Effects of Ni, Cr and W on the microstructural stability of multicomponent CoNi-base superalloys studied using CALPHAD and diffusion-multiple approaches

Abstract The alloying effects of Ni, W and Cr on the microstructural stability of CoNi-base alloys were investigated using a multicomponent diffusion multiple after being aged at 1000 °C for 1000 h. The diffusion multiple was carefully designed based on thermodynamic calculations. The relationships between alloy compositions and microstructural characteristics were established over a large compositional range using this single sample, and the alloying effects of Ni, W and Cr on the elemental partitioning behaviors between γ and γ′ two phases were thermodynamically analyzed using high-throughput calculation. The results together show that an increase of Ni content increases the γ′ volume faction in the long-term aged microstructures. However, the higher Ni content leads to the precipitation of the χ phase by promoting the partitioning of W from the γ′ phase to the γ phase. The decrease of W content dramatically reduces the γ′ volume faction, but the addition of Cr can properly counteract this effect by promoting the partitioning of Al and Ti from the γ phase to the γ′ phase. This study will be helpful for accelerating the development of novel γ′-strengthened multicomponent CoNi-base alloys, as well as providing experimental data to improve the thermodynamic database.