The role of nickel in the oxidation resistance of tungsten-based alloys

Abstract

In this work, W–N–Ni coatings were produced with different contents of nickel and nitrogen. The films were oxidised in pure air at increasing temperatures up to 800°C. An increase in the oxidation resistance upon the addition of an increasing amount of nickel was observed. The oxidation mechanism involves the formation of two nickel-rich, external oxide layers of NiO and NiWO4. The limiting step seems to be the outward diffusion of either Ni2+ or W6+ ions through the oxide layers. To retain the oxidation resistance of the amorphous W–N–Ni coatings at 800°C, it is necessary that crystallisation does not induce a dimensional stress capable of destroying the protective oxide layers.