Stainless and low-alloy steels additively manufactured by micro gas metal arc-based directed energy deposition: microstructure and mechanical behavior

Abstract Rising demands for miniaturization in industries such as aerospace and electronics have motivated advancements in metal additive manufacturing (AM), resulting in downscaled strategies using direct-energy deposition (DED) processes, now termed micro-DED ( µ -DED). Within this context, micro gas metal arc DED ( μ -GMA) has demonstrated the ability to deposit layers approximately 1 mm wide with a build rate of 30 cm 3 /h, positioning this technology between GMA-based DED and other µ -DED processes in terms of regarding dimensional accuracy and build rate. Despite promising initial results, further evaluation of the process impact on the microstructure and mechanical behavior of various alloys is necessary due to the pioneering nature of μ -GMA. The present work focuses on the evaluation of the microstructure (via scanning electron microscopy, energy dispersive spectroscopy, thermodynamic simulations, and electron backscatter diffraction analyses) and mechanical behavior (using nanoindentation maps) of single-layer depositions of low alloy and stainless steels using μ -GMA. In addition, traditional GMA-based DED using larger diameter wires was employed to deposit comparably alloys for further discussion. μ -GMA successively deposited a low-alloy steel with a microstructure composed of ferrite and martensite–austenite constituents, achieving a nanohardness (NH) of 3.1 GPa and an elastic modulus (NE) of 196 GPa. In addition, μ -GMA additively manufactured stainless steel with a microstructure composed of a γ matrix and δ-ferrite, exhibiting an NH of 3.7 GPa and an NE of 188 GPa. These results for both deposited materials are comparable to those reported in the literature for regular GMA-based DED depositions, indicating that this new variant has promising potential as a printing technology for small and detailed parts.