Gas Turbine Engine Blades Research Articles

Combined coating for turbine blades of high-temperature gas turbine engines

A combined coating for protecting turbine blades of high-temperature gas turbine engines is studied. Comparative tests of coatings under laboratory conditions and of coated blades in engine operation are performed. The microstructure of the coating is studied and the concentration profiles of alloying elements are determined by the method of x-ray diffraction analysis. Tests for high-temperature strength are performed.

Specific features of rhenium-alloyed single-crystal nickel superalloys

Experimental data are presented on the effect of introduction of up to 12 wt % Re on the structure and properties of ZhS-type complexly alloyed casting nickel superalloys intended for the blades of modern aviation gas-turbine engines. Rhenium alloying is found to increase the temperature of onset of melting of the alloys and the temperature of complete dissolution of a hardening γ′-Ni3Al-based phase in a nickel-based γ solid solution. Moreover, rhenium hinders diffusion processes. Rhenium is shown to harden a nickel-based solid solution more effectively than Hf, Ta, Nb, W, or Mo. As compared to the other refractory metals, rhenium more effectively increases the long-term strength of the ZhS-type alloys at 1000°C. In addition, it increases their operating temperature to 1150°C.

Thermal barrier coatings for enhanced efficiency of gas turbine engines

In the current paper, an attempt has been made to address the benefit as well as importance of optimisation of thermal barrier coatings system for super alloys after evaluating different thicknesses of ceramic thermal barrier coatings. The thickness of coatings plays a major role in deciding the life of coatings as lower thickness does not provide complete protection and higher thickness causes to reduce the coating life due to adherence problems. Therefore, determination of optimum thickness to obtain improved performance is highly essential. An optimum thickness of thermal barrier coatings has been determined successfully by conducting hot corrosion studies on various thicknesses. The optimised protective coating system enhances the life of super alloy by about six hundred times. The optimum performance of the designed coating system is due to the formation of a continuous and protective layer of a combined alumina and chromia scales. Based on the results, a degradation mechanism is proposed and showed that the protective properties of ceramic coatings are lost due to chemical reactions taking place under hot corrosion conditions. Finally, the necessity of application of optimum thick thermal barrier coatings with compositionally optimised NiCoCrAlY coating, which can protect the gas turbine engine blade materials significantly against both oxidation and hot corrosion conditions, is emphasized.

The Effect of Stagger Variability in Gas Turbine Fan Assemblies

Fan blades of high bypass ratio gas turbine engines are subject to substantial aerodynamic and centrifugal loads, producing the well-known phenomenon of fan blade untwist. The accurate prediction of the running geometry, as opposed to the cold geometry at rest, is crucial in the assessment of aerodynamic performance, vibratory response, and noise production of the fan. The situation is further complicated by the fact that some geometric variation is inevitable even for the state-of-the-art manufacturing processes used. The aim of this paper is to investigate the effect of static stagger variability on the dynamic untwist behavior of fan assemblies. An aeroelastic model was used to show that under certain conditions the stagger pattern changes significantly, both in form and amplitude, relative to the static configuration. At other conditions, a strong correlation between the running and static patterns is demonstrated.

Microstructure and mechanical properties of cast Ni-base superalloy K44

The Ni-base superalloy K44, developed recently in China, plays an important role in manufacturing blades of gas turbine engines due to its high temperature capability. The microstructure, deformation mechanism and mechanical properties of the Ni-base superalloy K44 have been investigated. Tensile properties and creep behaviors show abnormal variations with increasing temperatures, and the creep data can be fitted well with modified Dyson-McLean relation. transmission electron microscopy (TEM) observations confirmed that these behaviors are affected by the gamma' properties and the deformation mechanism at high temperature. On the basis of creep test results, Larson-Miller and Monkman-Grant plots for life prediction are made. The fracture characteristics of Ni-base superalloy K44 alloy at different temperatures and stress are also studied. (C) 2004 Elsevier B.V. All fights reserved.

Microstructure and mechanical properties of cast Ni-base superalloy K44

The Ni-base superalloy K44, developed recently in China, plays an important role in manufacturing blades of gas turbine engines due to its high temperature capability. The microstructure, deformation mechanism and mechanical properties of the Ni-base superalloy K44 have been investigated. Tensile properties and creep behaviors show abnormal variations with increasing temperatures, and the creep data can be fitted well with modified Dyson–McLean relation. transmission electron microscopy (TEM) observations confirmed that these behaviors are affected by the γ′ properties and the deformation mechanism at high temperature. On the basis of creep test results, Larson–Miller and Monkman–Grant plots for life prediction are made. The fracture characteristics of Ni-base superalloy K44 alloy at different temperatures and stress are also studied.

Measurements of Surface-Roughness Effects on the Development of a Vortex Produced by an Inclined Jet in Cross-Flow

This study examines the effects of surface roughness on the streamwise development of a vortex created by an isolated circular jet injected at 45 deg pitch and 90 deg skew into a crossflow. The study is motivated by the typical surface conditions encountered on in-service turbine blades of gas-turbine engines. Detailed measurements of the velocity field have been performed with a miniature four-wire probe at the jet exit plane, in the oncoming cross-stream boundary layer, and in a series of planes that capture the streamwise development of the vortex in the crossflow boundary layer up to about 15 jet-discharge diameters downstream of the jet. The paper presents the effects of surface roughness on the structure of the dominant streamwise vortex created by the interaction of the inclined jet with the mainstream, and documents the changes in the location, streamwise rate of change of circulation, and streamwise rate of diffusion of this vortex. Through these results, the change in the effectiveness of the vortex in energizing the boundary layer in the presence of surface roughness can be quantified.

Development of technology of nitride films manufacture for blades of gas turbine engines

Films of TiN on compressor blades of gas turbine engines are considered. Films are obtained with using plasma jet coater of capillary pulse-periodical plasmatrone. Diagnostics of films surface are performed.

Utilizing altered vibration responses of workpieces, such as gas turbine engine blades

An apparatus and method of utilizing natural frequency shifts of a laser shock processed workpiece to determine if sufficient laser shock processing has been accomplished.

On the Problem of Improvement of the Damping Ability of Rotor Blades of Contemporary Gas-Turbine Engines

We present the results of experimental investigations of the influence of structural and technological factors on the damping ability of lock joints of compressor blades carried out at the Pisarenko Institute of Problems of Strength of the National Academy of Sciences of Ukraine, study the possibility of using dampers mounted in shroud joints of turbine blades, and formulate some recommendations concerning the possibility of im proving the damping ability of rotor blades of contemporary gas-turbine engines.

Fatigue strength of metals and alloys modified by ion beams

The objective of the present research is the critical analysis of test results, dedicated to the effect of ion-beam irradiation conditions upon the fatigue strength of metallic materials. The shaped specimens, simulating the gas turbine engine blade operation and directly the blades, produced of titanium and nickel alloys as well as refractory steels by machining method are used as the study objects. The arc-pulsed ion implantation and irradiation of targets by the high-power pulsed ion beam were realised by means of Raduga-2, Temp-M and MUK accelerators. The irradiation conditions were varied within the following ranges: La, B, Sm and Hf ion implantation— E=30–80 keV (ion energy), j=1–5 mA/cm 2 (ion current density), f=30 Hz (pulse frequency), D=10 16–5×10 17 ion/cm 2 (irradiation dose); high-power pulsed ion beam irradiation—ions of carbon (60–70%) and protons, E=120–300 keV, j=30–200 A/cm 2, τ=50–100 ns (pulse duration), n=3–20 pulses (number of pulses). After irradiation, some targets were subjected to vacuum annealing for 2 h at their service temperature. Fatigue tests of initial and irradiated samples and blades were performed in air at the operating temperatures (450–650 °C) on the magneto-strictional vibrobanches with the loading frequency to 5000 Hz and low-frequency vibrobenches (50–80 Hz). The target surface state prior to and after tests was studied by electron Auger spectroscopy, scanning electron microscopy and X-ray structural analysis. The fracture surface was studied by optical and electron fractography. The test results showed that the endurance limit of samples and blades, subjected to the ion-beam irradiation with the post-process vacuum annealing at the optimum conditions, could be increased by 30–180% depending on an alloy type. Using the electron fractography, it was stated that the fatigue strength increase was associated both with the crack nucleation mechanism change and its growth rate deceleration. The extremely high endurance limit values were observed for patterns and VT8M titanium alloy blades with sharp edges after the high-power ion beam irradiation (pulse number: 15–20 at not high current density, j=60±10 A/cm 2) and vacuum annealing at 500 °C for 2 h.

Advanced Method for Single Crystal Casting of Turbine Blades for Gas Turbine Engines and Plants

A method for fabricating single crystal blades that combines the techniques of seed crystals and selection is suggested. The method realizes the advantages of both techniques, i.e., the high structural perfection and the possibility of fabricating single crystals with specified spatial orientation. Metallographic and x-ray diffraction analyses are used to study the processes of nucleation of the single crystal structure of blade castings fabricated from high-temperature nickel alloys by the method of selection and seed crystals. A commercial process for fabricating cast single crystal turbine blades by the new method is suggested.

Spouted bed metallorganic chemical vapor deposition of ruthenium on NiCoCrAlYTa powders

This paper reports on the spouted bed metallorganic chemical vapor deposition (SBMOCVD) of ruthenium on NiCoCrAIYTa commercial powders. The aim is to propose an economic, versatile and time saving process for the screening of the doping by platinum group elements of thermal barrier coatings applied on gas turbine engine blades, in order to improve their oxidation and corrosion resistance. Information on the spouting of the NiCoCrAIYTa powders and on the SBMOCVD reactor is provided in the first part of the paper. Following, two deposition routes for the CVD of ruthenium starting form ruthenocene are described. The first implies high temperature reaction with hydrogen and yields crystalline Ru nanoparticles on the surface of the powders. The second is a low temperature reaction with oxygen. It yields ruthenium oxide which in turn is reduced in situ to yield amorphous Ru. Both processes lead to uniform doping of the powders.

Engines

In the current paper, an attempt has been made to address the benefit as well as importance of optimisation of thermal barrier coatings system for super alloys after evaluating different thicknesses of ceramic thermal barrier coatings. The thickness of coatings plays a major role in deciding the life of coatings as lower thickness does not provide complete protection and higher thickness causes to reduce the coating life due to adherence problems. Therefore, determination of optimum thickness to obtain improved performance is highly essential. An optimum thickness of thermal barrier coatings has been determined successfully by conducting hot corrosion studies on various thicknesses. The optimised protective coating system enhances the life of super alloy by about six hundred times. The optimum performance of the designed coating system is due to the formation of a continuous and protective layer of a combined alumina and chromia scales. Based on the results, a degradation mechanism is proposed and showed that the protective properties of ceramic coatings are lost due to chemical reactions taking place under hot corrosion conditions. Finally, the necessity of application of optimum thick thermal barrier coatings with compositionally optimised NiCoCrAlY coating, which can protect the gas turbine engine blade materials significantly against both oxidation and hot corrosion conditions, is emphasized.

Modelling of the mechanical behaviour of the single-crystal turbinealloy CMSX-4 during thermomechanical loading

Turbine blades in gas turbine engines are subjected during operation totriaxial stress fields. For the description of the deformation behaviour ofanisotropic single-crystal blades, constitutive equations are required whichtake account of modifications to the deformation processes caused by evolutionof the γ/γ' microstructure during service (γ' rafting). Amicrostructure-dependent, orthotropic Hills potential, whose anisotropycoefficients are connected to the edge length of γ' particles, has beenapplied. The shape of γ' particles remains cubic below exposures at700 °C. At high temperatures (above 850 °C) the γ'particles coalesce to rafts, and the viscoplastic response of thesuperalloy is continuously modified. This reduces the creep resistance of⟨001⟩ orientated specimen. After tensile loading of the⟨001⟩-orientated specimens at 1000 °C, the rafting ofγ' in the (100) plane was observed as expected, whereas the⟨111⟩ specimens did not reveal γ' rafting. Torsionallyloaded specimens exhibited rafting only in the near⟨100⟩-orientated surface regions of the specimen. Thedeformation in the ⟨111⟩ tensile and ⟨001⟩ torsionspecimens occurred by octahedral slip of dislocations and not by cubic slip,as expected from theoretical considerations. Rafting did not occur in the⟨111⟩-orientated specimens. This anisotropy change is simulatedsuccessfully by the microstructure-dependent model.

Effect of foreign object damage on the fatigue strength of an xd™ γ-TiAl alloy

High cycle fatigue has become the leading cause of failure in gas turbine engine blades in recent years [1]. The majority of these failures were associated with surface damage such as foreign object damage (FOD). Therefore, the ability of a material to resist impact damage and the subsequent fatigue propagation of any cracks that may result has become a crucial design consideration. Substantial research has been conducted on the effects of simulated FOD in conventional turbine blade materials where the formation of cracks at the impact site was not a common occurrence [2,3,4]. However, impacts of more brittle materials, such as �-TiAl, would likely result in the formation of cracks. Steif et al [5] have examined the formation of cracks associated with impacts in several TiAl-based alloys. The effects of ballistic impacts on the fatigue behavior of a Ti-48Al-2Nb-2Cr �-TiAl alloy were examined by Lerch et al [6]. Fatigue strength was correlated with a somewhat arbitrary crack length with some success; however, no correlation with the long-crack fatigue threshold was made. The use of a fatigue threshold limit may be necessary for design of turbine blades given the limited fatigue crack growth resistance exhibited by �-TiAl. The present study investigates the reduction in elevated temperature fatigue strength of a Ti-46.8Al­ 2.1Nb-1.1Mn-0.1Si-1.4B alloy caused by simulated foreign object damage. This work is part of a larger effort to support the transition of �-TiAl to industrially relevant gas turbine engine applications.

Certain peculiarities of Zr−Cr−N coatings on steel blades of a gas-turbine engine compressor

The properties of compressor blades of a helicopter gas-turbine engine with an experimental ionplasma coating Zr−Cr−N, are compared to those with Ti−Zr−N basic composition. It is shown that, due to the structural properties, the experimental coatings make the blades more corrosion-resistant, and mitigate the dependence of their residual properties on the amplitude and the temperature of the preliminary vibrotempering.

Laser cladding of turbine blades

A comparative study of two different techniques for the application of wear-resistant coatings for contact surfaces of shroud shelves of gas turbine engine blades (GTE) has been conducted. Wear-resistant coatings were applied on In713 by laser cladding with direct injection of the cladding powder into the melt pool. Laser cladding was conducted with a TRUMPF-2500, CW-CO2 laser. The laser cladding was compared with commercially available plasma cladding with wire. Both plasma and laser cladded zones were characterized by optical and scanning electron microscopy. It was found that the laser cladded zone has a higher microhardness value (650–820HV) compared with that of the plasma treated material (420–440HV). This is a result of the significant reduction in grain size in the case of laser cladding. Unlike the plasma cladded zones, the laser treated material is free of micropores and microcracks.

Altering vibration frequencies of workpieces, such as gas turbine engine blades

A method of modifying the vibration resonance characteristics of a workpiece includes the steps of determining a vibratory resonance condition frequency of the workpiece, determining the mode shape of said vibratory resonance condition, locating an area on the workpiece that includes a maximum curvature for the determined mode shape and vibratory resonance condition frequency; then laser shock peening the located area to create residual compressive stresses within the workpiece to shift the determined vibratory resonance condition frequency. A workpiece such as a gas turbine engine blade is also disclosed.

Procedure and analysis of three-dimensional thermal stressed states of turbine blades with coatings subjected to thermal cycling

We propose a procedure of numerical analysis of three-dimensional thermal stressed states of machine parts with multiplayer heat-shielding coatings based on the use of the SPACE finite-element software package. A detailed analysis of thermal and stressed states of wedge-shaped models simulating the blades of gas-turbine engines with coatings of different thickness subjected to thermal cycling is performed. The character of the influence of the thickness of coatings on thermal and stressed states in the half-cycles of heating and cooling is studied.