Investigation of mechanically activated field-activated pressure-assisted synthesis processing parameters for producing
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h. Valot and L. Gosmain Laboratoire de Recherches sur la Re´activite´ des Solides, UMR 5613 CNRS, Université de Bourgogne, BP47870, 21078 Dijon Cedex, France
E. Gaffet Nanomaterials Group, UMR 5060 CNRS/UTBM, F90010 Belfort, France and GFA, GDR 2391 CNRS, BP47870, F21078 Dijon Cedex, France
F. Bernarda) Laboratoire de Recherches sur la Re´activite´ des Solides, UMR 5613 CNRS, Université de Bourgogne, BP47870, 21078 Dijon Cedex, France, and GFA, GDR 2391 CNRS, BP47870, F21078 Dijon Cedex, France
Z. Munir Department of Chemical Engineering and Materials Science, University of California, Davis, California 95616 (Received 2 April 2003; accepted 2 July 2003)
The parameters of the mechanically activated field-activated pressure-assisted synthesis (MAFAPAS) process, which were recently developed and patented for producing dense nanostructured materials, were studied in the case of the B2-FeAl intermetallic. Based on x-ray diffraction (XRD) experiments, residual stresses XRD analysis, relative density measurement, and secondary-electron microscopic observations, the optimal synthesis conditions (time, current intensity, and pressure) were studied. Fe + Al powders were comilled in a specially designed planetary mill to obtain a mixture of reactants at the nanoscale without the formation of any product. The milled mixtures were then subjected to a high density of alternating current (60 Hz ac, total current 1250 or 1500 A), a uniaxial pressure (70 or 106 MPa), and different times (from 2 to 5 min). This work confirms the reproducibility of the MAFAPAS process, showing the essential role of the mechanical activation step to produce a pure nanostructured material. In addition, the composition and the microstructure of MAFAPAS end-products depended on the processing parameters (time, current density, mechanical pressure). In particular, it was observed that the process of simultaneous synthesis and consolidation of the product introduced a high level of residual stresses. I. INTRODUCTION
Due to their attractive physical and mechanical properties, intermetallic compounds have been the focus of numerous investigations. Among these, aluminides such as Ti3Al, TiAl, Ni3Al, NiAl, Fe3Al, and FeAl have received the most attention as possible replacements for current high-temperature structural materials such as steels or superalloys.1 Of these, FeAl has received considerable attention as a material for many engineering applications, including its use in pipes, hot-gas filters, a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 10, Oct 2003
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heating elements, insulation wrappings, tooling, fabric and paper cutting, fasteners, and automotive exhaust manifolds.2 Its properties provide a desirable combination of high melting temperature, good thermal conductivity, high electrical resistivity at high temperature, high-temperature oxidation and sulfidation resistance, good corrosion resistance in many aqueous environments, goo
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