Elastic Properties of Novel Co- and CoNi-Based Superalloys Determined through Bayesian Inference and Resonant Ultrasound
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TRODUCTION
PROPELLED by incredible advances in engineering and materials science—and the promise of greater turbine efficiencies and reduced emissions—the operational limits of Ni-based superalloys have been extended to regimes that include periods at over 90 pct of their melting point,[1] all while maintaining considerable BRENT R. GOODLET, MARIE-AGATHE CHARPAGNE, SEAN P. MURRAY, WILLIAM C. LENTHE and TRESA M. POLLOCK are with the Materials Department, University of California, Santa Barbara, CA 93106, Contact e-mail: [email protected] LEAH MILLS is with the Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210. BEN BALES and LINDA PETZOLD are with the Department of Mechanical Engineering, University of California, Santa Barbara, CA 93106. Manuscript submitted December 30, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
mechanical loads in deleterious environmental conditions. Inherent limits exist for future development, as the melting temperature (or more accurately the liquidus and solidus temperatures) is intrinsic to the material and cannot be appreciably increased. This reality has spurred research and development of ordered intermetallic alloys such as NiAl-,[2] Nb-, and Mo-based refractory alloys,[3–6] and ceramic composites of alumina[7] and silicon carbide,[8] all with the goal of supplanting Ni-based superalloys for the most demanding high-temperature applications. However, these alternatives often suffer from poor fracture toughness and processing constraints that make their current use costly and limited,[3–5,9] especially considering the safety requirements for use in aerospace. Given the payoff for increased turbine engine operating temperatures and the limitations of current alternatives to Ni-based superalloys, considerable attention has been directed toward potential intermediate
solutions such as c c0 Co-based superalloys[10] and hybrid CoNi-based alloys.[11] The primary motivation for studying these alloys is clear, as the melting point of Co exceeds that of Ni by 40 C.[12] They also have the benefit of being cast and processed similar to existing Ni-based superalloys, minimizing the cost of development by leveraging existing infrastructure. Of course there are some outstanding issues that must be addressed before these alloys may become technically relevant, including: a low c0 solvus temperature,[13] poor oxidation resistance,[14] and in some cases a less favorable thermal expansion coefficient for adhesion of protective alumina as compared to Ni-based superalloys.[15] Due to the promise of future operating temperature improvements, this research focuses on measuring the single crystal elastic constants of select Co- and CoNi-based superalloys. Since turbine blades operate under nominally elastic conditions, elastic properties are critically important to design, though have not yet been measured for these new classes of Co-based materials. In a prior publication,[16] we demonstrated the first full Bayesian approach to determining elastic con
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