Exposure testing was performed on CoCrFeMnNi equiatomic high entropy alloy (HEA) produced via directed energy deposition additive manufacturing in NaNO3-KNO3(60–40 wt%) molten salt at 500 °C for 50 h to evaluate the corrosion performance and oxide film chemistry of the HEA. Potentiodynamic electrochemical corrosion testing, scanning electron microscopy, focused ion beam milling coupled with energy dispersive spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy were used to analyze the corrosion behavior and chemistry of the HEA/nitrate molten salt system. The CoCrFeMnNi HEA exhibited a higher passive current density during potentiodynamic polarization testing than steel alloys SS316L and 4130 and the high-Ni alloy 800 H in identical conditions. The oxide film was primarily composed of a (Mn,Co,Ni)Fe2O4spinel with a vertical plate-like morphology at the surface. Cr and Ni were found to be totally depleted at the outer surface of the oxide and dissolved in high concentrations in the molten salt. While Cr was expected to dissolve into the molten salt, the high concentration of dissolved Ni has not been observed with traditional alloys, suggesting that Ni is less stable in the spinel when Mn and Co are present.
The authors report on the evaluation of the oxide scale and the interface microstructure of a Cr–Nb–Ta–V–W refractory high entropy alloy (HEA) at elevated temperatures. The Cr–Nb–Ta–V–W HEA is oxidized at 700 and 800 °C in lab air and the substrate/oxide interface is investigated. Combined in situ X‐ray diffraction (XRD) coupled with ex situ scanning electron microscopy (SEM) and energy dispersive X‐ray spectrometry (EDS) analyses characterize the oxide scale and confirm the phases present in the substrate which have been previously identified in this alloy. The microstructure near the interface is studied for an indication of selective oxidation of this alloy. Cracking and porosity are found along the interface layer which grows directionally outward. Two main oxides are identified: a W‐based oxide with a needle‐like structure and a Cr oxide containing Ta that has a granular structure, primarily found in clusters. The oxide layers are porous, and no dense protective oxide is identified. It is found that when the temperature is increased to 800 °C, the oxide layer exhibits an increase in thickness. In situ XRD indicates that V is the first element to oxidize.
- Award ID(s):
- 1827745
- NSF-PAR ID:
- 10234523
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Engineering Materials
- Volume:
- 23
- Issue:
- 8
- ISSN:
- 1438-1656
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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