Abstract
The accumulation of sulphur atoms and small sulphide precipitates in oxide scales and substrates following the high temperature oxidation (at an oxygen partial pressure of 1 atm) of presulphidised Ni–Cr base alloys has been monitored by combining microstructural studies with analytical measurements. It has been shown that the distribution and chemical state of sulphur are modified according to the morphology and nature of the outer layers of oxide scale. This disturbance of the sulphur atom location influences the mechanical behaviour of the scale during isothermal oxidation and cooling treatments. Changes in scale microstructure (interfaces, precipitates, etc.) and modifications to oxidation mechanisms (cationic diffusion through the alloy and oxide, oxygen transport to the oxide/alloy interface, etc.) significantly change the stress relaxation process in the oxide scale and hence its adherence to the underlying alloy substrate.
MST/837
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