Microstructural evolution of a printed AISI 303 upcycled powder on a dissimilar substrate

Abstract

Additive manufacturing for new constructions or repairing purposes may deal with the use of dissimilar materials. Hence, the influence of interface between the substrate layer and printed one is crucial. This study delves into the impact of printed layers on the microstructure and hardness of an upcycled AISI 303 alloy produced by Direct Energy Deposition. Chemical composition distribution, phase and grain size evolutions were studied, accompanied with microhardness measurements.Microscopic analysis through chemical composition mapping and using electron backscatter diffraction technique for crystallography analysis revealed that the interface structure is strongly affected by the distribution of chemical composition and the heat received from subsequent printing. That means, a dominant transformation of austenite to martensite/ferrite occurs at the first layer printed on the top of the substrate. This is confirmed by hardness measurements (442 ± 15 HV0.1). This dominance (global martensite/ferrite distribution of 42%) is attributed to the reduction of Cr, Ni and Mn contents in the first layer, caused by Marangoni convection currents. This study confirms that subsequent printing favors the evolution of martensite/ferrite to austenite (global distribution of 75%) and grain growth, leading to hardness decrease to around 295 ± 34 HV0.1, leaving small difference with the printed AISI 303 alloy with a hardness of 235 ± 18 HV0.1.