Ultrafast high-temperature sintering (UHS) of WC and WC-containing ZrB2

Abstract

WC and ZrB2 are refractory ceramics with excellent thermophysical properties and melting temperatures exceeding 2800°C. Both materials require the application of external pressure and long sintering times for their consolidation. In particular, commercially available ZrB2 powders are intrinsically difficult to sinter and usually need long pre-processing steps such as high-energy ball milling. Ultrafast high-temperature sintering (UHS) is a recently developed technique that enables the consolidation of bulk ceramics within minutes. In the present work, pure WC was efficiently densified to above 98% in just 3 min by UHS. Moreover, small WC additions enhanced ZrB2 densification by activating liquid phase sintering. Samples containing 5 and 10 vol% WC were sintered to 95 and 96%, respectively, in 2 min. All the WC initially present in the blend reacts to form a liquid phase during sintering and solidifies as WB and (Zr,W)C upon cooling. The formation of a ZrB2-(Zr,W)B2 core-shell structure was detected in all the sintered composites. The hardness of UHS samples reaches 15 GPa (WC - ZrB2 composites) and 21 GPa (pure WC), similar to that measured in materials obtained by slower and more sophisticated pressure-assisted sintering techniques.