Modelling and analysis of the oxidation influence on creep behaviour of thin-walled structures of the single-crystal nickel-base superalloy René N5 at 980 °C

Creep test results of thin-walled specimens of the single-crystal nickel-base superalloy René N5 at 980 °C under vacuum as well as under air show different creep properties depending on material thickness and atmosphere. The differences in creep strength and strain were analysed based on a creep-oxidation model. The model specifies the primary and secondary creep stages of thin-walled specimens by a sequence of layers. The model takes different zones affected by oxidation into account. Four layers were experimentally observed and considered in the model: oxide layer, γ′-free layer, γ′-reduced layer and the two-phase substrate in the sample as centre. Material parameters for growth laws of each layer were identified both by experimental analyses and by thermodynamic simulations. The final creep-oxidation model characterizes the creep behaviour of samples with small thicknesses and low initial stress with high accuracy.