Question

Is it possible to have a copper–nickel alloy that, at equilibrium, consists of a liquid phase of composition 20 wt% Ni–80 wt% Cu and also an α phase of composition 37 wt% Ni–63 wt% Cu? If so, what will be the approximate temperature of the alloy? If this is not possible, explain why.

Answer 1

It is not possible to have a Cu-Ni alloy, which at equilibrium, consists of a liquid phase of composition 20 wt% Ni-80 wt% Cu and an phase of composition 37 wt% Ni-63 wt% Cu. From above figure, a single tie line does not exist within the + L region that intersects the phase boundaries at the given compositions. At 20 wt% Ni, the L-(+ L) phase boundary is at about 1200°C, whereas at 37 wt% Ni the (L + )- phase boundary is at about 1230°C.