Surface-Roughness Effects on Creep Performance in Ni-Based Single-Crystal Superalloys

Ni-based single-crystalSingle-crystal superalloysSuperalloys must endure high-temperatureHigh temperature oxidation applications where creepCreep is the main cause of failure. CoatingsCoating to protect against oxidationOxidation are not always applicable and oxidationOxidation should, therefore, be factored in. Thermogravimetric analysesThermogravimetric analysis were performed at 1000 °C on René N4 to obtain the oxidationOxidation rate \({K}_{p}\) depending on the surface roughness. It was observed a strong nonlinearity attributed to a transition between chemisorption and physisorption. The evolution of the oxidationOxidation rate was then phenomenologically modelled combining Lennard–Jones-type and Gaussian-type equations. The obtained expression was then implemented in a crystal-plasticity model used to predict the lifetime variation depending on the initial value of the surface roughness. The predicted lifetimes were then compared to the creepCreep experiments at 1000 °C/200 MPa. The evolution of the lifetime depending on the surface roughness matches the evolution of the oxidationOxidation rate depending on the roughness and, therefore, the model predictions. Clearly, the results point to the importance of considering the contribution of surface roughness not only for fatigueFatigue loading but also to creepCreep, which will allow to better understand creepCreep-fatigueFatigue interactions.