found two types of eutectic structure, termed lamellar and anomalous. 
Hollomon and Turnbull (3) investigated the solidification behavior 
of supercooled Pb-Sn alloy droplets (30 to 50 in dia) as a function 
of composition. Alloys were supercooled up to about 50°C and 
showed structures with "cylindrical" dendrites and interdendritic 
spaces occupied by "anomalous" eutectic. 
Powell and Colligan (21) investigated the microstructure of super- 
alv cooled hypereutectic Pb-67% Sn alloy. The final microstructure was 
dendritic with a eutectic matrix. B.L. Jones and co-workers (9) 
ching examined supercooled structure of Ag-Cu alloy. Their explanation of 
the structures of supercooled Ag-Cu alloy ingots has shown that there 
is coupled zone in this system. His "anomalous" structure consists 
of a coupled and an uncoupled zone. 
The structure of highly undercooled cobalt-tin alloy at hypoeutectic 
a compositions was studied by Kattamis as a function of degree of 
Ei supercooling. It was found that the cobalt rich o - phase was 
dendritic for low undercooling, became cylindrical for intermediate 
undercooling, and finally spherical for an undercooling higher than 
about 170°C. In each case, a normal or divorced eutectic occupied 
the space between the growth forms of the primary phase. 
erent Y.V. Murty and T.Z. Kattamis (8) studied the structure of highly 
supercooled cobalt-tin eutectic alloy and found that the amount of 
les anomalous eutectic increased with supercooling and with cooling rate. 
Both eutectics became finer with increasing supercooling and cooling 
dify rate and both consisted of the same two phases. They suggested two 
solidification models for explaining the formation of the observed 
microstructures. 
Scheil (22) distinguished between normal, anomalous and degenerate 
eutectics. The definition of these groups is somewhat vague, and it 
has been difficult to place some eutectics in the right group. Some 
investigators even claim that all eutectics are probably normal. The 
criterion of a normal eutectic, as defined by Scheil, is the 
orientation relationship between the phases - no such orientation 
ence, relationship is present in anomalous and degenerate eutectics. As 
ic the eutectic structure depends upon both nucleation and growth, he 
took the additional criterion that defines the group of eutectic - 
ber the nucleation behavior. Only one of phases can nucleate the eutectic 
crystallization, and in some systems no phase is effective. 
A definition of the various groups of eutectics may be given as 
follows: 
21Q