Conventionally, nickel-based superalloys have been used as a turbine blade. The nickel-base superalloys have limitations like high cost, high density and narrow composition tailoring range. There is a need to develop alternative alloys to overcome these limitations. The emerging field of High Entropy Superalloys (HESA) has caught attention of scientists across the world because of its exciting properties especially at elevated temperature. The nickel-based HESA has been identified with typical precipitation hardened FCC γ and ordered L12 γ’ microstructure like conventional Ni-based superalloys. The densities and cost of raw materials of HESAs are lower than conventional superalloys. Chen et al. and Zhau et al. have shown HESA exhibiting better tensile properties at temperature of interest of 800 °C. Tsao et al. evaluated the creep performance of HESAs till 982 °C and the performance is comparable with CMSX-2 alloy. Hence, HESAs can potentially replace conventional superalloys.
The thermomechanical processing (TMP) can be effectively used to enhance the performance of HESAs further. TMP constitutes of a series of plastic deformation and thermal operations to tune the microstructure consequentially enhancing the mechanical performance. The plastic deformation such as rolling of metals is known to strengthen the synthesized specimen through various mechanisms. The rolling combined with optimized heat treatment enhances the tensile properties in high entropy alloys from room to elevated temperatures.
The current research involves the selection of HESA composition using the thermodynamic simulations of ThermoCalc. The γ’ precipitate volume fraction at 800 °C, γ’ precipitate solvus temperature, cost and density were considered for selection of HESA composition for further studies. The selected HESA will then be synthesized using vacuum arc melting and homogenization route. The precipitation kinetics ageing studies will be done at 700,800 and 900 °C both experimentally and with simulations using Prisma. The microstructural analysis will be done by electron microscopy. The tensile creep, and stress rupture tests will be done on aged samples at 800 °C. The deformation mechanisms of aged samples at 800 °C will be explored. The effect of different TMP routes will be evaluated on aged samples. The microstructural and mechanical characterization like aged samples will be executed. This research puts a one step forward towards engineering the HESA at elevated temperatures and replacing conventional nickel-based superalloys.


Keywords: High entropy superalloy, thermomechanical processing, tensile, creep, microstructure stability.