Role of secondary γ′ precipitation and of hydrogen in the first stage of the plastic deformation of the γ matrix of a Ni base superalloy single crystal

A detailed analysis of the tensile properties at room temperature of fully γ AM3 nickel base superalloy single crystals was performed to understand the mechanisms of plastic deformation of the γ matrix of the AM3 industrial γ–γ′ superalloy. The nucleation of the small γ′ precipitates after aging at 750°C of the fully γ alloy strongly increases the critical resolved shear stress of [001] oriented single crystals and contributes to the observed coplanar dislocation motion. Hydrogenated samples exhibit a different behavior depending on the presence of γ′ microprecipitates: internal hydrogen increases the critical resolved shear stress of fully γ specimens whereas the main effect of hydrogen on the first stage of the plastic deformation of the aged samples is an enhancement of the localized plasticity.