# Microstructure and Corrosion Characteristics of IN 625 Coating on Additively Manufactured 316L Stainless Steel in As-Fabricated Condition

## TL;DR

This study examines how the microstructure and corrosion behavior of 316L stainless steel, produced via electron beam 3D printing, are affected by IN 625 coating and printing parameters.

## Contribution

The study reveals how additive manufacturing parameters and coatings influence corrosion resistance through microstructural and surface characteristics.

## Key findings

- Coating improved corrosion potential but increased corrosion rate when a contour scan strategy was not used.
- Contour scan strategy led to better corrosion resistance in as-fabricated samples compared to coated ones.
- Dross particles from the printing process caused defects in the coating, such as microcracks and cavities.

## Abstract

The microstructure and corrosion properties of electron beam powder bed fusion (EB-PBF)-fabricated 316L stainless steel are evaluated in the as-fabricated condition with and without the deposition of IN 625 coating. Different surface profiles were achieved by introducing layer thickness and a contour scan strategy as process variables. A potentiodynamic polarization test was used for corrosion testing, while state-of-the-art microstructural investigation techniques were employed to elucidate a possible link between the microstructure and corrosion properties of the samples. Results from this pilot study showed that the corrosion response was dictated by the combined effects of surface roughness, coating depth, coating morphology, and passive film characteristics. For specimens for which a contour scan strategy was not used, the coating hinted to an improved corrosion potential while it increased the corrosion rate for both layer thicknesses. On the contrary, for specimens where a contour scan was applied, as-fabricated samples trended towards better corrosion resistance than the coated samples. It is shown that the dross particles that are formed during EB-PBF processing influence the flattening mechanism of the coating, ultimately resulting in a coating deposit that is characterized by surface defects, microcracks, cavities, and incoherent splat boundaries.