Investigation of TaC precipitation hardening in Co-Re-based alloys

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Co-Re-based alloys have been proposed in 2007 as candidate materials for high temperature applications. They were investigated for the first time in the DFG research group FOR 727 Beyond Ni-Base Superalloys with respect to the interrelation between chemical composition, microstructure and oxidation behavior / mechanical properties, respectively. Precipitation hardening by tantalum carbides (TaC) was identified as particularly attractive strengthening mechanism. Yet, the depth of investigation was limited, focusing on one alloy composition only (Co-17Re-23Cr-1.2Ta-2.6C) and relatively short heat treatment cycles. Therefore, many questions regarding stability, precipitation kinetics and transformation behavior of the tantalum carbides remained open. Besides conventional microstructural characterization tools, in-situ neutron scattering turned out to be particularly valuable as it allows to gain crystallographic and morphological information for representative material volumes during high temperature annealing. In view of this situation a joint research program involving TU Braunschweig and TU München is proposed to thoroughly investigate the precipitation mechanism of tantalum carbides in Co-Re-based alloys. 3D tomography by dual beam microscopy at TU Braunschweig will be used besides the Heinz Maier-Leibnitz neutron source at TU München as essential tool for microstructural characterization. Overall objective is to explore the interrelationship between alloy composition, thermal loading and precipitation behavior of the tantalum carbides as necessary condition to fully exploit the strengthening potential of tantalum carbides during high temperature application of Co-Re-based alloys.