More Ductile Bulk Tungsten

This SBIR Phase I effort will develop and demonstrate a novel manufacturing process based on severe plastic deformation (SPD) to refine and enhance the microstructure-properties of bulk tungsten. Tungsten, with its many unique characteristics, plays an important role in nuclear reactors including for the nuclear thermal propulsion engine. The refractory metal, however, still has a number of shortcomings which still need to be addressed. These include a high ductile-to-brittle transition temperature, low ductility and poor fracture toughness, low machinability and fabricability, low-temperature brittleness, radiation-induced brittleness, and a relatively low recrystallization (RX) temperature compared to its operation temperature. The use of W above its RX temperature interminably can be unsafe because its mechanical properties decrease in such an environment. Low-temperature brittleness also imposes restrictions on the application of W as a structural material. And, given its high hardness, high brittleness, and poor machinability, W parts can be very costly and time-consuming to manufacture. Past efforts to increase the ductility of W were primarily directed on alloying, grain refinement, extreme working, area reductions, impurity reductions, and heat treatments. While ductile W currently exists in wire form (e.g., filaments) through extensive working and area reduction, this approach is clearly not practical for applications where bulk size parts are needed.