An X-ray diffraction study of strain localization and anisotropic dislocation contrast in nanocrystalline titanium

A detailed X-ray line broadening study in a ball-milled Ti sample is presented. It has been observed that ball milling leads to the formation of nanocrystalline grains and transforms partially to a fcc Ti phase after milling for 10 h. Milled samples show an inhomogeneous strain which increases with increasing milling time. The origin of such high strains is probably the dislocations present in the sample. The presence of a small number of stacking faults is also noticed, which, however, do not vary much with the milling time. Anisotropic line broadening of the fault-unaffected reflections is explained in terms of anisotropic dislocation contrast corresponding to [a] and [a + c] dislocations. Both edge and screw dislocations were predicted with a significant basal slip. A high dislocation density of about 10(11) cm cm(3) has been found in the milled samples.