Toward Post-Process-Free Fatigue Performance: In-Situ Heating and Heat Treatment of Additively Manufactured IN718

Abstract

This study investigated the microstructural characteristics and mechanical properties of IN718 fabricated using LPBF and focused on developing post-heating methods to enhance the mechanical properties of IN718. Three different heat treatments with various times and temperature ranges were examined, followed by standard aging. Samples were fabricated in horizontal and vertical orientations. Digital light microscopy, scanning electron microscope, X-ray diffraction, hardness, and fatigue tests were performed to characterize the microstructure and mechanical properties of IN718. The findings revealed that heat treatment at 980 °C enhanced the hardness, tensile strength, and fatigue life, whereas a further increase in the heat treatment temperature led to an increase in grain size and undesired precipitates. In addition, the work utilizes a high-temperature heat-assisted laser powder bed fusion to decrease thermal gradients, provide better control over cooling, and regulate the mechanical properties of the material. A heated bed with a temperature of 250 ^oC to 500 ^oC resulted in better mechanical properties compared to as-built samples and higher ductility compared to post-process heat-treated samples. This comprehensive study showed that optimizing the in-situ heating temperature has the potential to eliminate the need for post-process heat treatment for high-cycle fatigue performance. It also allows for a greater understanding of the fabrication and modification of the post-process heat treatment and in situ heating to optimize the mechanical properties of additively manufactured IN718.