Unidirectional solidification of monovariant eutectic Cu-Mg-Ni alloys: I. Planar interface stability criterion

Abstract

Alloys lying in composition along the monovariant trough of the Cu-Mg-Ni phase diagram were unidirectionally solidified, to obtain aligned microstructures. The composition range extended from the binary Cu-Mg eutectic to 10 at.% Ni. It is shown that for these alloys the simple constitutional undercooling criterion G/ R ≤ mC 0(1− k)/ Dk, holds for planar/non-planar interface breakdown if the true distribution coefficients k and liquidus slope m are applied for all alloy compositions C 0, assuming D to be constant. For this alloy system the use of single values of k and m estimated from alloys low in nickel would seriously misjudge the interface breakdown conditions at higher nickel concentrations.