The effect of grain boundary serration on creep resistance in a wrought nickel-based superalloy

Grain boundary serration, as a function of heat treatment parameters, and its effect on creep resistance have been investigated in a wrought nickel-based superalloy Nimonic 263. Grain boundary serration occurs in the absence of adjacent γ′ particles or M23C6 when a specimen is slow-cooled from solution treatment temperature. The average amplitude and wavelength of serrations can be controlled without a significant change in grain size and γ′ size by adjusting the heat treatment parameters of solution treatment time and cooling rate. Grain boundary serration leads to changes in M23C6 carbide characteristics: from granular to planar morphology, a lowered density, and the coherency pattern to two neighboring grains from consistent to zigzag. Creep resistance improvement due to serration is associated with a lower rate of cavitation and crack propagation through the modification of carbide characteristics, as well as grain boundary configuration.