Pressureless two-step sintering of ultrafine-grained high-entropy zirconate ceramics with excellent mechanical properties

The challenge of preparing dense ultrafine-grained high-entropy ceramics through conventional pressureless sintering is hereby addressed by a simple two-step sintering method. Ultrafine-grained (Ce0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 high-entropy zirconate with 99.2 % theoretical density and 135 nm grain size has been fabricated by pressureless two-step sintering for the first time. Compared to the conventional sintering, two-step sintering provides finer grain sizes and better microstructural uniformity, which yield excellent comprehensive mechanical properties with high hardness of 16.0 GPa, large elastic modulus of 262 GPa and high fracture toughness of 2.8 MPa·m1/2. It is believe that pressureless two-step sintering can be utilized to prepare other high-entropy ceramics with fine grain size and high quality.