Surface microstructure of an IN718 3D coating manufactured by Laser Metal Deposition

Laser Metal Deposition (LMD) is a well-known additive manufacturing (AM) process that offers the ability to repair metal parts, among other benefits. We have focused on IN718 parts that evolve in environments that strongly favor wear. Therefore, a good knowledge of the contact surface microstructure and its properties is necessary to better understand the tribological behavior of these parts. However, the microstructure of the top surface (which is most susceptible to wear) of IN718 coatings deposited by LMD is not particularly well documented in the literature. Most of the studies devoted to this alloy have focused on the study of the cross-sectional microstructure, and the few articles dealing with the top surface microstructure have been devoted to the Laser Powder Bed Fusion (LPBF) process. In this article, four IN718 coatings were successfully fabricated with high density using different scanning strategies. When viewing the microstructure from the top surface, the EBSD map showed a very heterogeneous microstructure with an alternation of fine and coarse grains. It also showed a weak overall texture, but a strong local texture within the fine and coarse grain region. EBSD analysis of the crosssectional area of the coated section also revealed a microstructure variation along the build direction (BD) with the appearance of small grains between layers after some layers have been deposited. Analysis of both sides of the coated part allowed us to get a better understanding of the final microstructure. We were able to show that this heterogeneous microstructure leads to a spatial variation of the top surface hardness, the pattern of which is directly related to the scanning strategy. Finally, we found that the surface hardness of IN718 LMD samples is higher than that of conventionally produced IN718, which is a promising result in terms of repairing metal parts with good tribological properties.

Automated summary

This study focused on the microstructure and properties of the IN718 material fabricated by Laser Metal Deposition (LMD). It was found that the top surface of the IN718 coatings exhibited a heterogeneous microstructure and spatial variation in hardness, which was directly related to the scanning strategy. The surface hardness of IN718 LMD samples was higher than that of conventionally produced IN718, which is a promising finding for repairing metal parts with good tribological properties.