Scott A. Uhland

New Process and Materials Developments in 3-Dimensional Printing, 3DP ™

The Three-Dimensional Printing (3DP ™ ) process has been modified to incorporate colloidal science for the fabrication of fine ceramic parts. Complex shaped alumina and silicon nitride components have been formed directly from 3-dimensional CAD files using submicron powders. Parts were built using a sequential layering process of the ceramic slurry followed by ink jet printing of a binder system. A well dispersed slurry and optimized printing parameters are required to form a uniform powder bed with a high green density. Liquid-powder bed interactions affect the geometry and internal structure of the component. The redispersion of the unprinted powder bed is critical in order to retrieve the printed components. The slurry and powder bed chemistry are the major factors controlling powder bed redispersion. The process is generic and can be readily adapted for new materials systems. Our research is currently focused on the fabrication of dielectric RF filters. Preliminary results have demonstrated the ability to successfully fabricate cylindrical RF resonators.

Assessment of the As-Cu-Ni system: An example from archaeology

Abstract During the early phase of the Middle Horizon in the southern Andes (ca. AD 400–800), the majority of bronze objects at the site of Tiwanaku (Bolivia) were made of a ternary Cu-As-Ni alloy. This highly unusual bronze alloy was cast into the form of I-shaped cramps to clamp together rectangular stone building blocks in monumental constructions. The cramps are about 19cm long and about 7cm wide at the two extreme ends of the “I”. The center section of the “I” is about 1.4 cm wide and 1.4 cm thick. In one design a cramp made of Cu-6.0 As-5.85 Ni-.27 Sb (wt.%) was cast in place into two abutting, “T-shaped” channels cut into the top surfaces of adjacent blocks. The shrinkage on solidification provided a clamping force to press the faces of the blocks together at the joint. The microstructure of the cramp shows substantial porosity and consists of a two-phase, coarse-grained, highly cored casting. The primary phase (about 79%0 is fcc Cu-base solution with AsCuNi (21%) in the grain boundaries, indicating that it formed from the mixture of liquid and fcc on cooling. An assessment of the ternary was conducted following the CALPHAD method using Thermo-Calc software, an existing binary phase diagram, and thermochemical information to define the Cu-Ni rich portion of the ternary. An existing description of the Cu-Ni system was used and the As-Cu and As-Ni assessments were derived and employed to define the ternary compound AsCuNi. No ternary solution terms were employed. The Gibbs energy of formation of this compound is assessed as -26000-2T(K) J/gm-atom and the congruent melting point calculated as 1043°C. The full binary and ternary assessment is presented.