Combined effect of SiC and carbon on sintering kinetics, microstructure and mechanical properties of fine-grained binderless tungsten carbide: A case of the DC arc plasma chemical synthesis WC nanopowders

The study investigates the density, phase composition, microstructure and mechanical properties of ceramics obtained by the Spark Plasma Sintering (SPS). Three groups of materials were investigated: WC ceramics (Group I), WC + C ceramics (Group II), and WC + C + SiC ceramics (Group III). Nanopowders of α-WC produced by DC arc plasma chemical synthesis and hydrogen annealing. Powder compositions for sintering contained colloidal graphite (0.3, 0.5% wt.) or graphite (0.3% wt.) and β-SiC (1, 3, 5% wt.). The effect of preliminary cold pressing, heating rate, and degassing time on the properties of ceramics has been investigated. The graphite concentration in the WC nanopowder compositions increases the shrinkage rate at the intensive shrinkage stage of SPS. The content of >0.3% wt. of С leads to abnormal grain growth and decreasing in the mechanical characteristics of the ceramics. The addition of SiC particles into the WC nanopowder reduces the maximum shrinkage temperature during SPS by ∼150 °C and allows to reduce the volume fraction of abnormally large grains. The kinetics of the initial sintering stage of WC + C + SiC powders was also analyzed using dilatometry at the conventional pressureless sintering (CPS) conditions. The CPS activation energies of WC + C and WC + C + SiC powders are close to the activation energy of diffusion of the carbon ¹⁴C along the α-WC grain boundaries. The SPS activation energies of WC + C + SiC powders turn out to be lower than the activation energy of the ¹⁴C of α-WC grain boundary.