Strong ductile bulk tungsten

Abstract

Tungsten has long faced the problem of limited to no ductility in bulk polycrystalline form, due in part to the low energy needed for intergranular fracture. This limited ductility can be overcome through processing by dramatically reducing the cross sectional area following a conventional temperature step-down method that improves ductility through elongation of grain boundaries and development of a {110} fiber texture along the length of the material. While this technology is over 100 years old, little progress has been made to improve the ductility of bulk material. In the current investigation plastically deformed bulk tungsten was observed to have a room temperature tensile ductility between 17% and 23% total elongation at failure in bend specimens, and a flexural yield strength near ~ 3GPa. This improvement in ductility following multipass equal channel angular extrusion processing appears to be caused by a similarity in microstructure and texture to that of ductile tungsten wire. The onset temperature for transition to noticeable ductility is seen to decrease dramatically with the level of plastic strain. The results indicate that severe plastic deformation processing at low homologous temperatures may be an effective way to improve the ductility and toughness of bulk tungsten and other brittle crystalline metals.