| Abstract Scope |
Transition metal carbides (TMCs) like TaC, NbC, ZrC, and TiC, also called ultra-high temperature ceramics (UHTCs), exhibit some of the highest known melting points of any material, and have potential use in fission and fusion engineering systems. Given this, UHTCs are being examined for applications like nuclear thermal propulsion (NTP), and TRISO fuel coatings for next-generation reactors which require higher operating temperatures than what is seen in the current nuclear landscape. Our recent results on this class of material show relatively high fracture toughness (up to ~8 MPa-m0.5) and thermal conductivity (up to ~50 W/m-K), with an increase in fracture toughness seen in some compositionally complex systems like (Nb, Ta) C as opposed to single cation systems. This provides motivation for the exploration of multi-cation systems comprised of these TMCs. While Spark Plasma Sintering (SPS) can quickly fabricate these materials, the shrinkage data may also be used to understand the sintering process. Shrinkage provides direct acquisition of consolidation mechanisms and kinetics of mass transport, providing subsequent insight into their thermomechanical properties such as creep or radiation defect behaviors. However, the acquisition and analysis of shrinkage during sintering is challenged by other sintering contributions, particularly applied pressure, chemical reaction, and particle arrangement. After isolation of these other factors, the sintering mechanism was examined to extend the study from single cation to multi-cation, compositionally complex materials. Additionally, indentation fracture toughness (IFT) (with reference SENB testing), and hardness were examined for single and multi-cation carbide variants of high quality, high density (>95%) samples. |