Ductility of recrystallized Zr-doped Ni₃Al alloys fabricated by isothermal hot-forging

Ductility of recrystallized Zr-doped Ni₃Al alloys, Ni-23Al-0.4Zr and Ni-23Al-2Zr, has been investigated by tensile tests at room temperature in dry oxygen. A cold-working a cast Ni₃Al alloy, followed by annealing for recrystallization, even if the alloy exhibits appreciable ductility, introduces microcracks, thereby resulting in a decrease in ductility. On the other hand, an isothermal hot-forging a cast Ni₃Al alloy successfully produces a recrystallized specimen having no internal microcracks, which enable us to evaluate the intrinsic ductility of Ni₃Al alloys. A recrystallized Ni-23Al-0.4Zr alloy produced by hot-forging exhibits elongation of more than 35%, whereas a recrystallized Ni-23Al-2Zr alloy obtained by hot-forging exhibits 3% ductility. The significant ductilization by alloying with 0.4% Zr is attributable to enhancement of the intergranular cohesive strength of Ni₃Al alloys by suppressing the segregation of S, which is contained in the starting materials, to grain boundaries through sulfide formation. The low ductility of the recrystallized Ni-23Al-2Zr alloy is consistent with the explanation based on an increase in ordering energy.