Some factors influencing the adherence of oxides on metals

Abstract

Abstract Some of the differences in adherence behaviour may be explained by differences in the respective physical properties of the films and the metals. The strength and plasticity of some of the oxides has been measured; the relative expansion coefficients are also important and it is thought to be the favourable nature of this which is responsible for the good adherence of NiO on nickel and more complex films on nickel‐base alloys. Another important factor is internal stress. The sources of stresses during the oxidation of copper have been estimated using a unilateral oxidation technique. With sufficient knowledge of the mechanical properties it is possible to calculate the actual stress levels in the growing oxide film. A further factor influencing adherence is the accumulation of trace or residual elements on the metalloxide interface. The technique of Peters and Engell has been used to estimate the effect of various elements at a concentration of 0.4 wt% on the adherence of scales on iron. The results fall into four groups; those that form mixed oxide scales with wüstite either spalled or were weakly adherent; those on noble metal alloys were nearly comparable with pure iron, but copper and tin had a detrimental effect. Scales containing As, Sb and P were weakly adherent but left a thin adherent layer on the metal surface. Cobalt and niobium had no effect.