Transmission electron microscopy of single and double aged 718Plus superalloy

► Volume fraction and size of γ′ precipitates increases with double aging. ► Increase in hardness is explained by the size and phase fraction of γ′ precipitates. ► Anti-phase boundary energy in the γ′ is estimated to be 0.2 Jm−2. ► Ni, Ti, Al and Nb increase in the γ′ phase, Fe, Co, Cr, Mo and W decrease. ► Evidence of a dense population of γ′ clusters 1-2 nm found.