The impurity formation energies of the sigma and gamma phases of Ni-based single crystal superalloys doped with W, Cr and Co in different sublattices have been investigated using first-principles based on the density functional theory. The bonding characteristics of the doped a phase were analyzed with the valence charge densities and the density of the states. The results of the calculations indicated that the typical refractory element W, which has a large atomic size, preferentially partitions into the sigma phase due to the nature of the bonding and the unique crystal structure with close-packed planes and large interstitial spaces. In addition, the site preference of refractory elements in gamma phase was in the order of W, Cr and Co. (C) 2014 Elsevier B.V. All rights reserved.