Optimization and characterization of functionally graded Fe/SS316L materials fabricated by direct laser deposition

In this study, the fabrication of Functionally Graded Materials (FGM) made of Fe and SS316L through the Direct Laser Deposition (DLD) method is investigated. To assess the influence of three key process parameters–laser power, scanning speed, and the ratio of the material composition–on the geometric features of single-pass tracks, such as height, aspect ratio, wetting angle, and dilution, a Box–Behnken response surface design was employed. Among these, the material composition ratio had the most significant influence, contributing to approximately 66% of the variation in height, 78% in aspect ratio, and 79% in dilution. The wetting angle was primarily influenced by the interaction between scanning speed and material composition ratio. Regression models were developed with high accuracy (R2 values ranging from 0.91 to 0.95), and model predictions were validated through experimental deposition of five single-pass samples. Based on the optimized conditions, a 15-layer FGM bulk specimen was successfully fabricated. SEM-EDS analysis confirmed a controlled compositional gradient with less than 15% deviation from the target, and microhardness measurements ranged from 468 HV in the SS316L-rich base to 329 HV in the Fe-rich top layers. These results confirm the feasibility of using DLD to fabricate FGMs with tailored geometry, composition, and mechanical performance.