Non-protective oxide formation in high entropy carbide ultra-high temperature ceramics

Bulk samples of high entropy ultra-high temperature ceramics (UHTCs) of composition (HfNbTaTiZr)C was fabricated via high energy ball milling and spark plasma sintering. ZrC bulk samples were also prepared via spark plasma sintering. Oxidation behavior of both carbide compositions was tested at 1500°C, 17000C and 1800°C using a resistive heating apparatus in one atmosphere reduced PO2 oxygen/argon gas mixtures for times up to 15 minutes. Oxidation kinetics were determined from the variation of material consumption vs. time. The oxide scale was characterized using SEM and EDS. The high entropy carbide exhibited grain boundary oxidation, non-protective oxide formation and higher material consumption rates in almost all cases, when compared to ZrC.