High-strength zirconium diboride-based ceramic composites consolidated by low-temperature hot pressing

Two compositions of ZrB2-based ceramic composites containing Si3N4, Al2O3 and Y2O3 have been hot-pressed at different temperatures between 1673 and 1773 K for 60 min in vacuum. The densification behavior of the composites was examined during the sintering process. The microstructures of the composites were characterized by scanning electron microscopy, and the crystalline phases were identified by x-ray diffraction. The effects of Al2O3 and Y2O3 additives on the densification behavior and flexural strength were assessed. A relative density of ~95% was obtained after sintering at 1723 K or higher temperatures. The microstructures of the composites consisted of (Zr,Y)B2, α-Si3N4 and Y3(Al,Si)5O12 phases. The room-temperature flexural strength increased with the amount of additives and approached 1 GPa

Polymer‐Derived Ultra‐High Temperature Ceramics (UHTCs) and Related Materials

Ultra-high temperature ceramics (UHTCs) represent an emerging class of materials capable of providing mechanical stability and heat dissipation upon operation in extreme environments, e.g., extreme heat fluxes, chemically reactive plasma conditions. In the last few decades, remarkable research efforts and progress were done concerning the physical properties of UHTCs as well as their processing. Moreover, there are vivid research activities related to developing synthetic access pathways to UHTCs and related materials with high purity, tunable composition, nano-scaled morphology, or improved sinterability. Among them, synthesis methods considering preceramic polymers as suitable precursors to UHTCs have received increased attention in the last few years. As these synthesis techniques allow the processing of UHTCs from the liquid phase, they are highly interesting, e.g., for the fabrication of ultra-high temperature ceramic composites (UHT CMCs), additive manufacturing of UHTCs, etc. In the present review, UHTCs are in particular discussed within the context of their physical properties as well as energetics. Moreover, various synthesis methods using preceramic polymers to access UHTCs and related materials (i.e., (nano)composites thereof with silica former phases) are summarized and critically evaluated