Effects of NbC additions on the microstructure and properties of non-uniform structure WC-Co cemented carbides

Abstract

In this work, the effects of NbC additions on microstructure and properties of non-uniform structure WC-7Co cemented carbides were investigated X-ray diffractometer, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), mechanical properties tester and electrochemical workstation, respectively. The results show that WC phase can be partially dissolved into the NbC to form a (Nb,W)C solid solution. According to EPMA analysis, the amount of W atoms, dissolving into the NbC grains, increases with the NbC addition. Moreover, when the content of NbC is beyond 1%, the WC-Co cemented carbides with non-uniform structure are formed with significant reduction of average grain size of WC. With NbC addition increasing from 0wt% to 2wt%, the hardness is increased from 1475MPa to 1570MPa while the fracture toughness decreased from 12.1MPam1/2 to 10.3MPam1/2. However, with the further addition of NbC, the hardness slightly decreased. With NbC addition between 0 and 1wt%, the TRS is gradually decreased from 2982MPa to 2745MPa, while, as the NbC content exceeds 1wt%, the TRS leveled off. Because of the decrease of grain size and the (Nb,W)C phase formation, caused by NbC addition, the crack defection was weakened, which led to the decrease of fracture toughness. Meanwhile, the corrosion resistance of non-uniform structure WC-Co cemented carbides can be significantly improved by adding NbC to the material due to increased α-Co in binder phase.