Correlation Between Solidification Microstructure and Corrosion Susceptibility of Additively Manufactured Inconel 625

Abstract

This study investigated the relationship between the solidification microstructure and the corrosion susceptibility of Inconel 625 fabricated by directed energy deposition (DED). Specimens were deposited under three coupled processing conditions, in which the laser beam diameter (800, 1200, and 1600 μm) was varied together with the hatch spacing, layer thickness, and laser power. The results were compared with those of a hot-rolled alloy. The DED specimens exhibited columnar dendritic structures with Nb and Mo enriched in the interdendritic regions, whereas the hot-rolled alloy exhibited a homogeneous equiaxed microstructure. The double-loop electrochemical potentiokinetic reactivation (DL-EPR) test showed that the degree of sensitization (DoS) tended to increase with increasing beam diameter, although all DoS values remained below 0.004. Reactivation occurred preferentially in the dendritic regions, which were relatively depleted in Nb and Mo. Kelvin probe force microscopy (KPFM) of the 800 μm specimen revealed that the Nb- and Mo-enriched interdendritic regions exhibited a surface potential approximately 40 mV higher than that of the dendritic regions, indicating local electrochemical heterogeneity. The increase in DoS coincided with an increase in the dendritic area fraction, suggesting that the fraction of Nb- and Mo-depleted regions is associated with the reactivation response under the present coupled conditions.