Nanophase powders are produced either by condensation of metal vapor (e.g., copper, palladium) or by mechanical alloying (TiAl) using ball milling. The powders are produced and handled in either purified inert gas or in ultrahigh vacuum. They are hot compacted in dies to produce cylinders that are close to theoretical density or they are further compacted by uniaxial pressing at elevated temperatures (sinter forging). Indentation creep and deformation during sinter forging are used to determine the mechanical behavior of the nanophase materials. The objective is to establish the mechanism of plastic deformation and determine a constitutive relation for these ultrafine grain size materials. The compacted specimens are also studied by x-ray diffraction, calorimetry, and microscopic techniques in addition to bulk density measurement.

This research is being conducted to examine the relationship between microstructure and mechanical performance in the Al;i2O;i3-ZrO;i2 eutectic system. The study will concentrate on densification processes, thermal instability associated with phase distribution of zirconia in this eutectic composite. The effect of processing on the microstructural-mechanical properties will be evaluated.

During sol-gel processing, structural developments occur as a result of network condensation. Consequently, the rigidity of the structure and the resistance it offers to the escaping solvent increase. Pressure gradients build and the gels risk to fracture. Using Brillouin light scattering in the course of the drying process, we monitor the complex mechanical modulus, characterizing the dynamic response of these gels on a molecular scale. This yields information concerning the change of elastic properties and viscous dissipation, as controlled by chemical composition and drying rates.

Monocalcium aluminate has been used as chemically bonding ceramic material to form innovative composite materials. Various synthesis methods have been investigated to determine the optimum chemical route for obtaining pure, single phase, high surface area powders. Additionally new synthesis techniques have been developed to fabricate coated powders. The objective has been to obtain unagglomerated homogeneously mixed dry powders suitable for dry powder processing. Using these and other powders as starting materials, various forming techniques have been developed to capitalize on the chemical bonding properties of calcium aluminate. Processing microstructure and property relationships have been investigated with an aim to achieving an optimum processing for cementitious composite materials.

We are carrying out rheological measurements (stress viscometry and oscillatory measurements) to probe the effects of free (nonadsorbed) polymeric species in concentrated, nonaqueous suspensions. Free polymer species influence particle-particle interactions, and, hence, suspension ``microstructure'' through depletion phenomena. However, relatively little is known about such phenomena even though free polymeric species are often present in significant amounts in these systems. Our observations have highlighted the importance of depletion stabilization in such systems. Ultimately, we aim to develop a theoretical model for this effect.

Gel casting is a near-net shape-forming process suitable for complex 3-D components. We are studying the gelation behavior of aqueous suspensions that contain high solids volume fraction in the presence of low molecular weight polymeric additives (e.g., polyvinyl alcohols). Such systems are environmentally benign and produce consolidated bodies with low organic content facilitating subsequent debinding processes.