Five competing companies, acting as a consortium, and two national laboratories are working together to develop highly advanced manufacturing technology. Joseph M. Keller Delphi Energy and Engine Management Systems, Flint, Mich. Jonathan D. French Advanced Cerametrics, Lambertville, N.J. Bruce Dinger and Mark McDonough CeramTec, Laurens, S.C. Brian Gold and Caroline Cloutier Superior Technical Ceramics St. Albans, Vt. Larry Carinci and Eric Van Horn Zircoa Inc., Solon, Ohio. Kevin Ewsuk Sandia National Laboratories, Albuquerque, N.M. William Blumenthal Los Alamos National Laboratory, Los Alamos, N.M.

A 3-D particle-packing simulation with a distribution of granule sizes. The integration of national laboratories into the equation of American technical ceramic component manufacturing positions American manufacturers more competitively in the global market. The resolution of problems and the explanation of phenomena common to all ceramic manufacturers have reduced the cost of higher performance components by: Improving yields; Developing closer net-shape tolerancing; Shortening total processing time and time to market. The Association of American Ceramic Component Manufacturers Consortium I (AACCMCI) continues to collaborate with Los Alamos National Laboratory and Sandia National Laboratories under a cooperative research and development agreement (CRADA) initiated in 1996. The CRADA has provided participating companies and collaborating laboratories with meaningful and successful results that have had a direct impact on ceramic component production. New powder characterization techniques have been used, raw material preparation and compaction processes have been improved, and financial benefits have accrued to the participants. SEM micrograph of spray-dried 99.5% alumina granules. The Problem Addressed From its conception, the purpose of this CRADA was to apply more science to the "art" of powder compaction. Density gradients in pressed-powder compacts result in shape distortion and unpredictable shrinkage that deleteriously affect manufacturing costs and reliability. Machining (hard grinding fired parts) to achieve the net desired shape can account for 50-90% of the total component cost. The need to understand the key contributors to density variations captures the interest of participating companies. The CRADA combines the laboratories' strengths in fundamental scientific understanding, powder characterization and computer modeling with the manufacturing expertise of the companies. Cumulatively, this team will develop technology to design and manufacture reliable, high-performance ceramic components in a more cost-effective manner. Click on the thumbnail for the larger version. Compaction curves for a fine-grain zirconia powder showing that higher densities are achieved at lower forming pressures in a high relative-humidity atmosphere. Taking a Technical Approach Two major segments of the CRADA should significantly impact ceramic manufacturing in the United States: The development of experimentally validated computer models to improve ceramic component design and manufacturing; The application of the models and process diagnostics necessary to understand and control the green-forming process of powder compaction during both mechanical and isostatic pressing. Studies were performed to characterize the commercial ceramic powders once they were spray-dried to form granules. Spray-dried granule characterization involved measuring flow rate, packing behavior and morphology. Powder compaction experiments also were run to evaluate pressing performance under a variety of conditions. Controlled changes were made to pressing additives, die materials, environmental conditions and other pressing parameters. Once the parts were formed, green and fired microstructures were analyzed by die dipping, ultrasound, optical and scanning electron microscopy (SEM), and X-ray computed tomography (XRCT). This provided the groundwork to develop and validate the computer models and process diagnostics being used by the CRADA today. Click on the thumbnail for the larger version. Compaction curves showing that 1 wt.% Al Stearate decreases the maximum pressing pressure and ejection force to form a fine-grain size zirconia-alumina compact. Progress to Date The most significant contributions of the CRADA are refined, discrete and finite element method (DEM and FEM) computer models that can be used to predict ceramic powder-compaction behavior. FEM stress, density and flow maps were generated to provide guidelines and diagnostics for die design and pressing. Of even more significance to the CRADA companies is the successful validation of computer-model predictions on the manufacturing floor. Improved characterization of ceramic powders and compacts has been critical to this end. For example, to support the FEM modeling effort, materials properties were obtained through adapted and refined soil-mechanics techniques (e.g., hydrostatic and triaxial compaction tests). Characterization tools also have been developed and improved to measure flow, friction, compaction and compact density. Powder/Granule Characterization Much of the effort to date has concentrated on optimizing spray-dried granule characteristics that have a huge impact on the process behavior of the granules and, consequently, the properties of the final part. Density and pore-size information on granulated ceramic powders has been determined using mercury intrusion porosimetry (MIP). Factors that affect the mean pore diameter are the primary particle size and size distribution of the grains making up the granule, binder type and concentration, and the granulation process. Analysis of the data from MIP also provides a method of measuring the bulk density of the granules. SEM has been effective for characterizing spray-dried granule size and morphology. Variable pressure SEMs allow for direct observation of granulated powders that contain organic binders. Images can be quickly and easily obtained without the additional difficulty of placing a conductive coating on the unfired ceramic material.

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