A study of creep behavior in refractory alloys for thermionic emitter applications

The creep behavior of HfC strengthened tungsten alloys was studied. An ultrahigh vacuum high precision creep test system was constructed for this purpose so that the samples could be heated up to 3000 K for heat treatment and creep strain could be measured from the creep sample inside the vacuum chamber. Creep tests were conducted in tungsten strengthened with 0.37 percent of HfC at temperatures between 2000 K to 2500 K for durations up to 8 weeks. To explain the creep behavior observed in this dispersion strengthened alloy, a creep model was proposed which accounted for the presence of HfC particles in the form of a back stress generated by these particles. This model was verified by the creep test data of a W-0.37HfC alloy tested under both extruded and recrystallized microstructural conditions. According to this model, the steady state creep of this type alloys was expected to increase with time due to the HfC particle coarsening and recrystallization under high temperatures. In contrast, conventional simple power law creep only predicts a constant steady state creep for these materials, which does not represent the microstructural evolution of the materials. In this study, the experimental study was designed to verify the semi-mechanistic phenomenological creep model developed for carbide particle strengthened tungsten alloys