Real Time Characterization of Solid/Liquid Interfaces During Directional Solidification

Abstract

A X-Ray Transmission Microscope (XTM) has been developed to observe in real time and in-situ solidification phenomenon at the solid/liquid interface. Recent improvements in the horizontal Bridgman furnace design provides real-time magnification (during solidification) up to 12OX. The increased magnification has enabled for the first time the XTM imaging of real-time growth of fibers and particles with diameters of 3-6 micrometers. Further, morphological transitions from planar to cellular interfaces have also been imaged. Results from recent XTM studies on Al-Bi monotectic system, Al-Au eutectic system and interaction of insoluble particles with s/I interfaces in composite materials will be presented. An important parameter during directional solidification of molten metal is the interfacial undercooling. This parameter controls the morphology and composition at the s/I interface. Conventional probes such as thermocouples, due to their large bead size, do not have sufficient resolution for measuring undercooling at the s/I interface. Further, the intrusive nature of the thermocouples also distorts the thermal field at the s/I interface. To overcome these inherent problems we have recently developed a compact furnace which utilizes a non-intrusive technique (Seebeck) to measure undercooling at the S/I interface. Recent interfacial undercooling measurements obtained for the Pb-Sn system will be presented. The Seebeck measurement furnace in the future will be integrated with the XTM to provide the most comprehensive tool for real time characterization of s/I interfaces during solidification.