Materials for High Temperature Applications: Next Generation Superalloys and Beyond: Next Generation Superalloys I
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

Monday 8:30 AM
February 27, 2017
Room: Pacific 16
Location: Marriott Marquis Hotel

Session Chair: Akane Suzuki, GE Global Research; Jonathan Cormier, ENSMA - Institut Pprime

8:30 AM  Keynote
The Drive for Greater Efficiencies: Creating New Materials to Meet the Challenge: David Shifler1; 1Office of Naval Research
     Materials life in gas turbine engines depend on a complex combination of temperature-stress-environment- time variable fields. Research must take a fresh approach to establish a solid science base that will achieve the development of new materials and coatings that will enable greater engine efficiencies. Establishment of this science base requires a comprehensive, multidisciplinary approach that dissects, then later reconnects the critical drivers that influence the performance and life of materials and coatings at high and ultra-high (above 1500°C) temperatures. This approach couples materials science, interfacial science, materials chemistry, diffusion, corrosion and electrochemistry, fluid and solid mechanics, multi-scale thermodynamic and kinetic modeling and simulation, mathematics, and atomistic characterization. Research should establish a basic understanding of performance-limiting mechanisms and control strategies to determine 3-dimensional, multi-scale effects of impurities, chemistries, and environments to maximize micro-mechanical interfacial strength, creep resistance, and thermal stability.

9:00 AM  Invited
Challenges and Future of Ni-based SX Superalloys Components: Jonathan Cormier1; 1ENSMA / Institut Pprime - UPR CNRS 3346
    Increasing the operating temperatures is the most reliable way to improve gas turbine efficiency of aero-engines and industrial gas turbines. A dramatic temperature increase has been obtained in the last four decades by adjusting chemical compositions of cast Ni-based superalloys and by using specific processing routes (e.g. directional solidification). However, despite the recent developments of the 5th and 6th generation of Ni-based SX superalloys, it seems that the expected gain in operating temperature by adjusting the chemistry are rather limited. In this presentation, a special focus will be paid to the improvements still possible in mechanical properties associated to the processing conditions of Ni-based SX superalloys, as well as the consequences of a low temperature plastic deformation introduced in the fabrication stages of SX blades. An overview of their performances under aero-engine certification conditions will also be proposed.

9:30 AM  
The Influence of Ta and Ti on Heat-treatability and γ/γ’-partitioning of High W Containing Re-free Nickel-based-superalloys: Nils Ritter1; Ralf Rettig1; Robert Singer1; 1University of Erlangen-Nuremburg
    This investigation deals with alloys designed by systematically varied amount of Ta and Ti to analyze their effect on heat treatability and partitioning behavior of the solid solution strengthening element W. Ta is more effective in shifting W partitioning behavior towards matrix phase compared to Ti whereas the combination of both reaches even better results. This behavior improves solid-solution-strengthening of the matrix phase. Ta stabilizes γ’-phase at high temperature more effectively compared to Ti but also increases the dissolution temperature of eutectic fraction. The combination of Ta and Ti is increasing eutectic fraction hardly whereas segregation is most severe in alloys containing only Ti. The solidus- and liquidus-temperature is strongly reduced by Ta+Ti and only Ti containing alloys. Therefore Ta is the better γ’ forming and strengthening element for maximum creep-performance at highest application-temperatures whereas Ti is useful in applications with great significance of density at intermediate temperatures.

9:50 AM  
Improved 3rd Generation Single Crystal Superalloy CMSX-4® Plus: Jacqueline Wahl1; Ken Harris1; 1Cannon-Muskegon
    Engine designs require SX superalloy turbine blades and vanes which operate at higher gas and metal temperatures beyond 3% rhenium-containing SX alloys used in commercial and military flight engines. These castings must have excellent high temperature properties, good castability, solution heat treatment, oxidation/hot corrosion resistance, coating compatibility and phase stability. The highest strength 3rd generation SX superalloys (6-7% Re) have exhibited secondary reaction zone phase instability, low temperature internal oxidation/hot corrosion attack and difficulty in production solution heat treatment. Also, 3rd generation SX alloys have high density, a disadvantage in terms of weight and inertia for rotating parts, and high cost from elevated Re content. In response, Cannon-Muskegon has developed and characterized a new SX superalloy with improved properties over CMSX-4 alloy, competitive to 3rd generation alloys. CMSX-4 Plus alloy has been scaled to 5,000 lb production heat status for flight engine testing programs scheduled for 2016 and 2017.

10:10 AM Break

10:30 AM  
Improvement of Creep Resistance at 950 °C/400MPa in Ru-containing Single Crystal Superalloys: Jiajie Huo1; Qianying Shi2; Qiang Feng1; 1University of Science and Technology Beijing; 2University of Michigan
    Microstructure features, including γ' volume fraction, γ-γ' lattice misfit, γ channel width, as well as dislocation substructure had significant influence on the creep performance in Ni-base single crystal superalloys. In this study, creep ruptured and interrupted tests (0.5% and 1.0% creep strain) were taken at 950 °C/400MPa and the microstructural features were quantified to characterize in two single crystal superalloys containing high level of Co and different levels of Mo and Ru additions. The alloy with high level additions of Mo and Ru exhibited more negative γ-γ´ lattice misfit and better creep performance. Large amounts of stacking faults were observed in the γ matrix after 0.5% creep strain and they were considered as a major factor to improve the creep performance. This study is helpful to understand the effect of microstructure on creep performance and get better knowledge of physical metallurgy in Ru-containing single crystal superalloys.

10:50 AM  
Improved Creep Strength of Nickel-base Superalloys by Optimized γ/γ'-partitioning Behavior of Solid Solution Strengthening Elements : Steffen Neumeier1; Martin Pröbstle2; Sven Giese2; Ralf Rettig2; Mathias Göken2; 1Friedrich-Alexander-Universität Erlangen-Nürnberg ; 2Friedrich-Alexander-Universität Erlangen-Nürnberg
    Solid solution strengthening of the γ-matrix is one key factor for improving the creep strength of single crystal nickel-base superalloys in the high temperature creep regime where dislocations climb along the γ/γ'-interface. Investigations on the creep properties of a series of alloys with constant Ni, Co, Al and Cr content and 3.6 at.% of Ir, Mo, Re, Rh, Ru, W and combinations of Re, Mo and W show that the diffusivity of the refractory elements in combination with their tendency to partition to the γ-matrix influences strongly the creep strength. Based on these findings the creep strength of a Re-free alloy was significantly improved by optimizing the partitioning behavior of the slowly diffusing element W through the addition of Ti. The Re-free alloy shows a creep strength similar to that of the Re-containing alloy CMSX-4.

11:10 AM  
Sources of Creep Dislocations in Ni-base, Single Crystal Superalloys Revisited: Farangis Ram1; Zhuangming Li2; Zailing Zhu3; Masood Hafez Haghighat2; Stefan Zaefferer2; Dierk Raabe2; Roger Reed3; 1Carnegie Mellon University; 2Max-Planck Institut für Eisenforschung GmbH; 3University of Oxford
    The origin of creep dislocations in Ni-base, single-crystal superalloys at intermediate stress and temperature regimes is revisited. Using cross-correlation EBSD, subgrain boundaries in uncrept state were mapped and quantified. They accommodate lattice rotations of below 0.2°. Using electron channeling contrast imaging (ECCI), we found that although subgrains emit creep dislocations, they only account for a small number of creep dislocations that are in their close vicinity. In contrast, large amounts of dislocations were observed to develop far away from any interface. Discrete Dislocation Dynamics (DDD) simulations showed that the major sources of creep dislocations are isolated, individual dislocations in the uncrept material. They are homogenously spread in small quantities 1011 m/m3 far from subgrain boundaries before creep begins and are activated after activation of dislocations in subgrain boundaries. Once activated, they emit avalanches of creep dislocation into boundary-free regions and increase the dislocation density by two orders of magnitude.

11:30 AM  
Influence of Stress Trriaxiality and Relaxation on the Creep Behavior under Oxidizing Conditions of the Nickel-based Single-crystal Superalloy CMSX-4: Experiments and Numerical Approach: Vincenzo Caccuri1; Jonathan Cormier2; Rodrigue Desmorat3; Clara Moriconi4; 1ENSMA -Institut P'/LMT Cachan/Safran Helicopter Engines; 2ENSMA -Institut P'; 3LMT Cachan; 4Safran Helicopter Engines
    In this work, the temperature, stress level and triaxiality dependence of the coupled creep/oxidation response of the nickel-based single-crystal superalloy CMSX-4, is investigated. In particular, the impact of stress relaxation close to notches, affecting local triaxiality, is studied through creep tests in air at very high temperatures (T > 1100°C) on specimens specifically designed to trigger this phenomenon. γ/γ’ microstructural evolutions of the material, observed after these tests, is analyzed through SEM characterizations and quantified by image analysis (sub-surface γ’ depletion, γ’ rafting orientation, γ channels thickness and oxidized zones) in order to take them into account in the development of the model. By performing different finite element simulations using more or less complex constitutive behaviors (Norton’s law, Polystar model), the impact of the stress relaxation and triaxiality on the oxidation and γ’ depletion kinetics is rationalized.

11:50 AM  
Determination of Gamma/Gamma Prime Lattice Misfit in Ni-based Single Crystal Superalloys at High Temperatures by Neutron Diffraction: Shenyan Huang1; Yan Gao1; Akane Suzuki1; Ke An2; 1GE Global Research; 2Oak Ridge National Laboratory
    Lattice misfit between Gamma and Gamma-Prime phases is one of the critical properties that influence thermal stability and high temperature mechanical behaviors of Ni-based single-crystal superalloys used in aircraft engines and power generation gas turbines. Lattice misfit can be altered by alloy composition, heat treatment conditions, and temperature, via Gamma and Gamma-Prime phase compositions. Determination of lattice misfit is an important step to link structure and properties and provide input for modeling microstructure and properties of single crystal superalloys. However, very few high-temperature misfit data are available in literature as accurate determination of lattice misfit for single crystals is not trivial. In this talk, experimental methods & challenges to measure misfit will be reviewed, and results (up to 2200°F) for commercial single crystal superalloys including René N4, René N5, CMSX4, PWA1484, will be presented. Effects of chemistry and heat treatment on lattice misfit will be discussed.