Net‐shaping of advanced ceramic composites by gelcasting into precision molds made by rapid‐prototyping

Abstract

Dense ceramic components of complex shapes are fabricated by combining the techniques of rapid prototyping and gelcasting (RPGC process). Free‐flowing slurries of ceramic powders are set into precision molds fabricated out of expanded polystyrene (EPS) from computer‐aided design files, employing subtractive manufacturing. The removal of the mold from gelled parts is often a serious problem when attempting to produce large and complex‐shaped products. The EPS molds have advantages over the commonly used acrylonitrile butadiene styrene (ABS) molds in this context. Process innovations led to easy demolding and near‐net shaping of components of large and complex geometries that required minimal machining. Fabrication of complex‐shaped products out of alumina with a density of 99%, flexural strength of 389 MPa, and fracture toughness of ∼3 MPa√m is demonstrated. The RPGC process is extended to fabricate composites of alumina and yttria‐stabilized zirconia (YSZ) with α‐alumina platelet inclusions, with enhanced fracture toughness. The components have exhibited uniform density across the body of large and complex‐shaped parts, uniform microstructures, and good mechanical properties. EPS molds are also cost effective for fabricating large parts. The process is generic, allows for easy design modifications to include corrections for shrinkage, and also enables uniform distribution of second phases.