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

B. Feng, A.K. Fetzer, A.S. Ulrich, M.C. Galetz, H.-J. Kleebe, E. Ionescu

Journal of the American Ceramic Society (2021), DOI: 10.1111/jace.18038

Feng2021

TEM bright field image of ZrB2/SiCN showing the achievement of preparing a fully dense ceramic composite via hot-pressing at 1800℃. Reprinted from Journal of the American Ceramic Society with permission from John Wiley and Sons.

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.

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