Synthesis of FeAl Hetero-Nanostructured Bulk Parts via Spark Plasma Sintering of Milled Powder
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0980-II05-10
Synthesis of FeAl Hetero-Nanostructured Bulk Parts via Spark Plasma Sintering of Milled Powder Thierry Grosdidier1, Gang Ji2, Frédéric Bernard3, and Sébastien Launois4 1 Université de Metz, d’Etude des Textures et Application aux Matériaux (LETAM), UMR CNRS 7078, Ile du Saulcy, Metz, 57045, France 2 Université de Metz, Laboratoire d’Etude des Textures et Application aux Matériaux (LETAM), UMR CNRS 7078, Ile du Saulcy, Metz, 57045, France 3 Université de Bourgogne, Laboratoire de Recherche sur la Réactivité des Solides (LRRS), UMR CNRS 5613, 9 avenue Alain Savary, Dijon, 21078, France 4 Commissariat à l'Energie Atomique, Département des Technologies des Nanomatériaux, 17 rue des Martyrs, Grenoble, 38054, France
ABSTRACT Spark plasma sintering (SPS) has been used in order to introduce nanocrystalline grains within fully dense FeAl consolidated parts. Hetero-nanostructured parts, consisting of nano, ultrafine and micrometric grains, have been successfully processed when milled - Y2O3 reinforced - FeAl powder was used. The large temperature differences that are spontaneously generated during the SPS process as well as the use of milled powder account for the formation of such interesting structures. The grain size distribution - that is suggested to be very potent to improve both strength and ductility - could be significantly modified by a proper selection of sintering temperature and holding time. INTRODUCTION Over a decade, an extruded material, called FeAl40 Grade 3 alloy, has been developed by CEA-Grenoble (France) at laboratory scale [1]. Thanks to its combined properties such as good mechanical strength, low density, low cost and availability of raw materials as well as excellent corrosion and oxidation resistances, this developed material is ready-to-use for some industrial applications - in the field of engines and power generation systems - to replace steels and nickel based alloys [2]. This material was produced by cold consolidation and hot extrusion of powders within which fine Y2O3 particles and nanostructure were introduced by mechanical milling in order to overcome the common limitations of FeAl such as brittleness at room temperature and poor creep resistance [3-6]. Such a powder metallurgy route eventually led to an alloy improved by grain boundary and oxide dispersion strengthening with a grain size of about 1.1 µm [7-12]. A study of the as-extruded material has shown that it possesses a high yield strength (over 1000 MPa) combined with reasonable ductility (tensile elongation ~5%) [13]. It was also suggested that the most effective way to improve the strength/ductility balance of FeAl is to further refine the grain size [13]. However, conventional hot extrusion processing is often performed at temperatures above 1000 °C and inevitably results in a coarsening of the nanostructure from the milled powder. In contrast, the high temperature is critically important to ensure a full densification of the material.
The advantages of spark plasma sintering (SPS) method are high thermo-efficien
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