Grain size refinement of additive manufactured Ce-TZP ceramics by coupled two-step pre-sintering and HIP

Ceria-stabilized tetragonal zirconia polycrystal (Ce-TZP) has exceptional fracture toughness and flaw tolerance due to facile t‒m phase transformation toughening. However, its wider-range applications are limited by its relatively low strength due to its large grain size and low transformation stress, which results in yield-like failure. Here, we combined additive manufacturing (AM), pressureless two-step sintering, and hot isostatic pressing (HIP), and addressed the challenging grain size refinement problem in Ce-TZPs. We successfully produced dense ultrafine-grained Ce-TZP ceramics with an average grain size below 500 nm, a three-point bending strength above 800 MPa, and a single-edge-notch-beam fracture toughness in the range of 11‒12 MPa·m^1/2. The critical roles of processing design, mixed Ce valences, and under- vs. over-stabilization of tetragonal polymorphs were noted. Our work offers insights and strategies for the future development of stronger and tougher Ce-TZP ceramics that can compete with tetragonal yttria-stabilized zirconia in various applications, including additive manufacturing.