As more industries look toward additively manufactured (AM) components to combat lead times, re-design, cost of complexity, etc., those industries are faced with re-evaluating the performance of AM-based materials as compared to their well-documented wrought or machined counterparts. A particular alloy of interest to many industries including aerospace and energy/power generation is Inconel 718 due to its resistance to oxidation and high temperature degradation [1]. Additively manufactured Inconel 718 parts typically receive a series of post-build heat treatments prior to deployment. If not properly controlled, these post-build treatments may introduce secondary precipitates and other inhomogeneities that will affect the parts’ mechanical properties and susceptibility to corrosion. This is specifically true of susceptibility to localized corrosion mechanisms that may lead to crack initiation, accelerated crack growth and ultimately premature failure. By utilizing electrochemical parameter testing to analyze for localized breakdown potentials, this work investigates the variation in tolerance to localized corrosion that results from common post-build heat treatment steps and the secondary phase precipitation that can ensue in Inconel 718 AM parts.

IN718 has good fabricability, high strength at elevated temperature, and corrosion resistance, and it is widely deployed in many aerospace and other high-performance applications. With the molten pool rapid solidification during laser powder bed fusion (L-PBF), the resulting microstructure is anisotropic and inhibits macro-segregation. The as-built condition usually exhibits lower mechanical properties. Four different heat treatment procedures were designed and tested to study the effect of different heat treatment parameters on the type of precipitates and grain size. The investigated heat treatment procedures showed the formation of equiaxed grain size and a significant amount of γ' and γ" particles at the grain boundary in addition to primary carbide types (MC). Three types of microstructure characteristics and grain size were achieved. Coarse grain size suitable for creep application was achieved by increasing the soaking time at the aging cycle. The formation of serrated grain boundaries suitable for good fatigue and creep properties was achieved by decreasing the stress relief cycle's soaking time and temperature. Fine-grain size, which is preferable for fatigue properties, was achieved by decreasing the soaking time at the solution annealing cycle.