Parametric dislocation dynamics simulation of precipitation hardening in a Ni-based superalloy

The precipitation hardening in Ni-based superalloys, which contain up to 73% volume fraction of cubic coherent γ′ precipitates in γ matrix, has been investigated by three-dimensional parametric dislocation dynamics. Dislocations glide under external stress on a (111) slip plane intersected by cubic γ′ precipitates. The critical resolved shear stress (CRSS), the stress to drive dislocations through precipitates, is evaluated for variations in various microstructural parameters: γ′ volume fraction, anti-phase boundary (APB) energy and γ channel width (i.e., precipitate/particle spacing). It is shown that the CRSS depends on the square root of the APB energy while being linearly proportional to the volume fraction of γ′. A microstructure with a non-uniform size distribution of γ′ has a CRSS that is 20–30% smaller than that of a microstructure with a uniform γ′ size of the same value as the average γ′ size in the non-uniform microstructure. This is due to some local channel widths larger than the average channel width, and larger channel widths allow easier bending of the dislocation line. Our results indicate that the channel width plays an important role in determining the CRSS in addition to the γ′ size. For channels narrower than 20 nm, the CRSS is found to increase with decreasing channel width but to depend only weakly on γ′ size.