GAT-2017 (Gamma Alloys Technology - 2017): Other Applications and Materials-Processes Development Efforts
Sponsored by: TMS Structural Materials Division, TMS: Titanium Committee
Program Organizers: Young-Won Kim, Gamteck LLC; Wilfried Smarsly, MTU Aero Engines AG; Junpin Lin, University of Science and Technology Beijing; Pierre Sallot, Safran Tech; Paul Withey, Rolls-Royce; Al Sommer, Del West Engineering, Inc; Rui Yang, Institute of Metal Research CAS; Florian Pyczak, Helmholtz-Zentrum-Geesthacht; Dennis Dimiduk, BlueQuartz Software, LLC

Tuesday 8:30 AM
February 28, 2017
Room: Pacific 17
Location: Marriott Marquis Hotel

Session Chair: Yuyong Chen, Harbin Institute of Technology; Marc Thomas, ONERA

8:30 AM  Invited
IC Engine Valves, an Application for Gamma Ti-Al Alloy Technology: Al Sommer1; 1Del West Engineering, Inc
    Racing venues such as Formula 1 and Moto GP currently use different gamma alloy compositions for intake and exhaust valves. Today’s heavily turbocharged race engines need intake valves where E/ρ is high, consistent with the material’s mechanical strength required for the application < 500˚C. The exhaust valve needs an alloy that has adequate fatigue, creep and corrosion resistance above 800˚C. The E/ρ characteristic of the exhaust valve is nowhere as important in the design of the exhaust valve as it is in the case of the intake. Microstructure and alloy chemistry play a much larger role in the selection of exhaust valve materials for turbo charged race engines than they do in the case of the intake. This work will present both materials test data and race engine performance results to attest to the above claim. An overview of how gamma Ti-Al valves are made will also be presented.

8:55 AM  
CAE-based Analysis of Structural Integrity for an Industrial Gas Turbine Blade Made from TiAl Alloy: Omid Sedaghat1; Siavash Zamani1; Saeed Asadi1; Fatemeh Heydari1; Ali Bakhshi1; 1MAPNA Turbine Blade Eng. & Mfg. Co. - PARTO
    Titanium Aluminide alloys deputes a promising solution for substitution of current Ni-based superalloys with new class of high temperature light weight alloys. In the present study, last stage blade of an industrial gas turbine was selected and service condition was simulated for the TiAl blade. To do so, thermo-physical properties of selected alloy were extracted to find temperature and stress distribution profiles during engine operation using CFD and FEM analyses. In the next step, moreover to vibrational analysis, creep damage mechanism was studied and analyzed to characterize the reliability according to the blade design criteria and comprehensive comparison was made between performances of selected TiAl alloy in contrast with previous Ni-based superalloy. Results show that stresses level could be significantly lowered by using TiAl alloy and advantages would be achieved in damage mechanisms controlling. However design specifications should be reviewed both in turbine side and current TiAl alloys side.

9:15 AM  
O-phase in a Lamellar TiAlNb Alloy Produced by Powder Metallurgy: Heike Gabrisch1; Uwe Lorenz1; Florian Pyczak1; Marcus Rackel1; Andreas Stark1; 1Helmholtz-Zentrum Geesthacht
    High specific strength, high temperature stability and good corrosion resistance make TiAl-alloys attractive candidates for structural applications in aero-engines. Depending on Al-content and alloying elements the alloys are composed of the major phases βo (cubic), α2 (hexagonal) and γ (tetragonal). In the ternary alloy Ti-42Al-8.5Nb (at.-%) improved high temperature strength and better room temperature ductility were attributed to the occurrence of an additional orthorhombic phase (O-phase) that form out of the parent α2 phase during thermal treatment. The O-phase with the ideal composition Ti2AlNb has been reported previously in other ternary alloys Ti-(12-31)Al-(12.5-37)Nb, but not for alloys in the present composition range. In this study the O-phase is identified by single crystal electron diffraction. The morphology of phases within α2 laths of lamellar (α2+γ) colonies is characterized by conventional imaging techniques, HAADF and high resolution imaging.

9:35 AM  
Preparation and Electron Beam Welding of Hot Packed Rolled Powder Metallurgy γ-TiAl Sheets: Zhengguan Lu1; Lei Xu1; Jie Wu1; Ruipeng Guo1; Rui Yang1; 1Institue of Metal Research, CAS
    Atomized powder with a normal composition of Ti-47Al-2Cr-1.8Nb-0.15B (at. %) was used to prepare powder metallurgy (PM) γ-TiAl preforms through hot isostatic pressing. PM method can obtain a more uniform chemical composition and finer microstructure than traditional casting route. Considering the poor room-temperature ductility, hot packed rolling process was studied to prepare PM γ-TiAl sheets and electron beam welding (EBW) of gamma sheets was conducted. Experimental results show that the hot temperature deformation behavior of PM gamma alloy was sensitive to rolling parameters. A set of rolling parameters was optimized to prepare PM gamma sheets with 2.5mm thickness. The microstructure and microhardness of FZ, HAZ and BM is different after welding while no obvious element segregation was observed. The tensile strength of welding joint was also tested, and tensile testing specimens all fracture in the FZ.

9:55 AM  
Why Grinding of Gamma Titanium Aluminide Makes Sense?: K. Philip Varghese1; 1Saint-Gobain Abrasives
    Manufacturing of γ-TiAl components is usually done through traditional processes such as machining, grinding or through non-traditional processes such as EDM, ECM etc. Compared to these processes, grinding is often recognized as the best method for achieving final part dimensions and surface characteristics on γ-TiAl components. Saint-Gobain Abrasives has been developing new grinding technology to use with these intermetallics, since 2011. With the use of modern grinding wheels composed of engineered grains and high-strength bond technology, it has been determined that grinding can remove material from γ-TiAl components more quickly and economically than machining, without inflicting damage to parts. This presentation will give a brief background of the traditional and non-traditional processes employed for manufacturing γ-TiAl components, educate the participants on the basics of grinding technology/terminology and the grinding process. It will also show data from the latest tests done on grinding of this advanced aerospace engine material.

10:15 AM Break

10:30 AM  Invited
Development of Cost-effective Processes for Gamma-TiAl Application: Rui Yang1; 1Institute of Metal Research CAS
    Gamma titanium aluminide materials are hard to deform and difficult to machine compared to conventional alloys, and the relatively high total cost from material to component associated with wrought processes may hinder their wider and quicker application. Successful application of a wrought-processed component largely depends on reaching a balance between ensuring the desired microstructure by a sufficient degree of deformation and reducing processing cost by minimizing deformation steps. On the other hand, near net-shape processes such as precision casting and powder metallurgy forming are of particular interest in dealing with this class of materials. In this talk, examples of the aforementioned three types of processes will be presented and their advantages and technical difficulties discussed.

10:55 AM  
Multi-direction Forging and Superplastic Deformation Characteristic of High Nb Containing TiAl Alloys: Bin Tang1; 1Northwestern Polytechnical University
    The γ-TiAl alloys are considered to be the most important candidate to replace Ni-based superalloys for jet engine. However, the intrinsic brittleness and hard processability of TiAl alloys limit the application. In the present work, the multi-direction forging route was applied to obtain a fine-grained and uniform duplex microstrucutre for the high Nb containing TiAl alloy with nominal composition of Ti–42Al–8Nb–0.2W–0.1Y (at.%). Results shows that the mean grain size in the billet is about 13 μm and a large amount of β/B2 phase was retained in the microstrcuture. The present alloy with fine-grained duplex microstrucutre was found have superplasticity at the temeprature exceeded 850C under an initial strain-rate of 10-4 s-1. The elongation can reach 100% at 850C under tensile stress and it will increse to 380% at 1000C. Further study found that the superplastic deformation mechanisms at 850C and 1000C are differernt from each other.

11:15 AM  
Titanium Aluminides under High-pressure, High Temperature and during Plastic Deformation: In-situ Studies by Neutron and Synchrotron Quantum Beams: Klaus-Dieter Liss1; 1Australian Nuclear Science and Technology Organisation
    In-situ neutron and synchrotron X-ray diffraction deliver unique and complementary insight into the microstructural evolution of metals at high temperature, during thermo- mechanical processing or under high pressure. Neutrons illuminate a larger bulk volume and reveal quantitative phase abundance, bulk texture, lattice parameter changes and other ensemble averaged quantities. They are particularly sensitive to characterize atomic order and disorder in titanium aluminides. In contrast, fine- bundled synchrotron high-energy X-rays deliver reflections from a number of individual grains. For each constituting phase, their statistics and behavior in time reveal information about grain growth or refinement, subgrain formation, static and dynamic recovery and recrystallization, slip systems, twinning, etc. Grain orientation correlation can be revealed and lattice strain gives complementary insight to the transformation and reaction processes. This presentation reviews pioneering experiments on titanium aluminides in reciprocal space, which nowadays serve the wider community.

11:35 AM  
Hot Forming of Titanium Aluminide Alloys Studied In Situ with Synchrotron Radiation: Andreas Stark1; Marcus Rackel1; Michael Oehring1; Norbert Schell1; Lars Lottermoser1; Florian Pyczak1; 1Helmholtz-Zentrum Geesthacht
    Several microstructure parameters, e.g. grain size, phase fractions or crystallographic texture, change during thermo-mechanical processing. But with conventional metallographic techniques the microstructure can only be analysed after processing. Thus the real high temperature conditions are often masked by lower temperature phase transformations or recrystallization. To overcome this problem we used a deformation dilatometer modified for working in the HZG synchrotron radiation beamline HEMS at DESY, Germany. Thereby, the evolution of the microstructure was directly observed by X-ray diffraction during hot forming while simultaneously recording the process parameters. We studied the hot compressive deformation of titanium aluminide alloys at different process temperatures between 1100C and 1300C. We observed the formation of crystallographic textures in γ-TiAl, α-Ti(Al) and β-Ti(Al) in situ and time resolved during hot forming. The influence of different phase fractions and process parameters on texture formation was analysed, which is necessary information for the determination of suitable process routes.

11:55 AM  
Fracture Behavior during Hot Tension Testing of High Nb Containing TiAl Alloys: Bin Zhu1; Xiangyi Xue1; Hongchao Kou1; Lin Song1; Jinshan Li1; 1Northwestern Polytechnical University
    Cracking during cooling process of castings or ingots seriously impedes the application of high Nb containing TiAl alloys. To understand this problem, fracture behavior during tensile tests of Ti-45Al-8.5Nb-(W, B, Y) alloy with as-cast microstructure was studied at low strain rates and various temperatures around brittle to ductile transition temperature(BDTT). It is shown that below BDTT, cracks initiated and lead to bulk fracture at a low strain. Above BDTT, the fracture elongation increased obviously. But some wedge cracks and cavities were observed at locations with low strain value on fractured specimens. These wedge cracks and cavities could form during cooling of TiAl components, and grow or propagate under thermal stresses at low temperatures. The initiation sites of cracks and cavities were observed associated with B2 phase and titanium borides above and below BDTT. This may provide a microstructural reason for cracking of TiAl alloys.