Formation of α-segregation and its impact on grain refinement in Ti-47.5Al-5Nb-2.5V-1Cr alloy

This paper presents a method for refining the coarse lamellar colonies in α-solidified TiAl alloys using α-segregation. The prerequisite of this method is control of the solidification rate. Isothermal holding at upper and/or middle of α phase region and control of cooling rate from α to (α+γ) phase region is also necessary for better refinement. In addition, the formation of α-segregation and characteristics of the refined lamellar colonies are studied. The results show that the formation of α-segregation is mainly related to the change of the phase transformation path caused by Al-depletion. Moreover, α-segregation is composed of two kinds of β phases, which can be distinguished by orientation relationship with matrix colony. Although the coarse colonies are refined, the refined colonies exhibit the same orientation as the parent colonies. Besides, the degree of α-segregation and the type of β phase will affect the local characteristics of the refined lamellar colonies.