In-situ micro-twinning of TiAl in the field ion microscope

Stress-induced transformations were observed in the γ phase of a two phase TiAl alloy and were manifested by the sudden appearance of newly formed regions in the field ion image having significant contrast difference from the matrix. This in-situ transformation was often accompanied by a slight shift of all or part of the atoms in the field ion image. The TiAl alloy investigated was found to be particularly prone to specimen failure on the application of the electric field, which suggests that the formation of these twin regions can lead to an unstable specimen geometry. Different types of contrast were observed depending on the position and orientation of the twinned region with respect to the previously untransformed γ matrix. Twinned regions may appear with dark or bright contrast in the field ion image and ultrathin microtwins can be generated that are similar in appearance to thin α2 laths.