Mechanical Properties Anisotropy of Isothermally Forged and Precipitation Hardened Inconel 718 Disk

Abstract

The present work describes the tensile and cyclic flow behavior of the as-received disk of Inconel 718 in solution treated and precipitation hardened condition at different locations and orientations. The disk shows moderately high values of anisotropy index indicating significant difference in uniform true strain along radial and tangential orientations. The tensile true stress–plastic strain curves exhibit two slopes defined by Ludwigson relation [\( \sigma = K_{1} \varepsilon^{{n_{1} }} + \exp (K_{2} + n_{2} \varepsilon ) \)]. The low-strain regime during tensile test is associated with low-strain localization between broad annealing twins and slips, while high-strain regime is related to the presence of large volume fraction of deformation twins and high-strain localization between narrow deformation twins. It appears that both the γ′ and γ″ play a critical role during low deformation regime while the role of γ″ precipitates becomes significant in high-strain regime. The stabilized cyclic true stress–plastic strain curves follow Ludwik relationship (σ = Ke n ) similar to that of high-strain regime of two-slope tensile curves. The true stress–strain curves show softening during cyclic test in comparison to that of monotonic condition and are independent of sample orientations and locations. The lower degree of cyclic softening associated with radial-oriented sample can be attributed to the alignment of δ-phase precipitates normal to the loading direction. The low ductility and low work-hardening exponent of radial-oriented sample in web region have been explained based on the dislocation storage capacity and dynamic recovery coefficient using Kock–Mecking–Estrin analysis.