Shear punch testing for evaluation of mechanical properties of post heat-treated Inconel 718 nickel-based superalloy fabricated by additive manufacturing

Abstract

Shear punch testing, as a cost-efficient miniature testing technique for investigating the mechanical properties under shear loading conditions, was utilized for the first time to elucidate the effect of post heat-treatment on the mechanical properties of additively manufactured Inconel 718 superalloy. Homogenization heat treatment was performed for the dissolution of undesirable Laves phase; while the aging treatment was performed on both as-built and homogenized superalloys for age hardening by precipitation of strengthening phases such as γ˝ phase. Better aging response and consequently superior shear properties were obtained by aging from the as-built condition, which were ascribed to the high dislocation density and more homogeneously dispersed precipitates in the microstructure. Moreover, by comparing the shear yield stress (SYS) with the tensile yield stress (TYS) and ultimate shear strength (USS) with ultimate tensile strength (UTS), the relationships of TYS = 1.71 × SYS and UTS = 1.72 × USS were obtained, which reveal that the experimental data points follow the von Mises criterion. Accordingly, these simple and useful formulae are consistent with the general expectations from the plasticity theory, and hence, it is possible to estimate the tensile or shear properties by performing one of these tests.