Transition metal solutes in Ni-based ternary model superalloys: Partitioning and effects on elastic properties from first-principles calculations

Alloying effects on the structural, elastic, as well as electronic properties of Ni-based model superalloys are systematically investigated by first-principles calculations. Twenty-seven transition-metal(TM) elements (3d:ScZn, 4d:Y-Cd, 5d:Hf-Au) are taken into account in Ni-based ternary model superalloys in detail for the first time. The partitioning behaviors and site preferences of ternary alloying elements are primarily predicted based on our calculated substitutional formation energies and partitioning coefficients, with previous atom probe tomography (APT) experimental results for comparison. Temperature dependence of partitioning behaviors of TM elements in model superalloys is also presented in this work. It is found that the partitioning behaviors of Cr, Mn, Tc, Ru and Os can be reversed at a specific temperature, and these elements just lie near the boundary between the two blocks of Ni-site preferences and Al-site preferences of TM elements on the periodic table. The bulk moduli, Young's moduli, shear moduli, ductile-brittle behavior, orientation-dependent elastic moduli and elastic anisotropy of Ni-based ternary model superalloys are systematically estimated. The calculated elastic parameters agree well with the available experimental results. The effects of TM elements on elastic properties are found to be closely associated with their d-electron number. The elements at the beginnings and ends of the TM series reduce these elastic properties, while the TM elements lying towards the center of each period can considerably increase these properties of superalloys, especially those elements with a half-filled d band, which exert greater influences on improving the elastic performance. Furthermore, different charge redistributions caused by each alloying addition can elucidate different effects thereof on the elastic properties of model superalloys to some extent. The stronger directional bonding and more covalent-like interaction between TM additions and host atoms lead to the superior elastic properties.