be Figures 5 and 6 shows the effect of supercooling on the structure. The 
minor phase (light etching) is the nickel-rich o phase, and the major 
phase (matrix) is the tin-rich n phase (Ni;Sn). The samples show a 
mixed lamellar and irregular structure. 
rh The fraction of irregular structure increasing with increasing super- 
£12.54 cooling (fig. 4). Increasing supercooling and cooling rate decre- 
ases size of Ni-rich a phase (fig. 3). This means that irregular 
eutectic becomes finer with increased supercooling and cooling rate. 
Lamellar eutectic spacing decreases with increasing supercooling 
(fig. 2). The photomicrograph of the specimen supercooled 100 deg. 
(fig. 5,6) shows that both phases of the "irregular" eutectic are 
continuous with the phases of the lamellar eutectic at the boundary 
between the two types of eutectic. Within the irregular eutectic 
regions the minor phase appears to be present as discrete particles. 
However, succesive polishing and examination of parallel sections 
approximately 10 microns apart showed that both phases were 
interconnected along a polyhedral network. 
Fig. 7 is a photomicrograph of an supercooled samnle 135 dec. 
Fig. 7 - Photomicrograph of Ni-32,5% Sn eutectic specimen 
supercooled 135 deg. Magnification 2200 times. 
Fig. 8 is a photomicrograph of a supercooled sample at low macgnifi- 
cation showing that the irregular eutectic regions have a "dendrite- 
‘ like" morphology. 
an 
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