Microstructure Study of Submicron WC Powder and WC-Co Alloys

摘要

TEM analyses in submicron WC-Co alloys reveal the presence of numerous clusters, formed by the pile up of several WC grains related by coincidence relationships. These special orientations are mainly ∑=2 grain boundaries that correspond to rotations of 90° about <101; 0> axes with the approximation c/a=1. Investigations carried out in the WC powder show that most particles are polycrystalline, also containing ∑=2 grain boundaries. Moreover, the WC grain shape is polygonal while it is a triangular prism in the WC-Co alloys. These results show that the WC grains undergo a strong transformation during sintering. The evolution of the powder particles during the sintering stage is discussed in relation with the morphology change of WC grains and stability of ∑=2 grain boundaries. This study suggests that a large part of clusters found in the sintered alloys originates from the powder.