More Ductile Bulk Tungsten

This SBIR Phase II effort will continue to develop and then scale up a novel manufacturing process based on severe plastic deformation (SPD) to refine and enhance the microstructure-properties of bulk tungsten.nbsp; Tungsten, with its many unique characteristics, plays an important role in nuclear reactors including for the nuclear thermal propulsion (NTP) engine.nbsp; The refractory metal, however, still has a number of shortcomings which still need to be addressed.nbsp; These include a high ductile-to-brittle transition temperature (DBTT), 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.nbsp; The use of W above its RX temperature interminably can be unsafe because its mechanical properties decrease in such an environment.nbsp; Low-temperature brittleness also imposes restrictions on the application of W as a structural material.nbsp; And, given its high hardness, high brittleness, and poor machinability, W parts can be very costly and time-consuming to manufacture.nbsp; Past efforts to increase the ductility of W were primarily directed on alloying, grain refinement, extreme working, area reductions, impurity reductions, and heat treatments.nbsp; 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.nbsp; Thus, a compaction deformation method under both controlled pressure and temperature along with compressive and shear deformation in a hot die system will be demonstrated here to quot;ductilizequot; W.