The samples were all examined at higher
magnification by SEM backscattered electron
imaging (BEI). Figure 7 shows the investment-cast
samples containing Zn and Si. Cu-rich areas (
β
-
phase) are revealed by dark contrast (due to their
lower atomic number) in the lamellar and degenerate
eutectic structure in the interdendritic regions.
There is no significant difference in microstructure
between the lower Zn- and Si- containing samples
as well as the standard sterling silver alloy sample.
However, a major microstructure change appears in
the samples containing 0.1-0.3wt%Si in which, the
lamellar eutectic structure tends to change to a degenerated structure.