STRUCTURES PRODUCED IN RAPIDLY SOLIDIFIED ALLOYS
MASSACHUSETTS INST OF TECH CAMBRIDGE
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An investigation was made of the dendritic structures formed during the solidification or freezing of relatively non-dilute engineering alloys. The form and dimensional character of the dentritic structure as influenced by the freezing rate and the properties of the cast structure were of principle interest. Arc deposits from consumable and non-comsumable W electrodes with Al, Cu, and Ni alloys were used. Such deposits are castings of a sort and the conditions of freezing can be closely controlled. The dendrite spacings increased parabolically with the energy input. Interdendritic undercooling in the order of 0.1 F, in dilute alloys appeared to be a property of the solvent metal, did not vary significantly from one solute element to another, and was quite independent of the rate of solidification. The arc deposits froze much faster than chill castings and had smaller dendrite arm spacings than would be expected in any casting process. The minimum time for effective solution heat treatment of arc deposits, as reflected in final properties, depended on dendrite spacing energy input. The dendrite arms in Al, Cu, and Ni alloys were generally parallel to the direction of heat flow.