The requirement to improve engine efficiency continues to stimulate the development of new nickel-based superalloys with exceptional strength and thermal stability. Recent studies have reported a novel y-y′-y″ dual-superlattice superalloy, with promising mechanical properties up to elevated temperatures. [1,2] The present work studies the effect of additions of Mo, W and Fe as well as variations in Nb and Al contents on the phase fraction, thermal stability, elemental partitioning, and mechanical properties of this alloy through a combination of heat treatments, scanning electron microscopy, atom probe tomography and hardness testing. 

The alloying additions were shown to have a strong effect on microstructure and partitioning, particularly 1.8 at.% Mo, which minimised microstructural coarsening during heat treatments while not significantly decreasing the y′ solvus temperature. A reduction of Nb by 0.6 at.%, strongly reduced the y′′ volume fraction, without affecting the y′ volume fraction. The reduced precipitate fraction led to a significant reduction in alloy hardness. Fe, substituted for Ni to achieve better processability and reduced material cost, decreased the y′ solvus temperature and caused more rapid microstructural coarsening during heat treatment but did not have an apparent effect on the alloy hardness. A reduction of Al by 0.4 at.%, reduced the y′ volume fraction and the y′ solvus temperature, without reducing alloy hardness. The addition of 0.9 at.% W decreased the y′ solvus temperature but increased both precipitate volume fractions. These data will be invaluable to inform future alloy design efforts.