The structures expected in a simple ternary eutectic system: Part II. The Al-Ag-Cu ternary system
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he previous paper, Part I] the ideas developed to predict the ranges of structure in a two component system were extended, and used to predict the structural regions in a three component system. This paper sets forth the results of the experimental work on determining these structural regions in the A1-Ag-Cu ternary system in which a ternary eutectic had been observed 2 to form from a-A1, CuA12 and Ag2A1. EXPERIMENTAL PROCEDURE The experimental apparatus for directionally solidifying specimens under a controlled temperature gradient and growth rate is shown schematically in Fig. 1. The specimens were contained in graphite crucibles 205 mm long, 6 mm OD and 4 mm ID, and directional solidification was achieved by withdrawing the graphite crucible at a constant rate from the hot zone of a wound resistance furnace into a water bath by means of a variable speed DC motor. The specimen could be quenched during growth by disengaging the motor drive and rapidly pulling the graphite crucible down into the water bath. A standard technique was employed in making up alloys of the required composition, from pure aluminum (99.9 pet), copper (99.9 pet) and silver (99.9 pct), and casting them into the graphite crucibles. After filling, a graphite crucible was inserted into the growth furnace and allowed to equilibriate for up to 30 min under an argon atmosphere before directional solidification was begun. The growth rate during each run was monitored by noting the specimen position v s time and steady state D. G. MCCARTNEY, formerly with Alcan Laboratories Ltd., Banbury, Oxon, United Kingdom, is now Research Student, Department of Metallurgy and Science of Materials, Oxford University, Oxford, United Kingdom, R M. JORDAN, formerly with Alcan Laboratories Ltd., is now with Alcan Canada Products, Arvida, Quebec, Canada, and J. D. HUNT is Lecturer, Department of Metallurgy and Science of Materials, Oxford University. Manuscript submitted May 14, 1979. METALLURGICAL TRANSACTIONS A
growth was continued for 50 mm before being terminated by rapid quenching into the water bath. The temperature gradient was not measured for each run but several runs were made with a thermocouple in the specimen to obtain a measure of the gradient. A fine alumina sheathed chromel/alumel thermocouple was placed transversely across the specimen and its output was measured as a function of time during growth. From this it was found that the temperature gradient in the liquid at the interface was approximately 12 ~ in all specimens. RESULTS The approach to the investigation of the two and three phase coupled regions was based on the published phase diagram 3 which is shown in Fig. 2. The ternary eutectic composition of Fig. 2, however, is not the composition which Cooksey and Hellawellz used to produce a fully ternary eutectic structure.
FURNACE
SPECIMEN
JACKET WATER BATH
Fig. I--Unidirectional growth apparatus.
ISSN 0360-2133/80/0811-1251 $00.75/0 9 1980 AMERICAN SOCIETY FOR METALS AND THE METALLURGICAL SOCIETY OF AIME
VOLUME 11A, AUGUST 1980--1251
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