Pressureless sintering of carbon-coated zirconium diboride powders

Carbon-coated zirconium diboride powders were sintered to near theoretical density at temperatures as low as 1900 °C without an external pressure. Relative density increased from ∼70% for uncoated ZrB2 to >99% for ZrB2 coated with at least 1.0 wt% carbon. Thermodynamic analysis indicated that carbon reacted with and removed oxide impurities (ZrO2 and B2O3) that were present on the particle surfaces, which promoted densification by minimizing grain coarsening. The effects of initial particle size and carbon content on densification, microstructure, and properties were investigated.