Papers by Keyword: Morphological Transition

Abstract: Alloys of exact monotectic composition can decompose at the monotectic temperature into different two phase microstructures. The minority phase can be arranged as fibers similar to eutectics, as string of pearls or as irregularly distributed droplets. The directional solidification of three Al-base monotectic alloys was investigated: Al-Pb, Al-In and Al-Bi utilizing aerogel base furnace technology to ensure constant gradient and solidification velocity over the processing length. The solidified microstructures are characterized as a function of temperature gradient ahead of the solidification front and the solidification velocity. The experimental results are presented in form of stability diagrams for the three microstructures showing the regions in which fibers, string of pearls or irregular morphologies exist. The inter fiber spacing is analyzed and presented in from of Jackson and Hunt type relations and the transitions between the microstructures are discussed.

Abstract: As a “bottom-up” approach to nanostructures for nanofabrication, self-assembled block copolymer thin films have received much attention not only thanks to the scale of the microdomains but also due to the convenient shape tunability. In order to realize applications of self-assembled block copolymer thin films in nanotechnologies, control over microdomain spatial and orientational order is paramount. In this paper, using atomic force microscopy (AFM), we studied systemically nanostructure transitions induced by post-solvent annealing in self-assembled block copolymer thin films. Furthermore, a variety of thin films with well-ordered nanostructures, which can be employed as templates for nanotechnologies, have been realized simply and at low cost.

Abstract: Coupled, regular eutectic growth of α(Al) and Al2Cu from ternary Al-Cu-Ag liquid alloys is investigated with focus on the formation and the characteristics of eutectic cells in unidirectionally solidified, polycrystalline, bulk samples. The topologic anisotropy of the lamellar eutectic leads to destabilization along the lamellae with elongated cells being intermediate to stable cells, irrespective of the crystallographic orientation of the phases. The formation of stable cellular patterns with elongated or regular cell structure is explained with reference to the crystal orientation of the phases α(Al) and Al2Cu, measured by electron backscatter diffraction (EBSD).