Perturbation of Parabolic Kinetics Resulting from the Accumulation of Stress in Protective Oxide Layers

Abstract

A frequent observation in metal oxidation is the development of subparabolic kinetics, variously described as cubic or quartic. Although a number of detailed mechanisms have been proposed to account for this effect, none seem generally applicable. This paper presents a model of the oxidation process which is divorced from such restrictions. It is argued that deviations from parabolic behavior occur as a result of the concurrent development of stresses within the oxide. It is shown that the presence of stress fields can influence significantly the rate of transport of vacancy defects within the oxide such that tensile stresses produce positive deviations and compressive stresses, negative deviations from parabolic behavior. The model is applied in detail to Zircaloy‐2 oxidation at 773°K. It is predicted that the kinetics should be insensitve to the oxygen potential of the environment and this has been confirmed by previous experimental work. In addition, the absolute value of the oxidation rate is closely predicted using measured values of diffusion coefficients and the observed gradual departure from parabolic kinetics with increasing oxide thickness is accounted for.

Oxidation kinetics of Y‐doped FeCrAl‐alloys in low and high pO2 gases

“…compressive oxide growth stress, which was claimed to affect the chemical potential of the mobile species in the scale. This was shown in earlier studies to be the case for zirconia scales on Zircalloy [7]. For FeCrAlY-alloys, however, no experimental evidence has been so far presented supporting the effect of the growth stress on the oxide scale growth rate.…”

Surface Chemistry and Extreme-Pressure Lubricant Properties of Dimethyl Disulfide

“…Films up to ∼20 µm in thickness are formed, and the shape of the curve for films grown at 575 K is parabolic where the film thickness X varies with time as X 2 ∝ t. This has been shown to be due to a growth mechanism in which the kinetics are limited by transport through the film. [37][38][39][40][41][42] At lower temperatures (523 K), the growth curve is essentially linear with time, suggesting that film growth is limited by the thermal decomposition of dimethyl disulfide at the surface. Note that these growth modes are essentially identical to those found for the thermal decomposition of CH 3 SH on iron.…”

Mechano-Chemical Aspects of High Temperature Oxidation: A Mesoscopic Model Applied to Zirconium Alloys

“…9,10 While the presence of high compressive stresses in the oxide layer was clearly demonstrated, their consequences on oxidation kinetics are still under discussion. A first idea was proposed by Evans 11 who related the variation of compressive stresses to the particular kinetics law followed by zirconium alloys during the pre-transition regime. During this regime, zirconium alloys obey the so-called "sub-parabolic" kinetic law, which means that the weight gain per surface unit can be written as:…”