Vacancy mediated alloying strengthening effects on γ/γ′ interface of Ni-based single crystal superalloys: A first-principles study

The vacancy effects on the site preferences of alloying elements Re, Mo, Ta and Cr at gamma/gamma' interface are studied using first-principles density functional theory. The alloying strengthening mechanism mediated by vacancy is also evaluated via calculating the Griffith work of fracture for gamma/gamma' interface as well as the energy barrier of vacancy migration at the interface. The calculated results show that a Ni vacancy on (001)gamma' plane does not change the most preferable substitution position of the alloying elements at corner-point Ni site on (001)gamma except Cr. These alloying elements in gamma' enhance the interfacial bonding strength of gamma/gamma' interface even with the presence of a neighboring vacancy, among which Re exhibits the best strengthening effect. The improvement in the gamma/gamma' interfacial strength is ascribed to the increased chemical bonding strength between the alloying atom and the nearest-neighbor host atom. Furthermore, a single Ni vacancy has higher migration energy barriers around the alloying solutes especially Re solute substituting on (001)gamma at gamma/gamma' interface, although the alloying solutes at these preferable sites have no contribution to the interfacial bonding strength. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.