Prestraining effect on creep behaviour of nickel base C263 superalloy

The effect of room temperature plastic deformation on the subsequent creep behaviour of C263 alloy has been studied. Creep tests were carried out at 800°C and prestraining was conducted in tension up to a level of 7·2%. Prestraining slightly increased the minimum creep rate. Progressive loss of creep life and fracture ductility was found with increasing amount of prestrain. Concomitantly, the density of grain boundary cavities increased significantly. It was also found that prestraining reduced the incubation time for cavity nucleation and promoted homogeneity of cavity distribution along grain boundaries. Cavity nucleation was found to be associated with stress concentration produced by slip bands. The increased activity of cavitation in prestrained specimens was related to an increased slip band density produced during prestraining. By calculation via a dislocation pile-up model, it was concluded that the high, sustained stress concentration built up ahead of slip bands was associated with cavity nucleation. Prolonged high temperature exposure resulted in platelike γ phase precipitation at grain boundaries. Its precipitation has been found to weaken grain boundary strength by producing microcracking, but in the present work this appeared to be of secondary importance.