Improving the homogeneity and reliability of ceramic parts with complex shapes by pressure-assisted gel-casting

Forming process plays an important role in the homogeneity and reliability of advanced ceramic products. Inspired by the surprising observation of pressure-induced solidification in colloidal forming processes, the authors have developed a new ceramics forming process, colloidal injection moulding, with the potential of forming large ceramic parts of complex shapes such as engine turbines and biomedical implants. This process combines the advantages of the conventional injection moulding and gel-casting processes of ceramics. Not only the efficiency but also the homogeneity of the green body is greatly improved owing to the pressure-induced solidification. It is also found that the inner stress generated by non-uniform solidification due to temperature gradient is responsible for the origination of microstructural defects in green body during colloidal-forming processes. A new strategy is taken to reduce the inner stress by adjusting the stiffness of the green body using a moderator additive. Ceramic products with complex shape such as engine turbines have successfully been fabricated with reduced defects.