Deformation and Damage Mechanisms of High Temperature Alloys: New Material & Design Considerations
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee
Program Organizers: Mark Hardy, Rolls-Royce Plc; Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346; Jeremy Rame, Naarea; Akane Suzuki, GE Aerospace Research; Jean-Charles Stinville, University of California, Santa Barbara; Paraskevas Kontis, Norwegian University of Science and Technology; Andrew Wessman, University of Arizona

Thursday 8:30 AM
March 3, 2022
Room: 263A
Location: Anaheim Convention Center

Session Chair: Jonathan Cormier, ISAE-ENSMA & Institut Pprime; Jean Charles Stinville, University of Illinois at Urbana-Champaign

8:30 AM
Tensile Ductility and Plastic Deformation Behavior of Polycrystalline Refractory Multi-principal Element Alloys: Leah Mills¹; Jean-Charles Stinville¹; Marie-Agathe Charpagne¹; Carolina Frey¹; Valéry Valle²; Noah Philips³; Daniel Gianola¹; Tresa Pollock¹; ¹University of California-Santa Barbara; ²Pprime Institut-Université de Poitiers; ³ATI Specialty Alloys and Components
    The high temperature strength of Refractory Multi-Principal Element Alloys (RMPEAs) is promising for extreme structural applications. However, ambient temperature tensile ductility is also important for processability. Microstructure development along cold-rolling and annealing processing paths and the mechanical performance of the RMPEAs Hf₂₀Nb₂₀Ta₂₀Ti₂₀Zr₂₀ and Hf₁₀Nb₃₅Ta₃₀Ti₂₅ are investigated. These two compositions were amenable to cold-rolling and the resulting fully recrystallized and single-phase microstructures are compared. Characterization of plastic deformation behavior in these polycrystalline materials by High-Resolution Digital Image Correlation (HR-DIC) in the scanning electron microscope is employed to investigate the heterogeneity of dislocation slip on a grain-to-grain basis, and locally at the scale of individual slip traces, as well as its relationship to macroscopic tensile properties.

8:50 AM
Composition and Heat Treatment Modifications of a New Low-cost Ni Base Wrought Alloy for Improved Creep Resistance and Elevated Temperature Ductility: Ning Zhou¹; Filip Van Weereld¹; Gian Colombo¹; ¹Carpenter Technology Corporation
    A new low-cost γ' strengthened wrought Ni base alloy was developed to offer higher temperature capability than 718 and lower cost than Waspaloy. Although this new alloy achieved superior elevated temperature strength (yield and UTS), it did not simultaneously match the creep performance and ductility with Waspaloy at elevated temperatures. Chemistry modifications were performed by fixing the amount of γ' forming elements including Al, Ti and Nb, to keep the equilibrium γ' fraction unchanged for good mechanical performance as well as processability, while varying elements such as Co, Ni, Fe and W to examine their impact on various properties including creep and ductility. Various heat treatments were also examined to balance the strength and creep resistance.

9:10 AM
A Comparative Analysis of the Low-cycle Fatigue Behaviors of HAYNES 244 Alloy and Waspaloy: Michael Fahrmann¹; ¹Haynes International
    Waspaloy is a legacy Ni-base superalloy that has found many uses in gas turbine engines, among those being stationary structural parts such as cases. A reasonably low coefficient of thermal expansion and adequate resistance to low-cycle fatigue (LCF) are key requirements for such applications. Recently developed low coefficient of thermal expansion, high strength HAYNESŽ 244Ž alloy offers temperature capability to 1400oF (760oC), albeit not at the same level of strength as Waspaloy. A test program was initiated to assess the LCF behaviors of both alloys in uniaxial strain-controlled mode at elevated temperatures. The performance of both alloys is compared, supported by an analysis of their fracture surfaces. Special emphasis is placed on the alloys’ cyclic hardening and softening behavior and its impact on fatigue life. Implications for resistance to thermal fatigue are discussed.

9:30 AM
Deformation Twinning during Elevated Temperature Testing in HAYNES^Ž 244^Ž Alloy: Thomas Mann¹; Michael Fahrmann²; Michael Titus¹; ¹Purdue University; ²Haynes International
    HAYNES^Ž 244^Ž alloy was designed as a high strength, low CTE alloy for use in advanced gas turbine engines. The alloy’s remarkable mechanical properties arise from the distribution of a novel intermetallic phase, the γ´´´-Immm Ni₂(Cr, Mo, W) phase, that enables complex deformation mechanisms over orders of magnitude of strain rates. We elucidated these deformation mechanisms and observed deformation twinning during elevated temperature tensile testing and low cycle fatigue, and more complex shearing and dislocation bowing mechanisms during high temperature creep. These mechanisms will be compared to other Ni-based superalloys strengthened through other intermetallic phases such as γ´ and γ´´, and we will detail how the Immm Ni₂(Cr, Mo, W) phase improves the strength, ductility, work hardening, and damage tolerance of this alloy.

9:50 AM
An In-situ SEM Elevated-temperature Investigation of Serrated Plastic Flow in a CoCrFeNiW-C Alloy : Shaolou Wei¹; Daniel Moriarty¹; Cem Tasan¹; ¹Massachusetts Institute of Technology
    Multi-component Co-alloys are a class of promising metallic materials for high-temperature applications. Provided the fruitful screening of their yield strength preservation trend depending on different alloy design strategies, systematic understandings of their plastic deformation response are still in lack. The present work is focused on the plastic deformation mechanisms of a CoCrFeNiW-C alloy at 650 oC, with emphases on dislocation slip activities and serrated plastic flow features. By integrating high-temperature in-situ scanning electron microscopy-based tests, statistical analyses, and theoretical calculations, the following mechanistic insights will be discussed: (1) what causes the serrated plastic flow response and thereby the transition in its module? (2) what are the embedded dynamic features amongst the serration incidents? and (3) what kind of deformation substructures are associated with the serrated plastic flow? Quantitative analysis of the dislocation slip mechanisms as well as their impacts on damage initiation will also be revealed in greater depth.