Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

Dislocation structures, chemical segregation, gamma', gamma '', delta precipitates, and Laves phase were quantified within the microstructures of Inconel 718 (IN718) produced by laser powder bed fusion additive manufacturing (AM) and subjected to standard, direct aging, and modified multi-step heat treatments. Additionally, heat-treated samples still attached to the build plates vs. those removed were also documented for a standard heat treatment. The effects of the different resulting microstructures on room temperature strengths and elongations to failure are revealed. Knowledge derived from these process-structure-property relationships was used to engineer a supersolvus solution anneal at 1020 degrees C for 15 min, followed by aging at 720 degrees C for 24 h heat treatment for AM-IN718 that eliminates Laves and delta phases, preserves AM-specific dislocation cells that are shown to be stabilized by MC carbide particles, and precipitates dense gamma', gamma '' nanoparticle populations. This "optimized for AM-IN718 heat treatment" results in superior properties relative to wrought/additively manufactured, then industry-standard heat treated IN718: relative increases of 7/10 % in yield strength, 2/7 % in ultimate strength, and 23/57 % in elongation to failure are realized, respectively, regardless of as-printed vs. machined surface finishes.