions would improve the life the lifetime of the turbine blades. This study investigates the flutter instability of an axial turbine blade under unsteady aerodynamic loading. The viscous Navier-Stokes equations with the SST-kω turbulence model are employed. The results show that the flutter phenomenon causes unsteady oscillations of the aerodynamic coefficients lift and drag.

Picosecond laser trimming of ceramic cores with porous multi-scale particle microstructure

The ceramic core, produced by hot injection molding, is one of the critical components for manufacturing high-performance aircraft engine turbine blades. However, the injection molding process will cause defects such as burrs and flashes in the fine structure of the formed ceramic core. Manual trimming is necessary, but the trimming quality is poor, and the yield is low. In this paper, the online trimming method of ceramic cores is studied. Based on the orthogonal experiment method, the optimal laser parameters for processing the ceramic core's porous multi-scale particle structure material were obtained. Further, the problems of the match head and tail phenomenon and dimensional accuracy improvement in trimming ceramic cores have been studied. A path optimisation method is proposed to improve the quality and accuracy of the trimming profile effectively. Finally, the overall process flow of ceramic core trimming is elaborated, and experimental verification is given. The results show that the ceramic core online trimming method proposed in this paper has advantages of high precision and high yield compared with the manual method, which will have substantial potential application value in the aviation field.

The Morphology and Solute Segregation of Dendrite Growth in Ti-4.5% Al Alloy: A Phase-Field Study

Ti-Al alloys have excellent high-temperature performance and are often used in the manufacture of high-pressure compressors and low-pressure turbine blades for military aircraft engines. However, solute segregation is easy to occur in the solidification process of Ti-Al alloys, which will affect their properties. In this study, we used the quantitative phase-field model developed by Karma to study the equiaxed dendrite growth of Ti-4.5% Al alloy. The effects of supersaturation, undercooling and thermal disturbance on the dendrite morphology and solute segregation were studied. The results showed that the increase of supersaturation and undercooling will promote the growth of secondary dendrite arms and aggravate the solute segregation. When the undercooling is large, the solute in the root of the primary dendrite arms is seriously enriched, and when the supersaturation is large, the time for the dendrite tips to reach a steady-state will be shortened. The thermal disturbance mainly affects the morphology and distribution of the secondary dendrite arms but has almost no effect on the steady-state of the primary dendrite tips. This is helpful to understand the cause of solute segregation in Ti-Al alloy theoretically.

Effect of Overheating Temperature on Thermal Cycling Creep Properties of K465 Superalloy

Turbine blades in aircraft engines may encounter overheating and suffer serious creep property degradation. In this study, the thermal cycling creep experiments were conducted on K465 superalloy under (900 °C/30 min–1100 °C/3 min)/50 MPa, (900 °C/30 min–1150 °C/3 min)/50 MPa and (1000 °C/30 min–1150 °C/3 min)/50 MPa. The investigated thermal cycling creep properties were dramatically degraded, and increasing the overheating temperatures significantly decreased the thermal cycling creep life. The secondary γ′ precipitates obviously dissolved and the area fraction decreased to around 35.2% under (900 °C/30 min–1150 °C/3 min)/50 MPa and (1000 °C/30 min–1150 °C/3 min)/50 MPa, which was almost half that after the standard solution treatment. The decline of the thermal cycling creep properties was mainly due to the significant dissolution of γ′ precipitates. The creep holes/cracks were mainly distributed at the M6C carbides and γ/γ′ eutectics interfaces, M6C carbides and γ′ film interfaces in the grain boundaries, and resulted in the final intergranular fracture.

Fractal Nature of Advanced Ni-Based Superalloys Solidified on Board the International Space Station

Materials science is highly significant in space program investigation, energy production and others. Therefore, designing, improving and predicting advanced material properties is a crucial necessity. The high temperature creep and corrosion resistance of Ni-based superalloys makes them important materials for turbine blades in aircraft engines and land-based power plants. The investment casting process of turbine blades is costly and time consuming, which makes process simulations a necessity. These simulations require fundamental models for the microstructure formation. In this paper, we present advanced analytical techniques in describing the microstructures obtained experimentally and analyzed on different sample’s cross-sectional images. The samples have been processed on board the International Space Station using the MSL-EML device based on electromagnetic levitation principles. We applied several aspects of fractal analysis and obtained important results regarding fractals and Hausdorff dimensions related to the surface and structural characteristics of CMSX-10 samples. Using scanning electron microscopy (SEM), Zeiss LEO 1550, we analyzed the microstructure of samples solidified in space and successfully performed the fractal reconstruction of the sample’s morphology. We extended the fractal analysis on the microscopic images based on samples solidified on earth and established new frontiers on the advanced structures prediction.

High temperature creep behavior of a cast polycrystalline nickel-based superalloy K465 under thermal cycling conditions

Turbine blades in aircraft engines may suffer serious microstructural degradation and even failure due to sharp overheating during service. In this study, a microwave heating creep testing rig was designed and developed to conduct the high temperature thermal cycling creep experiments, to reveal the overheating effect on the creep behavior of a conventionally cast Ni-based superalloy K465. The thermal cycling creep experiments were conducted under (900 ℃/30 min–1100 ℃/3 min)/70 MPa, combined with the comparative isothermal creep references under 900 ℃/70 MPa and 1100 ℃/70 MPa. The thermal cycling creep exhibited unique characteristics namely short creep life, high creep strain rate and high fracture strain. During the thermal cycling creep, secondary γ′ precipitates dissolved rapidly at higher creep temperature, while recovered partially at lower creep temperature. The obvious microstructural degradation of secondary γ′ precipitates was primarily responsible for the short life of the thermal cycling creep. When secondary γ′ precipitates recovered and coarsened, early shearing of the γ′ phase by entrapped interfacial dislocations occurred, especially at the concave locations of the secondary γ′ precipitates. The evolution of dislocations was mainly responsible for the high minimum creep strain rate of the thermal cycling creep. The creep voids/cracks initiated quickly and located at the interface of M6C carbides and γ/γ′ eutectic pools in the interdendritic regions and grain boundaries during the thermal cycling creep, and finally caused the intergranular fracture.