EBSD characterization of pure and K-doped tungsten fibers annealed at different temperatures

Electron Backscatter Diffraction was used to investigate the grain boundary character and triple junction distributions as well as the microtexture on drawn pure and potassium doped (60–75 ppm) tungsten wires. With an approximate diameter of 150 μm, pure W wires were annealed at 1300, 1600 and 1900 °C, whereas K-doped material was annealed at 1300, 1600 and 2100 °C. The annealing was performed under hydrogen atmosphere for 30 min. Both longitudinal and transversal sections were analyzed to assess anisotropic features. Up to 1600 °C, all conditions presented a strong <110> fiber texture parallel to the drawing axis. With increasing annealing temperature, the pure W material developed a more heterogeneous fiber texture while for the K-doped material, it remained homogeneous. Orientation correlation function (OCF) analysis suggested sub-grain coarsening as the recrystallization mechanism while grain boundary density and grain boundary character distribution exhibited anisotropic behavior, as well as the triple junction distribution network. On the other hand, the coincidence site lattices (CSL) distribution did not present any anisotropy and followed the empirical law of the inverse cubic root of Σ-value. For all conditions, the most abundant CSL boundaries were Σ3, Σ9, Σ11, Σ17b, Σ19a, Σ27a and Σ33a. Based on the statistics of the triple junction types and their resistance to intergranular cracking, it was revealed that increasing the annealing temperature might play a role in crack deflection since the resistance to intergranular crack growth is increased in the transversal section and reduced in the longitudinal section. This anisotropic behavior is preserved up to a higher annealing temperature in the K-doped material.