Aero-engine Turbine Blade Research Articles

Dynamics of a Turbine Blade with an Under-Platform Damper Considering the Bladed Disc’s Rotation

High-cycle fatigue (HCF) failure of the turbine blades of aero-engines caused by high vibrational stresses is one of the main causes of aero-engine incidents [...]

Research on the relationship between early surface deformation and microstructure evolution of Ni-based single crystal alloy

During the early service phase of Ni-based single crystal alloy (NSCA), the degree of its surface deformation is closely related to the service life. It is important to quantitatively characterize the surface deformation of NSCA from the microscopic scale. However, the studies on the quantitative relationship between the degree of surface deformation and the microstructure evolution of NSCA have not been found yet. Thus, we establish the theoretical relationship between the microstructure evolution of NSCA and its early surface deformation through nonlinear expression methods. The MD method is used to calculate the dislocation density change of NSCA in different crystal orientations, by which the variation of the characteristic parameter and the damage degree of NSCA are predicted. Moreover, the results of the MD simulation are consistent with the variation of nonlinear characteristic parameter obtained in the experiment, which further confirms the correctness of the theoretical relationship. This research will offer a theoretical basis for the predictive maintenance of aero-engine turbine blades.

Design optimization of aero-engine turbine blade and disc fixing

Design optimization of aero-engine turbine blade and disc fixing

Tool electrode wear compensation in block divided EDM process for improving accuracy of diffuser shaped film cooling holes

Diffuser shaped film cooling holes are increasingly being applied in the turbine blades of advanced aeroengines. It is a difficult problem to machine this kind of cooling holes due to their complicated shape and superalloy material. Currently, die-sinking electrical discharge machining (EDM) is regarded as an available process for machining the diffuser holes. However, the change of tool electrode shape caused by the electrode wear and difficult renew of dielectric fluid affect the processing precision. The worn tool electrode has to be replaced with a fresh one after machining one or several holes. The replacing procedure is time consuming to break the machining process. In the previous work, a novel block divided EDM process was proposed to efficiently machine the diffuser holes, but the machining accuracy needs to be further improved. In this research, the block divided EDM process firstly is analyzed and simulated in detail to know the key factor affecting the machined accuracy. Furthermore, a self-repair method and a profile error compensation method of the tool electrode wear are proposed for improving the processing accuracy. The self-repair method is to plan and control the rotation motion of the tool electrode for maintaining its shape. The profile error compensation method is to modify the Z coordinate of the tool electrode for decreasing the machining error. Machining experiments verified that the proposed methods can meet the accuracy requirements of the film cooling holes with diffusion angle error < 0.1° and average profile error < 10 μm.

Cracking, Microstructure and Tribological Properties of Laser Formed and Remelted K417G Ni-Based Superalloy

The K417G Ni-based superalloy is widely used in aeroengine turbine blades for its excellent properties. However, the turbine blade root with fir tree geometry experiences early failure frequently, because of the wear problems occurring in the working process. Laser forming repairing (LFR) is a promising technique to repair these damaged blades. Unfortunately, the laser formed Ni-based superalloys with high content of (Al + Ti) have a high cracking sensitivity. In this paper, the crack characterization of the laser forming repaired (LFRed) K417G—the microstructure, microhardness, and tribological properties of the coating before and after laser remelting—is presented. The results show that the microstructure of as-deposited K417G consists of γ phase, γ′ precipitated phase, γ + γ′ eutectic, and carbide. Cracking mechanisms including solidification cracking, liquation cracking, and ductility dip cracking are proposed based on the composition of K417G and processing characteristics to explain the cracking behavior of the K417G superalloy during LFR. After laser remelting, the microstructure of the coating was refined, and the microhardness and tribological properties was improved. Laser remelting can decrease the size of the cracks in the LFRed K417G, but not the number of cracks. Therefore, laser remelting can be applied as an effective method for strengthening coatings and as an auxiliary method for controlling cracking.

Viscoplastic analysis method of an aeroengine turbine blade subjected to transient thermo-mechanical loading

Viscoplastic analysis method of a turbine blade manufactured with directionally solidified (DS) superalloy under transient thermo-mechanical loading was investigated in depth. The second deviatoric stress tensor invariant was modified by a fourth-order tensor to simulate the anisotropic behavior of the DS superalloy. In order to capture the monotonic and cyclic behaviors of the alloy under non-isothermal conditions, temperature interpolation of a set of material parameters and the modification of internal state variables were performed. The model was implemented as a user subroutine (UMAT) in Abaqus for complex structure analysis. With the improved Chaboche constitutive model, the tensile and cyclic responses of the DS material GTD-111 under isothermal and non-isothermal conditions were carefully modeled and predicted with high accuracy. Finally, the model was implemented to simulate the transient thermo-mechanical behavior of a hollow turbine blade with a typical flight profile. The location-dependent thermo-mechanical fatigue response of the blade were determined and analyzed.

The effect of atmospheric plasma spray distance of the agglomerated maerogel coated on Inconel 625 substrate

ABSTRACTNano-structured silica aerogel, which is also known as maerogel, was synthesised from rice husk ash (RHA) by a Universiti Teknologi Malaysia (UTM) research team. This super lightweight solid (powder) material with low thermal conductivity was agglomerated into micro-size particles for use as a coating material. Sprayable maerogel coating has high potential for use in various thermal insulating applications such as in aeroengine turbine blade. The maerogel was coated on Inconel 625 via the atmospheric plasma spray (APS) method. Since the APS can deposit a wide range of coating powders and particle sizes with high deposition temperature, it has become a more suitable coating technique for maerogel coating. The coating spray distance of the APS was varied to study its effect on the maerogel coating in terms of microstructure, coating thickness, adhesion strength and thermal conductivity. The coating spray distance of 10 cm was the best spray distance, a parameter by which a homogenous microstructure with adequate coating thickness, adhesion strength and thermal conductivity was obtained.

The Fracture Analysis of Turbine Rotor Blade

Failure of aeroengine Turbine Blade in Wing seriously threatens Flight Safety, We used the emergence and development of blade cracks to discuss the causes of blade fracture. The results show that due to intergranular oxidation, alloy dilution, and thermal stress, fatigue crack spreads through the blade and results in blade fatigue fracture. During blade usage and maintenance, We avoid over usage and overheating of the engine to decrease time of maximum capacity usage.

Physics of failure-based reliability prediction of turbine blades using multi-source information fusion

Fatigue and fracture of turbine blades are fatal to aero engines. Reliability prediction of aero engines is indispensable to guarantee their safety. For turbine blades of aero engines, most recent research works only focus on the number of cycles and excavate information from a single source. To remove these limitations, a Physics of failure-based reliability prediction method using multi-source information fusion has been developed in this paper to predict the reliability of turbine blades of aero engines. In the proposed method, the fuzzy theory is employed to represent uncertainties involved in prediction. Case studies of reliability prediction under fuzzy stress with and without fuzzy strength are conducted by using a dynamic stress-strength interference model which takes types of cycles of aero engines into consideration. Results indicate that the proposed method is better in line with engineering practice and more flexible in decision making and it can predict the reliability of aero engine turbine blades to be an interval by utilizing the proposed linear fusion algorithm. In addition, the predicted interval contains results that are predicted by other commonly used information fusion methods Hence, the proposed method conduces to remove confusion made by selection of multiple methods.

An Electromagnetic/Capacitive Composite Sensor for Testing of Thermal Barrier Coatings.

Thermal barrier coatings (TBCs) can significantly reduce the operating temperature of the aeroengine turbine blade substrate, and their testing technology is very urgently demanded. Due to their complex multi-layer structure, it is hard to evaluate TBCs with a single function sensor. In this paper, an electromagnetic/capacitive composite sensor is proposed for the testing of thermal barrier coatings. The dielectric material is tested with planar capacitor, and the metallic material is tested with electromagnetic coils. Then, the comprehensive test and evaluation of thermal barrier coating system can be realized. The sensor is optimized by means of theoretical and simulation analysis, and the interaction between the planar capacitor and the electromagnetic coil is studied. The experimental system is built based on an impedance analyser and multiplex unit to evaluate the performance of the composite sensor. The transimpedances and capacitances are measured under different coating parameters, such as thickness and permittivity of top coating as well as bond layer conductivity. The experimental results agree with the simulation analysis, and the feasibility of the sensor is proved.

Nonlinear air-coupled thermosonics for fatigue micro-damage detection and localisation

Over the years, traditional active infrared thermography has played a pivotal role in ensuring that a component is free of any damage. However, whilst optical thermography is still not sufficiently sensitive to the presence of material micro-flaws, current vibro-thermography requires inspection solutions that are not always feasible, such as the use of coupling materials between the sensing probe and the monitored structure. This paper presents a valid alternative to current thermographic systems by developing and experimentally validating nonlinear air-coupled thermosonics for a contactless, rapid and accurate detection of fatigue micro-cracks in an aero-engine turbine blade. The proposed thermographic method combines the high sensitivity to micro-damage of nonlinear ultrasonic techniques with non-contact air-coupled ultrasonic transducers and thermographic equipment. Narrowband frequency sweeps were performed to identify local damage resonance frequencies in order to generate large vibrational amplitudes at the damage location and compensate for signal losses caused by the high acoustic impedance mismatch between the air and the sample. An infrared camera was then used to acquire the thermal response generated by frictional heat at the crack interfaces. Moreover, an image processing method based on a combination of morphological opening and a Savitzky-Golay smoothing filter was employed to enhance the quality of thermal images affected by anisotropic heating and thermal noise effects. Nonlinear air-coupled thermosonics experiments were validated with laser Doppler vibrometry scan measurements and compared with both flash and pulsed phase thermography. Thermal imaging results showed that the proposed nonlinear air-coupled thermosonics was the only thermographic technique able to detect fatigue micro-cracks, thus demonstrating its potential as an efficient and sensitive inspection tool for micro-damage detection in geometrically complex components.

Comparative Analysis of Flow Field in Mixed and Non Mixed Gas Electrochemical Machining for Aero-Engine Turbine Blade Cooling Holes

By the cooling holes in aero-engine turbine blade as the research object, this study focuses on two kinds of ECM methods, which are mix gas added to the nonlinear electrolyte (NaNO3) and non-mixed gas. Mixed and non-mixed gas ECM experiments of turbine blade cooling holes were carried out respectively. The corresponding two-dimensional CAD model of cooling hole was constructed combined with the experimental data and theoretical analysis. Numerical simulation analysis was carried out of the flow field base on the above models by using the fluid dynamics analysis software FLUENT. The influence flow velocity and flow velocity distribution on the machining accuracy and efficiency of ECM were investigated in detail. The vortex zone distribution of gas-NaNO3 mixed phase flow field and single NaNO3 solution flow field was analyzed qualitatively. The simulation results indicated that the flow velocity in the machining gap with mixed gas was significantly higher than the velocity during ECM process for cooling holes. The electrolytic products and heat were washed away completely, the electrolyte can be updated in time. Fluid vortex zone distribution was improved obviously, the flow field distribution became more uniform after mixed gas in ECM process. The machining accuracy and efficiency for cooling holes making may be improved greatly with gas mixed in electrolyte NaNO3.

Free vibration analysis of a pre-twisted sandwich blade with thermal barrier coatings layers

A rotating cantilever sandwich-plate model with a pre-twisted and pre-set angle has been developed to investigate the vibrational behavior of an aero-engine turbine blade with thermal barrier coating (TBC) layers. The classic von Karman plate theory and the first-order shear deformation theory are applied to derive the energy equations of the rotating TBC blade, in which the geometric shapes, the work ambient temperature, and the TBC material properties are considered. The Chebyshev-Ritz method is used to obtain the nature frequency of the rotating TBC blade. For static frequency and modal analysis, the finite-element method (FEM) is also applied to compare and validate the results from the Chebyshev-Ritz method. A good agreement is found among these kinds of methods. For dynamic frequency, the results are analyzed in detail concerning the influence of system parameters such as the thickness of the TBC layer, the working temperature, and the pre-twisted and pre-set angle. Finally, the Campbell diagram is demonstrated to analyze the resonance property of the cantilever sandwich TBC blade model.

Advanced Intermetallic TiAl Alloys

Challenging issues concerning energy efficiency and environmental politics require novel approaches to materials design. A recent example with regard to structural materials is the emergence of lightweight intermetallic TiAl alloys. Their excellent high-temperature mechanical properties, low density, and high stiffness constitute a profile perfectly suitable for their application as advanced aero-engine turbine blades or as turbocharger turbine wheels in next-generation automotive engines. Advanced so-called 3rd generation TiAl alloys, such as the TNM alloy described in this paper, are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments.

Phase Field Simulation of the Lamellar Microstructure Formation in TiAl Alloys

The details of the lamellar microstructure in TiAl intermetallic alloys, such as the lath thickness and interfaces type governs the strength, ductility, creep properties and the long term microstructure stability of the alloy. The lamellar microstructure coarsening may induce property degradation of materials when the working temperature is high especially for the aero-engine turbine blades. At the same time, the reliability of the structure will decreases dramatically during long term working. In order to customize highly stable microstructure in high temperature, the phenomenon of lamellar formation during the solid-solid α→α2+γ phase transformation in fully lamellar TiAl alloys was investigated by phase field simulations. The lamellar structure morphology obtained with simulation is coincides with the experimental results. It is found that the independent nuclei and twin-related nuclei co-exist in the nucleation stage for the random noise nucleation. During growth stage, the independent nuclei grow slowly or disappear for the interfacial energy and elastic energy minimization. While most twin-related nuclei survived. During the following coarsening stage, big nuclei swallow small nuclei for interfacial energy minimization. The statistical character of twin area fraction changes complicated during these processes and it will be analyzed in detail. These findings could shed light on the understanding of the lamellar formation and coarsening mechanisms during phase transformation in TiAl alloys.

MICROSTRUCTURE EVOLUTION AND INTERFACIAL FORMATION MECHANISM OF WIDE GAP BRAZING OF DD5 SINGLE CRYSTAL SUPERALLOY

Ni-based single-crystal superalloy DD5 has excellent high temperature properties, which is the preferred raw material for aero-engine turbine blade in recent year. In this research, DD5 superalloy was brazed by different contents of Ni-Co-Cr-W-B+DD99 mixed powder filler alloy. The microstructure evolution and interfacial formation mechanism of DD5 superalloy brazing joint were analyzed by SEM and EPMA. The mechanical properties of joint after solid solution treatment and aging treatment were tested. The results show that g-Ni primary phase formed firstly in the Ni-Co-Cr-W-B/DD99 interface during the brazing process, and then B element segregated and precipitated to fine granular M3B2 type boride. The residual liquid phase solidified and formed lastly to the M3B2 phase, g+g′ eutectic phase and g-Ni+Ni3B+CrB eutectic phase during cooling. With increasing the ratio of DD99 in mixed powder filler alloy, the low melting point eutectic phase and borides in the joint decrease and the uniformity of composition and microstructure of joint improve. When the ratio of DD99 increased to 70% (mass fraction) in the mixed powder filler alloy, it can be observed that element of B diffused to DD99 additive powder which result*国家自然科学基金项目51401210和51331005以及国家高技术研究发展计划项目2014AA041701资助 收到初稿日期: 2015-12-03,收到修改稿日期: 2016-04-17 作者简介:孙元,女, 1980年生,副研究员 DOI: 10.11900/0412.1961.2015.00622 第875-882页 pp.875-882

In Situ Characterization Techniques Based on Synchrotron Radiation and Neutrons Applied for the Development of an Engineering Intermetallic Titanium Aluminide Alloy

Challenging issues concerning energy efficiency and environmental politics require novel approaches to materials design. A recent example with regard to structural materials is the emergence of lightweight intermetallic TiAl alloys. Their excellent high-temperature mechanical properties, low density and high stiffness constitute a profile perfectly suitable for their application as advanced aero-engine turbine blades or as turbocharger turbine wheels in next-generation automotive engines. As the properties of TiAl alloys during processing as well as during service are dependent on the phases occurring, detailed knowledge of their volume fractions and distribution within the microstructure is of paramount importance. Furthermore, the behavior of the individual phases during hot deformation and subsequent heat treatments is of interest to define reliable and cost-effective industrial production processes. In situ high-energy X-ray diffraction methods allow tracing the evolution of phase fractions over a large temperature range. Neutron diffraction unveils information on order-disorder transformations in TiAl alloys. Small-angle scattering experiments offer insights into the materials’ precipitation behavior. This review attempts to shine a light on selected in situ diffraction and scattering techniques and the ways in which they promoted the development of an advanced engineering TiAl alloy.

Reliability-based low-cycle fatigue damage analysis for turbine blade with thermo-structural interaction

To improve the computational accuracy and efficiency of complex mechanical component like engine turbine structure, distributed collaborative response surface method is applied to the reliability analysis of aeroengine turbine blade low-cycle fatigue damage. The improved Manson–Coffin formulas with different confidence levels are established based on the linear variance regression analysis in the application of the fatigue data of nickel-based superalloy GH4133. The distributed response surfaces of strain range Δεt and mean stress σm are established by considering the randomness of the design sizes, working loads and material parameters. And then Δεt and σm are regarded as the basic input variables of fatigue life Nf to complete turbine blade low-cycle fatigue damage reliability analysis by the Miner cumulative damage theory. The probabilistic sensitivity analyses demonstrate that the fatigue performance parameters hold important influence on the low-cycle fatigue life of turbine blade. Through the comparison of methods, it is revealed that distributed collaborative response surface method is superior to response surface method in computational precision and efficiency, especially for low confidence level. The efforts give the conclusion that distributed collaborative response surface method is a promising approach in ameliorating the computational precision and efficiency of reliability analysis, which enriches the reliability theory and method of complex mechanical structure with multi-component and multi-failure mode.

Ultra-High Cycle Fatigue Behavior of DZ125 Superalloy Used in Turbine Blades

The high temperature ultra-high cycle fatigue (UHCF) behaviors of DZ125 superalloy used in aero-engine turbine blades were systematically studied. The results show that the fatigue fracture still occurs above 108 at the frequency of 20kHz, R=-1 and 700°C. There is a negligible frequency effect for the DZ125 superalloy, therefore, it is proposed that the ultrasonic fatigue testing could be expected as an accelerated fatigue testing method. Fatigue cracks originate from the subsurface of the specimens, where have no metallurgy defects or “fish eye” character. The crystal orientation change of the alloy is very little after fatigue.The maximum value changed for the elastic modulus of the alloy is about 30GPa after fatigue compared with that before fatigue.

Machining of a film-cooling hole in a single-crystal superalloy by high-speed electrochemical discharge drilling

Single-crystal superalloys are typical advanced materials used for manufacturing aeroengine turbine blades. Their unique characteristics of high hardness and strength make them exceedingly difficult to machine. However, a key structure of a turbine blade, the film-cooling hole, needs to be machined in a single-crystal superalloy; such machining is challenging, especially considering the increasing levels of machining efficiency and quality demanded by the aeroengine industry. Tube electrode high-speed electrochemical discharge drilling (TSECDD), a hybrid technique of high-speed electrical discharge drilling and electrochemical machining, provides high machining efficiency and accuracy, as well as eliminating the recast layer. In this study, TSECDD is used to machine a film-cooling hole in a nickel-based single-crystal superalloy (DD6). The Taguchi methods of experiment are used to optimise the machining parameters. Experimental results show that TSECDD can effectively drill the film-cooling hole; the optimum parameters that give the best performance are as follows: pulse duration: 12μs, pulse interval: 30μs, peak current: 6A, and salt solution conductivity: 3mS/cm. Finally, a hole is machined by TSECDD, and the results are compared with those obtained by electrical discharge machining. TSECDD is found to be promising for improving the surface quality and eliminating the recast layer.