The Σ = 2 and Σ = 13a grain boundary distributions in cemented tungsten carbides with/without metallic binders

Abstract

Cemented tungsten carbides with/without metallic binders were prepared through spark plasma sintering (SPS). The coincidence site lattice grain boundaries of the materials were characterized by electron backscattered diffraction (EBSD) technology. Misorientation angle distribution and grain boundary plane orientation distributions of Σ = 2 and Σ = 13a boundaries in the above WC materials are demonstrated. The reasons for the high fraction of Σ = 2 boundaries and the weaker misorientation texture at 30° in cemented tungsten carbides without metallic binders were discussed. It was found that the binder types have little effect on the high population of Σ = 2 boundaries in spark plasma sintered pure WC, WC-Co and WC with various ceramic binders such as Al2O3, ZrO2, Al2O3-ZrO2 and Al2O3-ZrO2-B2O3. In contrast, the mean grain size of WC carbides exhibits direct relation with the population of Σ = 2 boundaries. The coalescence mechanism during solid-state sintering are confirmed for eliminating the 90° boundaries and decreasing the intensity for habit planes distribution for Σ = 2 boundaries. The result support the theory that the preference of Σ = 2 low-energy boundaries in cemented carbides is rather dependent on the anisotropic surface energy of different planes than the cobalt content. This discovery facilitates to a better understanding of the origin of Σ = 2 boundaries in WC based materials.