The possibility of increasing the ductility of L12 stabilized aluminide alloys, by using networks of interfacial dislocations as sources of slip dislocations, was considered. A study was made of the effects of Cr, Ni and Cu upon the phases which were present in the stabilized alloys. It was found that, in Ti-rich compositions, plate-like precipitates of the tetragonal Al2Ti phase, with a (001)P habit plane, formed on the {100}M planes of the L12 matrix. In Cr-stabilized alloys, the Al2Ti/L12 interfaces were coherent but, in Ni- and Cu-stabilized alloys, networks of interfacial dislocations were present. It was shown that these networks accommodated a difference in lattice parameter between the L12 matrix and the a-value of the tetragonal Al2Ti phase which resulted from a slight decrease in the L12 lattice parameter that occurred when the stabilizing transition metal, Cr, was replaced by Ni or Cu. An analysis of these dislocations, using g•b rules and the image-matching of transmission electron microscopic images, showed that the networks were based upon intersecting arrays of orthogonal edge dislocations with ½<110>M Burgers vectors. Irregularities in the networks often led to the occurrence of segments, of these dislocations, which had a screw orientation. This then permitted them to act as potential sources of ½<110>{111}M slip dislocations in the L12 matrix. A comparison of compression data for Cr-, Ni- and Cu-stabilized alloys showed that the presence of such dislocation sources did not lead to an enhancement of the room-temperature ductility of Ni- or Cu-stabilized alloys.

C.T.Forwood, M.A.Gibson: Materials Science Forum, 1995, 189-190, 353-60