Effects of Cr and Al/W ratio on the microstructural stability, oxidation property and γ′ phase nano-hardness of multi-component Co-Ni-base superalloys

Three Co-30Ni-xAl-(15-x)W-1Ta-4Ti-yCr septenary alloys were systematically studied with the aim of developing multiple-component Co Ni-base alloys with balanced properties. The microstructural stabilities were investigated at 1000 degrees C and 1100 degrees C after long-term aging. The experimental results indicate that increasing the Cr content significantly reduces the microstructural stability and promotes the precipitation of mu phase; while increasing Al/W ratio increases the gamma' volume fraction and the gamma/gamma' lattice misfit. At the same time, increasing the Cr content increases the hardness of gamma' phase and increasing Al/W ratio shows the opposite effect. The APT results reveal that such effects should be mainly attributed to the change of elemental partitioning behaviors between the gamma and gamma' phases. Furthermore, increasing the Cr content and Al/W ratio predominantly enhances the oxidation resistance at 1000 degrees C, resulting in promising oxidation property which is comparable to commercial Ni-base superalloys Waspaloy and Udimet 720. Finally, the well balance of the microstructural stability, alloy density, gamma' phase hardness and oxidation resistance can be achieved. This study will be beneficial for the continuous efforts on the development of multi-component Co Ni-base superalloys for industrial applications. (C) 2020 Elsevier B.V. All rights reserved.