Analysis of growth (α)Al-Al3Fe eutectic composite IN SITU
Edward Guzik, Dariusz Kopyciński Akademia Górniczo-Hutnicza, Wydział Odlewnictwa, ul. Reymonta 23, 30-059 Kraków
Annals 3 No. 6, 2003 pages 110-114
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abstract In the part comprising the author’s own investigations of a shape of the solid-liquid interface irregular eutectic Al-Al3Fe, has been presented. The model takes into consideration the essential role of the faceted phase as the leading phase in the crystallization of such eutectic kind. The proposed shape of the crystallization front, characterized by a suitable function as well as applying the non-isothermal solid-liquid interface for modeling purposes allows calculation of the characteristic depression in the nonfaceted phase (e.g. α(Al)) and the protrusion of the leading phase Al3Fe. For the experimental verification of the elaborated shape of the solid-liquid interface the results of the unidirectional crystallization front of the eutectic under question as well as observations of the „freezed” crystallization of the eutectic in the Al-Fe alloys were utilized. Using a Bridgman apparatus for directional solidification, the structure of an oriented equilibrium Al-Al3Fe eutectic was determined over a range of low growth rate v, i.e. from 9.03 • 10–5 to 1.11 • 10–3 cm/s. The results of research on the directional solidification of eutectic Al-1.8% Fe alloy and Al-2.8% Fe alloy with addition of 0.1% V were described in [8]. For the two chemical compositions, i.e. Al-1.8% Fe and Al-2.8% Fe (with 0.1% V added) two types of eutectic were obtained, i.e. an irregular lamellar eutectic with typical branching and a regular rod-like eutectic. In composite of the first type an increase in the growth rate changed the irregular lamellar eutectic of the Eu1 type to a morphology characterized by the presence of parallel precipitates of Al3Fe in eutectic. The characteristic feature of the base structure was that, apart from Eu1 eutectic, it also contained precipitated dendrites of αAl phase. An increase in iron content by 1% changed the eutectic morphology from Eu1 to Eu2 of the rod-like type. Introducing vanadium hindered the transition from irregular eutectic to a regular one in the range of high growth velocities. In general terms it can be said that with increasing growth rate v the interlamellar spacing λ decreases in the eutectic structure of an Al-Fe composite in situ. Within the investigated range of eutectic growth rate v, the interlamellar spacing λ of the examined composite in situ and the velocity v follow the statistical relationships. Key words: irregular eutectic, interlamellar spacing, protrusion of faceted phase, solid-liquid interface