Temperature iron aluminides

Since a general understanding is that the strength of iron aluminides is lower than that of other aluminides of interest, the relevant research is relatively few. However, an excellent resistance to oxidation and corrosion was reported for iron aluminide of p-Fe-A1 type by Okada et al. [66] together with their mechanical properties at high temperatures. 

High Temperature Corrosion Behaviour of Iron Aluminides and Iron-Aluminium Chromium Alloys... 

The high temperature corrosion behaviour of different iron aluminides and iron-aluminium-chromium alloys containing 6-17 wt% aluminium, 2-10 wt% chromium and additions of mischmetal has been investigated in both air and hot process gases. 

It is more difficult to establish a protective A1203 scale at lower temperatures than at higher temperatures, particularly on alloys of relatively low aluminium concentrations thus, an iron aluminide containing 8 wt% Al formed more extensive sulphides at 500°C than at 700°C, although a protective oxide scale prevented significant sulphidation of an alloy containing 12 wt% Al at either temperature. 

Many of the intermetallic compounds are very difficult to process into thin sheets because they exhibit very low ductility at ambient temperatures. Powder metallurgical techniques coupled with tape casting have been employed to process these materials into continuous thin sheets which, after removal of the polymer binder and plasticizer, can be sintered and rolled to full density with a sequence of cold work and annealing steps. The use of tape casting has recently been reported for the production of iron aluminide (FeAl) thin sheets with excellent properties. We believe that this processing technology can be used for other intermetallic compounds, especially for the production of continuous thin sheets. 

The maximum temperature at which iron aluminides have sufficient strength for structural application (600-650 C) is significantly lower than temperatures at which they have maximum resistance to corrosion (>900 °C). One approach to boosting the high-temperature mechanical properties has been the development of oxide dispersion-... 

Given that Fe-Al intermetallics were among the earliest intermetallics investigated, a historical perspective of Fe-Al alloy development will be presented. This is followed by a discussion of the oxidation behavior of Fe3Al and FeAl in air. Because of interest in their use in complex, corrosive environments, a detailed discussion of the oxidation behavior of iron aluminides in intermediate temperature (<800°C) environments containing species such as sulfur, chlorine, and carbon will also be presented. 

The high-temperature oxidation behavior of Fc3Al-based iron aluminides has been well documented in recent years (Pint et al., 1999 c Tortorelli and Natesan, 1999). The critical Al concentration for exclusive AI2O3 formation is reduced by addition of Cr (Tortorelli and DeVan, 1992) or increased by addition of Ni (Tomaszewicz and... 

In carburizing environments, if the relative partial pressures of oxygen and carbon favor AI2O3 stability and the temperature is such that the kinetics of AI2O3 formation enable rapid coverage of the alloy surface, iron aluminides would be expected to have very... 

Klower J. High Temperature Corrosion Behaviourof Iron Aluminides and Iron- Aluminium-Chromium Alloys In Grabke HJ, Schiitze M, editors. Oxidation of intermetaUics. Weinheim - Germany Wiley-VCH Verlag GmbH 1997. p. 203-20. 

Fie] Field, R.D., Zindel, J.W., Fraser, H.L., The Intercellular Phase in R idly Solidified Alloys Based on the Al-Fe System , Scr. Metall, 20,415-418 (1986) (Crys. Stracture, Experimental, 8) [1987Die] Diehm, R.S., Mikkola, D.E., Effects of Mo and Ti Additions on the High Temperature Compressive Properties of Iron Aluminides Near FcsAl , Mater. Res. Soc. Symp. Proc. High-Temp. Ordered Intermetallic Alloys II, 81,329—334 (1991) (Experimental, Phase Relations, Meehan. Prop., 8)... 

Risl] Risanti, D.D., Sauthoff, G., Strengthening of Iron Aluminide Alloys by Atomic Ordering and Laves Phase Precipitation for High-temperature Applications , Intermetallies, 13(12), 1313-1321 (2005) (Crys. Stmeture, Experimental, Meehan. Prop., Morphology, Phase Diagram, Phase Relations,, , 37)... 

Lee and Lin (1999) studied the oxidation, mixed oxidation-sulphidation and hot corrosion of ductile iron aluminide Fe3Al with Cr addition at temperatures of 605-800°C. They observed that hot corrosion of iron aluminide was significantly more severe than oxidation and mixed oxidation-sulphidation. According to Lee and Lin, this can be attributed to the formation of aluminium sulphide at the metal-salt interface as a result of high sulphur potential in the molten salt at the oxide-metal interface. 

Iron aluminides, including Fc3 A1 and FeAl, are of interest for high-temperature stmctural applications since they have relatively high melting points, excellent oxidation, carburisation, sulfidation, and hot corrosion resistance, relatively low density and low material cost. The major advantages that can be derived from the use of iron aluminides include the following [215,216] ... 

Tortorelli P F and Natesan K (1998), Critical Factors Affecting the High-Temperature Corrosion Performance of Iron Aluminides, Mater Sci Eng, A258, 115-125. 

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