GAT-2017 (Gamma Alloys Technology - 2017): Keynote and Aero-Engine Blades Applications
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

Monday 8:30 AM
February 27, 2017
Room: Pacific 17
Location: Marriott Marquis Hotel

Session Chair: Dennis Dimiduk, BlueQuartz Software; Alain Couret, CEMES

8:30 AM Introductory Comments : Young-Won Kim, Gamteck

8:40 AM  Keynote
Development and Application of Gamma TiAl Components: Wilfried Smarsly1; Joerg Esslinger1; 1MTU Aero Engines GmbH
    Advances in gas-turbine development are driven by the need to reduce fuel consumption, emissions and costs. From the material aspect, these requirements enhanced the development of highly creep and oxidation resistant materials of greater temperature potential than titanium alloys and of lower density than nickel superalloys. After almost three decades of intensive fundamental research and development activities, titanium aluminides based on the ordered γ -TiAl phase have found applications in automotive and aircraft engine industry. The advantages of this class of innovative high-temperature materials are their low density and their good strength and creep properties as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods or even forging. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments.

9:15 AM  Invited
Advancement of Plasma Cold-hearth Melting for Production of Gamma Titanium Aluminide Alloys within Arconic: Ernie Crist1; Fusheng Sun1; 1Arconic Titanium & Engineered Products
    Utilization of gamma titanium aluminide alloys in aerospace and automotive/industrial applications has placed significant demand on melters of these materials for products to be used in cast, wrought, and direct-machining applications. There is also a growing demand for input stock used in gas atomization of powders. Current technologies used in ingot manufacturing include plasma arc melting, vacuum arc melting, and induction skull melting + centrifugal casting. Subsequent processing may include forging, re-melting + casting, or machining directly into components. Over the past four years, Alcoa Titanium & Engineered Products (ATEP) has developed a robust melting method using plasma cold-hearth melting technology, including the design and implementation of a new 3-torch system being utilized for production of Ti-48-2-2 cast bars. General discussions concerning plasma cold-hearth melting, manufacturing challenges, and metallurgical attributes associated with cast Ti-48-2-2 ingots will be reviewed.

9:40 AM  
Advances in the Systems and Processes for the Production of Gamma Titanium Aluminide Bars and Powder: Rob Haun1; 1Retech Systems, LLC
    This paper will present recent advancements relating to the production of gamma titanium aluminides at Retech Systems LLC. Results will be focused on the successful system development for 53 mm, 80 mm, 100 mm and 200 mm diameter ingots, in lengths up to 1000 mm. Also to be presented will be our experience with powder production equipment and processes for those selected gamma titanium aluminide alloys. All our developments have focused on cost-effective production for both product forms and the implications regarding economic analysis will also be discussed.

10:00 AM Break

10:15 AM  Invited
Implementation of γ-TiAl Alloys for Low Pressure Turbine Blades: Opportunities and New Challenges: Pierre Sallot1; Guillaume Martin1; Stéphane Knittel1; 1SAFRAN
    Titanium aluminide has been for years identified as a solution for weight reduction in the LPT (Low Pressure Turbine) of a turbo-engine. The improved specific mechanical properties of these intermetallic alloys, when compared to Ni-based superalloys, have pushed Safran and other major aero-turbine producers to introduce them in their latest and newest generations of turbines. Today, TiAl LPT blades are a reality as they enter in mass production phase. Different alloy compositions as well as production routes have been developed and adapted to various applications and specific requirements. This application-oriented development leads to different alloy families, but we will focus in the talk on the ones able to handle higher stresses and temperatures. In addition to mechanical properties, oxidation resistance and ageing in air environment are major challenges to overcome.

10:40 AM  
Study on Milling of a TiAl Alloy under Minimum Quantity of Lubrication Condition: Sajjad Kolahdouz1; Siavash Zamani1; Fatemeh Heydari1; Ali Bakhshi1; 1MAPNA Turbine Blade Eng. & Mfg. Co. - PARTO
    New design concepts of gas turbines are mainly based on increasing operational efficiency, reliability and environmental compatibility. For this reason, advanced classes of materials and manufacturing processes should be employed to meet the desired criteria. In the present investigation, efforts have been made to study on effective phenomena during milling of a TiAl alloy and to improve the machining process using MQL condition. To do so, surface roughness and microstructure of machined work-piece moreover to changes in cutting forces are studied. Experiments were designed using Taguchi method in 4 levels. Also, the machining mechanisms in Titanium Aluminide alloys were fully evaluated and discussed. Results show that by using optimized MQL condition for milling of TiAl alloy, 10 to 30 percent decreasing in cutting forces and a more controlled machining affected zone in microstructure could be achieved with no significant change in surface roughness.

11:00 AM  Invited
Titanium Aluminide Investment Casting Technology Development: Matthias Bünck1; Todor Stoyanov1; Rüdiger Tiefers1; Jan Schievenbusch1; 1Access e.V.
     TiAl alloys have successfully been introduced in civil aircraft engines over the last years and a significant order volume increase is expected in the near future. Due to its beneficial buy-to-fly ratio, investment casting bears the highest potential for cost reduction of all competing production technologies for TiAl-LPTB. In the last decade, Access has developed and optimized investment casting technology especially for the production of TiAl-parts. While these parts meet highest requirements, establishing series production and further lowering internal scrap rates are present challenges. In order to meet these goals, Access is being certified according to Aircraft Standards, aiming at qualifying produced parts on Technology Readiness Level 6. The present work gives an overview over the phases of development and certification. A generic blade is used as a demonstrator to address design and process and to demonstrate the steady quality improve to meet required specifications.

11:25 AM  
High Temperature and High Strain Rate Deformation Behavior of Powder Metallurgical TiAl-Nb Composite: Yong Liu1; Bin Liu1; Qihong Fang2; Xiang Zan3; 1Central South University; 2Hunan University; 3Hefei University of Technology
    Powder metallurgy becomes more and more important in processing TiAl intermetallics, esp. for TiAl-based composites. In this presentation, TiAl composites with the addition of ductile Nb particles were produced by hot isostatic pressing and subsequent hot extrusion. The microstructures consist of lamellar-structured or duplex matrix and elongated Nb-rich fibers. Since TiAl intermtallics are used for high temperature applications, the high strain rate (~1300 s-1) and high temperature (~800 C) deformation behavior was evaluated on both the matrix and composites. The results indicated that TiAl generally show a higher strength under dynamic condition than under static condition, and the deformation mechanism is mainly controlled by twinning and shear banding. Finally, constitutive equations based on Zerrilli-Armstrong model were built up, and the deformation and the effect of Nb-rich fiber were discussed. In general, powder metallurgical TiAl-Nb composites show promising properties in the high temperature and high impact applications.

11:45 AM  
Plastic Deformation Behaviour and Crack Initiation Mechanisms of γ-TiAl in High Temperature, High Cycle Fatigue: Thomas Edwards1; Fabio Di Gioacchino1; Nigel Martin2; Mark Dixon2; William Clegg1; 1Department of Materials Science and Metallurgy, University of Cambridge; 2Rolls-Royce plc
    The limited plasticity of γ-TiAl alloys is such that a threshold approach to fatigue lifing is used. In this work, the high cycle fatigue deformation behaviour of Ti-45Al-2Nb-2Mn(at.%)-0.8vol%TiB2 in different microstructural states has been studied from room temperature to 700 °C to understand how plasticity causes cracking and how this depends on microstructure. The near-surface plastic strain field and the build-up of local strains were measured, using high resolution digital image correlation (DIC) of a remodelled gold speckle pattern, and analysed together with the orientation maps of the same regions obtained by electron backscatter diffraction (EBSD), both before and after testing steps. From these results, flaw nucleation behaviour of the γ-TiAl alloy was investigated considering colony and lamellar-scale features, and further studies based on the lamellar plastic anisotropy are discussed. At high temperature, the shear generated upon slip and twinning was associated with debonding at colony boundaries and boride particles.