An X-ray topographic study of the behaviour of vacancy loops formed during the high-temperature oxidation of magnesium crystals

Abstract

Abstract X-ray topography observations together with in situ weight-gain measurements have been used to study the defect structure of magnesium crystals oxidized at 550°C in air, as a function of oxide thickness. It is shown that during the initial stages of oxidation, i.e. where the oxide remains coherent, unfaulted loops, many with b = [0001], grow with increasing time of exposure. However, during the period of oxidation when decohesion of the metal-oxide interface becomes pronounced, the surface acts as a vacancy sink and continued annealing causes the loops to shrink and eventually disappear. The results are discussed in terms of previous electron microscopic observations reported on the oxidation characteristics of magnesium.