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

Abstract

Ultrahigh temperature ceramics, so-called UHTCs, represent a class of materials that can operate under extreme conditions such as ultra-high temperatures (i.e., beyond 2000℃). [1][2][3] They have been investigated within the context of aerospace, for example, leading edges and control surfaces for atmospheric re-entry, hypersonic flight, and scramjet propulsion or with respect to nuclear power applications such as fuel cladding materials or non-oxidic fuels. 2,[4][5][6] UHTCs are characterized by tremendously high melting points, high hardness, stiffness and strength even at (ultra)high temperatures as well as high thermal conductivity. 7-10 Despite their highly attractive properties, there are still challenges related to the development of UHTCs, for example, concerning their sluggish self-diffusion which impedes their sintering ability, [11][12][13][14][15][16] or their rather fair ultrahigh temperature oxidation/ corrosion resistance. [17][18][19][20][21][22][23] In order to overcome these issues, secondary phases, typically silicon-containing, are considered for the sintering of UHTCs and to additionally provide an improvement of their oxidation behavior. Typically, 10-20 vol.% of silica former phases such as SiC, Si 3 N 4 or metal silicides, for example, MoSi 2 have

Prevention of SiC‐fiber decomposition via integration of a buffer layer in ZrB2‐based ultra‐high temperature ceramics

“…Three different buffer layers were prepared, each of which contained ZrB 2 plus 5 vol% of either α‐Si 3 N 4 (Bayer AG, Leverkusen, Germany; Baysinid ST, mean particle size 0.15 μm, main impurities (wt%): 1.60 O, 0.20 C, 0.005 Al) or PDC powders with the general formula SiCN or SiHfBCN, synthesized according to Yuan et al 31 . and Feng et al 32 . Each powder mixture was ball milled for 24 h in ethanol using silicon carbide media.…”

“…Commercial powders were employed to prepare the mixtures to assemble the FGM. As structural matrix, ZrB 31 and Feng et al 32 Each powder mixture was ball milled for 24 h in ethanol using silicon carbide media. The slurries were dried in a rotary evaporator and the powders de-agglomerated.…”

Temperature‐dependent mechanical and oxidation behavior of in situ formed ZrN/ZrO2‐containing Si3N4‐based composite

“…17,18 Among many additives, zirconium-based compounds (e.g., ZrB 2 , ZrC, ZrN, and ZrO 2 ) are regarded as ideal candidates with remarkable mechanical and high-temperature stability. [19][20][21] Guo et al 22 prepared a ZrB 2 -containing Si 3 N 4 -based composite at a low temperature of 1500 • C. It was found that the addition of ZrB 2 promoted the phase transition of Si 3 N 4 from α to β, and the obtained composite exhibited improved fracture toughness and bending strength of 9.8 MPa⋅m 1/2 and 702.0 MPa, respectively. Sayyadi-Shahraki et al 23 Although promising, the methods involving processing and preparation of ceramic composites still face practical difficulties, which weaken the final properties of the ceramic composite.…”

“…A large number of studies have confirmed that the incorporation of secondary phases not only affects the phase evolution and microstructure of the material but also enhances the strength and toughness compared to that of the monolithic materials 17,18 . Among many additives, zirconium‐based compounds (e.g., ZrB 2 , ZrC, ZrN, and ZrO 2 ) are regarded as ideal candidates with remarkable mechanical and high‐temperature stability 19–21 . Guo et al 22 .…”