Recent progress of alumina ceramics by direct ink writing: Ink design, printing and post-processing

Alumina (Al₂O₃) ceramics are one of the most widely employed advanced ceramics by industries. However, traditional forming methods have not been able to meet the demands of fine shape design and high-precision fabrication for advanced functional applications. 3D printing technologies are progressively gaining consideration in many manufacturing sectors for their ability of designing complex shapes and customized parts. Extrusion-based 3D printing technology, known as direct ink writing (DIW), is an adaptable, simple, and eco-friendly forming process and amongst the most used for ceramics. In the last several years, significant advancements have been made in alumina ceramics with complex designs by the DIW forming technique. This review presents recent progresses in creating dense and porous alumina ceramics using DIW. It provides a detailed description of printable ink formulation strategies and their effects on the sinterability of dense and porous alumina shapes. Ink composition and printing parameter effects on the final properties of DIW alumina are discussed. Concurrently, key ink rheology and post-processing parameters for desired alumina shapes are identified. The review also provides a pathway to overcome the technical challenges in achieving a high density or lightweight alumina monolith by DIW.