Fabrication of thin-walled Inconel 718 microchannels by LP-DED: influence of deposition strategy on geometric fidelity, surface texture, and post-processing feasibility via hybrid manufacturing

Abstract Additive manufacturing (AM) offers significant potential for fabricating microchannel heat exchangers (MCHEs) by overcoming the geometric limitations and material waste associated with conventional manufacturing methods. While laser powder bed fusion (L-PBF) enables high-resolution features, it remains constrained in scalability, particularly for large or multi-material structures. In contrast, laser powder directed energy deposition (LP-DED) provides greater flexibility but faces challenges in achieving thin walls with surface quality comparable to L-PBF. This study investigates the feasibility of fabricating Inconel 718 microchannels using a small laser spot size (0.8 mm) in LP-DED, with particular emphasis on the influence of deposition strategy and process parameters. Thin walls with thicknesses ranging from 0.579 mm to 0.674 mm were successfully produced using previously optimized conditions. The results demonstrate that deposition strategy plays a decisive role in geometric fidelity. A continuous scanning path without a U-path resulted in severe defects, including material accumulation, wall tearing, and height inconsistencies. In contrast, the implementation of a U-path strategy significantly improved dimensional uniformity. The non-continuous strategy (300 W, 1500 mm/min, 4 g/min) minimized height variation and ensured corner stability, albeit with slightly increased surface roughness and waviness. Conversely, higher scan speeds (2000 mm/min) combined with a continuous U-path reduced internal roughness and waviness. Dimensional analysis confirmed high reproducibility across larger channels, while smaller channels (0.3 × 2 mm 2 ) were prone to partial blockage due to powder adhesion, necessitating post-processing. Micro-milling was successfully applied, reducing the average surface roughness (Ra) from 11.16 µm to 0.75 µm. Furthermore, detailed surface characterization revealed intrinsic waviness, with W sm ranging from 919 µm to 3180 µm and W z from 29 µm to 76 µm. This inherent topography, characteristic of the LP-DED process, presents a promising opportunity for future research, as it may be leveraged to enhance thermal–hydraulic performance similarly to intentionally created through other manufacturing methods.