Dislocation structures representing individual slip systems within the α phase of a Ti–6Al–4V alloy deformed in tension

Abstract

The current work performed a detailed examination of the dislocation structures associated with individual slip systems within the α phase of a Ti–6Al–4V alloy subjected to tensile deformation as a function of crystallite orientation. Tensile samples were deformed as part of an in-situ synchrotron experiment at a strain rate of 3 × 10−4 s−1 to a strain of about 0.07. The dislocation type, arrangement and density within eighteen randomly selected grains were examined post-mortem using transmission electron microscopy, complemented by the automatic determination of individual crystallite orientations through precession nanodiffraction. The Schmid factor values for all possible hcp slip systems were then calculated for each of the grain orientations and these were allocated to one of the four slip domains, representing prismatic, basal, first-type pyramidal <a> and first-type pyramidal <c+a> slip, on the basis of both the Schmid factor value and dislocation structure character. The deformation took place entirely through dislocation glide and the slip system selection and dislocation densities were governed by the global Schmid factor values. Prismatic slip was a prevalent deformation mode, followed by basal slip. The <a>-type dislocations present after deformation typically possessed a dominant screw component, with those representing prismatic slip typically being of a pure screw type, and displayed a strong tendency to adopt a screw character already during straining. Deformation also caused the formation of <c+a> dislocations, located in the first-type pyramidal planes, that typically occupied entire interiors of the close-to-[0001] oriented grains and were mainly of a mixed character.