On the eutectoid decomposition of α→γ+τ₁ in a Ru-containing TiAl alloy

For the first time, the eutectoid decomposition α→τ₁+γ and the crystalline orientation relationship in a Ru-containing TiAl alloy were studied. The lamellar and netlike eutectoid microstructures were observed. In the former case, the eutectoid lamellar τ₁ phase nucleated attaching to the intragranular leading precipitated γ laths, with an orientation relationship of {0001}_α//{111}_γ//{220}_τ1 and <112¯0>_α//<110>_γ//<111>_τ1. In the later case, the netlike eutectoid leading phase τ₁ was found to nucleate both at grain boundary and intragranular region with the same orientation in a eutectoid nodule and the eutectoid product γ phase inherited the orientation of the adjacent one. However, no specific orientation relationship in such eutectoid decomposition was determined. The discrepancies of the morphology and orientation relationship dominated by the competition of two leading phases were revealed.