Spark Plasma Sintering Specificity in Nanoscale and Submicron WC—25 wt % TiC Powders

Abstract

The mechanisms behind sintering nanopowder WC—25 wt % TiC compositions with titanium carbide of varying dispersion are investigated. WC–TiC ceramics are made using spark plasma sintering (SPS) in vacuum within the temperature range of 1000–1400°C at a heating rate of 50°C/min under an applied pressure of 70 MPa and at different dwell times. Plasma‑chemical tungsten monocarbide nanopowders and nano- and submicron‑sized titanium carbide powders are used as initial materials. The microstructure, phase composition, and density of the sintered ceramics are examined. It is demonstrated that SPS allows making WC–TiC ceramics with a homogenous ultrafine-grained structure (0.2–0.5 μm). X-ray phase analysis reveals forming and evolving (W,Ti)C solid solution during sintering. The sintering kinetics exhibit a multistage behavior characteristic of the SPS process developing in WC–TiC systems. It is established that the use of nanoscale titanium carbide particles leads to earlier dominance of mass transfer along grain boundaries and interphase contacts due to an increased fraction of active contact areas. In contrast, submicron TiC particles result in a more pronounced maximum shrinkage rate associated with the rapid involvement of larger material volumes in the diffusion flux. The presence of vacancies in the carbon sublattice of titanium carbide plays a key role in activating diffusive mass transfer and in forming the (W,Ti)C solid solution.