Pressureless sintering of zirconium diboride using boron carbide and carbon additions

The synergistic roles of boron carbide and carbon additions in the enhanced densification of zirconium diboride (ZrB2) by pressureless sintering have been studied. ZrB2 was sintered to > 99% relative density at 1900 degrees C. The combination of 2 wt% boron carbide and 1 wt% carbon promoted densification by removing surface oxide impurities (ZrO2 and B2O3) and inhibiting grain growth. Four-point bending strength (473 +/- 43 MPa), Vickers' microhardness (19.6 +/- 0.4 GPa), fracture toughness (3.5 +/- 0.6 MPa.m(1/2)), and Young's modulus (507 GPa) were measured. Thermal gravimetry showed that the combination of additives did not have an adverse effect on the oxidation behavior.