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Microstructural evolution of a Mo-10W-2Re-0.5HfC alloy was studied in the temperature range of 298 K to 2200 K. The typical characteristics of the microstructure were curly deformation bands, with nucleation at boundaries and subgrain coalescence. The recrystallization temperature of the Mo-10W-2Re-0.5HfC alloy was determined to be near 1950 K, which is comparable with 2125 K for W-4Re-0.35 HfC and 2000 K for W-0.35 HfC. Microhardness tests were performed before and after 1 hour of vacuum annealing and the results indicate that the mechanical strength of Mo-10W-2Re-0.5HfC is lower than that of W-4Re-0.35 HfC or W-0.35 HfC. X-ray diffraction and pole figures indicate that this particular alloy exhibits the primary texture (110) and secondary texture (112) which is normally observed in B.C.C. metals such as Molybdenum. The creep strengths of W-4Re-0.35HfC, TZM-Mo, and W-25Re-30Mo were evaluated and compared at the same stress level.

The effects of collector heat pipe orientation upon the electrical and thermal performance of a planar thermionic converter were investigated. The high heat throughput of the converter must be carried away from the collector following electrical power production. The planar thermionic converter tested employs chemical-vapor-deposited rhenium on molybdenum electrodes, a separately heated two-phase cesium reservoir, and a radiantly coupled, electric emitter heater. The collector also functions as the evaporator end cap for the liquid sodium heat pipe. The converter fixture places the heat pipe in the reflux mode (evaporator below the condenser) and allows orientational changes of 15, 30, 45, and 60 degrees from the vertical. It was determined that the thermionic output performance is a relatively weak function of orientation angle in the range of 0 to 60°. As the emitter temperature increased, the effect of orientation on the converter performance increases.