The interdendritic segregation and problems with hot shortness can be reduced by means of a homogenization treatment. Consider an alloy such as Cu-40% Ni. If a casting is heated to a temperature below the nonequilibrium solidus, the nickel atoms in the centers of the dendrites diffuse to the interdendritic regions; copper atoms diffuse in the opposite direction as demonstrated in Fig1. Since the diffusion distances are relatively short, only a few hours are required to eliminate most of the composition differences. The homogenization time is related to:
(Eq1)
t =
cS 2
Ds
A small S reduces the diffusion distance and permits short homogenization times.
Microsegregation between dendrites can be reduced by a homogenization heat treatment. Counterdiffusion of nickel and copper atoms may eventually eliminate the composition gradients and produce a homogeneous composition.
