Papers by Keyword: Morphological Stability

Abstract: The morphologicalstability of a planar interface with the inclusion of the anisotropic surface tension is studied. The dispersion relation is obtained by means of the multi-variable expansion method. The result shows that the morphological stability of the solidification system in the extremely short wave region depends on the undercooling. As the anisotropic surface tension parameter increases the perturbation growth rate of the interface increases and the solidification system in the extremely short-wave region tends to destabilize.

Abstract: The evolution of our understanding of dendritic and eutectic growth is presented. The control of both phenomena is essential in solidification processing. In this article, the development of the most important concepts which evolved over essentially one century will be described. Some of the original contributions which came from solid state transformation theory will also be included. This paper traces the history of the experimental and theoretical (analytical) work but leaves the numerical approach of the last 25 years for future papers.

Abstract: Solidification is a dynamic phenomena and, as a consequence, it is of major interest to be able to investigate this process by in situ and real time observation. With synchrotron sources, this can be achieved by applying X-ray Imaging techniques (Radiography and Topography). Hence it is possible to follow the dynamical selection of solidification pattern on metallic alloys and to observe strain effects during growth process. In this paper, we present results obtained by using separately the two imaging techniques for the study of the microstructure formation during Al – Ni alloys solidification.

Abstract: Within the frame of the ESA research program SETA, “Solidification along a Eutectic Path in Ternary Alloys”, experiments have been performed focussing on several distinct subtopics. One of these subtopics is to study coupled growth along the univariant eutectic reaction: L → α + β. In this paper, the influence of the growth velocity v on the morphology of the solid/liquid interface is evaluated in a ternary Al-Cu-Si alloy with a composition close to the univariant eutectic groove L → α(Al) + θ-Αl2Cu. Different structural regions can be identified in terms of the stability of the solid-liquid interface (morphological stability) and the stability of the coupling (competitive growth) during unidirectional solidification as function of the solidification parameters. It is found that two-phase planar growth with a lamellar arrangement can be obtained at a sufficiently low growth rate v. The measured interlamellar spacing follows the Jackson and Hunt relationship λ2v = constant. At a higher growth velocity first a destabilisation of the solid/liquid interface is observed and finally competitive growth is observed revealing primary θ-Al2Cu growing ahead of the eutectic interface. It is assumed that the cellular break-up is a two-step process related to the crystallography of the system. Fitting the different morphologies into one microstructure map, an extension of the coupled zone concept as has been proposed for binary alloys is necessary.