The cluster-plus-glue-atom models of solid solution CuNi alloys: A first-principles study

The solid solution alloys containing short-range order (SRO) structure, such as CuNi alloys, are not well structurally described using conventional quasi-disordered models. Based on the first-principles calculations, the optimal cluster-plus-glue-atom (CPGA) models of six typical solid solution CuNi alloys were demonstrated. These CPGA models are better to be used to describe the microstructure of the six CuNi alloys at the atomic scale from the viewpoint of energy. Our further study shown that the stabilities of CPGA models are highly related to the symmetry of initial CPGA models and the aggregation degree of solute atoms in CPGA models. In the condition of low solute Ni concentration, the stability of CPGA model is mostly determined by the symmetry of initial CPGA model, the CPGA model with high symmetry is more stable. As the concentration of solute Ni increasing, the aggregation degree of solute Ni atoms in CPGA models plays more and more important role. The CPGA model with higher aggregation degree of solute Ni is more stable. The simple selection method of optimal CPGA models, therefore is proposed, and which can be extended to other bielement solid solution AB alloys with positive mixing enthalpy of A-B. Using the selected CPGA models, we found the third additive atoms having negative mixing enthalpy with solvent and solute atoms prefer to reside the central site of characteristic principal cluster (CPC) of CPGA, and thereby enhancing the stability of alloys. Our studies provide a distinctive perspective to select the optimal CPGA models of solid solution alloys containing SRO structure and design alloy using the optimal CPGA model. (C) 2017 Elsevier B.V. All rights reserved.