Influence of Microstructure on the Mechanical Properties of Ground State Structures in Substitutional Ordered Alloys

Experiments confirm the co-existence of ground state crystal structures in ordered alloys predicted from first-principles calculations using the disorder-to-order transformation in Ni₄Mo alloy as a model system. However, it is demonstrated that knowledge of atomic arrangements in these structures may not be sufficient to predict properties due to the influence of microstructure. Spontaneous recrystallization in the Ni₄Mo alloy is found to embrittle an otherwise intermetallic compound with ground state structure combining high strength and high ductility. It is concluded that ground state structures determined from first-principles calculation may not necessarily play a governing role in the case of Ni₄Mo alloy due to the microstructural effect.