Fracture Behavior of Thin-Walled Inconel 718 Manufactured with Selective Laser Melting

The use of additively manufactured Inconel 718 produced with Selective Laser Melting (SLM) is becoming increasingly common in the aerospace industry. This is due to the ability to rapidly make complex geometries using SLM while maintaining a material composition with inherent resistance to elevated temperatures. Characterization of the fracture properties for thin-walled Inconel 718 produced with SLM is not widely documented. This study characterizes the effects of post-processing on the fracture properties of SLM Inconel 718. Upon the application of hot isostatic pressing, heat treatment per AMS 5663, and a combination of both these processes, the fatigue crack growth rate of thin-walled SLM Inconel 718 increases. The highest fatigue crack growth rate occurred for specimens with only heat treatment applied. Microscopy and material characterization have been conducted on several specimens to provide additional context to the fatigue crack growth rate test results. Additionally, determination of the crack tip plastic zone size, by way of material characterization testing and fracture mechanics, was evaluated for the various post-processing techniques. The test results suggest that a shift away from plane stress conditions in thin-walled structures made from heat-treated SLM Inconel 718 may contribute to decreased cycles to failure when subject to low amplitude, displacement control cycles. Based on these findings, thin-walled Inconel 718 produced with SLM may exhibit improved fatigue crack growth performance without heat treatment.