Densification of nanocrystalline powders. Field Activated Sintering of Tantalum nanopowders.
Final rept. 9 Jun 2000-8 Jun 2003
CALIFORNIA UNIV DAVIS DEPT OF CHEMICALENGINEERING AND MATERIALS SCIENCE
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This work focused on the specifics of densification of nanocrystalline powders using an externally applied pulsed electrical current. Studies were performed to characterize the surface structure of select metal nanopowders Ni, Al and Ta and understand differences due to handling and storage conditions. For the oxygen sensitive Ta, methods were designed to clean previously coated nanoparticle surfaces. Grain growth behavior of nanocrystalline materials was characterized by in-situ TEM with and without an externally applied electrical current. An integrated heatingelectrical biasing holder was designed and built for in-situ TEM coarsening studies. For field sintering of nanomaterials, a more detailed characterization of the commercial SPS machine was required, and temperature evolution and distribution, and heating rate effects were evaluated. Based on the experience in SPS sintering of conventional parts 19 mm in diameter and 5 mm thick from Ni nanoparticles, large specimens thickness up to 19 mm were sintered for mechanical testing. Ta nanopowders 40 nm were sintered to a final density of 12.9 gcm3 at 1200 C. The graincrystallite size very small 2. 5 nm. This was also attributed to a phase transformation from tetragonal to cubic in Ta. Mechanical property characterization is being performed on large Ni specimens and sintered Ta at ARL, Aberdeen Proving Ground, Maryland.
- Inorganic Chemistry
- Fabrication Metallurgy