Evolution of microstructure, texture and grain boundary character distribution of potassium doped tungsten fibers annealed at variable temperatures

The effect of the annealing temperature on the microstructure and grain boundary character distribution of potassium doped tungsten fibers made of drawn wire was investigated by Electron Backscatter Diffraction. Samples, with a diameter of 148.7 μm, in the as-received condition and annealed at 1300, 1600, 1900, 2100 and 2300 °C were analyzed at the center of the transversal sections. Up to 1900 °C, a uniform microstructural coarsening and primary recrystallization followed by normal grain growth was observed. Between 1900 and 2100 °C abnormal grain growth took place. The strong texture (<110> parallel to the drawing axis) remained present in all conditions. With increasing the annealing temperature, the low angle grain boundary fraction increased at the expense of high angle grain boundaries while the amount of coincidence site lattice boundaries reached its maximum at 1600 °C. At this temperature, the most resistant configuration of triple junctions against intergranular crack propagation was obtained.