Technical Note: Observations Regarding the Effects of Nitrogen Addition to the Aluminum-Tungsten System by Reactive Sputter Deposition

Reactive direct-current magnetron sputter deposition was applied to produce aluminum-tungsten-nitrogen (Al-W-N) ternary alloys. By this process, nitrogen-containing solid solution alloys were formed through careful regulation of the nitrogen partial pressure. Nitrogen content was controlled such that an intermetallic subnitride material formed, rather than a stoichiometric nitride. Nitrogen addition to the Al-W binary system imparted exceptional resistance to localized corrosion in 0.1 M sodium chloride (NaCl). Surface analysis by x-ray photoelectron spectroscopy (XPS) indicated nitrogen promoted oxidation of tungsten relative to the binary Al-W, as evident from comparison of the native air-formed oxides. The enhanced oxidation of tungsten was believed to result from a reduction in the activity of the aluminum metallic species due to substoichiometric Al-N-type bonding. Nitrogen alloying in the Al-W-N system also was associated with distinct changes in peak shape in the direct Bremsstrahlung excited Al_KLL Auger spectrum, which indicated a mixture of Al-Al and Al-N-type bonding. The demonstrated effect of nitrogen alloying on oxidation behavior of tungsten may provide fundamental insight into the "synergistic" effects of nitrogen alloying observed in iron-based systems.