Composition design of nickel-base superalloys based on cluster structural model

Composition of Ni-base superalloys was investigated using a cluster-plus-glue-atom model, then a basic Ni-Cr binary cluster lormula [Cr-Ni₁₂] Cr₃ was proposed where [Cr-Ni₁₂] cluster was a Cr-centered cuboctahedron surrounded by 12 Ni atoms in FCC lattice and three Cr atoms represented glue atoms. By alloying the basic cluster formula, Ni-base alloy series with a general cluster model [(Al/Ti/Nb)-(Ni/Fe/Co)₁₂] (Cr/Al)₃ were designed. φ10 mm alloy rods were prepared and heat-treated at 1373 K for 2 h. Experimental results show that the alloys with one Al atom in cluster formula have extremely line γ' particles precipitated in the γ matrix which has a weak strengthening effect. In contrast, a lot of larger γ' particles with a size range of 30 ~ 60 nm precipitated in the [Al-(Ni₁₀ Fe₂)] (Cr₂Al) alloy with two Al atoms, thus the hardnesses ol the alloys are improved. That Al, Ti and Nb occupied the cluster center in equal proportion makes the [(Al_1/3 Ti_1/3 Nb_1/3)-(Ni₁₀ Fe₂)] Cr₃ alloy have the highest hardness, being 2.86 GPa.