ELEVATED-TEMPERATURE DEFORMATION MECHANISMS IN NI3AL

The creep behavior of single crystalline Ni3Al(Ta,B) was investigated over the temperature range 760-1115 degrees C under compressive stress es ranging from 30 to 700 MPa. The results reveal two different deform ation 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 ra te is faster than the minimum creep rate at the reduced stress and dis location substructure consisting of homogeneously distributed curved d islocations suggests that the dominant deformation mechanism is viscou s dislocation glide. For region II, a stress exponent of 4.3, a normal primary creep behavior, a creep transient after a stress reduction wh ere the initial creep rate is lower than the steady-state creep rate a t the reduced stress and evidence for subgrain formation suggests that the dominant deformation mechanism is dislocation climb. It is believ ed that viscous dislocation glide in Ni3Al(Ta,B) is controlled by inte rdiffusion, whereas climb is controlled by Al lattice diffusion.