Tensile behavior of single crystal nickel-based superalloys at 650°C

Abstract

The yield strength (YS) of single crystal Ni-based superalloys is a critical factor for low temperature low cycle fatigue and Out-of-phase thermomechanical fatigue durability of turbine blades. The chemical composition of this class of alloys appears to have a major role in their low temperature tensile behavior. Indeed, alloying elements modify the antiphase boundary (APB) energy of the γ′ phase and so its resistance to shearing. To investigate the influence of the chemical composition on the YS, 18 superalloys of different generations were tensile tested at 650 °C. The results show a significant YS evolution of up to 250 MPa between the first generation and the following generations. The YS differences are mainly attributed to the contributions of γʹ which in turn is dependent on the γʹ phase composition. An EDNNB model was adapted to estimate the APB energies for the aforementioned set of alloys using Thermo-Calc data. Ta and Ti elements appear to be the most efficient γ′ strengtheners. The higher their content is, the higher the APB energy is and the stronger the alloy is in terms of tensile YS. Several alloys also exhibit an important strain hardening.