Nanoindentation and high temperature oxidation behavior of ZrB2–20SiC-(0–10 wt.%) Ta UHTCs

Abstract ZrB2-20 vol% SiC composite was fully densified with the addition of tantalum (from 2.5 to 10 wt%) using multi stage spark plasma sintering (MSSPS). The microstructural phases of core-ZrB2 and rim-(Zr,Ta)B2 along with ZrO2, (Zr,Ta)C phases were observed with the addition of tantalum refractory metal to ZrB2–SiC. Both the nanoindentation and Vickers hardness of ZrB2 composites exhibited similar trend and almost same hardness values. However, maximum nanoindentation hardness (18.62 GPa) and elastic modulus (451.60 GPa) were measured for ZrB2-20 vol% SiC with 10 wt% Ta. The increase in amount of tantalum reduces the specific weight gain and oxide layer thickness, hence ZrB2-20 vol% SiC with 10 wt% Ta exhibited better oxidation resistance compared to other compositions after oxidation at 1600 °C for 10 h. In all the compositions, the cross-sectional microstructure of oxidation tested samples consists of three different layers such as top passive silica layer, intermediate SiC-depleted layer and unreacted bulk.