Elevated Temperature Notch Sensitivity of Inconel 718 Manufactured by Selective Laser Melting

Notched alloy 718 tensile specimens prepared by selective laser melting (SLM) and wrought bar were tested at 550, 650, and 750 °C. SLM specimens were tested with either an as-printed or a machined notch. For both types there was a decrease in strength with an increase in test temperature; however, the as-built notches are more sensitive to increases in test temperature than the machined notches. At 550 °C, the machined notch exhibits a roughly 20% higher tensile strength over as-built, while at 750 °C there is a 75% increase in strength. The notched strength ratio decreased with temperature for both types of SLM notches samples, while for wrought samples it increased. The temperature dependence of the difference in strength between the two SLM samples indicates that surface roughness—and the corresponding stress intensity factor—are not the only influences on notched strength. Fractography of tested specimens showed a difference in the intergranular crack propagation depth between as-built and machined notches, demonstrating a difference in the environmental susceptibility based on notch preparation that is due to microstructural differences arising in the SLM process that are preserved through heat treatment.