Additive manufacturing of yttrium-stabilized tetragonal zirconia: Progressive wall collapse, martensitic transformation, and energy dissipation in micro-honeycombs

For zirconia-based technical ceramics, the unique advantages of micro-architecture geometries combined with the potent mechanical and functional properties have been challenging to implement owing to additive manufacturing restrictions. In this work, we present a stereolithography-based additive manufacturing approach involving slurry development for yttrium-stabilized tetragonal zirconia polycrystals (Y-TZP), followed by printing using a custom-built large-area projection micro-stereolithography system. After post-processing, i.e., polymer burnout and sintering, 98% relative density is reached in the printed Y-TZP parts. Thanks to the good manufacturing quality, the bulk-scale Y-TZP micro-honeycombs are able to display typical stretch-dominated behavior in out-of-plane compression, showing elastic loading (Stage I) and protracted brittle failure of individual walls over a significant strain (Stage II). For a Y-TZP micro-honeycomb consisting of 5 x 4 hexagonal cells with a wall thickness of 300 mu m and a cell diameter of 1.40 mm, the energy dissipation density is measured to be 9.45 J/g, substantially higher than other ceramic honeycombs and packings reported earlier. This energy dissipation capability is mostly attributed to the progressive wall collapse seen in Stage II deformation, in which the perimeter walls are preferentially fragmented relative to the interior walls. According to finite element analysis, this phenomenon is a result of the deviation from uniaxial compression and the presence of stress gradients in the perimeter walls. We also find evidence for stress-induced martensitic transformation in the YTZP micro-honeycomb after compression, which may be another contributor to the observed energy dissipation capability.