Field Assisted Sintering Technique Compaction of Ultrafine-Grained Binderless WC Hard Metals

Tungsten carbide (WC) powder having a crystallite size around 55 nm and the Brunauer-Emmett-Teller specific surface area 2.75 $m^2//g$ was sintered using the field assisted sintering/spark plasma sintering technique. Sintered samples were investigated using different analytical methods providing detailed information on the microstructure and mechanical properties of materials. Density and porosity of specimens were determined using the Archimedes principle and optical and scanning electron micrographs. The X-ray diffraction investigations provided the information on the crystal real structure and crystallite sizes. The electron backscatter diffraction measurements yielded the details about the grain size, frequency, and distributions of grain boundaries. Finally, the essential mechanical properties of sintered samples were obtained from the hardness and fracture toughness measurements. The influences of individual sintering conditions: sintering temperature and sintering time especially, on the microstructure and mechanical properties of sintered specimens were derived. Fully compact samples having the Vickers hardness HV10 around 29 GPa and fracture toughness $K_{Ic}$ approximately 7.2 MPa $m^{1//2}$ were sintered from temperatures of 1800C and holding times 1 min. Specimens sintered at lower temperatures showed lower density which resulted in a significant drop in the sample hardness.