Time-Resolved X-Ray Microtomography Observation of Intermetallic Formation Between Solid Fe and Liquid Al
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TRODUCTION
THE interaction between liquid aluminum and solid iron has been the subject of many researchers, and a wealth of information concerning intermetallic formation can be found in the literature.[1,2] It has been observed that two main intermetallic phases are formed, namely, a thin layer of Fe4Al13 on the aluminum side and a much thicker layer of Fe2Al5 on the iron side, exhibiting a specific tongue-like structure[3,4] growing toward the iron matrix.[5] Kwon and Lee[6] proposed that the tongue-like morphology is related to the iron grain size, while other studies stated that this morphology is mainly due to the anisotropy of the crystallites that grow preferentially along their c-axis, independent of the iron matrix.[1,3,7] Additional studies showed that temperature[8] or alloying elemental addition[9] modifies the shape of the tongues. However, these measurements are based on post mortem observations that cannot report on the shape evolution during reaction. Currently, in situ X-ray tomography observation of metals, whether in solid or liquid state, is a useful tool giving precious information on phase transformation[10,11] in, e.g., binary liquid–solid systems such as Al-Ga[12,13] or Al-Cu[14] The current study proposes, through in situ X-ray microtomography, to follow the time evolution of the intermetallic layer with a resolution of 2 minutes of an Al-Fe system, at a temperature of 973 K (700 °C), GUILLAUME PASCHE, PhD Student, CE´CILE HE´BERT, Professor, Director, and AI¨CHA HESSLER-WYSER, MER, are with the Centre Interdisciplinaire de Microscopie E´lectronique, E´cole Polytechnique Fe´de´rale de Lausanne, 1015 Lausanne, Switzerland. Contact e-mail: guillaume.pasche@epfl.ch MARIO SCHEEL, Postdoc, is with the European Synchrotron Radiation Facility (ESRF), 6 rue Jules Horowitz, 38043 Grenoble, France. ROBIN SCHA¨UBLIN, MER, is with the Centre de Recherche en Physique des Plasmas, E´cole Polytechnique Fe´de´rale de Lausanne. MICHEL RAPPAZ, Professor, Director, is with the Laboratoire de Simulation des Mate´riaux, E´cole Polytechnique Fe´de´rale de Lausanne. Manuscript submitted December 21, 2012. Article published online May 23, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
for a material volume of about 1.5 mm3 and with a cubic voxel of 1.2 lm in size. With this in situ observation method, the intermetallic formation can be identified and followed over time, giving complementary information on the mechanisms involved in the tonguelike morphology and particularly on the thickening of the tongues.
II.
EXPERIMENTS
X-ray absorption microtomography was performed on the ID15A beam line of ESRF, Grenoble, France using a monochromatic beam. The fast micro-tomography series were collected using a high-resolution tomography setup of ESRF.[15] The detector consists of a 25-lm-thick LuAG:Ce scintillator screen that converts the X-ray photons into visible light photons. This image is magnified by a 109 mirror optics and is collected by a high-speed CCD camera, the DALSTAR Pantera 1M60. The high flux of the ID15 high-
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