Oxygen diffusion studies in oxide scales thermally grown or deposited on mechanically loaded metallic surfaces (MS-P2)

Abstract

The high temperature growth of oxides on metallic surfaces mechanically in loading is not well understood yet. The knowledge of the growth of oxides on static surfaces and of the mechanical behavior of the metal/oxide system does not give account of the synergetic effects between the load and the growth of the oxide. The formation of cracks on the oxide scales, their healing and the role of the load on the oxygen diffusion processes have been studied on pure nickel and zirconium samples in creep. The use of oxygen-18 to study the oxygen diffusion and the determination of local oxygen-18 diffusion profiles with use of the nuclear reaction 18O(p, α) 15N show a sharp influence of the load. The application of the load induces an increase of the oxygen diffusion coefficients until two orders of magnitude (typically from around 10 −15 cm 2 s −1 to around 10 −13 cm 2 s −1 in NiO thermally grown on nickel monocrystals). However, this enhancement decreases with the increase of the load. As the oxide scales are multilayered and as spalling and regrowth may occur, RBS mapping of the local thickness of the oxide stripes is also performed. This technique helps in understanding the formation of the microstructure and of the damaging process during the mechanical loading.