Sponsored by: MDMD Powder Metallurgy Committee and FEMS (Federation of European Materials Societies)
Program Organizers: Dr. David L. Bourell, The University of Texas at Austin, Materials Science & Engineering, MC C2201, Austin TX 78712; Dr. Liisa Kuhn-Spearing, Laboratory for the Study of Skeletal Disorders and Rehabilitation, Harvard Medical School, Children's Hospital, 300 Longwood Avenue, Boston MA 02115; Professor Dr. Herbert Gleiter, Karlsruhe Research Center, P.O. Box 3640, D-76021 Karlsruhe, Federal Republic of Germany
Tuesday, AM Room: Grand G
February 6, 1996 Location: Anaheim Marriott Hotel
Session Chairperson: Dr. Liisa Kuhn-Spearing, Laboratory for the Study of Skeletal Disorders and Rehabilitation, Harvard Medical School, Children's Hospital, 300 Longwood Avenue, Boston MA 02115
NANOSCALE MAGNETIC MATERIALS - AN OVERVIEW OF PROCESSING AND PROPERTIES: Robert D. Shull, Magnetic Materials Group, Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg MD 20899
Nanocrystalline materials represent one of the most active laboratories in recent times for the atomic tailoring of materials with specific properties and property combinations. For magnetic materials, new magnetic behavior, enhanced magnetic properties, and unusual property combinations are observed when some critical length scale (e.g., grain size or separation distance) is reduced to dimensions comparable to the magnetic exchange length. In addition, the properties may depend upon whether the reduction in size of this critical length was in 1, 2, or 3 directions. The preparation of such materials also presents special problems, largely because of the magnetic dipolar attraction between the ferromagnetic species. For composite materials, a special subset of nanostructured materials, the preparation route is particularly important. In this presentation a review will be presented of many of the techniques which have been found successful for the preparation of nanometer-scale magnetic materials and how the nanometer dimensionality effects their magnetic character.
SYNTHESIS AND HIGH MECHANICAL STRENGTH OF AL-BASED ALLOYS CONSISTING MAINLY OF NANOSCALE CRYSTALLINE, QUASICRYSTALLINE AND AMORPHOUS PARTICLES: Akihisa Inoue, Institute for Materials Research, Tohoku University, Sendai 980-77 Japan
The application of rapid solidification to Al-based alloys was found to cause the formation of nanoscale mixed structure consisting of amorphous plus nanogranular fcc Al phases, nanogranular icosahedral plus Al phases, and coexistent nanogranular amorphous plus Al phases. The particle size is about 3 to 5 nm for the nanogranular Al phase, 30 to 50 nm for the icosahedral particle and about 10 nm for the nanogranular amorphous phase. These mixed phase alloys exhibit high mechanical strength of 1300 to 1560 MPa combined with good bending ductility. It is to be noticed that the strength level exceeds largely that for Al- based amorphous single phase alloys. The nanoscale Al particles precipitate via a growth mechanism from the amorphous matrix, but the icosahedral and amorphous particles precipitate as a primary phase from supercooled liquid during rapid solidification. The detailed mechanism for the formation of the new nanophase structures as well as their nanostructural feature will be described.
SYNTHESIS OF NANOCRYSTALLINE ALLOY POWDERS: S.A. Pirzada, T. Yadav, Nanomaterials Research Corporation, 10960 N. Stallard Place, Tucson AZ 85737
Synthesis of nanocrystalline alloy powders was investigated using a novel thermal process. This thermal process continuously vaporizes the metallic precursors and uses Joule- Thompson expansion to control the nucleation process. The design has enabled the synthesis of nanosize powders of several commercially important alloys, such as NiAl, FeNi3 and FeTi. The powders produced were characterized by various techniques for phases, size, morphology, size distribution, surface area, etc. The powder size typically ranged from 20- 50 nm. This is a scaleable process to produce nanosized materials and is economically attractive. The design and the experimental results will be discussed.
9:55 am BREAK
PRODUCTION AND CONSOLIDATION OF NANOPHASE METALLIC AND CERAMIC POWDERS: L. He, J.- S Yin, E. Ma, Department of Mechanical Engineering, Louisiana State University, Baton Rouge LA 70803
Mechanical milling/alloying has been employed to produce nanophase metallic materials such as metals (e.g., Fe), intermetallics (e.g., Fe3Al), and composites (e.g., Fe- Cu). An aerosol synthesis route is being developed for nanophase ceramics (e.g., TiO2). These inexpensive powder synthesis routes yield relatively large quantities of nanophase powder materials for consolidation studies. A sinter forging process is developed to consolidate the powders into dense bulk samples while maintaining nanoscale microstructures. The process is effective for full- density processing not only for ceramics, but also for nanophase metallic materials prepared by mechanical alloying. In addition, nanophase ceramic- based composites (e.g., Al203/Al) and their sintering densification procedures have also been investigated. Preliminary results of the modeling of the densification processes and mechanical property measurements of consolidated bulk samples will also be reported.
FORMATION AND PROPERTIES OF NANOSTRUCTURED MATERIALS BY THE LOW ENERGY CLUSTER BEAM DEPOSITION TECHNIQUE: A. Perez, P. Mélinon, V. Dupuis, J. Tuaillon, B. Prével, JP. Perez, V. Paillard, Départment de Physique des Matériaux, Université Claude Bernard LYON I, F-69622 Villeurbanne, France
Intense and stable beams of clusters of various materials in the size range from few atoms to few thousands of atoms can be produced using the inert gas condensation sources. In the gas phase, depending on the source parameters, these clusters generally exhibit specific atomic and electronic structures interesting to stabilize to form cluster assembled materials with original properties. For this purpose the low energy cluster beam deposition technique has been recently developed. It consists in depositing selected mass distributions of neutral clusters having the very low energy gained in the supersonic expansion at the exit of the source. In this case, clusters do not fragment at the impact upon the substrate leading to the formation of controlled nanostructures. Both nanocrystalline films grown by random stacking of incident clusters or individual clusters embedded in a co-evaporated matrix can be prepared by this technique. After a brief review of cluster production, analysis, and deposition techniques, the specific nucleation and growth processes which govern the formation of cluster assembled films will be presented. Then, some characteristic examples (covalent: C, Si, and magnetic metals: Fe, Co, Ni) of cluster assembled films and cluster embedded in matrices, with original structures and properties will be reported.
SYNTHESIS TECHNIQUES, MICROSTRUCTURE AND MECHANICAL PROPERTIES OF NANOSTRUCTURED CERAMICS: Horst Hahn, Technical University Darmstadt, Department of Materials Science, Thin Films Division, Hilpertstraße 31/D, 64295 Darmstadt Germany
The synthesis of nanostructured materials using gas condensation processing is well established. The current knowledge for the synthesis of nanostructured ceramics (oxides, nitrides, carbides) including a novel technique, called chemical vapor condensation (CVC), using pyrolysis of chemical precursors, will be reviewed. Due to the ultrafine grain size and the narrow grain size distribution, sintering and creep deformation are enhanced and are observed at temperatures below 1/2 TM. Various models of creep deformation and superplasticity and their extension to the nanometer regime will be discussed with an emphasis on a new model which is based on grain boundary sliding as the rate controlling process.
OXIDATION AND GAS ADSORPTION IN AIR BY NANOCRYSTALLINE NICKEL AND COPPER SYNTHESIZED BY SPUTTERING: R.L. Holtz, Geo-Centers, Inc., 10903 Indian Head Hwy., Fort Washington MD 20744; V. Provenzano, Materials Science and Technology Division, Code 6323, U.S. Naval Research Laboratory, Washington, DC 20375
A key processing issue for nanocrystalline metals is their reactivity due to
the high specific surface area, and how this reactivity effects the handling of
nanocrystalline powder. Exposure of these materials to air results in
significant adsorption of gases, rapid initial rates of oxidation, and in many
cases spontaneous ignition. To quantify the reactivity of nanocrystalline
metals, and to better understand these phenomena and the implications for
processing, we have synthesized nanocrystalline Ni and Cu and measured the
weight gain as a function of time while exposed to room air. The n-
with particle sizes of around 5 nm were produced by the sputtering method
which yields the cleanest possible starting material. We analyze the air weight
gain data in terms of gas adsorption and oxidation processes, and contrast the
results for the nanocrystalline metals with micron-
Ni and Cu powders.
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