Interaction of tantalum with reinforcements in γ TiAl

Evidence suggests that tantalum alloying additions can segregate to fiber or reaction zone interfaces in TiAl. The behavior depends on the reinforcing material being studied. Inhomogeneities in tantalum concentration in TiAl owing to segregation are a matter for concern. Other refractory metal additions may also segregate, since they behave similar to tantalum. Samples of Ti-47Al-2Ta with a few reinforcing fibers were hot isostatically pressed. The fibers used were Al 2O 3-ZrO 2 and Si 3N 4, uncoated and coated with TiC or TiB 2. These samples were heated for times up to 500 h at 982 °C in order to simulate potential use temperatures and times. Backscattered scanning electron microscopy, energy dispersive X-ray analysis and electron microprobe analysis were used for the examination. Results include a sixfold increase in tantalum at the interface between a TiB 2 coating on a Si 3N 4 fiber and the matrix, while an uncoated fiber shows an increasing tantalum content in the fiber and reaction zones.