Effect of heat treatment conditions on the microstructure, surface roughness, dimensional accuracy, and geometric tolerances of inconel 718 alloy produced by selective laser melting

In this study, the effects of different heat treatment conditions applied to Inconel 718 alloy produced by the Selective Laser Melting (SLM) method on microstructure, surface roughness, dimensional accuracy, and geometric tolerances were experimentally investigated. Five specimens with nominal dimensions of 22 & times;22 & times;55 mm were produced; one was kept as the as-built sample, while the others were subjected to heat treatment under the conditions of 980-1.5h, 800-1h, 800-4h, and 800-32h. Microstructural analyses indicated that the heat treatments reduced the melt pool traces and resulted in a more homogeneous structure. Surface roughness measurements showed that the average roughness value of the as-built sample was 12.946 & micro;m, whereas roughness decreased under all heat treatment conditions. The lowest value was measured as 10,065 & micro;m after aging at 800-32h, corresponding to an improvement of 22,25 %. In terms of dimensional accuracy, the lowest deviations were obtained in the as-built specimen. In contrast, under the 800-32h condition, maximum deviations of up to 0.86% were detected in certain dimensions. Parallelism tolerances increased after long-term aging, whereas the lowest deviation in perpendicularity tolerance was obtained under the 980-1.5h condition. The findings indicate that while long-term aging improves surface quality, it may adversely affect certain dimensional and geometric characteristics.