A Comparison of Microstructure and Microhardness Properties of IN718 Fabricated via Powder- and Wire-Fed Laser-Directed Energy Deposition

The objective of this work is to compare the microstructure and microhardness properties of IN718 deposited by both powder- and wire-fed laser-directed energy deposition (L-DED) processes. The powder-fed L-DED is carried out on an Optomec LENS (R) system while the wire-fed L-DED is performed in an in-house custom-built system. Several single-layer single-track specimens are fabricated using different combinations of process parameters to down-select the optimal process parameters for both systems. The finalized parameters are, thereafter, used to build thin-wall specimens having identical designs. The specimens are characterized using optical and electron microscopy as well as microhardness measurements. The results demonstrate that the powder-fed specimen, built using optimal process parameters, does not exhibit any distortion. On the contrary, the wire-fed specimen, built with optimal process parameters, show lesser porosity. Differences in elemental segregation are also detected in the two specimens. For example, nitrides and carbides are observed in the wire-fed specimen but not in the powder-fed specimen. The microhardness measurements reveal the powder-fed specimen has higher microhardness values compared to the wire-fed specimen. These results can be used to fabricate parts with sequential powder and wire deposition to achieve biomimetic structures of varying microstructure and microhardness properties.

Automated summary

The objective of this study was to compare the microstructure and microhardness properties of IN718 deposited by powder- and wire-fed laser-directed energy deposition (L-DED) processes. Single-layer single-track specimens were fabricated using different process parameters to determine the optimal parameters for both systems. Thin-wall specimens with identical designs were then built using the finalized parameters and characterized using microscopy and microhardness measurements. The results showed that the powder-fed specimen had no distortion while the wire-fed specimen had less porosity. Differences in elemental segregation were also observed, with nitrides and carbides present in the wire-fed specimen but not in the powder-fed specimen. Microhardness measurements revealed higher values for the powder-fed specimen compared to the wire-fed specimen. These findings can be applied to fabricate parts with varying microstructure and microhardness properties using sequential powder and wire deposition to achieve biomimetic structures.