Microstructure and Corrosion Behavior of Functionally Graded Wire Arc Additive Manufactured Steel Combinations

Abstract

Functionally graded materials (FGM) have gained many interests for various applications and are designed to match special requirements in local properties (e.g., corrosion behavior), which highly determines the component's lifetime. The corrosion behavior is strongly dependent on the chemical composition and the microstructure of the designed materials. Therefore, two FGM combinations are designed using wire arc additive manufacturing (WAAM) with a linear changing material deposition from G 3Si1 to G 19 9L Si (combination 1) and G 18L Nb to G 19 9L Si (combination 2). The microstructure at different positions is analyzed using optical light microscopy (OLM), scanning electron microscopy with attached energy dispersive X-ray spectroscopy (SEM/EDS), and X-ray diffraction (XRD). The electrochemical corrosion behavior in 0.6 m NaCl solution is determined by cyclic potentiodynamic polarization (CPDP) including SEM imaging after CPDP to determine the pit size and morphology. The phase formation sequences of ferrite (α and δ), martensite, and types of austenite are discussed regarding the chemical gradient. The pitting corrosion resistance is enhanced for both combinations in direction to G 19 9L Si due to the increase in Cr and/or Ni, while the pit morphology changes in dependence of the presence of various microstructures.