Elevated-temperature deformation mechanisms in Ni3Al

The creep behavior of single crystalline Ni3Al(Ta,B) was investigated over the temperature range 760–1115 °C under compressive stresses ranging from 30 to 700 MPa. The results reveal two different deformation mechanisms as a function of applied stress and temperature. For region I, a stress exponent of 3.2, an inverse primary creep behavior, a creep transient after a stress reduction where the initial creep rate is faster than the minimum creep rate at the reduced stress and dislocation substructure consisting of homogeneously distributed curved dislocations suggests that the dominant deformation mechanism is viscous dislocation glide. For region II, a stress exponent of 4.3, a normal primary creep behavior, a creep transient after a stress reduction where the initial creep rate is lower than the steady-state creep rate at the reduced stress and evidence for subgrain formation suggests that the dominant deformation mechanism is dislocation climb. It is believed that viscous dislocation glide in Ni3Al(Ta,B) is controlled by interdiffusion, whereas climb is controlled by Al lattice diffusion.