γ'' variant-sensitive deformation behaviour of Inconel 718 superalloy

Strengthening in Inconel 718 superalloy is derived from dislocation interaction with γ'' precipitates, which exist in disk-shaped three possible orientation variants with their {100} habit plane normal to each other. The interactions between dislocations and γ'' precipitates vary according to the γ'' orientation variants, which makes the deformation behaviour complicated and difficult to reveal experimentally. In this work, γ'' variant distributions of Inconel 718 samples were tailored by ageing heat treatment under either tensile or compressive stress. The γ'' variant-sensitive deformation behaviours were then studied by in situ tensile tests via neutron diffraction at room temperature. It is demonstrated that yielding first takes place in grains oriented with parallel to the loading direction. An identical lattice strain response to applied stress of both the γ matrix and the γ'' precipitates was observed during yielding, suggesting that dislocations shearing through the γ'' precipitates is predominant at this stage. Variations in yield strength for samples with different γ'' variant distributions were observed, which can be attributed to different strengthening that arises from interactions between dislocation and different γ'' variants