# Additively Manufactured Inconel 718 Low-Cycle Fatigue Performance
## 4 Conclusions
Fatigue Life Knockdown Due to Temperature and Surface Condition: The 1000 \({}^{\circ}\)F test condition exhibited a larger knockdown in fatigue life due to surface conditions compared to the 24 \({}^{\circ}\)C (75 \({}^{\circ}\)F) test condition. Specifically, the 538 \({}^{\circ}\)C (1000 \({}^{\circ}\)F) as-printed specimens had an average knockdown of 62.8%, while the 24 \({}^{\circ}\)C (75 \({}^{\circ}\)F) as-printed specimens showed an average knockdown of 8.5%. This significant difference underscores the detrimental effect of elevated temperatures on the fatigue performance of as-printed surfaces. This study underscores the critical role of surface finish in enhancing the fatigue performance of L-PBF Inconel 718 components. Improving surface finish through post-processing techniques can significantly reduce the number of crack initiation sites and extend fatigue life, particularly at elevated temperatures. The findings emphasize the necessity of considering operating temperatures in the design and application of L-PBF Inconel 718 components, as elevated temperatures can drastically increase the susceptibility to crack initiation at surface defects. This necessitates additional measures to mitigate this effect. The practical implications of this work are particularly significant for structural applications requiring high material performance under cyclic loading conditions. As demonstrated, the rough surfaces produced by the L-PBF process can severely reduce fatigue life, restricting the use of these components in high-stress or safety-critical environments. For L-PBF to be viable in such applications, parts must either be designed with sufficient safety margins to account for the fatigue debit caused by surface roughness or undergo post-processing techniques to mitigate these effects. Methods such as machining, polishing, shot peening, or chemical surface treatments can effectively reduce surface roughness, eliminate stress concentrators, and enhance fatigue resistance. These improvements not only ensure compliance with stringent safety and performance requirements but also expand the potential uses of L-PBF components across industries. Additionally, enhancing fatigue life through surface refinement minimizes the risk of premature failure, resulting in longer service life and reduced maintenance or replacement costs. However, the added time and expense of post-processing must be carefully weighed against the performance benefits to ensure the economic viability of L-PBF components in demanding applications. Future work should aim to optimize both the L-PBF process parameters and post-processing techniques to minimize surface defects and enhance the mechanical properties of fabricated components. Developing a deeper understanding of the interplay between processing conditions and material behavior is critical for the reliable application of L-PBF. Inconel 718 in demanding aerospace and gas turbine environments. Particular focus should be placed on refining contour processing parameters (i.e., laser power, laser speed, or scan strategy) to achieve smoother as-printed surfaces directly from the manufacturing process [14]. Furthermore, the effectiveness of post-processing methods such as machining, polishing, shot peening, and chemical surface treatments in improving surface finish and mitigating fatigue debit should be thoroughly investigated [28]. During the investigation of post-processing techniques to improve surface roughness, it would also be beneficial to correlate defect size to fatigue life and understand how well these post-process techniques reduce defect sizes. While this study highlights the impact of surface roughness on L-PBF processes, future research should also explore alternative additive manufacturing methods that might better address the fatigue life concerns related to surface roughness. By broadening the scope of investigation, the potential for achieving superior fatigue performance in AM components across various processes and applications can be further realized.