Influence of the Co/Ni Ratio and Dendritic Segregations on the High-Temperature Oxidation Resistance of Multinary Co-Rich Superalloys at 850 °C and 1050 °C

Abstract Excellent inherent oxidation resistance is a prerequisite for the use of superalloys in many high-temperature applications. To achieve this goal, typically continuous alumina and chromia scale growths are assured through sufficient Cr Al additions. Since intended γ / ′-microstructure only stable within certain compositional window, maximum concentrations these protective forming elements are, however, dependent on overall alloy composition. The latter severe drawback, especially Co-rich superalloys, as content often insufficient reaching desired growth. In recent years, addition significant Ni levels was identified to improve properties case simple model systems. study, we compare behavior two complex multinary single-crystalline ′-strengthened that differ regarding their Co/Ni ratios commercial Ni-base superalloy CMSX-4. Therefore, time-resolved isothermal gravimetric analysis (TGA) synthetic air at 850 °C 1050 100 hours, scanning electron microscopy (SEM), probe microanalysis (EPMA) were conducted. results point out high Co-content beneficially affects °C, meaning CMSX-4 slightly outmatched by competitors. contrast, (most Ni-rich) performed best and, clearly, an increasing deteriorate resistance. This temperature-dependent influence nominal ratio shown be pronounced dendritic regions. Consequently, could determine kinetics.