The effect of phosphorus additions on densification, grain growth and properties of nanocrystalline WC-Co composites

To control the grain growth of nanocrystalline WC-Co cemented carbides by phosphorus (P) doping was studied in spark plasma sintering (SPS). Experimental results show that the use of small amount of phosphorus dopant to chemically-activated sintering of the nanocrystalline WC-Co composites could enhance the sinterability, promote the low temperature densification, and decrease the sintering temperature of the WC-Co nanocomposites. With only 0.3 wt.% P additions, full density WC-7Co cermets were obtained at temperature as low as 1000°C, which is 100°C lower than that of the undoped counterparts in spark plasma sintering of the nanocomposites. By phosphorus doping in WC-Co nanocomposites, the grain growth of WC-Co cemented carbides could be inhibited to some extent, as a result WC-7wt.% Co-0.3 wt.% P cemented carbides with average WC grain size of 200 nm were achieved, which can be attributed to the lower sintering temperature resulting in a decrease of grain boundary mobility. Mechanical properties measurements show that P doping could lead to a great increment of hardness, but at the same time a little sacrifice of fracture toughness of the nano-WC-Co cemented carbides.