Dynamic embrittlement of boron-doped Ni 3Al alloys at 600°C

Abstract

Boron-doped Ni 3Al alloys, with and without 0.5at.%Hf, were tensile tested in vacuum and in oxidizing environments at 600°C. Tensile ductility was found to be strongly dependent on test environment, with much lower ductilities observed in air than in vacuum. The loss in ductility is accompanied by a change in fracture mode from transgranular to intergranular. The severity of this environmental effect on elevated-temperature ductility is also affected by preoxidation in air as well as by the aluminum content of the aluminide. Tests of preoxidized specimens indicate that the embrittlement is due to a dynamic effect simultaneously involving localized stress concentrations, elevated temperature, and gaseous oxygen. The oxygen embrittlement becomes less severe with a decrease in aluminum concentration from 24 to 21 at.%.