Dislocation configurations in two phase TiAl alloys. I. Annealed and indented structures

Abstract

Two alloys of nominal composition Ti-48 Al and Ti-47.5 Al-2.5 Cr with small grain sizes and fully lamellar structures have been compared in terms of mechanical properties and of the dislocation configurations present before and after deformation. The first part of the study shows the effect of hardness indentations on the slip steps, crack initiation and propagation and dislocation activity in zones where different amounts of strain have taken place. It appears that the action of local stresses produced by hardness indentations is that of promoting glide of the slip systems already present in the annealed materials. Although large densities of ordinary 1/2 dislocations are responsible for the strains achieved locally in the γ phase, these do not promote large ductilities of the alloys. Since propagation of deformation cannot occur across the α2/γ interface, microcracks form and the material as a whole behaves in a brittle manner.