Improved properties of additively prepared Inconel 718 alloy post-processed with a new heat treatment

Abstract

In this study, an alternative heat-treatment route has been explored to optimize the mechanical as well as the fatigue properties of Ni-based 718 alloy fabricated using additive methods. The test coupons were prepared using the laser-based powder bed fusion technique and post-processed with a new heat-treatment condition (NHT): solution treatment at 1130°C for 2hr followed by water cooling (WC) and the artificial aging at 730°C for 13hr followed by furnace cooling (FC). It was found that the NHT parameters enhanced the mechanical properties as well as the fatigue properties as compared to the standard heat-treatment (SHT) conditions: solution treatment at 980°C-1hr-FC followed by two-step artificial aging 720°C-8hr-FC(55°C/hr up to 620°C) + 620°C-8hr-FC. The NHT condition resulted in a more homogenized and recrystallized microstructure with a higher volume fraction of γ′ and γ′′ precipitates, high-angle coincidence site lattice (CSL) as well as the twin boundaries and marginally reduced grain size. The microhardness, tensile strength, and fatigue strength after the NHT condition were improved by ∼15%, ∼16%, and ∼12.5%, respectively, and it was mainly accredited to the high volume fraction of fine strengthening precipitates and homogenized microstructure.