Deformation and fracture behavior of a directionally solidified β/γ′ Ni-30 At. pct Al alloy

Abstract

The effect of a ductile γ'-Ni 3 Al phase on the room-temperature ductility, temperature-dependent yield strength, and creep resistance of β-NiAl was investigated. Room-temperature tensile ductility of up to 9 pct was observed in directionally solidified β/γ' Ni-30 at, pct Al alloys, whereas the ductility of directionally solidified (DS), single-phase [001] β-NiAl was negligible. The enhancement in ductility was attributed to a combination of slip transfer from the ductile γ' to the brittle β phase and extrinsic toughening mechanisms such as crack blunting, deflection, and bridging. As in single-phase Ni 3 Al, the temperature-dependent yield strength of these two-phase alloys increased with temperature with a peak at approximately 850 K. The creep strength of the β/γ' alloys in the temperature range 1000 to 1200 K was found to be comparable to that of monolithic β-NiAl. A creep strengthening phase needs to be incorporated in the β/γ' microstructure to enhance the elevated temperature mechanical properties.