
Structure
of alloys 51
As the alloy cools further, so the dendrites grow. At 1200°C the expected
composition of the solid material would be 62 per cent copper-38 per cent
nickel, the liquid having the composition 78 per cent copper-32 per cent
nickel. So the percentage of copper has increased from the 53 per cent at the
liquidus temperature, while the percentage of nickel has decreased. If the
dendrite is to have
a
constant composition, movement of atoms within the solid
will have to occur. The term
diffusion
is used for the migration of
atoms.
The
nickel atoms will have to move outwards from the initial dendrite core and
copper atoms will