Microstructure and anodic electrochemical behavior of additive manufactured Hastelloy X alloy via directed energy deposition

The microstructure characteristics and anodic electrochemical behavior of Hastelloy X fabricated by directed energy deposition were investigated in this work. The microstructure of as-deposited Hastelloy X mainly consisted of columnar dendrites along the deposition direction. The dendrite trunk was the γ matrix, and the inter-dendritic region was composed of the Mo-rich γ phase and carbides. After solution heat treatment, the dendrites disappeared and the carbides were randomly distributed in the γ matrix. The samples in two different states presented different polarization behaviors because of their microstructural differences. After transpassive dissolution, the surface morphology of the as-deposited sample was uneven due to preferential dissolution in the inter-dendritic region. This uneven morphology could be dramatically improved by increasing the applied current density during dissolution or solution heat treatment before dissolution. It was also determined that the existence of a transpassive film reduced the current efficiency and hindered the dissolution of metal. This study could provide an effective theoretical guidance for electrochemical machining of directed energy deposited nickel-based superalloys.