Monolithic ZrB2‐based UHTCs using polymer‐derived Si(Zr,B)CN as sintering aid

In the present work, dense ZrB2‐based monoliths were produced via hot‐pressing of ZrB2 powders coated with amorphous polymer‐derived SiCN, SiZrCN, or SiZrBCN at relatively moderate temperatures (i.e., 1800℃). Thus, ZrB2 particles were embedded in polymer‐derived ceramic shell were realized by coating their surface with the corresponding polymeric precursors (polysilazane, Zr‐modified polysilazane, Zr‐ and B‐modified polysilazane, as for SiCN, SiZrCN, and SiZrBCN; respectively), followed by cross‐linking at 200℃ and pyrolysis at 1100℃ in Ar atmosphere. The obtained monolithic samples were carefully characterized concerning their phase composition and microstructure. Typically, the densified samples exhibit a homogeneous microstructure consisting of ZrB2 grains and a multi‐phasic polymer‐derived ceramic grain boundary phase (β‐SiC, t‐BCN, ZrO2, and ZrC). The prepared monoliths exhibited fair hardness values, that is, 12.5, 14.2, and 13.3 GPa for ZrB2/SiCN, ZrB2/SiZrCN, and ZrB2/SiZrBCN.