Intermetallics titanium aluminides

Recently, a great interest has been placed on intermetallic titanium aluminides the two systems under development are based on Tis A1 and TiAl compounds, which promise temperature capabilities of 800 °C and 980 C, but great efforts have to go into the achievement of ductility, toughness and oxidation resistance above 650 C. 

Metal-Ceramic Composites. Metals such as aluminum, titanium, copper and the intermetallic titanium aluminide, which are reinforced with silicon-carbide fibers or whiskers show an appreciable increase in mechanical properties particularly at elevated temperatures. These composites are being considered for advanced aerospace structures.1 1... 

Schiitze M, Schumacher G, Dettenwanger F, Homauer U, Richter E, Wieser E and MoUer W (2002), The halogen effect in the oxidation of intermetallic titanium aluminides ,... 

The melting point of titanium is 1670°C, while that of aluminium is 660°C.142 In kelvins, these are 1943 K and 933 K, respectively. Thus, the temperature 625°C (898 K) amounts to 0.46 7melting of titanium and 0.96 melting of aluminium. Hence, at this temperature the aluminium atoms may be expected to be much more mobile in the crystal lattices of the titanium aluminides than the titanium atoms. This appears to be the case even with the Ti3Al intermetallic compound. The duplex structure of the Ti3Al layer in the Ti-TiAl diffusion couple (see Fig. 5.13 in Ref. 66) provides evidence that aluminium is the main diffusant. Otherwise, its microstructure would be homogeneous. This point will be explained in more detail in the next chapter devoted to the consideration of growth kinetics of the same compound layer in various reaction couples of a multiphase binary system. 

Titanium aluminides are ordered intermetallics and hence have lower diffusivity and high elastic modulus. These compounds are stronger than the conventional titanium alloys and are suitable for high temperature applications. But these compounds have low ductility due to the planarity of slip in these compounds. 

P. R. Subramanian, M. G. Mendiratta, D. M. Dimiduk and M. A. Stucke, Advanced intermetallic alloys - beyond gamma titanium aluminides Mat. Sci. Engg., A239-240 (1997) 1-13. 

Y. Nishiyama, T. Miyashita, S. Isobe, T. Noda Development of Titanium Aluminide Turbo-Charger Rotors. In S. H. Whang, C. T. Liu, D. P. Pope et al. High-Temperature Aluminides and Intermetallics. TMS, Warrendale (1990) 557-584. 

P.A. Beaven, F. Appel, B. Dogan, R. Wagner Fracture and Ductilization of Gamma-Titanium Aluminides. In C. T. Liu, R. W. Cahn, and G. Sauthoff (eds.) Ordered Intermetallics - Physical Metallurgy and Mechanical Behaviour. Kluwer Acad. Publ. Dordrecht (1992) 413-432. 

In industrial applications the environments usually contain more than one reactant. For example high temperature oxidation occurs in air by the combined attack of oxygen, nitrogen and quite frequently water vapour. However, most of the studies concerning the oxidation resistance are performed in dry oxygen or dry air. The oxidation behaviour of the intermetallic phases of theTi-Al system has recently received considerable attention. The influence of water vapour on the oxidation of titanium aluminides has not been studied intensively. There are only a few studies of the high temperature corrosion of titanium and its alloys. 

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-... 

The present monograph was first written as a chapter for Volume 8 of the series Materials Sdence and Technology A Comprehensive Treatment , edited by Robert W. Cahn, Peter Haasen, and Edward J. Kramer (Volume Editor Dr. Karl Heinz Matucha). Its aim is to give an overview of intermetallics, which is both detailed and comprehensive and which includes the fundamentals as well as applications. The result is an extended, critical review of the whole field of intermetallics with an emphasis on those intermetallic phases which have already been applied as functional or structural materials or which are currently the subject of materials developments. A historical introduction and a discussion of the relationship between atomic bonding, crystal structure, phase stability and properties is followed by a discussion of the major classes of intermetallics. The titanium aluminides, nickel aluminides, iron aluminides, copper phases, A15 phases. Laves phases, beryllides, rare earth phases, and siliddes are reviewed. In particular, the crystal structures, phase diagrams, and physical properties as well as the mechanical and corrosion behavior are treated. The state of developments as well as prospects and problems are discussed in view of present and future applications. The publisher has decided to publish the review as a separate monograph in order to make it accessible to a wider audience. 

Matsugi K, Ishibashi N, Hatayama T, Yanagisawa O (1996) Microstmcture of spark sintered titanium-aluminide compacts. Intermetallics 4 457 67... 

Of the titanium aluminide intermetallic phases, only TiAl2, TiAl3, and certain t phase compositions can form a protective AI2O3 scale over a wide range of temperatures in air. They will be treated first, followed by the y, oui, and orthorhombic phases. 

Comparison of the creep behavior of conventional titanium alloys and titanium aluminide intermetallics. 

Hanamura T, Dcematsu Y, Morikawa H and Takamura J (1991), Improvement of oxidation resistance and ductihty in titanium aluminides by small addition of Vb or VIb elements , Intermetallic Compounds (JIMIS-6), Sendai, Japan Inst Met. 

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

Intermetallic compounds titanium aluminides [55-60], nickel aluminides [61-64], iron aluminides [65-68] and molybdenum silicides [69,70]. 

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