The as-cast microstructures of the standard
935 sterling silver alloy (93.5Ag-6.5Cu) prepared
by investment and metal mould casting are given in
Figure 4. Both microstructures consist of cored Ag-
rich (
α
-phase) dendrites with small amounts of
interdendritic eutectic
constituent. The faster
cooling rate during solidification of the sample cast
in the metal mould has given a much finer grain
size and dendrite arm spacing than the investment
cast sample resulting in the higher observed
hardness of the metal mould sample. Almost no
macropores appeared in the as-cast microstructure
of the standard sterling (no Zn or Si addition)
prepared by investment casting, while macropores
in size of 10
μ
m are normally appeared in the
metal mould cast sample.