Solid solutioning in equiatomic alloys: Limit set by topological instability

• A series of fcc structured equiatomic solid solutions were designed.
• The solid solution limit in multi-component equiatomic alloys was explored.
• Topological instability sets the solid solution limit.
• Decomposition occurs when the lattice strain reaches a critical value of 0.018.

Solid solutioning in equiatomic alloys becomes an interesting and timely topic, considering the current interest at high-entropy alloys (HEAs) in the materials community. In the circumstances where there is no such a differentiation of the solvent and solutes, it is intriguing to explore the solid solution limit in HEAs. In this work, a series of fcc structured equiatomic alloys were specially designed, following the valence electron concentration rule, to study the solid solutioning in the assumed pseudo binary Ni–X (X = Co, Fe, Cr, Cu) systems. The solid solution limit of the multi-component equiatomic alloys was found to set by the topological instability. The decomposition of the single-phase solid solution occurred when the lattice distortion reached a critical strain of 0.018.