Microstructure and mechanical properties of wire drawn tungsten

Tungsten (W) shows a pronounced transition from ductile deformation behaviour at high temperatures to brittle behaviour at low temperatures (ductile-to-brittle transition). Undeformed, coarse-grained W exhibits transition temperatures around 200 °C to 300 °C, rendering it unsuitable for structural applications at room temperature. The transition is shifted to lower temperatures by cold-working W in wire drawing, rolling or a severe plastic deformation process. Sufficiently cold-worked W materials deform plastically at room temperature and below. The reasons for the shift of the transition temperature are connected to the deformation-induced microstructural changes. We performed the first systematic study of the relationship between microstructure and deformation mechanisms on a series of sequentially drawn potassium-doped W wires. The deformation behaviour and the strength of the wires were investigated using tensile tests and transient mechanical tests at room temperature; the microstructure was characterised using electron backscatter diffraction (EBSD). Quantitative results on the deformation-induced microstructural evolution and its effect on the mechanical properties will be presented. Furthermore, possible theories on the reasons for the shift of the ductile-to-brittle transition upon cold-working are discussed.