Microstructure and cellular transition characteristic of Ti-42Al-3Nb-1Mo-0.1B alloy

The microstructure and cellular transition characteristics of an intermetallic Ti-42Al-3Nb-1Mo-0.1B (at.%) alloy were investigated. The as-cast microstructure of the alloy is mainly composed of (α2+γ) lamellar structure and (β+γ) mixture structure, which distributes along the boundaries of the lamellar colonies. In order to study the phase transformation of lamellar structure at aging temperature, a two-step heat treatment was carried out. After the first step of annealing treatment at 1,260 °C, the microstructure with relatively finer lamellar space and (γ+β/B2) mixture structure is obtained. Aging treatment, as the second heat treatment step, has significant influence on the microstructure, attributing to a cellular reaction of α2+γ→ γ+β. With the increase of aging temperature, the (α2+γ) lamellar structure continues to dissolve, whereas the contents of both the equiaxed γ and β/B2 grains continuously increase. Besides, the orientation of lamellae α2, equiaxed γ and equiaxed β/B2 in the cellular transition region follows a specific relationship of {0–11}β β//{0001}α2 α2//{1–11}γ γ.