Nanostructures through Channel Die Pressing

Continued interest in the enhancement of warhead liner performance has led to a number of studies focused on liner material ductility and consistency. Specifically, cold upset forging and annealing have been shown to produce significant grain refinementand texture development in liner plates of various materials. However, in tantalum, and possibly other warhead metals, variations in thermo-mechanical processing among different mills can persist as inconsistencies in the final plate, even following theextensive changes in microstructure occurring in cold forging and subsequent annealing. Equal-channel angular pressing (ECAP) is a material conditioning process, involving grain boundary engineering, which by intensive shear deformation is able to produceultrafine grain sizes (nanostructures), without changing the overall shape of the piece. Application of this process to condition 2.5-inch diameter bar stock segments prior to the cold forging of plates could potentially erase any material bias fromprevious processing. Nanostructured metal also offers the potential for enhanced performance in tantalum or HCP metals due to its unusual combination of high strength and high ductility. This project will apply this sequence to three warhead materials,characterize the resulting structures and deliver 9-inch diameter plates to Eglin for testing.