Titanium aluminides properties

Table 15. Properties of Titanium Aluminides, Titanium-Base Conventional Alloys, and SuperaHoys ...

P/M processing of titanium aluminides results in more consistent product quaHty than the conventional casting process, and offers novel alloy/microstmcture possibiHties and improved ductiHty. Processing trends include use of high (1200—1350°C) temperature sintering to improve mechanical properties of steel and stainless steel parts. 

Ferreira, A., Meyers, M. A., and Thadani, N. N., Dynamic compaction of titanium aluminides by explosively generated shock waves Microstructure and mechanical properties. Metall. Trans. A, 23A,3251 (1992). 

Titanium aluminide alloys based on Ti3 A1 and TiAl are of interest as construction material for high temperature components particularly in aerospace industry. Good mechanical properties can be attained with alloys consisting of y-TiAl with 3 to 15 vol% a2-Ti3Al. The disadvantages are the low ductility and the inadequate oxidation resistance at service temperatures of 700-900°C [1]. A fundamental understanding of the oxidation behaviour is necessary in order to improve the corrosion resistance. The formation of the oxides on the alloy surface depends on the temperature, the oxygen partial pressure of the corrosive atmosphere, and the thermodynamic activities of Ti and A1 in the alloys. 

N.S. Choudhury, H.C. Graham, J.W. Hinze Oxidation Behavior of Titanium Aluminides, Z.A. Foroulis, F.S. Pettit, Eds., Proceedings of the Symposium on Properties of High Temperature Alloys (Tlte Electrochemical Society, Princeton, N.J.), (1976), pp. 668. 

Table 2. Properties of alloys based on the titanium aluminides TijAl and TiAl compared with conventional titanium alloys and nickel-base superalloys (Morral, 1980, Lipsitt, 1985a Kim, 1989 Kim and Froes, 1990 Froes et al., 1991).

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. 

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... 

Alloys based on y-TiAl, also called gamma titanium aluminides, excel due to their high strength per unit density. These alloys contain the Q 2-phase Ti3Al as a second phase and are further alloyed with other elements for property optimization. The composition range is Ti-(45 8) Al-(0-2)(Cr, Mn, V)-(0-5)(Nb, Ta, W)-(0-2)(Si,B, Fe, N) (at.%). Further components such as Hf,... 

Source R. Boyer et al., Microstructursd/Property FtelatlonsNps in Titanium Aluminides andAlioys, The Minerals, Metals, and Materials Sodely, 1991,p511-520... 

Mis] Mishurda, J.C., Perepezko, J.H., Phase Equilibria in Ti-Al Alloys , Microstructure-Property Relationships in Titanium Aluminides and Alloys, Kim. Y.W., Boyer, R.R., (Eds.), 3-30 (1991) (Phase Diagram, Phase Relations,, , 75)... 

Table 11.1 Properties of titanium aluminides, titanium-base conventional alloys and superalloys (from Kim and Froes, 1990, reproduced with permission)...

Up to 4 wt% H can be dissolved in titanium alloys at elevated temperatures. This hydrogen can then be used to improve processibility, and final mechanical properties are enhanced after its removal. Removal of the hydrogen can be easily achieved by vacuum annealing (Ref 7, 8). This thermomechanical processing technique allows ti-tanium aluminides to be processed at reduced temperatures (Ref 7-10) and results in a finer micro-structure (Ref 7,8,10,11). 

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