Formation mechanisms of microstructure imperfections and their effects on strength in submicron cemented carbide

•Pore-Co-pool and porous structure are the main imperfections for WC-10wt.%Co.•A concentric-octagon step tower structure is found on inner surface of pore-Co-pool.•The formation of the porous microstructure is explained by Co-liquid migration pressure.•Imperfections can be decreased through optimal starting powders and processes.•A subsection linear relation between the size of imperfections and strength is obtained.

The characteristics and formation mechanisms of microstructure imperfections in two sets of submicron WC–10wt.%Co cemented carbides, which are fabricated by vacuum and low-pressure sintering, respectively, are deeply analyzed. Main imperfections are pore-Co-pool in the vacuum-sintered samples. The number of pore-Co-pool is obviously reduced by low-pressure sintering, but many porous microstructures with poor-Co or Co-free are easily introduced; the impurity segregation is also easily formed. Transverse rupture strength (TRS) of samples is strongly affected by the characteristics and size of imperfections. Two linear relationships between TRS and pore size are experimentally established, and a critical pore size has been calculated to be 28.8 μm.