Optimized processing of high density ternary hafnium-tantalum carbides via field assisted sintering technology for transition into hypersonic applications

Ultra-high temperature ceramics (UHTCs) present great opportunities for hypersonic applications, but densification via conventional sintering is challenging and often requires sintering aids, limiting UHT applications. Field-assisted sintering technology (FAST) can produce dense, mechanically-robust components without the need for sintering aids. In this work, we have developed an optimized set of FAST processing conditions without sintering aids for various compositions in the (Hf,Ta)C ternary system. The novel processing approach yields high-density ceramics with minimal grain growth. It was found that 50 vol% HfC (∼55 mol%) demonstrated record-breaking nanohardness (41.45 ± 1.37 GPa), Vickers microhardness (30.2 ± 3.1 GPa), and elastic (indentation) modulus (590.12 ± 10.64 GPa). These peak mechanical properties arose from the balance of two underling structure-property relationships: solid solution strengthening and the Hall-Petch effect. The interplay of these compositionally-linked phenomena yields an optimal regime of superior mechanical properties. Combining this interplay with optimized FAST parameters, superior ternary HfC-TaC ceramics can be realized for next-generation hypersonic applications.