Turbine Disk Research Articles

Gradient microstructure evolution under thermo-mechanical coupling effects for a nickel-based powder metallurgy superalloy－Dynamic recrystallization coexist with static recrystallization

In order to withstand special working conditions, it is of great significance to manufacture turbine disks with a gradient microstructure (disk core with fine and uniform grains and disk edge with coarse grains) along the radial direction. A new and effective forming way-gradient hot deformation is proposed, and a gradient structure from the edge to the center can be obtained. In the present work, the gradient deformation behavior, dynamic recrystallization kinetics, and microstructural evolution of a nickel-based powder metallurgy superalloy are studied by thermal gradient compression. Dynamic recrystallization kinetics of this superalloy is established. Recrystallization fraction increases from 72.6 %–93.6 % because of the gradient deformation degree. Microstructure changes significantly from the center to the edge along the radial direction, and average grain size ranges from 6.65 μm to 15.62 μm. There is a big difference between experimental value and calculated data of recrystallization fraction, which indicates that dynamic and static recrystallization take place in different areas simultaneously. Static recrystallization can coexist with dynamic recrystallization in the trapezoid sample by gradient hot deformation. The difference between experimental and calculated results is the static recrystallization, and the maximum values of static recrystallization fraction is around 30 %. A great number of dynamic recrystallization grains distribute along pre-existing grain boundary, second phases and twin crystal. The main means of static recrystallization nucleation is the bulge of original grain boundaries.

An application of active learning Kriging for the failure probability and sensitivity functions of turbine disk with imprecise probability distributions

For the reliability analysis with imprecise probability distributions, the failure probability and its sensitivity are always denoted as the functions of distribution parameters. The computation of those functional relationships remains a challenging task due to the intensive computational burden. To further improve the computational efficiency, this work proposes a new computational method based on the classical active learning Kriging model with U learning function. The Kriging model is constructed with a group of initial point and updated by the best contributing samples selected from different sample spaces corresponding to discrete distribution parameters, which guarantees the prediction ability in the variation range of distribution parameters. Consequently, the functions of failure probability and sensitivity can be estimated by the same Kriging model, which avoids re-constructing Kriging models corresponding to different distribution parameters. Several examples including two numerical examples and three engineering practices are investigated to validate the reasonability and superiority of the proposed method. Finally, the proposed method is applied to the fatigue life reliability and sensitivity analyses of a turbine disk structure.

Tool wear mechanisms in laser-assisted milling of Nickel-based superalloys

Nickel-based superalloys are widely used in the manufacturing of aero-engine turbine disks, compressor disk, and other essential parts. The processing mechanisms result in low machinability due to the combined properties of high-temperature hardness, mechanical strength, and wear resistance. Laser-assisted machining (LAM) is a hybrid method to machine difficult-to-cut materials with the advantage of high machining efficiency, low tool wear, and high machining quality. In order to maintain the constant preheating temperature, the infrared temperature measurement point is set as a feedback value, and the laser energy is controlled by the system to ensure the milling zone preheating temperature maintaining a stable value. Laser-assisted milling (LAML) and conventional milling experiments are conducted on Inconel 718 using TiAlN coated carbide tools. Tool wear mechanisms are analyzed to investigate the influence of machining parameters on tool wear. The main results indicate that tool wear mechanisms in LAML are similar to the conventional milling, and adhesion wear is found to be the primary phenomenon leading to the milling tool wear. Tool life is longer in LAML due to the soften material and decreasing impact action on the milling tool. Besides, PVD and CVD coated carbide milling tools are used in LAML, and the experimental results show that CVD coated tool is better at the higher temperature, and it is more suitable for LAML of Inconel 718. At last, orthogonal experiments for the tool life are conducted using CVD coated tools, and the influence factors and estimation method of tool life are presented.

Influence of γ’ precipitate on deformation and fracture during creep in PM nickel-based superalloy

FGH96 is a powder metallurgy nickel based superally used for turbine disk of aero-engines. In the present study FGH96 alloy with four different γ′ precipitate microstructures were produced via solution heat-treatment with different cooling rates, and the maximum cooling rate reached 400 ​°C/min which was a super cooling rate for Nickel-based superalloy. The creep tests were conducted for PM FGH96 alloy under the testing condition of 704 ​°C and 690 ​MPa. The relationship between the creep properties and the distribution of γ’ precipitate was established. The creep mechanism was analyzed by using TEM and ACTEM, and the dislocation movement was studied at the atomic scale. The creep strain rate was calculated through a physically based crystal slip model established based on crystal plasticity. The calculated results were consistent with the test ones, illustrating the validity of the model. The fracture mechanism was also investigated, and the results showed that the creep cracks generated on the surface due to the oxidation. It was observed that the cracks propagated in different ways depending on the different average diameters of ​γ′ ​precipitate. With the decrease of the average ​γ’ ​precipitate size, the critical shearing stress increased and the resistance of the dislocation slipping increased. The fracture mechanism for the primary stage transformed from intragranular to intergranular due to the change of dislocation slipping.

Evolution of geometrically necessary dislocation at the γ-γ′ interface and its effect on tensile deformation behaviour of disk super alloy

Abstract The evolution of geometrically necessary dislocation density (GND) at the γ and primary γ′ interface during tensile deformation of turbine disk alloy was studied. Extensive electron microscopy analysis (i.e. EBSD and TEM) was carried out to explore the structure and GND evolution at the γ-γ′ interfaces. It is found that GND value is highest for tensile test specimens at 800 °C, whereas the lowest for tensile specimen tested at 350 °C, and this is attributed to γ/γ′ misfit (δ) value. At high-temperature tensile deformation (i.e. at 720 and 800 °C) specimen starts necking just after the yield point, compared to RT, 350 and 650 °C tensile tested specimens. It is evidenced from GND values and grain interior distortion that localized plastic deformation in γ-matrix near to γ-γ′ interfaces is the primary reason for necking just after yielding of material. Higher GND values and grain interior distortion are caused by the greater value of δ at high test temperature due to difference in thermal expansion between γ and γ′.

The Accuracy of Finishing WEDM of Inconel 718 Turbine Disc Fir Tree Slots.

Servicing aircraft engines sometimes requires manufacturing only a single piece of a given part. Manufacturing a turbine disc using traditional methods is uneconomical. It is necessary to use a different machining method recommended for small lot production. One of the proposed methods is WEDM (wire electrical discharge machining). The article presents the results of the research on finishing WEDM of Inconel 718 turbine disc fir tree slots. The influence of infeed, mean gap voltage, peak current, pulse off-time, and discharge energy on the shape accuracy, surface roughness, microcracks, and the white layer thickness were determined. Mathematical models were developed based on the DoE (Design of Experiment) analysis. The statistical significance of the models was verified with the ANOVA (Analysis of Variance) test. The machining parameters control methods that allow achieving the required shape accuracy, surface roughness, and surface layer condition were presented. The obtained surface roughness was Ra = 0.84 μm, the shape accuracy of the slot in the normal-to-feed direction was Δd = 0.009 μm, the profile shape accuracy was Δr = 0.033 μm, and the thickness of recast (white) layer was approximately 5 μm.

Conditioning of Leakage Flows in Gas Turbine Rotor–Stator Cavities

Abstract Ingress is the penetration of hot mainstream fluid into the cavity formed between the turbine disk (rotor) and its adjacent casing (stator). Gas turbine engine designers use rim-seals fitted at the periphery of the disks, and a superposed sealant flow—typically fed through the bore of the stator—is used to reduce, or in the limit prevent, ingress. Parasitic leakage enters the cavity through pathways created between mating interfaces of engine components. Owing to the aggressive thermal and centrifugal loading experienced during the turbine operating cycle, the degree of leakage and its effect on ingress are difficult to predict. This paper considers the potential for leakage flows to be conditioned in order to minimize their parasitic effect on disk cooling, and ultimately engine, performance. Measurements of static and total pressure, swirl, and species concentration were used to assess the performance of a simple axial clearance rim-seal over a range of nondimensional leakage flow rates. A computational model was used to provide flow visualization to support the interpretation of flow structures derived from the experiments. Data are presented to investigate the effects of swirling the leakage flow in accordance with, and counter to, the disk rotation. The injected momentum from the leakage created a toroidal vortex in the outer part of the cavity. Coswirl was found to improve the sealing effectiveness by up to 15% compared to the axially introduced baseline and counterswirled configurations. Varying the momentum of the leakage flow was considered by passing consistent mass-flows through a range of leakage outlet areas. Increasing the momentum was seen to increase the influence of the toroidal vortex on the flow structure in the cavity, which in turn influenced the sealing effectiveness.

Contact stress analysis and fatigue life prediction of turbine disc–blade attachment with fir‐tree tenon structure

AbstractFir‐tree tenon structure, as a commonly used scheme in the connection of turbine blades and discs, plays a critical role in the reliability and integrity of aeroengine turbines. This work mainly deals with the contact and fatigue analyses of a turbine disc–blade attachment with fir‐tree tenon structure. Firstly, based on Hertz contact theory, a three‐dimensional (3D) model of surface‐to‐surface contact is established, and contact stress analysis is performed based on finite element (FE) simulations. The simulated contact stress distribution agrees well with the Hertz contact theory. Particularly, the rounding processing does not relieve the stress concentration. Then, contact stress analysis on the fir‐tree tenon structure is performed, and a stress gradient‐based model is utilized for fatigue life evaluation together with contact stress analysis. Results show that the proposed solution yields acceptable predictions compared with field estimations.

Model characterization and mechanical property analysis of bimetallic functionally graded turbine discs

In advanced propulsive systems, a turbine disc bears vast mechanical and thermal loads under its working conditions of high-temperature gradients and high rotational velocity.The complex working conditions of aero-engine turbine discs place stringent performance requirements on the materials used. With dual organizations and superior composite performances, bimetallic functionally graded turbine discs have become a focus in the research of high thrust-to-weight ratio aero-engines. To study the mechanical properties of new bimetallic functionally graded materials under service conditions, we propose a volumetric fraction expression and adjustable composition distribution parameters that are suitable for simulating the composition distribution of bimetallic functionally graded turbine discs. On this basis, a characterization model for functionally graded materials based on the analysis of the internal thermodynamic properties of bimetallic turbine discs is established. The thermodynamic properties and fatigue performances of functionally graded materials under service conditions are analysed. Mechanical property simulations of functionally graded turbine discs are performed using different composition distribution parameters, and reasonable ranges are determined for the various composition distribution parameters. The results show that bimetallic functionally graded turbine discs are suitable for high-stress-gradient and high-temperature-gradient environments with lower weights than those of current GH4169 alloy turbine discs.

Vibration Characteristics and Simulation Verification of the Dual‐Rotor System for Aeroengines with Rub‐Impact Coupling Faults

To study the rub‐impact fault between the dynamic and static parts of the rotor system of aeroengines, the dual‐rotor system of a typical aeroengine is introduced and taken as the research object. The analytical kinetic model is established based on the Lagrange equation considering the structural characteristics of the dual‐rotor system, the coupling effect of the intermediate bearing, and the rub‐impact fault between the high‐pressure turbine disc and the casing. The dynamic characteristics of the dual‐rotor system under the rub‐impact fault are analyzed, and the change rule of the rub‐impact shape is obtained. The vibration coupling and transfer among the high‐pressure rotor and the low‐pressure rotor are revealed. The influence of the unbalanced position and the speed of high and low rotors on the vibration response of the dual rotor is obtained. The sensitivity of the vibration response of the dual rotor at different test points to rub‐impact stiffness, clearance, and friction coefficient is compared. The simulation model is established based on the rigid‐flexible coupling multibody dynamic simulation platform. The analytical results and simulation results are compared, which have a good consistency. The theoretical research can deepen the understanding of the nature and law of aeroengine rotor operation, expose the possible faults and design defects, greatly improve the development efficiency and quality, reduce repeated physical tests, reduce the development risk and cost, and accelerate the development process. This study can provide a theoretical basis for the monitoring and diagnosis of engine rub‐impact faults and provide theoretical and practical reference for the establishment of the vibration fault test and analysis method system.

Modelling the Geometrical Accuracy for Different Part Geometries and Process Parameters when Broaching Fir-Tree Slots in Turbine Disks

Constructive measures in the design of aircraft engines aiming for CO2 and NOx emission reduction result in miniaturization of the components, e.g. the rotating turbine disks. The resulting filigree structures determine a reduction of the resistance against elastic workpiece deformations during the machining process. This leads to increasing demands on the cutting process to maintain the required form and position tolerances. In turbine disks, fir-tree slots as the fixing for the turbine blades are classified as safety-critical components. Currently, the profiled slots are manufactured by broaching. In order to guarantee the required component quality of the resulting fir-tree structure, it is necessary to examine the tool design systematically. By using FE simulations, it is possible to predict geometrical deviations after broaching and to perform counter measurements in tool design.In this paper, an innovative approach is presented, which combines an empirical-analytical cutting force model and numerical FE simulations to model the elastic deformations during the cutting process. Therefore, empirical cutting force information are used as input data for the dynamic FE simulations. The results are then analyzed regarding the achievable form and position tolerances when broaching profile grooves. This paper presents a parameter study on workpiece and process parameters and an evaluation of their impact regarding the geometrical accuracy in broaching.

An efficient global reliability analysis method for turbine disc’s multi-failure modes considering importance distribution technology

This paper presents an improved efficient global reliability analysis (EGRA) method for a turbine disc considering the importance distribution of multi-failure modes, such as low cycle fatigue (LCF) and creep-fatigue (CF). Failure mode effects and criticality analysis (FMECA) technology is firstly used to analyse the criticality and occurrence probability of each failure mode. Importance factor S is then proposed to quantify the importance of the corresponding failure mode. In order to improve the reliability analysis’s efficiency, expected feasibility function (EFF) criterion in sequential sampling method is selected through numerical experiments to generate the samples of random variables. Secondly, EGRA method is established by combining sampling method with Kriging model, in which the performance function is fitted using the key sampling points near both the failure boundaries and high uncertainty region. On the basis of EFF criterion, the composite EFF criterion applied to EGRA method is developed. This method avoids repeated analysis on non-significant failure modes, which further improves the reliability analysis’s efficiency for the multi-failure modes system. Through a binary nonlinear example, it is proved that the prediction accuracy is 99.8% compared with Monte Carlo method. Moreover, the computational time of reliability is reduced by half compared with EFF criterion, which proves the prediction efficiency of composite EFF criterion. Finally, the reliability analysis on a turbine disc is conducted using the improved EGRA method combining with the failure mode importance distribution technology. Results show that the fatigue life at 99.9% reliability is decreased by 7.4% after considering the importance of failure modes, indicating that the ignoration of failure modes’ importance would lead to a more dangerous prediction result.

Effect of anisotropy on creep of rotating functionally graded disc with varying thickness

Creep study of rotating functionally graded (FGM) disc reinforced with non-linear SiC p with varying thickness has been analyzed using Hills yield criterion. The disc comprises of matrix of pure aluminium embedded with silicon carbide particles (SiC p ). The analysis of stresses and strains as a result of disc rotation have been calculated. Stresses and strain rates are significantly affected by varying reinforcement gradient in the disc. The FGM disc having varying thickness along the radius shows lowest strain rates for anisotropy constant G/F and H/F less than 1 which further reduces with increase in particle gradient. Thus, better design of turbine discs can be obtained by selecting appropriate material anisotropy and optimum disc profile.

Detection of Cracks in Aerospace Turbine Disks Using an Ultrasonic Phased Array C-scan Device

Crack detection in an aerospace turbine disk is essential for aircraft- quality detection. With the unique circular stepped structure and superalloy material properties of aerospace turbine disk, it is difficult for the tradi... | Find, read and cite all the research you need on Tech Science Press

Justification of Geometry and Loading Conditions of the Imitation Model of the GTE Turbine Disc

Justification of Geometry and Loading Conditions of the Imitation Model of the GTE Turbine Disc

Reliability analysis and optimization of turbocharger turbine of marine low speed diesel engine under complex load

In this paper, aiming at the reliability analysis and optimization of jth series marine low-speed diesel engine supercharger of Chongqing JIANGZENG Shipbuilding Heavy Industry Co., Ltd., a response surface mathematical model is constructed by using 62 groups of dispersive simulation analysis data to verify the accuracy and effectiveness of the mathematical model. Based on this, Monte Carlo sampling is carried out to obtain the reliability of turbine disk is 0.943, and the reliability of turbine blade is 0.96 Reliability optimization space. Based on NSGA-II multi-objective genetic algorithm, the reliability of turbine disk and turbine blade is optimized by taking the stress value and machining cost of turbine disk and turbine blade as the objective function. The reliability of turbine disk and turbine blade is 1, the stress value of turbine blade is optimized by 4.7941%, the stress value of turbine disk is optimized by 3.0136%, the machining cost of turbine blade is optimized by 15.5087%, and the machining cost of turbine disk is optimized by 3.9907%. Finally, the results of genetic algorithm and simulation analysis are compared, the difference is less than 5%, which shows that the data based on NSGA-II multi-objective genetic algorithm has practical application reference value.

Improved Whale Optimization Algorithm and Turbine Disk Structure Optimization

Improved Whale Optimization Algorithm and Turbine Disk Structure Optimization

Efficient Calibration of a Turbine Disc Heat Transfer Model Under Uncertainty

This paper presents a novel surrogate modeling approach that enables the application of Bayesian calibration to a gas turbine disc finite element (FE) heat transfer model. The surrogate modeling process begins with two transformations of the FE model predictions: first, principal components analysis “rotates” the multivariate FE model outputs into an uncorrelated and dimension-reduced subspace; second, active subspace (AS) reveals a linear combination of model parameters that form a simple mapping to individual principal components (PCs). These transformed input–output (i.e., active parameter to PC) relationships are found to enable standard polynomial regression fits to form the PC–AS surrogate model. The measured temperatures are also transformed into the model’s PC-space during calibration. The Bayesian calibration approach helps to address the inherent model-form uncertainties (e.g., approximations of complex boundary airflows), measurement uncertainties, and the ill-posed nature of inverse problems. The estimated uncertainties are instructive for use of the model predictions in postcalibration activities, for example, in determining model quality for use in turbine disc lifing analysis.

Initiation and Propagation Characteristics of Multi-Source Fatigue Crack in Superalloy Disk

The multi-source fatigue crack growth characteristics of a turbine disk were studied via high-speed rotating low cycle fatigue test, fracture analysis and crack growth simulation analysis. The results show that the fatigue initiation life N0 of Superalloy disk and its simulation parts is less dispersive and similar, and the S-N0 curve of the material is not conservative to predict the N0 of the disk. The fracture of eccentric hole of disk is multi-source fatigue fracture, and the surface characteristic of the crack L/D decreases rapidly from 7.5 to 2, which is obviously different from the single source fatigue crack growth. Because of the long and thin stress distribution at the eccentric hole and the small dispersivity of GH698 crack initiation life, it's relatively easy to crack on the plane A of the eccentric hole, which is prone to multi-source fatigue. At the stage of a ≥ 1.23 mm, the reverse life of crack propagation fracture of 2# and 5# eccentric holes is consistent, and the error between the simulation value of single source fatigue crack propagation life and the reverse life is below 5%. In the stage of 0.61 mm ≤ a < 1.23 mm, the simulation crack growth rate of 5# eccentric hole of multi-source is close to that of fracture inversion. Accurate simulation analysis of multi-source crack growth needs to define the initial crack accurately, at the same time, consider the influence of existing fatigue damage on crack growth.

Integrated TEM/transmission-EBSD for recrystallization analysis in nickel-based disc superalloy

Turbine discs in gas-turbine engines always experience high-temperature and high-stress environment. Extensive investigations have been performed towards achieving high performance. Deformation behaviors and degradation factors above normal service temperature are important to be comprehensively understood for further development and optimization of turbine disc superalloys. In this study, the low cycle fatigue behaviors were investigated under total strain amplitude control in U720Li disc superalloys. The results revealed that with the increasing strain, the number of dislocation increased and dislocation configuration transferred from pile-up at the matrix/γ′ precipitates interfaces to penetrating into γ′ precipitates. The great extent of recrystallization was found above the normal service temperature through transmission-EBSD combined with TEM analysis. The low cycle fatigue property above the normal service temperature was weakened to a large extent after recrystallization of small-angle grains formed by the dislocation substructures and movements. Large extent of local recrystallization could also provide much more sites for the crack initiation and propagation.