Low‐Temperature Superplastic Forming of High‐Entropy Oxides

High‐entropy oxides (HEOs) are being extensively studied for various functional applications, but there is limited research into the mechanical behavior of these materials, especially at elevated temperatures. Bulk (Co, Cu, Mg, Ni, Zn)O (transition metal (TM)‐HEO) samples are formed into dome shapes at 800 °C and 70 kPa. Deformation experiments and finite element analysis (FEA) reveal that TM‐HEO has a creep stress exponent of n = 0.6, indicating that TM‐HEO deforms through superplastic deformation and exhibits shear‐thickening behavior. Comparisons of experimental strain rates to those calculated using existing superplasticity mechanism models signify that TM‐HEO deforms through grain boundary sliding accommodated by a solution‐precipitation mechanism from a secondary phase. A Cu‐rich tenorite phase, commonly observed in the grain boundaries of TM‐HEO, is proposed as the secondary phase facilitating deformation. It is important to highlight here that the superplastic deformation behavior in TM‐HEO is active under modest temperature and pressure conditions, as noted above. Low‐temperature superplastic deformation will provide a powerful method of manufacturing HEO ceramics into net shape parts, greatly expanding their potential applications.