Advances in the fabrication of functionally graded materials using extrusion freeform fabrication

The Extrusion Freeform Fabrication technology (EFF), developed by Advanced Ceramics Research, Inc. (ACR) offers tremendous potential for net shape rapid prototyping of polymers, metals, and ceramics, as well as their hybrids such as functionally graded materials (FGMs). Two unique EFF systems capable of rapid prototyping monolithic polymer, metal, and ceramic parts have been developed and entail the sequential deposition of layers of self supporting viscous suspensions or highly loaded thermoplastics using a computer controlled extrusion head. In particular, the extrusion head builds up a 3D body by sweeping out a path based on a CAD virtual image. For the fabrication of FGMs, the EFF systems are modified to contain two extruders which dispense dissimilar materials into a small mixing head. The composition of the bi-component extrudate is controlled by proportioning the raw material feedrate from the two extruders. In this manner, the composition can be continuously graded to produce a FGM component. The ACR EFF technique offers the advantages of being able to form the body into almost any shape which can then be processed through traditional powder metallurgical or ceramic firing routes. This approach is inexpensive and potentially feasible for grading between any thermodynamically compatible ceramic-metal, ceramic-ceramic, or metal-metal material combination.