Interfacial Dislocation Structure Research Articles

A transmission electron microscope study of a directionally solidified γ/γ′-Cr 3C 2 eutectic

The crystallography of a directionally solidified eutectic alloy consisting of aligned Cr 3C 2 fibres in a γ/γ′ matrix was examined by transmission electron microscopy. The (orthorhombic) fibres and (cubic) matrix were aligned with 〈110〉 m〈001〉 f growth direction. There were two preferred orientation relationships, which were characterised by low index fibre/high index matrix interface planes. The preference for the observed interface planes is explained on the basis of a low misfit between atomic rows in the interface, which is able to account qualitatively for the observed interfacial dislocation structure.

Precipitation in star sapphire II. Elastic accommodation of the precipitate

Abstract The growth of rutile needle precipitates in star sapphire is accompanied by an interfacial dislocation structure in the rutile-sapphire interface, and a set of pyramidal dislocations which climb into the sapphire matrix. In addition, the rutile is internally twinned. The dislocation array in the interface provides almost perfect accommodation for the lattice mismatch between precipitate and matrix. These interface dislocations are vacancy-type loops and are formed by the rejection of interstitials into the matrix, due to a combination of elastic and chemical effects accompanying precipitation. The rejected interstitials cause the formation of the set of climbing dislocations. The twinning provides improved lattice matching between rutile and sapphire, but the twin orientation is such that twins cannot have formed by shear to accommodate growth stresses; rather they are growth twins formed either during the early stages of growth or perhaps during nucleaten of the precipitates.

Interphase interfaces of AuAg and AuPd

The interfacial microstructure of {001} twist interphase boundaries in AuAg and AuPd bicrystal thin film couples has been investigated by transmission electron microscopy. The bicrystal thin film couples were produced by a new technique described herein. Examination of the bicrystal films showed that orthogonal grids of interphase boundary dislocations of 〈110〉 type formed in the {001} low-angle twist interphase boundaries of both AuAg and AuPd systems. The interfacial dislocations of AuAg interphase boundaries are similar to those of AuAu, i.e., almost screw in character. In AuPd interphase boundaries, the interfacial dislocations show the mixed edge and screw character as expected. The high-angle {001} twist interphase boundaries of AuAg and AuPd were also studied. The concidence lattice concept was applied to study the high-angle twist interphase boundaries. Several critical angles were obtained for both AuAg and AuPd systems. Orthogonal grids of secondary dislocations were observed in the {001} twist interphase boundary of AuAg thin film couples with the twist angle near 36.9°, the critical angle corresponding to the coincidence of ∑ = 5. Experimental evidence of the interfacial dislocation structure of the high-angle twist interphase boundaries of AuPd has not yet been obtained. However, diffraction patterns do show the coincidence character in agreement with what was predicted.

The misfit dislocation structure of an InGaAs/GaAs heterojunction with low misfit

The dislocation structure in an InGaAs/GaAs heterojunction with an epilayer thickness of 8 μm and a misfit of 0.003 was studied by X-ray topographic techniques. Misorientations in the approximately square cross-grid of dislocations permit the three-dimensional nature of the dislocation structure in the epilayer to be studied. The evidence presented here suggests that a source other than one of those previously favored is the dominant contributor to the interfacial dislocation structure; the most likely possibility is that the majority of dislocations are introduced at sources created by interactions of gliding threading dislocations.