Load-carrying capabilities of refractory alloys for space reactor power applications

To achieve sufficient thermodynamic efficiency, space nuclear power systems must operate above 10000C. A quantitative evaluation of the existing mechanical properties data for the refractory alloys relevant to space nuclear power systems design lifetimes up to seven years at temperatures up to 14000C is being conducted. The most important properties for space nuclear power systems are long-term high-temperature (>10000C) creep strength and ductility, low-temperature (<4000C) fracture toughness [including ductile-to-brittle transition temperature, (DBTT)], and ductility at high strain rates; of special concern are the above properties for weldments of refractory alloys, composition, applied stress, test temperature, test environment (e.g., vacuum, lithium), and thermomechanical treatment (TMT) history. Currently being evaluated are, in order of ascending mp, selected alloys of niobium (e.g., Nb-1% Zr, Nb-1% Zr-0.1% C), molybdenum (e.g., Mo-13% Re), tantalum (e.g., ASTAR-811C), and tungsten (e.g., CVD W and W-25% Re). Creep properties of these alloys have been correlated via Larson-Miller, Manson-Hafered, and other empirical parameters; creep equations have been developed from these correlations. 12 figs., 8 tabs