Sylvie Lartigue-Korinek

Disconnection arrays in a rhombohedral twin in α-alumina

Interfacial defects, such as grain boundary dislocations, play an important role in the creep behavior of alumina. In the present work, interfacial defects are analyzed in detail using a Volterra approach without a reference to a near-coincidence description. We investigate disconnections (boundary steps with dislocation character) in a diffusion-bonded alumina bicrystal, with a misorientation close to the rhombohedral twin, by conventional and atomic resolution electron microscopy. The bicrystal contains two arrays of parallel disconnections with Burgers vectors that have alternating equal and opposite twist components, so there is no long-range stress field. This configuration is discussed in terms of the stability of different grain boundary disconnection arrangements. The complex core structure of the defects is revealed by high resolution electron microscopy using exit wave reconstruction. It is shown that the defects are dissociated into two partials that delimit grain boundary segments with alternating structure.

On the atomic structure of an asymmetrical near Sigma=27 grain boundary in Copper

The atomic structure of an asymmetrical near Σ = 27 {525} tilt grain boundary (GB) in copper is determined by coupling high-resolution transmission electron microscopy and molecular dynamics simulation. The average GB plane is parallel to {414} in crystal (1) and {343} in crystal (2). The detailed GB structure shows that it is composed of facets always parallel to {101} and {111} in crystals (1) and (2), respectively. The atomic structure of one facet is described using the structural units model. Each facet is displaced with respect to its neighbours by a pure step, giving rise to the asymmetry of the GB plane orientation. The energy of this asymmetrical GB is significantly lower than that of both the {525} symmetrical and the {11,1,11}/{111} asymmetrical Σ = 27 GBs. One GB region displays another atomic structure with a dislocation that accounts for the misfit between interatomic distances in the {414} and {343} GB planes.

Interactions between dislocations and interfaces – consequences for metal and ceramic plasticity

Abstract Interactions between dislocations and grain boundaries contribute significantly to plastic behaviour in polycrystalline metals. But a full understanding of the processes and of their influence on plastic response has yet to be achieved. In the present paper, the elementary interaction mechanisms, from the entrance of dislocations in grain boundaries to the relaxation of the resulting intergranular stresses, are briefly reviewed. They are examined for two types of deformation tests and two types of materials: low temperature deformation and relaxation in copper and creep behaviour of alumina. Only the comparison between the response at different scales (nanoscopic, microscopic and mesoscopic) allows us to analyse the response of grain boundaries to an applied stress and to propose an interpretation of their role in macroscopic behaviour. This work may be considered as a preliminary step towards “Interface Engineering”.

Analysis of dissociated dislocations in a deformed bicrystal close to the rhombohedral twin orientation in α-alumina

Abstract A bicrystal close to a rhombohedral twin orientation in α-alumina has been deformed by compression at high temperature. After deformation the twin contained a periodic array of intrinsic dislocations. This configuration is interpreted by the decomposition of incoming basal lattice dislocations into interfacial disconnections and further interactions between sessile and glissile products. The dislocations are widely dissociated and the separation width between partials being close to 30 Å. The translation state of the interfacial structure between partials is different from those of the perfect twin. Possible structural models are envisaged and simulated using ab initio calculations and the less efficient Streitz and Mintmire modelling. One model in particular fits the experimental image rather well. The interfacial energies are higher than those estimated using elasticity theory.