Ultrafast high-temperature sintering (UHS) is currently emerging as a powerful tool to consolidate ceramics in the seconds/few minutes timescale. It employs graphite felts as resistive heating elements that, due to the low thermal capacity, can be heated to ultrahigh temperatures in a matter of seconds.

Herein, we report the ultrafast high-temperature sintering of refractory ceramics with a specific focus on pure ZrB2, binderless WC, B4C/ ZrB2 and WC/ ZrB2 composites. The results show that effective densification can be attained in a very short time scale even considering micrometer-sized powder in pressure-less conditions. The densification is a result of rapid heating combined with extreme temperatures (approaching 2,500°C). In these conditions, composites are evenly densified via liquid phase sintering mechanisms, where the liquid phase is constituted by molten boron carbide or eutectic liquid formed between ZrB2 and WC. Homogeneous and dense microstructures can be obtained and accompanied by extraordinary grain coarsening kinetics once the liquid phase forms. Preliminary mechanical characterization by hardness tests provides promising results which are substantially comparable with those obtained by pressure-assisted sintering.

On the other hand, the rapid heating conditions can also facilitate the densification of oxide ceramics including YSZ where the non-conventional heating leads to a modified “densification pathway” and to a different microstructural evolution. The UHS of YSZ is also shown to be hugely dependent on the UHS atmosphere, the latter affecting the densification kinetics, phase evolution and electrochemical properties.
The thermal history of the sample is studied by calibrated finite element modeling that allows a deeper understanding of the involved heating rates