Role of precipitation and solute segregation on micro-scale deformation of additively manufactured Inconel 718

Abstract

Inconel 718, a Ni-based superalloy, was prepared by powder laser bed fusion (P-LBF) additive manufacturing (AM) method. AM of the Inconel 718 is challenging, as this particular alloy possesses a higher melting point, as well as resistance to temperature, which induces ‘hot-cracking’. Thus, the selection of proper input parameters are essential, which was successfully achieved in this present study. The microstructure exhibits a hierarchical structure, that starts with equiaxed and sub-cellular (∼100–600 nm) grains, and ends up on the formation of melt-pool and grain boundaries. This structure is exceptional and completely dissimilar to that of wrought alloy, which is infested with twins and precipitates of different secondary phases. However, the effectiveness of such microstructure of L-PBF alloy towards material's strength was undermined, as it lacks the presence of abundant precipitates, which is the major contributor to the strength of such alloys. The strength of the L-PBF processed alloy was in the range of 413–491 MPa and 562–665 MPa respectively, for yield and ultimate compressive strength. This was marginally higher than that of wrought alloy (408 MPa of Yield and 656 MPa of compressive strength). This was attributed to the absence of abundant gamma/gamma double prime (γ'/γ'') phases, and the presence of laves and delta (δ) phases, that are inferior towards the overall strengthen of the Inconel 718. Cross-sectional SEM and TEM investigation of the deformed micro-pillars confirmed the prevailing deformation mechanism that can be attributed to the slip/share plane formation in the presence of dislocation loops.