Unraveling the anisotropic corrosion behavior along the building direction in laser powder bed fusion processed Hastelloy X

Abstract

In this study, cubic Hastelloy-X was manufactured by laser powder bed fusion process. A systematic investigation focused on the microstructure and anisotropic electrochemical corrosion behavior along the building direction was conducted. Distinctive columnar dendritic features across melt pool boundaries were consistently observed in the top (HX-T), middle (HX-M), and bottom (HX-B) regions along the building direction. A significant reduction in Mo content from the HX-T to the HX-B was observed, attributed to preferential segregation of Mo during the solidification process. Typical fish-scale molten pool was observed in the HX-B and HX-M, while HX-T consisted of strip molten pool in addition to fish scale molten pool. All samples showed the typical characteristics of Goss texture <110>//BD. HX-M sample showed the largest grain size, highest intensity ∼6.35 mrd and lowest kernel average misorientation value as compared to HX-T and HX-B associated with the remelting of the former solidified layer due to the newly deposited layer. Electrochemical analysis including electrochemical impedance spectroscopy and potentiodynamic polarization scans were conducted in 10 wt% NaCl electrolytes at constant temperature of 25 ± 1 °C. HX-T showed the lowest corrosion rate as compared to HX-M, HX-B (0.55, 23.16 and 16.01 mpy for HX-T, HX-M and HX-B, respectively). The surface morphology of corroded samples revealed that the formation of a compact passive film due to the presence of high atomic % of Mo in HX-T restricted the chloride ions from the electrolyte to penetrate and react with the metal samples subsequently enhancing the corrosion resistance.