Excellent thermal stability and their origins in γ′ precipitation-strengthened medium-entropy alloys

The outstanding thermal stability of coherent γ′ phases at 1073 K in Ni₄₆Cr₂₃Fe₂₃Al₄Ti₄ and Ni₄₆Cr₂₃Co₂₃Al₄Ti₄ medium-entropy alloys were systematically investigated. The coarsening behaviors of coherent γ′ phase in the investigated alloys follow the classical Lifshitz-Slyozov-Wagner (LSW) model. The γ/γ′ lattice misfit plays an important role in the morphology evolution and coarsening behavior of γ′ phase. The lower γ/γ′ lattice misfit helps to maintain the spherical morphology of γ′ phase and leads to a lower γ/γ′ interfacial energy. The small γ/γ′ lattice misfit (0.087%) and interfacial energy (1.73 mJ/m²) in Ni₄₆Cr₂₃Fe₂₃Al₄Ti₄ alloy result in the sluggish coarsening behavior of coherent γ′ phase. Reducing γ/γ′ lattice misfit and decreasing interfacial energy should be effective strategies for developing γ′-strengthened high/medium-entropy alloys for high-temperature application.