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.