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Research Papers

Preliminary Design, Modeling, Production, and First Evaluation Tests of a Ti–Al Gas Turbine Blade

[+] Author and Article Information
Andrea Brotzu

Department of Chemical Engineering,
Materials and Environment,
University of Roma “Sapienza,”
Via Eudossiana 18,
Rome 00184, Italy
e-mail: andrea.brotzu@uniroma1.it

Roberto Capata

Mem. ASME
Department of Mechanical and
Aerospace Engineering,
University of Roma “Sapienza,”
Via Eudossiana 18,
Rome 00184, Italy
e-mail: roberto.capata@uniroma1.it

Ferdinando Felli

Department of Chemical Engineering,
Materials and Environment,
University of Roma “Sapienza,”
Via Eudossiana 18,
Rome 00184, Italy
e-mail: ferdinando.felli@uniroma1.it

Daniela Pilone

Department of Chemical Engineering,
Materials and Environment,
University of Roma “Sapienza,”
Via Eudossiana 18,
Rome 00184, Italy
e-mail: daniela.pilone@uniroma1.it

Enrico Sciubba

Fellow ASME
Department of Mechanical and
Aerospace Engineering,
University of Roma “Sapienza,”
Via Eudossiana 18,
Rome 00184, Italy
e-mail: enrico.sciubba@uniroma1.it

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received June 6, 2016; final manuscript received January 11, 2017; published online March 27, 2017. Assoc. Editor: Huiling Duan.

J. Eng. Mater. Technol 139(3), 031005 (Mar 27, 2017) (8 pages) Paper No: MATS-16-1169; doi: 10.1115/1.4035894 History: Received June 06, 2016; Revised January 11, 2017

The aim of this work is to design a lightweight, creep-resistant blade for an axial single-stage micro-gas turbine. The selected process was casting of an intermetallic titanium/aluminum alloy. All the project phases are described, from the preliminary thermodynamic and geometric stage design, to its three-dimensional (3D) modeling and the subsequent finite element method–computational fluid dynamics (FEM-CFD) analysis, to the manufacturing process of the single rotor blade. The blade making (height 7 cm and chord 5 cm, approximately) consisted in a prototyping phase in which a fully 3D version was realized by means of fused deposition modeling and then in the actual production of a full-scale set of blades by investment casting in an induction furnace. The produced items showed acceptable characteristics in terms of shape and soundness. Metallographic investigations and preliminary mechanical tests were performed on the blade specimens. The geometry was then refined by a CFD study, and a slightly modified shape was obtained whose final testing under operative conditions is though left for a later study. This paper describes the spec-to-final product procedure and discusses some critical aspects of this manufacturing process, such as the considerable reactivity between the molten metal and the mold material, the resistance of the ceramic shell to the molten metal impact at high temperatures, and the maximal acceptable mold porosity for the specified surface finish. The CFD results that led to the modification of the original commercial shape are also discussed, and a preliminary performance assessment of the turbine stage is presented and discussed.

Copyright © 2017 by ASME
Topics: Design , Blades
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References

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Figures

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Fig. 1

Axial turbine stage computational scheme

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Fig. 2

A view of the rotor blade and the SolidWorks® model for thermal calculations

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Fig. 4

TiAl alloys thermal conductivity

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Fig. 5

The results of the FEM analysis

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Fig. 6

(a) Nozzle guide vanes (NGV) and rotor profiles at the hub and (b) NGV and rotor profiles at the tip

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Fig. 7

Left—hub contours: (a) static pressure, (b) static temperature, and (c) turbulent kinetic energy and right—tip contours: (a) static pressure, (b) static temperature, and (c) turbulent kinetic energy

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Fig. 8

The final 3D blade model

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Fig. 9

Rotor blade model with riser and 3D print of the blade

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Fig. 10

The three 3D prints (the final one is on the right)

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Fig. 11

Realization of the cast mold

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Fig. 12

As cast blade after the extraction from an uncoated mold (a) and a coated mold (b)

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Fig. 13

Macrograph of the blade section

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Fig. 14

Optical micrograph showing the alloy microstructure

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Fig. 15

Scanning electron microscope (SEM) micrograph showing lamellar colonies (L) and γ grains (γ)

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Fig. 16

Specimens mass gain with time in cyclic oxidation tests

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Fig. 17

SEM micrograph showing the cross section (a) and the oxide morphology (b) of the specimen treated at 1073 K for 120 h [2]

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