HVEM in situ observation of dislocation processes in the γ′-hardened superalloy NIMONIC 105

Abstract

The critical dislocation configurations in the γ′-hardened nickel-base superalloy NIMONIC 105 have been investigated by in situ deformation experiments. Single-crystal thin foils were deformed in a high-voltage electron microscope operated at 300 kV. Two types of specimens which differed in their γ′-particle dispersion, were studied: S1 contained γ′ precipitates of 52 nm diameter; S2 was bimodal. The diameters of the γ′ particles of the two classes were 52 nm and 263 nm. The most important results are: (a) In S1 as well as in S2, dislocations cut through the γ′ precipitates. (b) Dislocations glide in pairs. (c) In both types of specimens the γ′ particles of 52 nm diameter cause the leading dislocation of a pair to bow out very far; sometimes the critical configuration resembles the Orowan configuration. The trailing dislocation of a pair is far less bent. (d) The large γ′ precipitates present in S2 are very strong obstacles to the glide of dislocations. They first bypass these γ′ particles and cut through them later. (e) No Orowan loops were found.