metals Article Synthesis of Intermetallics in Fe-Al-Si System by Mechanical Alloying Kateˇ rina Nová 1, *, Pavel Novák 1 , Filip Pr ˚ uša 1 , Jaromír Kopeˇ cek 2 and Jaroslav ˇ Cech 3 1 Department of Metals and Corrosion Engineering, University of Chemistry and Technology, 166 28 Prague, Czech Republic; panovak@vscht.cz (P.N.); prusaf@vscht.cz (F.P.) 2 Institute of Physics of the Czech Academy of Sciences, 182 21 Prague, Czech Republic; kopecek@fzu.cz 3 Department of Materials, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, 120 00 Prague, Czech Republic; Jaroslav.Cech@fjfi.cvut.cz * Correspondence: novakx@vscht.cz; Tel.: +42-022-044-4055 Received: 22 October 2018; Accepted: 19 December 2018; Published: 25 December 2018   Abstract: Fe-Al-Si alloys have been recently developed in order to obtain excellent high-temperature mechanical properties and oxidation resistance. However, their production by conventional metallurgical processes is problematic. In this work, an innovative processing method, based on ultra-high energy mechanical alloying, has been tested for the preparation of these alloys. It has been found that the powders of low-silicon alloys (up to 10 wt. %) consist of FeAl phase supersaturated by Si after mechanical alloying. Fe 2 Al 5 phase forms as a transient phase at the initial stage of mechanical alloying. The alloy containing 20 wt. % of Si and 20 wt. % of Al is composed mostly of iron silicides (Fe 3 Si and FeSi) and FeAl ordered phase. Thermal stability of the mechanically alloyed powders was studied in order to predict the sintering behavior during possible compaction via spark plasma sintering or other methods. The formation of Fe 2 Al 5 phase and Fe 3 Si or Fe 2 Al 3 Si 3 phases was detected after annealing depending on the alloy composition. It implies that the powders after mechanical alloying are in a metastable state; therefore, chemical reactions can be expected in the powders during sintering. Keywords: powder metallurgy; intermetallics; mechanical alloying; iron aluminide; iron silicide 1. Introduction Over the past few years, materials based on intermetallic compounds are increasingly used thanks to their wide range of properties. For example, shape memory alloys (e.g., NiTi) are very attractive, as well as materials for high-temperature use, such as NiAl or TiAl. Other examples are FeAl or Fe 3 Al intermetallics, which are used in strongly oxidizing or sulphidizing environments in combination with high temperatures [1–4]. Intermetallic compounds based on Fe-Al are considered to be very promising materials for industrial applications due to their low cost and high specific strength combined with excellent creep resistance, as well as their oxidation resistance at high temperatures [2,5,6]. Fe-Al-Si system is of high interest because iron is the most common impurity in Al alloys, while Si is used as an alloying element [7]. Impurities come to Al mainly during recycling, when some iron-containing material cannot be magnetically separated from Al completely [8]. Within cast Al-Si alloys, Fe and Si form hard and brittle ternary phases, which influence corrosion and wear resistance [7]. One author´s previous work [4] showed that the Fe-Al-Si phases need not be considered as detrimental phases in Al alloys, but can instead be used for advantages in high-temperature service, because the addition of Si to binary Fe-Al system improves oxidation resistance and thermal stability [9,10]. Based on this fact, a completely new grade of Fe-Al-Si alloys has been developed at UCT Prague during the Metals 2019, 9, 20; doi:10.3390/met9010020 www.mdpi.com/journal/metals