Creep Behavior of Quinary γ′-Strengthened Co-Based Superalloys
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First-principles DFT methods are combined with an experimental approach to characterize the creep behavior of quinary Co-based L1\(_2\)-containing superalloys at elevated temperature conditions. Temperature-dependent SISF energies have been modeled, combining 0 K formation energies with vibrational free energy calculations to assess deformation mechanisms at finite temperature. Two different Co-Al-W alloys, containing the maximum possible amount of DFT-identified d-block alloying additions, were identified and cast as single crystals via the Bridgman process. Creep tests have been performed at two primary testing conditions, one at 900 \(^\circ \)C and the other at 982 \(^\circ \)C. Transmission scanning electron microscopy (TSEM) was performed at 30 kV in a scanning electron microscope to rapidly characterize the defect substructures. We observe a coupled APB/SISF/APB defect structure in Co-based superalloys at the low-temperature condition, similar to the defect structure observed in CoNi, in spite of containing no Ni. At 982 \(^\circ \)C, there is no evidence of faults and precipitates instead contain antiphase boundaries. The role of composition and temperature-dependent fault energies in the deformation process is addressed.
This research was supported by a Grant from the National Science Foundation (NSF-DMREF-1534264). Computational resource support was provided by the Center for Scientific Computing at the CNSI and MRL: an NSF MRSEC (DMR-1121053) and NSF CNS-0960316. We would like to thank Chris Torbet for his assistance in casting and machining of the specimens.
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