Experimental characterization of Inconel 625 powder stream and single track deposited on SS400 steel by direct laser metal deposition

Abstract

Directed laser metal deposition (DLMD) offers significant potential for producing high-performance coatings and functional components, yet the effect of powder feed rate on coaxial powder stream stability and its correlation with single-track deposition quality remains insufficiently investigated. This study characterizes the Inconel 625 powder stream using light-sheet imaging and grayscale intensity analysis at feed rates of 5–30 g/min. The powder stream consistently converged at approximately 9 mm below the nozzle exit, independent of feed rate, ensuring stable alignment with the laser beam without adjusting the stand-off distance. The transverse profiles exhibited a Gaussian-like distribution. Based on these findings, single-track deposition on SS400 steel produced stable geometry, a fine cellular-to-columnar dendritic microstructure (primary dendrite arm spacing of 2.2–2.3 μm), uniform microhardness of 206.7–209.5 HV (about 25% higher than the substrate), and no porosity, lack-of-fusion, or solidification cracks. These results establish a direct link between powder stream characteristics and deposition quality, providing practical guidelines for robust DLMD processing of Inconel 625 on carbon steel substrates.