  The study investigates the density, phase composition, microstructure and
mechanical properties (microhardness, fracture toughness) of binderless WC +
SiC and WC + SiC + C ceramics obtained by Spark Plasma Sintering (SPS).
Nanopowders of a-WC produced by DC arc plasma chemical synthesis were used as
raw materials. Powder compositions for sintering contained graphite (0.3, 0.5%
wt.) or b-SiC (1, 3, 5% wt.) with 0.3% wt. graphite. It was shown that WC + 1%
wt. SiC + 0.3% wt.C ceramics have a homogeneous fine-grained microstructure,
high relative density, increased microhardness and Palmquist fracture toughness
(Indentation Fracture Resistance). The kinetics of the initial sintering stage
of WC + C and WC + C + SiC powder compositions was also analyzed using
high-temperature dilatometry at the conventional pressureless sintering (CPS)
conditions. The CPS and SPS activation energies of WC + SiC powder at the
intensive shrinkage stage were determined using the Young-Cutler model. The CPS
activation energies of WC, WC + C and WC + C + SiC powder compositions are
close to the activation energy of diffusion of the carbon C along the a-WC
grain boundaries. The SPS activation energies of WC + C and WC+ C + SiC powder
compositions turn out to be lower than the activation energy of the C of a-WC
grain boundary.
