Microstructure and Formation Mechanism of β Eutectoid Decomposition in a γ‐TiAl Alloy with Ru Addition

A eutectoid decomposition of β→α + τ₁ occurs during water quenching (WQ) and the corresponding formation mechanism in a γ‐TiAl alloy with Ru addition is studied. A novel morphology consisting of outer lamellar and inner net‐like eutectoid microstructure is observed. The α and τ₁ products are determined to nucleate and grow with the same crystalline orientation in a eutectoid aggregation, respectively. No specific crystalline orientation is confirmed between α and τ₁. The eutectoid reaction is found to be controlled by diffusion. Moreover, α and τ₁ grow in a synchronous manner. The outer lamellar region absorbs Ti, but excludes both Ru and Al atoms to the center of the β matrix during the eutectoid reaction. Correspondingly, the high Ru and Al contents promote the sidewise growth of τ₁ lamellae and result in the distinctions in microstructure with the outer lamellae.