Abstract
In this study, the effect of rhenium addition (2, 4, and 6 wt pct) and building orientation (0 and 90 deg) on the microstructure and corrosion resistance of Inconel 718 (IN718) alloy processed by selective laser melting (SLM) was investigated. Microstructure characterization showed that the as-built IN718-Re alloys consist of columnar grains growing parallel to the building direction (Z-axis). Each columnar grain was characterized by a fine columnar/cellular dendritic substructure with Nb- and Mo-rich Laves phases and MC-type carbides embedded in the interdendritic spaces. Rhenium addition segregated to γ phase dendrites which resulted in an increase of the columnar/cellular substructures width with increasing Re content. Due to a strong microstructure anisotropy of SLM-processed IN718-Re alloys, the corrosion properties were examined for mutually perpendicular planes: XY (90 deg samples) and XZ (0 deg). The presence of rhenium enhanced the corrosion resistance of IN718 alloy in 0.1 M Na2SO4 and NaCl solutions at both exposed planes. The corrosion current density was significantly reduced for IN718-Re alloys and increasing Re content correlated with a more positive shift in corrosion potential. Moreover, the XY plane possessed better corrosion resistance than the XZ plane due to the higher fraction of laser overlapping areas observed for the XZ plane.
Highlights
SELECTIVE laser melting (SLM) is an additive manufacturing (AM) technique which enables the production of nearly fully dense 3D metal parts in a layer-by-layer fabrication process
scanning electron microscope (SEM) observations in the XZ plane reveal that the microstructure of as-built samples is dominated by columnar grains with a width of 10 to 30 lm and a length of several hundred microns (Figures 2(d) and (e)) which are elongated along the building direction (Z-axis)
The arc-shaped melt pools can be noticed in the XZ plane (Figure 2(d)) which demonstrates the development of layers during laser beam manufacturing
Summary
SELECTIVE laser melting (SLM) is an additive manufacturing (AM) technique which enables the production of nearly fully dense 3D metal parts in a layer-by-layer fabrication process. Subsequent 50- to 100-lm-thick powder layers are melted and consolidated by a focused laser beam to obtain a given computer-aided design (CAD) model.[1,2,3,4] Such processing allows the direct manufacture of metal parts with complex geometries with little to no further machining. This significantly reduces the material waste and investment cost for machining tools.[5].
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