Effect of Synergistic Alloying of Co and Mo on Solidification Microstructure and Properties of NiAl-Based Eutectic High-Entropy Alloy

NiAl-based alloys possess desirable characteristics such as lightweight, high modulus, and excellent oxidation resistance, making them promising materials for aerospace and other applications. However, the limited room-temperature plasticity of NiAl alloy hinders its manufacturing and practical use. The incorporation of Mo and Co through alloying treatment can significantly enhance the room-temperature plasticity of NiAl-based alloys. A series of eutectic high-entropy alloys, (NiAl)65V20Cr10Mo5−xCox (x = 0, 1, 2, 3, 4, and 5), were fabricated through non-consumable vacuum melting. The influence of Co and Mo contents on the microstructure and mechanical properties of these alloys was investigated. The findings indicate that the phase composition of the alloy remains unaffected by the presence of Mo and Co in its content. With an increase in Co content and a decrease in Mo content, the primary B2 phase gradually increases in the alloy, leading to a microstructural transition from complete eutectic structure (x = 0) to hypoeutectic structure (x > 1). The strength of the alloy exhibits an initial increase followed by a decrease. At low Co contents, the fracture strength and strain of the alloy experience significant enhancement. (NiAl)65V20Cr10Mo3Co2 demonstrates superior compressive properties, with its yield strength, fracture strength, and plasticity reaching 1761 MPa, 3009 MPa, and 33.5%, respectively. The changes in the mechanical properties of alloys are primarily attributed to solid solution strengthening, lattice misfit, fine crystal strengthening, and relative variations in phase content.