High-throughput exploration of alloying effects on the microstructural stability and properties of multi-component CoNi-base superalloys

Abstract The effects of substituting W with γ′ formers (Al, Ti, Ta, Mo and Nb) on the microstructural stability of a base model superalloy Co-20Ni-7Al-8W-1Ta-4Ti were studied using a high-throughput diffusion-multiple approach. A substantial amount of composition-microstructure data was obtained from a single sample, enabling deeper understanding of the alloying effects. It was found that alloy 15Al0W still contains stable γ′ phase at 1000 °C for 1000 h even with a W content of zero. However, the γ′ volume fraction of this alloy was far lower than other W-containing alloys, indicating that W plays an important role on retaining the stability of the γ′ phase. Except for Ti, substituting W with other γ′ forming elements promotes the precipitation of detrimental phases, with a potency of Nb > Ta≈Al > Mo > Ti. The Nb content should be carefully controlled due to its strong effect on inducing the precipitation of the χ phase. The literature data for W-free alloy systems were discussed in comparison to the current W-containing alloy system in order to analyze the role of W in stabilizing the γ′ phase at high temperatures. Furthermore, the γ′ strength and density of more than 300 alloys from the investigated diffusion multiple were analyzed using classic models established for Ni-base superalloys, to guide the alloy design aiming to achieve higher strength to weight ratio. The substitution of W with Ti or Al could significantly reduce the alloy density, but would also decrease the γ′ strength to some extents. These negative effects could be counterbalanced by moderate additions of Ta and Nb. This study will be helpful for the accelerated design of multi-component CoNi-base superalloys to achieve light weight and high strength.