1997 TMS Annual Meeting: Monday Abstracts

SHAPING AND FORMING OF HIGH PERFORMANCE POWDER PRODUCTS: Session I

Session Chair: Dr. Phillip Parrish, MATSYS Inc., Arlington, VA

2:00 pm

3-D HIP MODELING: RESULTS ON NON-AXISYMMET4RIC PARTS: W.B. Eisen, Crucible Research Center, 6003 Campbell's Run Rd., Pittsburgh, PA 15205

Abstract not available.

2:30 pm

MODELING OF THE POWDER/MONOTAPE METHOD FOR TITANIUM MATRIX COMPOSITE CONSOLIDATION: C.C. Bampton, K.J. Newell, Rockwell Science Center, P.O. Box 1085, Thousand Oaks, CA 91358

A computer model, Discrete Element Consolidation Analyzer (DECA), is described which was developed with support from Wright Laboratory, to assist in the optimization and control of the so-called tape-cast powder monotape processing method for titanium matrix composite consolidation. DECA simulates the viscoplastic densification of a randomly packed spherical titanium alloy powder aggregate and continuous fiber array by hot pressing. Using state variable analysis together with automated remeshing, the model performs a continuous simulation of powder particle contact-contact interaction, free surface evolution and void closure. A unique capability of this model is the realistic simulation of the final random powder packing geometry, prior to consolidation, following the debulking, i.e., binder off-gassing, and powder settling and fiber rearrangement, of the initial tape-cast powder/fiber monotape.

3:00 pm

A DENSIFICATION CONSTITUTIVE MODEL FOR POWDER BASED ALUMINUM MATRIX COMPOSITES MATERIALS: Erik J. Jilinsk, John J. Lewandowski, Dept. of Material Science and Engineering, Case Western Reserve University, Cleveland, OH 44106; Paul T. Wang, The Aluminum Company of America, Alcoa Technical Center, Alcoa Center, PA 15169

Intelligent, cost effective processing of powder based materials requires an understanding of the key physical variables during processing and the ability to implement these variables into suitable analytical models that can describe the overall consolidation behavior of the powdered material during fabrication. In this presentation, a modified form of the Gurson continuum level densification model, derived through a micromechanical approach, is developed and applied to an aluminum metal matrix composite reinforced with SiC particulate. The results of this model, also applicable to short or chopped fiber reinforced powder based composite material, capture the influence that volume fraction of reinforcement has on the densification of the powder based aluminum alloy metal matrix composite and provides the first step of the analytical framework needed for designing a process model capable of describing the consolidation behavior of the composite material during a powder forging type fabrication process.

3:30 pm

MODELING THE HOT CONSOLIDATION OF METAL POWDERS AND METAL-MATRIX COMPOSITES: R.E. Dutton, S.L. Samiatin, Materials Directorate, Wright Laboratory, WL/MLLM, Wright-Patterson AFB, OH 45433

The modeling of the deformation and densification behavior of metal powders during hot consolidation processes was treated through the application of a continuum yield function and associated flow rule modified to incorporate microstructure effects such as grain growth, pore size, and pore geometry. It was shown that consolidation behavior can be described over the entire range of densities through two parameters, Poisson's ratio and the stress intensification factor, which are readily measured using uniaxial upset tests. The accuracy of the material modeling approach was validated by comparing the densification predicted from both a simple analytical model and an FEM with observed behavior during the die-pressing of monolithic gamma titanium aluminide powder and the hot-isostatic pressing of tapecast monotape composite layups comprising alpha-two titanium powder and continuous silicon carbide fibers. In addition, the effect of pore anisotropy on the yielding and flow behavior of partially consolidated powder compacts was addressed.

4:00 pm

PHYSICAL MODELING OF THE EARLY STAGES OF METAL POWDER CONSOLIDATION AND COMPARISON TO EXISTING ANALYTICAL MODELING APPROACHES: David P. DeLo, Henry R. Piehler, Dept. of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213

The important mechanisms during the early stages of metal powder consolidation are not well understood nor are they properly included in consolidation models. The result is that models tend to underpredict strain-rates, particularly during the early stages of consolidation. In a series of interrupted HIP experiments, PREP Ti-6Al-4V powder was consolidated in thin-walled containers, and the resulting partially consolidated specimens examined metallographically. Stereo micrographs of fractured specimen surfaces were examined qualitatively and quantitatively to gain insights into early stage mechanisms and appropriate modeling approaches. Evidence of particle rearrangement was found throughout the early stages of consolidation. Contact areas between particles increase in size at a much slower rate than is predicted by popular mechanistic models. Particle size effects, including rigid body motion of larger particles facilitated by preferential deformation of small particles, contribute to rearrangement. The critical assumptions required for common mechanistic and continuum models are not consistent with the observed mechanisms and behaviors requiring new modeling approaches that are consistent with the observed behavior.

4:30 pm

CONSOLIDATION OF NANOSTRUCTURED METAL POWDERS BY RAPID FORGING: PROCESSING, MODELING, AND SUBSEQUENT MECHANICAL BEHAVIOR: G.R. Shaik, Walter W. Milligan, Dept. of Metallurgy and Materials Engineering, Michigan Technological University, Houghton, MI 49931

Nanostructured metals are a potentially-promising class of materials with ultrafine grain sizes. A limitation on commercial implementation of nanostructured materials has been grain coarsening during consolidation. In this research, attritor-milled powders with 20 nm grain sizes inside micrometer-sized powder particles were consolidated by induction heating and rapid forging of cold-pressed compacts. Grain growth was limited by minimizing the time at consolidation temperature. Fully-dense materials were obtained at relatively low temperatures around 500°C. The consolidation process was successfully modeled with the Arzt-Ashby-Easterling HIP model, modified slightly for geometrical constraints, stress state and the nature of the nanostructured metal. Modeling and mechanical testing indicated that creep dominated the consolidation process, apparently due to the ultrafine microstructures. Mechanical properties at ambient and elevated temperatures. We gratefully acknowledge the support of the Air Force Office of Scientific Research, under grant F49620-94-1-0255, which is monitored by Dr. Walter Jones, and the National Science Foundation, under grant DMR-92-57465, which is monitored by Dr. Bruce MacDonald.