Effects of graphite on the microstructure and properties of ultrafine WC-11Co composites by spark plasma sintering

Ultrafine WC-11Co hard metals added with different proportions of graphite were prepared by spark plasma sintering at 40 MPa/1200 degrees C for 5 mm, and the influence of graphite as free carbon on the microstructure and mechanical properties were investigated. The XRD analysis showed that decarbonization could be prevented by adding graphite. Compact hard metals composed of finer and more homogeneous WC grains with little flaws can be achieved after 0 wt.% to 1.5 wt.% graphite was added. The hardness and fracture toughness increase initially with increasing graphite content, and with over 1.5 wt.% they descend due to coarse grains and more defects. Therefore, 1.5 wt.% graphite is the optimal addition content in view of the hardness and transverse rupture toughness. Furthermore, the coercive force decreases while the saturated magnetic intensity increases with the increase of graphite content.