Aluminides alloy developments

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. 

As concluding remarks about these techniques, their increasing interest and the advantages of their combination with other techniques, we may mention, as an example, that within the European research project COST 535, concerning the Thermodynamics of Alloyed Aluminides , a meeting (Diisseldorf, December 2004) was dedicated to The Diffusion Couple Technique , presenting the principles of the method and the results obtained in the examination of several alloy systems. Zhao (2004) has developed an efficient variant of the diffusion couple technique (the diffusion multiple approach ). 

J.H. Park and G. Dragel, Development of Aluminide Coatings on Vanadium-Base Alloys in Liquid Lithium, Eusion Reactor Materials Semiannual Progress Report for the Period Ending, DOE/ER-0313/13, 1993, pp.405-410. 

Examination of the specimens after exposure confirmed that thin protective scales had developed and were retained on the iron aluminides and on the other alloys, except where large weight gains were recorded, in all three environments. The scales on the iron aluminides at 700°C were essentially A1203, as confirmed by X-ray diffraction... 

The titanium aluminide TiAl - often designated as y phase - crystallizes with the tetragonal LIq structure (CuAu-type) which is shown in Fig. 1. The LI o structure results from ordering in the f.c.c. lattice (Al), i.e. it is basically a cubic structure which is tetragonally distorted because of the particular stacking of the atom planes, as is seen in Fig. 1. The ratio of the lattice parameters c and a is cja = 1.015 at the stoichiometric composition and the density is 3.76 g/cm (Kim and Dimiduk, 1991), whereas for TiAl-base alloys the range 3.7-3.9 g/cm is given (see Table 2). This density is still lower than that of TijAl and has made the titanium aluminides most attractive for materials developments. 

New structural intermetallic alloys for high-temperature applications are at the center of the present interest in intermetallics, which is still growing. A few developments, which are based on the classic phases NijAl, TijAl and TiAl, and which are known as the nickel aluminides and the titanium aluminides, are on the brink of commercialization, but even these developments are still at an early stage compared with other developments of advanced materials, e.g. the modern engineering ceramics. Much more experimental and theoretical work is necessary to solve the processing problems and to ad-... 

Kim Y W (1995b), Trends in development of gattuna TiAl alloys . Gamma Titanium Aluminides, Las Vegas, TMS. 

Rowe R G (1990), Recent developments in Ti-Al-Nb titanium aluminide alloys , High-Temperature Aluminides and Intermetallics, Indianapolis, TMS. 

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