Observation and analysis of weak-fringing faults in Ti-6 wt% Al

Weak-fringing faults have been observed in planar slip bands in a Ti-6wt%Al alloy by transmission electron microscopy. The magnitude of the contrast was observed to increase with the number of dislocations shearing a particular region in the slip plane, and the fringe contrast was observed to saturate along a slip band. The fault fringes were determined to be caused by a residual displacement of the form R = (1/n)(11 (2) over bar0). An upper bound on the magnitude of increasing R for prism slip bands was estimated to be between 1/145 (11 (2) over bar0) - 1/104 [11 (2) over bar0] using quantitative image matching simulations. 104 The sign of R is found to be antiparallel to the direction of the Burgers vector b of the a-type dislocations in the slip bands. It was also observed that fringe contrast was always weaker for basal slip bands. Comparison with image simulations indicated that the magnitude of the residual displacement is smaller on the basal plane. The origin of the residual displacements is attributed to the relaxation processes associated with destruction of short-range order in this alloy.