A New Model of Stress Generation During Scale Growth Limited by Cation/Vacancy Diffusion

Abstract

The stress generation during growth of cation-diffusing scales on pure metals is described in terms of intrinsic misfit for a grain boundary in oxides. This model is derived from the experimental observations by means of in situ x-ray strain measurements for the oxides grown on single crystal surfaces of copper. A change in the grain boundary structure which occurs by altering the relative amount of the twin-related oxide orientations present in the oxides on (001) or (111) face of copper leads to a change in the stress generation behavior. Compressive stresses are observed in the oxide with scale thickness of a few micrometers below the brittle-ductile transition temperature of the bulk oxide(300 ~ 400°C). The model which is based on the coincident site lattice model may explain the origin of stresses arising during the growth of cation-diffusing scales at rather moderate temperatures.