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An experimental study was performed to identify the effects of dynamic strain aging (solute drag) and metallurgical instabilities under thermomechanical loading conditions. The study involved a series of closely controlled thermomechanical deformation (TMD) tests on the solid-solution-strengthened nickel-base superalloy, Hastelloy X.™4 This alloy exhibits a strong isothermal strain aging peak at approximately 600°C promoted by the combined effects of solute drag and precipitation hardening. Macroscopic thermomechanical hardening trends are correlated with microstructural characteristics through the use of transmission electron microscopy. These observations are also compared and contrasted with isothermal conditions. Thermomechanical behavior unique to the isothermal database is identified and discussed. The microstructural characteristics were shown to be dominated by effects associated with the highest temperature of the thermomechanical cycle. Results clearly reveal that the deformation behavior of Hastelloy X is thermomechanically path dependent. In addition, guidance is given pertaining to deformation modeling in the context of a macroscopic unified thermoviscoplastic constitutive theory. An internal state variable is formulated to qualitatively reflect the isotropic hardening trends identified in the TMD experiments.
thermomechanical deformation (TMD), dynamic strain aging, thermovisco plastic modeling, solute drag, Hastelloy X, ™, precipitation hardening, microstructural instabilities
Research Engineer, Sverdrup Technology Inc., LeRC Group, Brook Park, OH
Chief, NASA Lewis Research Center, Cleveland, OH
Professor, University of Akron, Akron, OH