No abstract

No abstract

Abstracttic solidification occurs in a binary systenl when a single liquid phase ormed into two solid phases which arein equilibrium with the liquid temperature. There have been' two detailed surveys (BCady (1,) evin ( 4 ) ) oE the structures that are found in binary eutectic illoys, has been written about the details of the process by which these monest type of eutectic structure is that which is described a s . The appearancc under the n~icroscope of a s~i t a b l -~. ,~r e~a r e d surin Fig. 1, in which it will be seen that the two phases appear t o account for the origin of this structu:e was b y ry is that crystallization of one phase starts by nuclese solidifies until 'the resulting change in the coInsufficient t o cause the other phase to, nucleate; the and the process is reversed. This results in the altertwo phases. Fig. 2 A different view was taken by Vogcl (10); he considered t h a t the larnellar appearance corresponded to the existence of the two phases in the form of rods, or more accurately polygonal prisms, with their axes perpendicular t o the interface. Crystallization of the two phases would occur simultaneously, and I I the instantaneous condition would be a s represented in Fig. 3. Experimental investigation of this question by Straurnanis and Braaks (G, 7) proved that, in five alloys which were examined, the structure was lanlellar and that the lamellae were approximately perpendicular to the interface. This appears to have been the only investigation in which the direction of heat flow was Itnown, and it offers very strong support for the views of Vogel a s opposed to those of Tammann. Recent work by Elwood and Bagley (3) has shown tlie existence of definite crystallographic relationships between the interpenetrating components of a eutectic grain.Recent Ibork by Thall and Chalrners (9) on the structure of aluminumsilicon eutectic alloys shows that the modification of the structure, by rapid freezing or by the additio~i of sodium, can be accounted for by making certain assumptions with regard to eutectic freezing. ;One of these assumptions is that the two phases are formed simultaneously (as in Fig. 3) and another is that, instead of the interface being smooth, it has the form represented in Fig. 4 which the interface between the dark phase and the liquid is in advance of the interface between the light phase and the liquid. This assumption is made on the basis of the fact that the rate of advance of the interface is determined by the heat flow across it and by the latent heat of fusion of the solid phase. The surface of one phase will tend t o lead if its thermal conductivity is higher and f its volume latent _heat is lower than those of the other phase.T h e present investigation was undertaken in order to examine the validity of these assumptions and to provide further experinlental evidence about the process of eutectic solidification. 'Experimental ConsiderationsThe object of the experimental work was to study the geometry of the structure and of the solid-liquid interface in rela...

No abstract

No abstract