Udimet 720Li as a potential alternative for optimised aeroengine turbines: Thermophysical and thermomechanical characterisation under wide-ranging testing conditions

Abstract

The need to reduce fuel consumption and emissions is driving advances in aeroengine performance. Efficiency gains are limited by the capacity of the turbine material to withstand the high thermomechanical loads of the combustion process. Nickel-based alloy Udimet 720Li has emerged as a promising alternative to the most widely used Inconel 718 for critical aeroengine components. Nonetheless, its material properties under industry-relevant conditions remain understudied, hindering industrial implementation. Furthermore, discrepancies in the methodology for applying adiabatic heating correction in thermomechanical tests on nickel-based alloys prevent comparability of studies and alloys. This paper presents the thermophysical and thermomechanical properties of forged and heat-treated Udimet 720Li to enable advanced aeroengine design and manufacture. A novel adiabatic heating correction procedure is also proposed for thermomechanical tests. Thermophysical properties (specific heat, density, diffusivity, thermal expansion, and conductivity) were characterised for temperatures 20–1200 °C. Thermomechanical properties were obtained for temperatures 20–1100 °C and strain rates 0.01–100 s-1 with cylinder compression tests. The results show that Udimet 720Li exhibits higher thermomechanical properties than Inconel 718 at elevated temperatures and can withstand greater in-service temperatures (8–23 %) due to the higher γ’ strengthening phase content which remains stable up to 760 °C.