DED Powder Modification for Single-Layer Coatings on High-Strength Steels

In the design of L-DED (laser-directed energy deposition) cladding processes, the chemical composition of the metallic powders is typically assumed to match that of the intended coating. However, during the deposition of the first layer, dilution with the substrate alters the weld metal composition, deviating from the nominal powder chemistry. Although the application of multiple layers can gradually reduce this dilution effect, it introduces additional complexity and processing time. This study proposes an alternative strategy to counteract substrate dilution from the very first deposited layer, eliminating the need for multilayer coatings. Specifically, to achieve a corrosion-resistant monolayer of AISI 316L stainless steel on a high-strength, quenched-and-tempered AISI 4140 steel substrate, a dilution-compensating alloy powder is added to the standard AISI 316L feedstock. Single-layer coatings, both with and without compensation, were evaluated in terms of chemical composition, microstructure, and corrosion resistance. The results show that unmodified coatings suffered a chromium depletion of approximately 2 wt.%, leading to a reduced pitting potential of Ep = 725 ± 6 mV in synthetic seawater. In contrast, the use of the compensation alloy preserved chromium content and significantly improved corrosion resistance, achieving a pitting potential of Ep = 890 ± 9 mV.

Funding: This work has been funded by the Basque Government under the ELKARTEK program project ReIMAGIN (grant number KK-2023/00096).

Acknowledgments: The authors thank Oier Barrenetxea, Xabier Lasheras, and Ana Fernández for their support in the design and manufacture of the CP, from the foundry keel blocks to the delivery of the sieved powder, Rodolfo González-Martínez for his support in the scanning electron microscopy work, and the 3D Lab Sp. z o. o. for their support in setting the atomization conditions of the CP bars.