Atomic-scale understanding of the unilateral thickening of γ lamellae during α to γ phase transformation in Ti48Al2Cr2Nb alloy

The unilateral thickening of γ lamellae during α to γ transformation was investigated by examinations of surface reliefs and atomic steps of γ lamellae. The results show that the rounded corners of terraces and the steps prefer to form mainly on one side of the γ lamella, and Shockley partial dislocations with same and with very random Burgers vectors construct the steps. It indicates γ lamellae grow in a mixture of two scenarios of Shockley partial dislocations. The differences of γ/α interface stability and element concentration on the two sides of γ lamella contribute to the unilateral thickening.