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Near-Surface Analysis of Magnetron Sputtered AlCrNbYZrNx High Entropy Materials Resolved by HAXPES

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Al 1s spectra collected using photon energies of 2, 4 and 6 keV. The left hand side shows the overlaid spectra for all as-deposited AlCrNbYZrNx samples at all energies, with the intensities normalised to the oxide component. Solid (dotted) vertical line indicate position of metal (nitride) components. The centre panel shows the curve fits of the 0, 37 and 49 at.% N samples measured with a photon energy of 6 keV. The shaded areas from the curve fits have been used to create the bar charts on the right where the metal is in grey, the nitride-like (or oxynitride) is in blue and the oxide is in yellow.

Author: Aishwarya Srinath, Kristina von Fieandt, Stefan Fritze, Leif Nyholm, Erik Lewin, Rebecka Lindblad Institute: ''Uppsala University'' Applied Surface Science
URL: /Results/Publications/2024/202409/Near-surface-analysis-of-magnetron-sputtered-AlCrNbYZrNx-_2024_Applied-Surfa.pdf
Date: 2024 Instruments: HAXPES Lab, EW4000

Hard X-ray photoelectron spectroscopy (HAXPES) was used to perform a non-destructive depth profile of AlCrNbYZrNx (x = 0 to ∼50 at.%) thin films. The outermost native oxide of the pristine thin films contained the highest coordination oxides of every metal. Substoichiometric oxides or oxynitrides were found underneath. After exposure to 1.0 M HCl, increases in the most highly coordinated oxides of Cr, Nb, and Al in films with up to 37 at.% N were observed, suggesting that the low coordination oxides and oxynitrides in the subsurface had been further oxidised and were intermediary compounds in the passivation process. Al and Y oxides were lost to the HCl electrolyte, in agreement with their respective Pourbaix diagrams. The film with 49 at.% N showed little to no change in the data due to its high porosity which led to the oxide being detected at all probed depths. The metal core level spectra revealed a preferential order in which nitrogen bonded with the different metals. Nitrogen interacted first with Y, then Zr, then Al and Nb, and lastly Cr as the nitrogen content was increased. 

In addition to this figure, the publication includes 4 more data sets for the as-deposited AlCrNbYZrNx high entropy alloy films. In a conventional alloy, the corrosion rate is largely determined by the thermodynamic and kinetic stability of its major metal. This restricts the utility of the alloy to the stability window of one metal. High entropy alloying strategies could significantly broaden the range of conditions in which an alloy is used. 

The left hand side of each figure shows the core level spectra collected for every AlCrNbYZrNx film using photon energies of 2, 4 and 6 keV. The elemental metal position (solid black line) and the metal nitride position (dotted line) are also demarcated and were obtained by curve fitting. The curve fits, shown in the centre of each figure, are shown for the 0, 37 and 49 at.% N samples measured with a photon energy of 6 keV. Dotted lines (bgr) show the modelled background and solid black lines (sum fit) shows the sum of all fitted peaks, including the background. The right hand side of Figs. 1–5 shows a bar chart representation of the different components (metal, metal in N environment, metal oxide) acquired from the curve fits. 

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