Study on the microstructure, phase transition and hardness for the TiAl-Nb alloy design during directional solidification

The solute segregation is greatly connected with the microstructure evolution during the directional solidified TiAl-Nb alloy. S-segregation leads to solute Al rich in the interdendritic liquid and Nb rich in the dendrite, which can promote the L + β + α peritectic reaction at the high growth rates. Peritectic α phase envelopes the primary β phase firstly by nucleation, and then the dissolution of primary β phase and the growth of peritectic α phase happen through the β → α transition, during which the further β segregation lead to the multi-phase structure (α2/γ lamellar and B2 phase) and the inhomogeneous solute distribution.235