ISSN 1061-3862, International Journal of Self-Propagating High-Temperature Synthesis, 2008, Vol. 17, No. 3, pp. 1–6. © Allerton Press, Inc., 2008. 1 1. INTRODUCTION Iron aluminides are excellent candidates for use at high temperatures because of a combination of attrac- tive considerations, including low cost, high specific strength, high specific modulus, low density, and high oxidation resistance [1, 2]. However, commercializa- tion of these intermetallics has been limited because of the low ductility exhibited at room temperature [3–5]. Consequently, refining grain size to the nanocrystalline level has been suggested as a way to improving strength and enhancing ductility and toughness [6]. Indeed, nanocrystalline materials exhibit unusual and promis- ing physical, chemical, and mechanical properties [7– 9]. However, conventional methods in which iron alu- minides are processed, including casting, hot-rolling, and powder metallurgy [10, 11] do not yield nanostruc- tured products. High-energy ball milling of powder mixtures has been shown to be an efficient technique for the prepara- tion of nanomaterials. However, with this technique it is necessary to add a consolidation step to obtain a fully dense material. Different processes have been devel- oped to consolidate nanoparticles, including hot press- ing [12–14]. This technique, however, can result in sig- nificant grain growth, in some cases as much as three orders of magnitude. The full benefit of nanostructured materials can only be preserved if the consolidation method does not lead to a significant grain growth. Plasma activated sintering (PAS) is such a method, which has been shown to retain the fine grain size while producing near theoretical density materials [15]. A few years ago, the simultaneous effect of electric field combined with pressure applied during combustion, using the field-activated pressure-assisted synthesis process [16, 17], was found to be suitable to produce dense intermetallic compounds in a one step. Conse- quently, the application of this previous technique start- ing from mechanically activated powder mixture was investigated [18]. The method has been used to simul- taneously synthesize and consolidate nanostructured materials such as FeAl [19, 20], NbAl 3 [21], and MoSi 2 [22] as well as composites [23]. Iron aluminide, FeAl, is an ordered bcc structure which contains thermal defects. In this, as well as in other B2 structured intermetallics, non-stoichiometric deviations (FeAl with greater or less than 50 at % Al) are compensated for by the generation of constitutional defects. There are two types of defect structures in the B2 crystal: antistructure defect and triple defect. The antistructure defect results in an antisite atom for a con- stitutional defect of a rich phase, and a pair of antistruc- ture defects for thermal defects (FeAl + AlFe). The tri- ple defect structure consists of antisite A atoms for A- rich constitutional defects and α -sublattice vacancies for B-rich constitutional defects. Thermal defects are generated as two A site vacancies and one antisite A atom (2 V Fe + FeAl + FeAl) [25, 26]. The concentration Thermal Stability of FeAl Intermetallics Prepared by SHS Sintering S. Paris a, b , C. Pighini a , E. Gaffet b , Z. A. Munir c , and F. Bernard a a ICB-UMR 5209 CNRS, Université de Bourgogne, BP 47870, F-21078, Dijon, France b UMR 5060 CNRS/UTBM, Site de Sévenans, BP 449, 90010 Belfort Cedex, France c Department of Chemical Engineering and Materials Science, University of California, Davis, California, 95616 USA e-mail: sparis12000@yahoo.fr; fbernard@u-bourgogne.fr Received July 11, 2008 Abstract—The microstructural evolution of dense nanostructured FeAl produced by mechanical and field acti- vation was investigated over a range of annealing temperature from room temperature to 750°C. In-situ and ex- situ X-ray diffraction experiments were performed to determine the evolution of the crystallite size and micro- distorsion rate during annealing in an inert atmosphere. The results show the existence of two temperature domains: (i) below 500°C, the crystallite size remained relatively unaffected while the microdistorsions were eliminated and (ii) above 500°C, the crystallites exhibited significant growth leading to the destruction of the nanostructure. In addition, the microhardness change versus the crystallite size was consistent with prediction of the Hall–Petch effect. Keywords: SHS, FeAl, nanostructure, X-ray diffraction, powder metallurgy, microhardness, annealing PACS numbers: 81.05.Je, 81.05.Mh, 81.16.Be, 81.20.Ka DOI: 10.3103/S106138620803@@@@