METHODS OF MEASURING OXIDATION GROWTH STRESSES

Stresses developed isothermally at temperature in both the oxide layer and metal substrate as a consequence of the oxidation process are known as 'growth stresses'. They seem to be an indigenous feature of all oxidation systems and, consequently, offer a potential threat to the long-term integrity of protective oxide layers. To be in a position to provide a comprehensive prediction of lifetime behaviour, it then becomes necessary to characterize the growth stresses for any particular metal/oxide system of interest. An important part of this process is the measurement of both the sign and magnitude of the stresses produced. This paper surveys current experimental methods of performing such measurements and pays particular attention to the advantages and disadvantages of each. Accordingly, critical descriptions are provided of mechanical methods, where shape changes are analysed to deduce the level of stress, X-ray diffraction techniques and also the emerging application of Raman microscopy.