The immiscibility found in Cu-Fe alloys in the liquid state has been reinvestigated by the determination of the liquidus of these alloys as well as of the equilibrium of the liquid alloys at 1450° and 1540°, special attention being paid to the existence of a very small amount of carbon in the alloys. The results obtained are as follows; -
(1) On the liquidus curve of the pure Cu-Fe system no particular point can be found, and, consequently no monotectic reaction (as shown in Fig. 1) is likely to occur, (2) The existence of one per cent of Al, Ni, Pb, Sn or Zn in Cu-Fe alloys, consisting of 50 per cent. of Cu and 49 per cent. of Fe, does not cause the separation of the liquid into two layers. (3) In the C-Cu-Fe system two liquids co-exist in equilibrium at 1450° (Fig. 3) and 1540° (Fig. 4). Each heterogeneous zone lies very near the side (
F'K' in Figs. 3 and 4) corresponding to the binary system consisting of Cu and Fe, but it does not cut that side, having a definite clearance (about 0.02_??_0.03 per cent. in carbon content) between the zone and the side. (4) Therefore it may be safely concluded that in the Cu-Fe alloys no separation of liquid into two phases take place, either when they are pure or have a carbon content of less than 0.02_??_0.03 per cent. in the range of temperatures up to 1540° and probably in a still higher range, while they separate into two liquid layers, when they contain more than the above percentage of carbon. The amount of carbon necessary to cause the separation varies as the content of iron in the alloy the larger the amount of iron in this the more carbon it must contain. (5) The temperature coefficient of the mutual solubility of the conjugates is found to be positive (Fig. 3 and 4), differing from the results found in the published reports (Fig. 1 and 2). It has also been explained how the temperature coefficient may falsely be taken as negative by a prcof of the fact that the higher the temperature at which the alloy is heated the greater the amount of carbon absorbed by it.
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