Binary 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. 

In the present study the oxidation behaviour of three binary titanium aluminidcs, Ti45 Al,Ti48Al and Ti50Al (additions given in at.%), as well as a number of ternary alloys with Nb contents between 2 and 10 % were studied at 900°C in order to clarify the apparent contradictory effect of nitrogen on the oxidation resistance of titanium aluminides. 

Effect of aluminum content on room-temperature tensile elongation and hardness of binary y titanium aluminide alloys. Hardness values at 1000 °C (1830 °F0 are also shown. Note the single-phase y region and the two-phase (o +y) region. 

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