Alloy Ti3Al-based

Pn >erty H-based alloys Ti3Al-based intermetallic materials HAl-based intermetallic materials Ni-based superalloys... 

Various TiyAl-based alloys have been developed with niobium as a major alloying element and further components for obtaining an optimised balance of strength, formabUity, toughness, and oxidation resistance. The alloys are two-phase or three-phase. Current Ti3Al-based alloys with engineering significance are listed in Table 3.1-23. 

McKee DW (1993), Oxidation and protection of Ti3Al-based intermetalhc alloys . Mat. Res. Soc., Symp. MRS, 288, 953-958. 

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. 

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,... 

Mechanical Properties. Elastic properties of TiAl-based materials are compiled in Table 3.1-32. Strength, ductility, and toughness of the TiAl-based alloys are sensitive functions of both composition and microstructure which is controlled by prior processing [1.59]. Characteristic data are shown in Table 3.1-33 for various alloys. Different property data for the same alloy composition indicate the effect of different prior thermo-mechanical treatments. It is noted that TiAl-based alloys are prone to hydrogen/environmental embrittlement depending on the amount of q 2 from Ti3Al [1.60]. Creep and fatigue data are available [1.59,61]. 

Usually y-TiAl-based alloys contain Q 2-Ti3Al as a second phase and are, therefore, subject to hydrogen uptake and hydrogen/environmental embrittlement depending on the amount of Q 2-Ti3Al. 

The intermetallic compounds Tiy A1 and TiAl are studied for high-temperature materials developments. Extensive accounts [ 1.52,57] are the sources of the data presented here. In Table 3.1-21 the property ranges of Ti3Al- and TiAl-based alloys are compared to those of conventional Ti alloys and Ni-based superalloys. 

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