In situ Observation of the Initial Stage of γ Lamella Formation in Ti48Al2Cr2Nb Alloy

In situ observation is carried out in Ti48Al2Cr2Nb (at%) alloy to obtain a comprehensive understanding on the growth mechanisms of γ lamellae. The results reveal that the grain-boundary nucleated γ embryos occur first and grow into the adjacent α grains. Both the γ lamellae nucleated at the grain boundary and within α grain prefer to grow in pair by nucleation of the new γ lamella adjacent to the precedent γ lamella or branching of the growth tip. The widening of γ lamellae is controlled by the migration of α/γ interface, and the distance between growth pairs directly influences the lamellar width. The EBSD results exhibit that the two γ lamellae in growth pairs have a true-twin or pseudo-twin relationship. The underlying growth mechanism of γ lamellae is discussed.