Materials for High Temperature Applications: Next Generation Superalloys and Beyond: Intermetallics and Additive Manufacturing of Superalloys
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee, TMS: Refractory Metals Committee
Program Organizers: Akane Suzuki, GE Global Research; Martin Heilmaier, Karlsruhe Institute of Technology (KIT); Pierre Sallot, Safran Tech; Stephen Coryell, Special Metals Corporation; Joseph Licavoli, NETL - Department of Energy; Govindarajan Muralidharan, Oak Ridge National Laboratory

Wednesday 8:30 AM
March 1, 2017
Room: Pacific 16
Location: Marriott Marquis Hotel

Session Chair: Helmut Clemens, Montanuniversitaet Leoben; Haruyuki Inui, Kyoto University

8:30 AM  Invited
Iron Aluminides: Recent Alloy Developments and Industrial Processing: Martin Palm1; 1Max-Planck-Institut für Eisenforschung GmbH
    It is known since long that Fe–Al alloys based on Fe3Al (D03) and FeAl (B2) have an excellent corrosion and wear resistance. Because of considerable lower density and appreciable costs, they could provide an alternative to stainless steels and Ni-base superalloys. However, inadequate strength at high temperatures still delays any wider application of these alloys. Through novel alloy concepts, e.g. precipitating fine-scaled borides or Laves phases along grain boundaries, coherent microstructures or increasing the D03/B2 transition temperature, substantial progress in strengthening iron aluminide based alloys at high temperatures has been achieved. This progress as well as economic considerations led to a renewed interest in these materials by industries. Casting, rolling, forging and additive manufacturing of these advanced iron aluminides was successfully performed and the microstructure/property relations of the industrially processed alloys were established.

9:00 AM  Invited
Directionally Solidified Ni-Al-X Ternary Eutectics for High-Temperature Applications: G. Liu1; P. Hallensleben1; J. Frenzel1; X. Liu1; J. Pfetzing-Micklich1; E. P. George1; 1Ruhr University Bochum
    Many of the materials that have been considered for high-temperature applications (beyond superalloys) suffer from one or more drawbacks including insufficient strength at elevated temperatures, brittleness at low temperatures, and poor oxidation resistance. However, recent preliminary reports in the literature on arc-melted ternary eutectics containing Ni, Al, and a refractory metal, indicate that some of them can exhibit high strength combined with reasonable tensile ductility at room temperature. This potentially overcomes two of the major drawbacks of high-temperature intermetallics and composites. Here we report on the composition dependence of the microstructure and mechanical properties of directionally solidified Ni-Al-X ternaries. In addition to results of microhardness and nanoindentation measurements, we will also report results of tensile tests performed on select compositions. Wherever possible, the overall behavior of the composites will be quantitatively correlated with the properties of the constituent phases.

9:30 AM  
Novel High Strength Eutectic Intermetallics: Chandrasekhar Tiwary1; Vilas Gunjal1; Abhishek Sharma1; Kamanio Chattopadhyay1; Dipankar Banerjee1; 1Indian Institute of Science
    We describe a new class of superalloys based upon combinations of intermetallics as fine scale eutectic structures in the Ni-Al-Zr system. The effect of alloying additions on the structure and morphology of these eutectics is described. The microstructural stability of the as-cast material as function of long term thermal exposure is examined. Tensile and compressive properties as function of strain rate and temperature and microstructural length scales has been evaluated. The alloys show extremely high strength approaching 2 GPa upto temperatures of 700C with tensile ductility between 3-4 % at room temperature. Plastic deformation processes at room temperature have been examined in tensile tested samples and related to fracture processes in the alloys. Preliminary creep studies are reported. We have also examined the oxidation behaviour of these alloys under isothermal and thermal cycling at temperatures exceeding 900C.

9:50 AM Break

10:10 AM  Invited
Plasticity of Hard and Brittle Materials at Micron-meter Size Scales: Haruyuki Inui1; Kyosuke Kishida1; Norihiko Okamoto1; 1Kyoto University
    There are many hard materials that are considered to be candidates for structural applications under extreme conditions such as very high temperatures. But, one of the common characteristics for these hard materials is their brittleness at ambient temperatures. Many of them need very high temperatures for plastic flow. So, even, fundamentals for plasticity such as operating slip systems and their CRSS values have yet to be known for many of them. However, there is a chance for these hard materials to plastically deform in the form of micropillars of the micron-meter size even at ambient temperature, from which we can obtain the information of operating slip systems and their CRSS values. The results obtained for some brittle transition-metal silicides of the M5Si3-type such as Mo5Si3, Nb5Si3 and Mo5SiB2 and those of the MSi2-type such as MoSi2, VSi2, CrSi2, NbSi2 and TaSi2 will be presented.

10:40 AM  Invited
Advanced γ-TiAl Based Alloys: Helmut Clemens1; Svea Mayer1; 1Montanuniversität Leoben
    Intermetallic TiAl alloys are already used as engineering lightweight high-temperature materials in aircraft and automotive engines. In this presentation the alloy design rules, which have been applied for the development of a β-solidifying γ-TiAl-based alloy, the so-called “TNM alloy” with excellent hot-deformability, will be explained. The TNM alloy is already used in a particular eco-friendly and fuel-saving aero-engine, which is powering the Airbus A320neo. Besides the considerations which have led to the selected alloying elements, the heat treatments conducted subsequent to conventional hot-forging are discussed. In this context it will be shown how novel characterization techniques, e.g. in-situ high-energy X-ray and neutron diffraction, have been employed to accelerate both alloy and process development. The microstructural parameters, which influence the elongation at fracture and creep behavior will be emphasized. Finally, the potential to improve the mechanical properties of the TNM alloy by means of micro-alloying with C and Si is addressed.

11:10 AM  
Microstructure–property Relationship in Next Generation TiAl Alloys: Soumya Nag1; Akane Suzuki1; Manuel Acosta2; Michael Weimer2; Bernard Bewlay1; 1GE Global Research; 2GE Aviation
    In the recent years, extensive investigations of TiAl alloys have led to their commercial implementation in the aerospace and automobile industries. Next generation alloys with an improved balance of mechanical and environmental properties has been achieved via major (group VB and VIB) and minor (group IIIA and IVA) elemental additions. In the present study the relationship between microstructure and room and elevated temperature tensile properties was investigated for several cast and heat-treated 2nd-generation TiAl alloys with modified chemistries. Property variation was observed based on the type of microstructure (near-lamellar vs duplex) and specimen location (prepared near or far from center of cast slab). Quantitative microstructural characterization of these specimens were conducted via electron back-scatted diffraction, scanning electron microscopy and polarized light microscopy.

11:30 AM  
Additive Manufacturing of High Temperature Alloys: An Emphasis on the Current State and Future Direction of Ni-base Superalloy Processability in AM: Michael Kirka1; Ryan Dehoff1; 1Oak Ridge National Laboratory
    While nickel base (Ni-base) superalloys have been widely utilized for gas turbine engine applications among others in cast and wrought forms for well over 70 years, the limits of the alloy family are beginning approached. However, fabricating Ni-base superalloys through additive manufacturing (AM) techniques is relatively new and lacks the deep understanding of the structure-property relations of the materials fabricated through the traditional techniques. Further, challenges exist in relating the formation of defects to process parameters, and the influence of repeated rapid thermal gyrations and high cooling rates on the unique liquid-solid, and solid-solid phase transformations in the AM processed Ni-base superalloys. To be covered in this talk is the current state and challenges in processing Ni-base superalloys spanning the highly weldable to the traditionally non-weldable via AM techniques, and the future direction and needs for processing future advanced high temperature alloys utilizing AM processes.

11:50 AM  
Microstructure Characterization of Single-crystal René N5 Fabricated through Scanning Laser Epitaxy: Amrita Basak1; Suman Das1; 1Georgia Institute of Technology
    Scanning laser epitaxy (SLE) is a powder-bed additive manufacturing process that was exclusively developed to repair and manufacture gas turbine hot-section components made of nickel-base superalloys. Microstructures of the as-deposited René N5 were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron back scatter diffraction (EBSD), X-ray diffraction (XRD), and microhardness test (MHT) measurements. SEM investigations showed the presence of fine /γ′ phases and eutectics in deposit region. EDS measurements showed the eutectics to be Ta-rich. EBSD measurements indicated single-crystal growth in the deposit region. XRD investigation revealed the presence of strong <100> morphology in the deposit region. MHT measurements demonstrated higher hardness values in the deposit region compared to the substrate region. The increase in the hardness values might be attributed to the finer microstructure, minor compositional differences or residual stress buildup. This work is sponsored by the Office of Naval Research through grants N00014-14-1-0658.