ANTIPHASE BOUNDARIES IN TI48A12MO

The microstructures of samples of Ti48Al containing either 0.5 at.% Mo or 2 at.% Mo have been assessed in as-east samples and in samples quenched from a range of temperatures between 1000 and 1350-degrees-C. It has been found that the structure of the cast samples reflects the difficulty of obtaining equilibrium structures in such alloys. The microstructure of samples quenched from 1350-degrees-C was found to be dominated by antiphase domains (APDs), twins and stacking faults in the gamma phase in 2 at.% Mo alloy but not in the 0.5 at.% alloy. The origin of the APDs is discussed in terms of the influence of Mo on the phases in equilibrium at high temperatures in Ti48Al and the transformations occurring during quenching. It was found that the antiphase boundaries showed strong contrast under all imaging conditions and detailed image simulation has shown that the displacement, R, between APDs, is 1/2[101] + DELTAR where DELTAR = 5% of R.