Turbine Disk Research Articles

Effect of extrusion ratios on microstructure evolution and strengthening mechanisms of a novel P/M nickel-based superalloy

A novel P/M nickel-based superalloy is developed with an excellent combination of strength and ductility for use in turbine disks. This superalloy is prepared through hot isostatic pressing (HIP) and subsequent hot extrusion (HEX) with different extrusion ratios (λ). The effects of λ on the evolution and mechanism of γ′ precipitation behavior, grain refinement, microtexture, and mechanical properties are systematically studied. As λ increases, the primary γ′ phase fraction decreases from 17.22% to 8.47%, and the precipitation morphology changes from an irregular to a spherical shape. Increasing λ is beneficial to dynamic recrystallization. Fully recrystallized fine grains with a diameter of 4.47 μm are obtained at an optimal λ = 5.0, a decrease of 76% compared with the HIPed alloy. Abnormal grain coarsening was observed at a higher λ with 8.5 owing to the lack of γ′ pinning and a stronger driving force for grain boundary migration induced by deformation heat. The yield strength (YS) and ductility of the HEXed alloy are over 30% higher than those of the HIPed alloy, thanks to refined grains and the γ′ phase. The alloy extruded with λ of 5.0 exhibits a high YS of 1376 MPa with a ductility of 22.6% at room temperature and a YS of 1208 MPa with a ductility of 18.3% at 700 °C, which are better than those of other superalloys. A multi-mechanistic strengthening model is constructed by correlating the chemical composition, size and fraction of γ′, grain size, and YS. The calculations suggest that precipitation strengthening contributes more than 60% of the YS. Extrusion can dramatically enhance the YS of the superalloy owing to the increment of grain boundary strengthening and precipitation strengthening. This work provides a practical route and theoretical support for optimizing microstructure and enhancing the mechanical properties of a HIPed P/M nickel-based superalloy.

Yang transform–homotopy perturbation method for solving a non‐Newtonian viscoelastic fluid flow on the turbine disk

AbstractIn this paper, a new method is suggested and implemented to find an analytical approximate solution for a non‐Newtonian viscoelastic fluid flow on the turbine disk, used to cool the axisymmetric channel that has a porous wall. The new method depends on combining the algorithms of Yang transform and the homotopy perturbation method (HPM) named Yang transformation–homotopy perturbation method (YTHPM). To ensure the correctness of the method, we compared the results of YTHPM with the ones obtained by the numerical method (Runge–Kutta 4th order) and by other methods as reported in the literature; a good agreement was observed. Additionally, the effect of the power‐law index, Prandtl and Reynolds numbers on the velocity, and heat transfer was studied. The results that we obtained by using the new method confirm that this method has high accuracy and efficiency compared with other methods, used to find the analytical approximate solution for the current problem. Furthermore, the graphs and tables of error show the validity, utility, and necessity of this method.

ВИКОРИСТАННЯ АДИТИВНИХ ТЕХНОЛОГІЙ ДЛЯ ОТРИМАННЯ ЗАГОТІВОК ДИСКІВ ТУРБІН ТУРБОНАСОСНИХ АГРЕГАТІВ

This paper presents the results of research work, the main task of which was to assess the possibilities and prospects of using Direct Metal Laser Sintering - the technology of direct sintering of powder) DMLS for the manufacture of blanks for turbine turbine disk blades with blades (turbine rotor), as well as conducting analytical work to identify both advantages and disadvantages over other traditional methods.

Effect of surface integrity generated by machining on isothermal low cycle fatigue performance of Inconel 718

Critical aero-engine components such as turbine discs must withstand severe cyclic stresses, which can eventually lead to low cycle fatigue (LCF) failures. These components are made of difficult-to-cut alloys and machining conditions that are employed in the last stage of the manufacturing chain must be correctly defined to avoid the generation of an adverse surface condition (tensile residual stresses, excessive surface roughness or microstructural defects) that will accelerate fatigue failure. The analysis presented in this paper is aimed at understanding the isothermal LCF behaviour of turned Inconel 718 workpieces and finding quantitative correlations with the surface integrity. For this purpose, two Inconel 718 forged discs were face turned at cutting conditions employed in the aero-engine manufacturing industry using two different tools (1.2 mm and 4 mm nose radius respectively). The surface integrity produced by the face turning process was characterised in both discs: surface topography, residual stresses and surface layer anomalies. Specimens extracted from both discs were tested in load control at 450 °C to obtain LCF fatigue behaviour. Importantly, interrupted isothermal LCF fatigue tests were conducted and residual stresses were measured by the X-ray diffraction technique at the surface of the tested specimens to study the role of residual stresses in the LCF fatigue behaviour. For the tested conditions, the specimens machined with 4 mm nose radius showed 1.3–1.4 times longer fatigue lives than the specimens turned with 1.2 mm nose radius. These results are in agreement with the better surface integrity generated with the 4 mm nose radius, mainly because it induced lower tensile residual stresses. A novel local approach was implemented to understand the influence of surface integrity (surface roughness, surface residual stresses and altered stress-strain properties of the surface layer) on the isothermal LCF fatigue behaviour of both machined discs. Interestingly, a satisfactory correlation was found between the maximum applied stress in the surface layer and the isothermal LCF fatigue life employing the local approach.

Quantitative Analysis of Aeroengine Turbine Disk Surface Crack under Natural Magnetic Field

ABSTRACT Aiming at surface cracks of aeroengine turbine disk, a weak magnetic detection technology without excitation is proposed. Signal processing is performed using blind source separation (BSS). Support vector machine (SVM) is used to realize quantitative evaluation. Four nickel-base superalloy test blocks with defects are designed. The magnetic induction intensity of the test block is collected by a weak magnetic detection instrument. Then, the signal processing based on BSS is carried out. Finally, SVM is used to quantitatively analyze the weak magnetic signal before and after BSS. Results show that SVM estimation accuracy of defect length, width, and depth is 90%, 94%, and 71% after BSS, respectively. These findings are 14%, 8%, and 23% higher than the estimation accuracy prior to BSS.

Study on machining performance in grinding of Ni-base single crystal superalloy DD5

The Ni-base single crystal superalloy DD5 is commonly employed in critical parts of turbine blades and turbine disks in aeronautical engines. To improve the surface machining quality, single-factor experiments were carried out to investigate the changes of grinding force, surface morphology, and chip morphology under different grinding conditions (dry, conventional flood, minimum quantity lubrication). The experiments showed that the conventional flood lubrication and minimum quantity lubrication (MQL) could enormously reduce the surface roughness, grinding force, and work-hardened layer thickness of DD5. At the depth of 5 ~ 15 μm, the DD5 subsurface microhardness decreased sharply with the increase of depth, and the microhardness under different grinding conditions was in the order of dry grinding, conventional flood, and MQL. However, at the depth of 20 ~ 150 μm, the DD5 subsurface microhardness tended to equilibrate and fluctuate around 540 HV. In addition, compared with dry grinding, the degree of chip serration was obvious in flood or MQL environment, and its chip formation frequency fluctuated less and chip formation was stable. Within the experimental parameters, the MQL grinding machining method obtained the lowest surface roughness and the highest surface quality with the lowest associated cost, which is the ideal grinding and cooling lubrication method for the Ni-base single crystal superalloy.

Design of a gust generator and comparison of model wind turbine and porous disc wake flows in a transverse gust

This paper outlines the similarities and differences between the wake characteristics of a porous disc and model wind turbine under transverse gust loading which is generated via a two-vane wind tunnel gust generator. Phase-locked two-dimensional two-component (2D2C) particle image velocimetry (PIV) measurements show that the capability of a porous disc in representing a wind turbine increases under gust loading. Compared to the uniform inflow case, normalized streamwise velocity plots of the porous disc and model turbine are in a better agreement under gusty inflow condition particularly in the near wake region. Comparison of the wake centerlines reveals a similar wavy wake pattern with no significant phase lag suggesting that the gust dynamics is the dominant factor in the determination of the wake dynamics.

Broaching force prediction of nickel-based superalloy based on material parameter identification

The broaching process of the nickel-based superalloy determines the aero-engine turbine disc mortises performance; thus, the broaching force should be analyzed principally. The aim of the study is to reveal the material constitutive law for the nickel-based GH4169 alloy broaching force prediction. However, the GH4169 material constitutive model may just be verified by the hot compression tests at the limited high-temperature conditions. The residual stress-based finite element updating (FEU) inverse method was used to optimize the GH4169 material parameters. And the finite element (FE) model for the whole multi-stage processing of the turbine disc billet was simulated with high efficiency and accuracy, where the wide forming temperature range would be the critical factor for the consequent broaching analysis. The cutting conditions were tested to measure the residual stresses in the multi-stage formed GH4169 alloy disc billet by the layer removal method. The objective function (OF) designed with the experimental-numerical residual stresses were optimized successfully. The GH4169 alloy broaching force predicted with the identified thermo-mechanical material constitutive model in this study was satisfied with the validation test results, and the influence of cutting parameters on the broaching force distribution design could be effectively controlled, which could guarantee the high dimensional accuracy and the excellent reliability of the aero-engine turbine disc.

A data-driven roadmap for creep-fatigue reliability assessment and its implementation in low-pressure turbine disk at elevated temperatures

High-reliability life design process not only can ensure system safety in service, but also can provide scientific life management during the maintenance period. The objective of the present work is to develop a roadmap for creep-fatigue reliability assessment. Material-level data accumulations and theoretical foundations of creep-fatigue including creep-fatigue constitutive and multi-axial damage models are introduced. Afterwards, a low-pressure turbine disk under a typical creep-fatigue load waveform is applied as a case study to demonstrate how to perform creep-fatigue reliability assessment by using this roadmap in practice. Precise weakness hotspots are identified at the mortise joint of turbine disk. Based on hotspot-based strategy, it is found that the surrogate model assisted by an optimized machine learning method enhances significantly the computational efficiency. Accordingly, the probabilistic creep-fatigue life with considering multi-sources uncertainty obeys lognormal distributions. In the aspect of failure probability analysis, the current probabilistic damage interaction diagram method with creep-fatigue interaction gives conservative reliability assessments and excellent universality as compared to traditional ones mainly used in the low cycle fatigue field. Last but not least, joint failure evaluation of the turbine disk is discussed to comprehensively consider potential failure occurrence in an averaged hot region instead of a single hotspot.

Evaluation of oblique laser shock peening effect of FGH95 superalloy turbine disk material

There are many influence factors and characterization indexes for the processing effect of laser shock peening (LSP) on metal materials, and the influence mechanism is complex. The FGH95 superalloy used for turbine disk manufacturing was taken as the research object in this paper. Taking the laser energy, beam diameter and the number of impacts as test factors, the three-factor and the three-level orthogonal experiment was carried out by taking 4 J, 6 J, 8 J laser energy, 3 mm, 4 mm, 5 mm beam diameter, one, two and three times of impacts， respectively. The nine characterization indexes data were obtained by test instruments and equipment, such as residual stress, microhardness and surface roughness. The coalitional game method and gray relational improved TOPSIS method were used to establish an evaluation index system of oblique laser shock peening (OLSP) effect to explore the influence of laser processing parameters on material properties. The results show that the evaluation method and index system are highly feasible and can be used to evaluate and compare the strengthening effect of different processing samples efficiently, comprehensively and scientifically. When the laser energy is 8 J, the beam diameter is 3 mm and the number of impacts is 3, the gray correlation relative closeness degree is 0.7869, with the relatively best strengthening effect for the FGH95 superalloy. Under the index weight set in this paper, the comprehensive material properties of the FGH95 superalloy is improved by 3.72 times compared with the unimpacted sample. Based on the sample data evaluated, when the laser energy of 6 ~ 7.5 J, 2 or 3 impacts, the beam diameter of 4 ~ 5 mm, the comprehensive material properties of FGH95 superalloy after LSP are close to the comprehensive material properties obtained by the relatively optimal process parameters. Therefore, under the premise of ensuring the quality of strengthening, from the consideration of cost and timeliness, the process parameters with slightly lower laser energy and fewer impact times can be selected. The evaluation index system has essential reference significance for reducing the experimental workload, saving the experimental cost, and promoting and applying laser impact processing technology.

Fluorine Effect for Improving Oxidation Resistance of Ti-45Al-8.5Nb Alloy at 1000 °C.

In-depth analyses of the anti-oxidation behavior and structure of γ-TiAl alloys are of great significant for their maintenance and repair in engineering applications. In this work, fluorine-treated Ti-45Al-8.5Nb alloys and fluorine-treated oxidized specimens with artificial defects were prepared by isothermal oxidation treatment at 1000 °C. Several characterization methods, including SEM, EDS, XRD and TEM, were used to evaluate the surface microstructure of the fluorine-treated Ti-45Al-8.5Nb alloys and fluorine-treated oxidized specimens with artificial defects. The results indicate that the fluorine promoted the formation of an outer protective film of Al2O3, which significantly improved the oxidation resistance. The microcracks of oxidized specimens with the artificial defects provided a rapid diffusion passage for Ti and O elements during the 1000 °C/2 h isothermal oxidation treatment process, resulting in the quick growth of TiO2 toward the outside. The fine Al2O3 constituted a continuous film after the 1000 °C/100 h isothermal oxidation treatment. In particular, Al2O3 particles grew toward the substrate, which was ascribed to the good oxidation resistance and adhesion. These results may provide an approach for the repair of protective oxide film on the surface of blades and turbine disks based on γ-TiAl alloys.

Effects of Manufacturing-induced Operating-conditions Amplified Stresses on Fatigue-life Prediction of Micro Gas Turbine Blades – A Simulation-based Study

This study investigates the influence of residual stresses induced by the manufacturing process, on the fatigue life prediction of micro gas turbine blades manufactured by laser metal deposition additive manufacturing technique and heat-treated at different heat-treatment parameters. Finite element modelling, using commercial software Abaqus CAE ® and FE-Safe ®, was used to simulate the turbine blade and disk assembly’s operations and analyze induced stresses, as well as estimate the life cycle of the assembly. Results show internal stress build-ups, up to 400 MPa in magnitude can be induced in engineered components right from the point of additive manufacture, the effects of which can become amplified to as much as double that scale or more by the time the component is in operation. As much as between 75% to 300% fatigue life prediction error reduction can hence be attained by simply accounting for induced stress contribution of the process of its manufacture, rendering cost-saving condition-based monitoring and maintenance/overhaul decision making options.

Productivity Enhancement of Aircraft Turbine Disk Using a Two-Step Strategy Based on Tool-Path Planning and NC-Code Optimization

Most of the parts of an aircraft require the use of lightweight and high-strength materials. Since aircraft parts mainly use mechanical cutting processes, which are the most suitable material removal mechanism, to minimize changes in material properties, it is necessary to develop an optimal cutting tool and cutting solution for each material. This work aims to enhance productivity and reduce the production cost of an aircraft turbine disk through designing a cutting strategy and optimizing the cutting conditions using a simulation approach. The number of tools was reduced from eight to six compared to the existing process conditions for semi-finishing and finishing of a turbine disk, and a new tool path was proposed through simulation. The cycle time was reduced by about 24%. NC-code optimization was performed through feed-rate optimization considering cutting force and chip thickness. As a result, cycle times were reduced by about 14%. Through tool-path optimization and NC-code optimization, it was confirmed that the total cycle time was reduced by about 54%, and tool wear was significantly improved.

Shape optimization method for axisymmetric disks based on mesh deformation and smoothing approaches

Axisymmetric disk structures with complex contour curves are widely used in aero-engines. The shape optimization is generally carried out to reduce the stress level of axisymmetric disks. In this article, a shape optimization method for axisymmetric disks based on radial basis function (RBF) mesh deformation and Laplace smoothing approaches is proposed. This method can obtain the optimized reduced control points selection of mesh deformation under the influence of design space based on greedy algorithm. RBF mesh deformation is used to change the axisymmetric contour shape. And after deformation, the local mesh quality is monitored and improved by Laplace smoothing. In this article, two illustrative examples used in aero-engines are carried out to validate the effectiveness of the proposed method, including an independent optimization of a turbine disk and a collaborative optimization of a turbine disk with a deflector for minimizing the maximum equivalent stress. To improve the computational efficiency, a two-dimensional (2D) axisymmetric FE model is established. Compared with initial results, optimized results in two examples obtained by the proposed optimization method reduce the maximum von Mises stress by 8.02% and 9.25%, respectively. It can be concluded that the proposed method has significant potential in the shape optimization design of axisymmetric disks.

Oblique laser shock peening effect of the FGH95 superalloy with a PCA and comprehensive index

As a metal surface strengthening technology, oblique laser shock peening uses the force effect of pulsed laser beams to significantly improve the mechanical properties of materials and prolong service life. However, the processing of metal parts still requires a high cost for testing the quality of the finished product. At present, there is no systematic and complete measurement method or evaluation system for the finished products of oblique laser shock peening technology. In this paper, a principal component analysis method and a comprehensive index method are organically combined to construct a method for evaluating the effect of oblique laser shock peening of FGH95 superalloy turbine disks. We measured 10 real data of FGH95 superalloy specimens after oblique laser shock peening by using the orthogonal test method and verified the data. Based on the evaluation results, we put forward a series of suggestions to improve the quality of oblique laser shock peening of FGH95 high-temperature turbine disks, providing a certain reference and guidance for processing FGH95 superalloy turbine disks.

Tool wear monitoring of high-speed broaching process with carbide tools to reduce production errors

Real-time monitoring in CNC machine tools is focused on the early detection of tool wear, and in this way to assess part piece quality. The machining process known as broaching is critical for firtree slots (dovetails) production in turbomachinery components, such as turbine disks. Tight tolerances on one hand, even less than 5 µm in firtree-slots pressure faces, and high productivity on the other, are the two main requirements. Besides, broaching tools are very expensive and the cutting edges wear must be estimated during the process; in fact, tool wear in difficult-to-cut materials machining may cause a waste not only in terms of the tool but also of the very expensive workpieces. Broaching usually is one of the last operations in the process chain, so components start the operation with a very high-added value. Hence, only one bad slot implies an unrecoverable piece and therefore a huge waste of time and money.In this paper, a monitoring method for efficient broaching is proposed by combining real-time monitoring and off-line tool wear inspection. Firstly, the cutting tool characteristics are defined, and those affected by tool degradation. Secondly, some broaching cycles were carried out while measuring a) process accelerations through two accelerometers, b) cutting force by load cells, and c) motor drive consumption. They were simultaneously recorded. Furthermore, the sensitivity between tool wear and broaching process natural frequencies is established.Finally, a series of experimental tests were executed for verification, showing the useful approach for daily life production. The paper focuses on signals and their sensitivity to significant process variations.

Residual stresses in forged IN718 turbine discs

Abstract Residual stresses play an important role in the production of forged components like turbine discs. Variations in the processing parameters can lead to different residual stress states, which complicate subsequent processing steps, e. g. turning to the final shape. Therefore, a deeper understanding of the residual stress evolution during thermo-mechanical processing and the resulting distortions during machining is essential in order to optimize the manufacturing process with respect to cost efficiency and quality of the product. Consequently, the development of residual stresses in a forged turbine disc made of nickel-based superalloy IN718 was simulated using a finite element (FE) model. The experimental verification of the model was done by independently performed neutron strain scanning. For the studied forged and subsequently water-quenched disc the obtained residual stresses agree well with the stresses predicted by the used FE.

Calibration and validation of fatigue lifetime model in complex structures based on multi-level data

A method of model calibration and validation is established for structures with complicated structural features in the presence of multi-level experiments and censored data. Fatigue lifetime models are established comprised of three levels, where Bayes network was introduced to connect model predictions and experimental data. To avoid iterative calculation, calibration models in component-like and component levels are reconstructed explicitly. Normal distributions are applied to approximate the observed censored data, and the scatter area metric is proposed for model validation. A simulation example and the reliability analysis of the bolt hole in the turbine disc are applied to verify the proposed method.

900 °C oxidation resistance of Ni-base superalloys alloyed with different refractory elements

Refractory elements are added to strengthen the Ni-based superalloys for turbine disks, while the effects of these elements on the oxidation resistance remain to be investigated systematically to continually improve the working temperature. In this work, the effects of typical strengthening elements, including Ta, W, Mo, Hf and Nb, on the isothermal oxidation behavior of Ni-based superalloys at 900 °C were studied. The results indicated that increasing concentrations of Ta, W, and Mo enhanced the oxidation resistance, while adding 4 wt% Nb and 2 wt% Hf accelerated the oxidation rates in different degrees, which was explained in terms of diffusion and phase precipitation.

The high-cycle fatigue properties of selective laser melted Inconel 718 at room and elevated temperatures

Aero-engine turbine disk is always subjected to cyclic loading at room and elevated temperatures. Therefore, as one of the typical high-temperature materials, selective laser melted Inconel 718 superalloy was chosen to perform high-cycle fatigue tests at 25 °C, 450 °C and 650 °C and investigate the effect of temperature on fatigue damage mechanism. The locations of fatigue crack initiation are surface and subsurface defects at room temperature, and become subsurface and internal facets at elevated temperatures. An analyzed stress intensity factor and El-Haddad model were performed to assess the effect of defects on fatigue performance at room temperature. By means of electron back scattered diffraction, the fatigue damage mechanisms at elevated temperatures were elucidated. Based on the general relationship between fatigue and tensile strengths of metallic materials, an accurately quantitative relationship among fatigue strength and temperature was proposed.