1414 Ti4822 yTiAl

Gamma titanium aluminides are a class of alloys undergoing significant development for use in a variety of aerospace applications [30]. The alloys are quite remarkable in that they have increasing yield strength with increasing temperature. At room temperature, however, the alloys are very brittle and are difficult to form. These alloys are difficult to cast, work, and weld, and there has been much work on the development of cost-effective forming techniques using powder metallurgy techniques [31]. Laser-based free-form techniques present interesting possibilities with respect to the cost-effective manufacture of y-titanium aluminide alloys. There has been little work done on these alloys to date, although this will change in the near future.

Work performed at Penn State under the direction of Crucible Research was undertaken to obtain preliminary chemical and tensile data on laser forming of Ti-48Al-2Cr-2Nb alloy and has been reported by Moll et al. [32].

Figure 14.11 shows a cross section of the X-Z plane of a monolithic block of Ti-48Al-2Cr-2Nb produced at Penn State. The block was approximately 250 mm long by 75 mm high by 30 mm wide. Microstructures of the as-deposited and heat-treated material are shown in Figure 14.12. Note that pass lines are evident,

FIGURE 14.11 y-TiAl (Ti-48Al-2Nb-2Cr) processed at Penn State.

FIGURE 14.11 y-TiAl (Ti-48Al-2Nb-2Cr) processed at Penn State.

FIGURE 14.12 y-TiAl (Ti-48Al-2Nb-2Cr) as-deposited (right) and heat treated 1338°C 0.5 h AC + 871°C 4 h AC.

these are probably due to solute banding similar to that observed in multipass weldments. The microstructure is fully lamellar.

Mechanical properties and chemical information for as-deposited material are shown Tables 14.13 and 14.14.

TABLE 14.13 Mechanical Properties of y -TiAl (Ti-48Al-2Nb-2Cr)

Test Temp

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