Materials for High Temperature Applications: Next Generation Superalloys and Beyond: Superalloys: Mechanical Behavior
Sponsored by: TMS Structural Materials Division, TMS: Refractory Metals Committee
Program Organizers: Govindarajan Muralidharan, Oak Ridge National Laboratory; Martin Heilmaier, KIT Karlsruhe; Benjamin Adam, Oregon State University; Mario Bochiechio, Pratt & Whitney; Katerina Christofidou, University of Sheffield; Eric Lass, University of Tennessee-Knoxville; Jeremy Rame, Naarea; Sallot Pierre, Safran; Akane Suzuki, GE Aerospace Research; Michael Titus, Purdue University

Monday 2:00 PM
March 15, 2021
Room: RM 8
Location: TMS2021 Virtual

Session Chair: Michael Titus, Purdue University; Mario Bochiechio, Pratt & Whitney


2:00 PM  
Damage Mechanisms Involved during Very High Cycle Fatigue of a Coated and Grit-blasted Ni-based Single-crystal Superalloy: Alice Cervellon1; Luciana Bortoluci Ormastroni2; Tresa Pollock1; Fernando Pedraza3; Jonathan Cormier2; 1University Of California Santa Barbara; 2Institut Pprime; 3LaSIE
    The very high cycle fatigue (VHCF) regime of Ni-based single-crystal superalloys is mostly controlled by the size and nature of internal defects, typically large casting pores inherited from the solidification process. At the component scale, these alloys are coated in order to ensure sufficient oxidation/corrosion resistance. The impact of such surface deposition on the VHCF properties at 1,000°C has been assessed in this work.The deposition of an MCrAlY coating has been observed to reduce the VHCF life of CMSX-4 alloy compared to a polished surface. Damage mechanisms involved in the interdiffusion zone accelerate the early crack growth stage and the resultant fatigue life. Special attention was paid to the cellular recrystallization found in the interdiffusion zone and induced by the grit-blasting process applied to the specimens prior to the coating deposition. Uncoated grit-blasted specimens were independently studied to assess the impact of this process on the VHCF properties.

2:20 PM  Invited
Enhancing the Creep Strength of Next Generation Disk Superalloys via Local Phase Transformation Strengthening: Timothy Smith1; Timothy Gabb1; Katelun Wertz2; Joshua Stuckner1; Laura Evans1; Ashton Egan3; Michael Mills3; 1NASA Glenn Research Center; 2AFRL; 3Ohio State University
    A new disk superalloy has been developed by NASA to improve high temperature creep performance utilizing the recently discovered local phase transformation strengthening mechanism. Creep tests were performed at 760°C and 552MPa, to approximately 0.3% plastic strain, a regime where the formation of γʹ shearing modes such as superlattice extrinsic and intrinsic stacking faults are active. The new alloy exhibited superior creep performance over the current state-of-the-art superalloys, ME3 and LSHR. High resolution characterization confirmed the formation of the strengthening η phase along superlattice extrinsic stacking faults and χ phase along superlattice intrinsic stacking faults. In addition, creep deformation analysis via scanning transmission electron microscopy appears to show a significant reduction in microtwin formation as compared to LSHR and ME3. This improvement in creep performance was also accompanied by an improvement in both room temperature and high temperature strength.

2:50 PM  
Quantifying Deformation Processes Resulting in Local Phase Transformation Strengthening: Ashton Egan1; Veronika Mazanova1; Timothy Smith2; Timothy Gabb2; Timothy Hanlon3; Michael Mills1; 1Ohio State University; 2NASA Glenn Research Center; 3GE Research
    Despite improved understanding of factors controlling high temperature strength, there are still questions concerning the intermediate creep regime dominated by planar defects and microtwinning. A hypothesis is that these deformation mechanisms, and therefore strain rates, are controlled by local segregation events surrounding the leading partial dislocations. Of particular interest are alloys exhibiting Local Phase Transformation (LPT) strengthening at planar defects. In this work, [001] and [110] oriented single crystal analogues of commercially available ME501 and newly developed NASA Alloy were studied to extract fundamental parameters (e.g. activation energies and creep exponents) relating to SESF/microtwin and SISF/ribbon deformation modes while remaining unaffected by grain boundary effects. Scanning Transmission Electron Microscopy was used to study local atomic structure and segregation profiles relating to these processes. As the alloys are similar except content of χ formers, this quantification reflected the extent of LPT strengthening. Interrupted testing also allowed for examination of deformation/microstructural evolution.

3:10 PM  
Solute Segregation at Intrinsic Stacking Faults in Disordered Face-centered Cubic Ni-Co Solid Solution: First-principles and Thermodynamic Modeling: Dongsheng Wen; Longsheng Feng1; Yunzhi Wang1; Michael Titus2; 1The Ohio State University; 2Purdue University
    Displacive-diffusive phase transformations that involve complex shearing, reordering, and diffusion mechanisms in the L12-gamma’ phase during high temperature creep have recently been observed in Ni-, NiCo-, and Co-based superalloys and have been correlated with high temperature mechanical properties of these alloys. To better understand these processes, we have determined the equilibrium intrinsic stacking fault composition, unsegregated stacking fault energy (SFE), and segregated SFE in the disordered face-centered cubic Ni-Co solid solution as a function of composition and temperature. Comparisons to experiments show that the segregated SFE, calculated via first-principles, matches within 5% of experimentally-determined SFEs. Furthermore, we found that the predicted segregation enthalpy matches well with bulk thermodynamic calculations. The predicted segregation energy is also used to evaluate thermodynamic properties of the stacking fault and then compared to its bulk counterpart. The implications for improving high temperature mechanical properties will be presented, and new alloy design strategies will be discussed.

3:30 PM  
Partitioning of Cu and Si Contaminants in a Ni-based Superalloy and their Effect on Creep Properties: Martin Detrois1; Zongrui Pei1; Kyle Rozman1; Michael Gao1; Jonathan Poplawsky2; Paul Jablonski1; Jeffrey Hawk1; 1National Energy Technology Laboratory; 2Oak Ridge National Laboratory
    The choice of stock material to form an alloy composition affects the overall purity of the final product. Two Al raw material sources were selected for incorporation into an advanced Ni-based superalloy which resulted in low purity alloys (containing 0.138 wt.% Cu and 0.019 wt.% Si) and high-purity alloys (containing less than 0.003 wt.% Cu and 0.010 wt.% Si). Atom-probe tomography (APT) revealed Si partitioning at the grain boundaries, MC-carbide/γ, M3B2-boride/γ-γ′. Copper primarily segregated to the γ′ precipitates. An average of 2.4x decrease in creep life and 4.3x decrease in creep ductility was measured in the low purity alloys, which was attributed to the embrittlement caused by Si segregation to grain boundaries. Furthermore, Si reduced the positive effect of B segregation to grain boundaries on creep performance. Monte Carlo simulations were performed to describe the partitioning of Cu and Si atoms to either γ or γ′ phases.

3:50 PM  
Deformation of the γ’’’-Ni2(Cr, Mo, W) Phase during Mechanical Testing: Thomas Mann1; Michael Fahrmann2; Michael Titus1; 1Purdue University; 2Haynes International
    Haynes® 244® alloy was designed as a high strength, low thermal expansion alloy which is strengthened by the γ’’’-Ni2(Cr, Mo, W) phase. Studies of the deformation behavior of the γ’’’-Ni2(Cr,Mo) precipitates present in Haynes® 242® alloy have shown that slip and twinning are the dominant deformation mechanisms at room temperature in standard tension and compression. The addition of W to Haynes® 244® alloy and the corresponding 10% increase in yield strength suggest a potential change in mechanisms and/or strong dependence of the planar defect energies with respect to W content. Density functional theory (DFT) calculations show the possibility of a favorable slip pathway for some variants, and a large barrier for slip in others that could preclude slip and favor twinning. TEM analysis of the deformed microstructure will be made and compared to the predictions of the first principles calculations as well as analyzed for the effect of variant orientation.

4:10 PM  
Mechanical Properties and Microstructural Characterization of Cast Haynes 282 for Advanced Ultra-supercritical (A-USC) Applications: Ling Wang1; Kinga Unocic1; Peter Tortorelli1; Xiang Chen1; 1Oak Ridge National Laboratory
    Precipitation strengthened Ni-based alloys are leading candidate materials for Advanced Ultra-Supercritical (A-USC) plants with steam conditions up to 760oC (1400oF)/35 MPa (5 ksi). This project focuses on evaluating representative specimens from the largest sand casting of Haynes 282 (pour weight of 3,175 kg). The tensile test results of Haynes 282 casting over the temperature range 20-816oC exhibited lower tensile strength and ductility in comparison with the wrought reference Haynes 282. However, the creep rupture tests of the cast alloy under 700-788oC presented similar Larson-Miller parameter as the wrought material, with the creep rupture time range between 1,515 and 5,452 hours. Characterization involved scanning electron microscopy (SEM) and scanning transmission electron microscopy (S/TEM) in conjunction with energy dispersive x-ray spectroscopy to understand the microstructural changes, dislocation structure, carbides distribution and the morphology of the gamma prime precipitates exposed to elevated temperatures and to establish relationship between microstructures and mechanical properties.

4:30 PM  
Microstructure and Mechanical Properties of a Centrifugal Cast Ni-Based Alloy: Govindarajan Muralidharan1; Shivakant Shukla1; Jim Myers2; 1Oak Ridge National Laboratory; 2Metaltek International
    Generation 3 Concentrated Solar Power Systems are being targeted for operating temperatures greater than 700°C. Ni-based alloy such as Haynes®282® has the potential to satisfy the high temperature mechanical property requirements but cost and availability are major factors to be considered in its use. Components such as piping can be manufactured at a lower cost using a centrifugal casting process and can be produced on demand thus improving flexibility. This talk will present the effect of centrifugal casting and subsequent heat-treatment on the microstructure, high temperature tensile and short-term creep properties of Haynes®282® and compare these with that obtained from traditional wrought processing. This work was supported by the US Department of Energy - Solar Energy Technologies Office Concentrating Solar Thermal Power Program. This research was conducted by Oak Ridge National Laboratory, which is managed by UT Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE).