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Lathe Ttarned

Shot Peened

Glass Bead Blasted

40 100 300 S00

Cyclic Life-%

FIGURE 8.9 Effects of surface condition on LCF life of Ti-6Al-4V at 21°C (70°F) [26].

The FCGR performance generally parallels fracture toughness, with the caveat that severe corrosive environments (such as 3.5% NaCl solution) can adversely affect the FCGR by an order of magnitude. An example of the strong influence of microstructure on FCGR for the Ti-6Al-4V alloy is shown in Fig. 8.13 [26], with the P-2 annealed condition significantly better than the mill-annealed material.

The a and near-a alloys generally exhibited superior high-temperature behavior (Fig. 8.14) [25]. The reason why these alloys have replaced steels in advanced jet engines is clearly demonstrated in Fig. 8.15 [25], with the titanium alloys now used to about 600°C (1110°F). Generally these alloys contain Si for enhanced creep behavior (Fig. 8.16) [25].

First Crack

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