Hot isostatic pressing of 3D printed alumina-toughened zirconia

Lithography-based ceramic manufacturing (LCM) is a capable additive manufacturing (AM) or three-dimensional (3D) printing technology for producing ceramics with high precision and excellent mechanical properties similar to conventionally manufactured components. This AM method is a digital light processing-based vat-polymerization technique that allows the curing of photosensitive ceramic slurry in a layer-wise fashion by irradiating selected pixels (40 µm in the current study) within a layer (with a layer height of 25 µm). Subsequent thermal post-processing of the 3D-printed green parts includes debinding, which removes the organic matrix, and densification of the parts by sintering. Alumina-toughened zirconia (ATZ) offers high mechanical strength, fracture toughness, and biocompatibility, and has recently been adapted for use in LCM technology. ATZ is an excellent material for different load-bearing applications like artificial hip joints or areas where high hardness and wear resistance are needed such as cutting tools. To further improve the ceramic properties of the 3D-printed ATZ components eliminating residual porosity while maintaining a fine and homogeneous microstructure are important characteristics. To achieve this, hot isostatic pressing (HIP) was evaluated to reduce the part porosity and suppress excessive grain growth during sintering. To compare conventional pressureless sintering in air with HIP, the same test specimen geometry (2.1 × 2.5 × 25 mm) was 3D-printed and thermally processed using both conventional sintering and HIP. While the final relative densities for both techniques were greater than 98.5%, the achieved characteristic strength (four-point bending tests) of ATZ produced by HIP (>1200 MPa) was significantly exceeding that of conventional sintering in air (650 MPa).