Sintering behavior of spherical mono-sized tungsten powder

Compared to commercially reduced tungsten powders with relative sinter densities of ρ/ρth = 0.87…0.92, the achievable relative sinter density of spherical powders reached only 74% of the theoretical density. Besides the already known “saddle-shaped” neck profiles, crystallographic defined neck contours were found whose symmetry corresponds to the surface crystallography of a tetracaidecahedron. The kinetic of the neck growth obeys the known cubic time law. The activation energy of the neck growth amounts to Q = 315 ± 44 kJ/mol. Simultaneously with the neck growth, there occurs an increasing transformation of the spherical particle habit into defined surface facets. The results will be discussed under consideration of the effects of direct sintering and the potassium bubble effect.