Results and Discussion
Vickers Hardness Measurement
Figure 1. shows the effects of Zn and Si on
Vickers hardness of the sterling silver alloys
produced by investment and metal mould casting.
It is clearly seen that the samples prepared by the
torch melting/metal mould route have higher
hardness levels than the samples prepared by
investment casting. The standard 935Ag sterling
alloy cast in a metal mould has a hardness around
66 HV compared to around 56 HV for the alloy
cast into an investment mould. The hardness level
in investment cast samples is about 5-10 HV lower
than for the equivalent samples cast in a metal
mould. Independent from alloy composition the
Vickers hardness depends on the cooling rate
during solidification and is
always consistently
higher for samples obtained by metal mould
casting due to the higher cooling rate.