| Lightweight metallic honeycomb structures having low density and high strength are potentially useful materials in a wide variety of applications. These materials can be employed as replacements for bearing and support structures, for impact and sound absorption, for thermal management, and in multifunctional capacities where the benefits of both metallic character and low density are required. Extrusion of these architectures represents a novel and economical alternative to conventional honeycomb fabrication.; Extrusion is a material forming process that allows the shaping of cohesive plastic body into a linear form having constant cross section. The plastic body is a paste; well mixed material composed of solids, liquids, and processing aids. Control of paste rheology and optimization of flow and die variables are necessary to the extrusion of articles having complex geometry.; By extruding paste compositions of raw material powders, mixed in the appropriate proportion to produce alloy materials upon reduction, lightweight ceramic honeycomb can be formed. The green ceramic honeycomb is then reduced to alloy in a controlled atmosphere heat treatment.; In this investigation, high quality, green extruded honeycomb structures were fabricated. The model equations used to describe high viscosity suspension behavior were applied to paste formulations to predict properties. To accomplish the goals of this research, it was necessary to consider: (1) Raw material characterization, ensuring consistency between batches and allowing prediction of paste behavior; (2) Mechanics of the fluid phase and the paste, using capillary rheometry to determine paste properties; (3) Characteristics of the fluid phase and the paste, including methods to estimate and experimentally determine maximum solids content and the hydrodynamic constant; (4) Model development, applying the equations that describe high viscosity suspensions to pastes, allowing prediction of extrusion variables over a wide compositional range; (5) Shear zone behavior, and the influence and limitations the shear layer places on fine extrusion. |
