The deformation which was generated by the intrinsic structure of faceted close-packed (11¯1)Ni3Al||(0l0)Ni3Nb interfaces was observed by means of high-resolution electron microscopy. The interfaces separated the Ni3Al (γ') and Ni3Nb (δ) lamellae of a directionally solidified eutectic alloy. Three typical interfacial regions were examined. In region I, a series of 10 consecutive linear singularities was analysed. Six of them (A to F) had differing core structures. They fully or partially accommodated the 2.1% length misfit, according to the sequence: A-A-A-B-C-A-D-E-A-F. Of these singularities, A, B and C were dislocation ledges whereas D and E were linked to a triple-node junction which involved γ', δ and an interfacial γ' nano-twin. The F limited an interfacial fault. Three types of Burgers vector content were found (relative to the γ' lattice). These were: (i) 90º, (1/6)[¯1¯12] for A, D, E, F; (ii) 30º, (1/6)[¯21¯1] for B; and (iii) 60º, (1/6)[¯4¯11] or (1/6)[¯1¯41] for C. The latter contributed to the accommodation of angular misfit. Only the 90º Burgers vector content belonged to the γ'-DSC lattice. It was deduced that the observed hetero-interface consisted of at least 4 different interfacial regions having different energies. In regions II and III, the hetero-interfaces exhibited other complex atomic structures which involved γ' interfacial Σ3 nano-twins. In region II, a linear singularity which was linked to a triple-node junction had a Burgers vector content of (1/2)<110>, and partially accommodated an angular misfit. In region III, 3 consecutive linear singularities had the same 90º Burgers-vector content, in spite of their quite different environments. One of them interacted with a nearby 60º γ' super-partial, so that the total dislocation content was (1/6)[2¯1¯5] or (1/6)[¯12¯5]. It was concluded that the determination of the linear singularity structures at close-packed hetero-interfaces was more complicated than had been previously realized.

Atomic Scale Observation of the Displacement Fields Generated by the Intrinsic Defects of {111}Ni3Al/(010)Ni3Nb Close-Packed Interfaces. Bonnet, R., Loubradou, M., Dahmen, U.: Philosophical Magazine A, 2000, 80[10], 2233-56