Many important commercial casting alloys,
such as cast irons and Al-12% Si, are effectively
simple binary eutectics. These alloys have attractive founding
properties, such as good fluidity and little tendency to
form pores or exhibit hot tearing, primarily because they
solidify without a mushy zone.
The growth mode of eutectics can be rationalised in terms of the energetics of the
solidification process. Consider first the phase diagram of a simple eutectic system and
the corresponding free energy curves.
| Note first how the relative positions of the
free energy curves for the liquid and solid phases tend to change as the temperature is
lowered. |
Use the white slider to the right
of the lower graph to plot the two graphs for a range of different temperatures.
Note how the common tangents from the free energy curves (upper graph)
"construct" the phase diagram below it.
You can also change the interaction parameter, W, to obtain
eutectic systems of different solubilities
