Development of complex shaped alumina parts by gelcasting and additive manufacturing

Abstract

Gelcasting is a fabrication method for achieving near net shape of complex alumina parts capable of high performance. The processes used in gelcasting are similar to processes often used in conventional ceramic forming process. However, the relative high costs involved in the fabrication of non-porous moulds required by the process makes it uneconomical for new developments and low volume productions. In this study, an inexpensive and efficient way involving negative additive manufacturing and gelcasting was used to achieve the fabrication of complex geometries of alumina parts that cannot be formed by conventional methods. Additive manufacturing through fused deposition modelling of ABS filament was used to produce moulds for investment casting. Low toxicity monomers were identified and from these, the rheological behaviour of suspensions was optimized to successfully fabricate complex geometries by ensuring satisfactory mould filling. The suspension contained a ceramic powder, dispersing medium and organic monomers was poured into the non-porous ABS mould and a gel formed. The mould was then dissolved away in acetone to obtain the complex shaped part. Different complex geometries of alumina with near full densities (≤99.6%RD) were achieved using a 40vol% solids loading and 0.3wt% co-polymer of Isobutylene and maleic anhydride monomer system. This fabrication process enables low cost production of complex shaped alumina parts. The alumina components produced exhibited properties similar to those that are produced using traditional processing techniques. The ceramic components had relative densities up to 99%.The hardness and fracture toughness were measured to be 18GPa and 3.8MPa.√m respectively after pressure-less sintering at 1650°C in air for 3hrs.