Studies on the a → γ phase transformation mechanism in Ti[sbnd]48at.% Al alloy by high-resolution electron microscopy

Abstract The α → γ phase transformation, which occurs during quenching and produces extremely fine α2-γ lamellae, is discussed in relation to the analysis of the α2-γ interface structure. In a high-resolution image obtained from the growth edge of a γ plate in the α2 matrix, steps that were always found to be (0002)α2 or (111)γ planes high were observed at the α2-γ interface. This indicates that the α → γ phase transformation is performed by the migration of (a/3) 〈1100〉hcp Shockley partial dislocations on alternate 〈1100〉hcp planes to change the stacking sequence AB… to ABC….Chemical analysis by analytical transmission electron microscopy with energy-dispersive X-rays showed that the α2 and γ plates have the same composition, so that the α2→γ phase transformation which occurred during quenching can be interpreted as being composition invariant when these results are taken into consideration, it is suggested that the transformation is marterisitic.