Thermal Oxidation Mechanism of W-1.1wt% Ni Films Sputtered on Steel

Abstract

W-1.1 wt.%Ni films having a beta-W structure were deposited on a steel substrate by using the magnetron sputtering method. Their oxidation resistance in air was inferior at temperatures above 600 degrees C due mainly to the formation of tungsten oxides. They oxidized to an outer NiO layer that was formed by outward transport of Ni and an inner (WO3 + NiWO4)-mixed oxide layer that was formed by the inward diffusion of oxygen. At the same time, substrate elements, such as Fe and Cr, diffused outward toward the film surface to be incorporated in the oxide layer.