Effect of Heat Treatment on Inconel 718 Metallic Part Produced by SLM Method

Abstract

Additive Manufacturing (AM), primarily Selective Laser Melting (SLM), has revolutionized the manufacture of high-grade metal parts. Due to the flexibility in design complexity and the relative economy in material use, SLM has found the place of a cutting-edge technology achieving near-full density and fine microstructures. Being an Inconel 718, this nickel-based superalloy has found an application mainly in aerospace and power-generation sectors, where it is highly valued for its superior mechanical behavior at elevated temperatures and resistance to oxidation and corrosion. However, repeated thermal gradients applied at a very short time scale during the SLM process may induce material defects, such as internal voids, residual stresses, and brittle phases, which may reduce component life.This study examines the influence of postheat treatment on internal porosity and grain structure of SLM fabricated Inconel 718. Eight cubic specimens were prepared using a Renishaw AM500 system; four specimens were tested for porosity and the rest of the specimens were used for microstructural analysis. The heat treatment was carried out at 980 °C in ambient air using a precision temperature-controlled furnace. Porosity was analyzed via image thresholding according to ASTM E1245, while structural changes were inspected using optical and scanning electron microscopy (SEM).The porosity was much decreased: 67% in perpendicular sections and 76% in parallel sections. Treatment also had a strong microstructural refinement effect as it dissolved Laves phases, precipitated γ′/γ″ strengthening phases, and created more equiaxed grains; all of it pointing to a better mechanical behavior with respect to tensile and fatigue properties. Therefore, the present results point to the necessity of tailored post processing for increasing the dependability and structural quality of the Inconel 718 components fabricated by SLM. Further mechanical testing shall be done to verify these enhancements.