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

Abstract

Ceria-stabilized tetragonal zirconia polycrystal (Ce-TZP) has exceptional fracture toughness and flaw tolerance, due to facile <em>t</em>-<em>m</em> phase transformation toughening. Yet its wider-range applications are limited by relatively low strength, due to large grain size and low transformation stress resulting in yield-like failure. Here we combined additive manufacturing, pressureless two-step sintering, and hot isostatic press (HIP) and addressed the challenging grain size refinement problem in Ce-TZP. We successfully produced dense ultrafine-grained Ce-TZP ceramics with average grain size below 500 nm, three-point bending strength above 800 MPa, and 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 in future development of strong tough Ce-TZP ceramics to compete with tetragonal yttria-stabilized zirconia in applications including additive manufacturing.