Creep properties and deformation mechanisms of a Ni2Co1Fe1V0.5Mo0.2 medium-entropy alloy

The creep properties of a Ni2Co1Fe1V0.5Mo0.2 medium-entropy alloy (MEA) in the temperature range 973–1073 K, and under the stresses 150–200 MPa, have been investigated in detail. The Ni2Co1Fe1V0.5Mo0.2 MEA possesses excellent creep properties at 973 K/150 MPa and 973 K/175 MPa. The stress exponent n was calculated to be 3.1 at 973 K, suggesting the dominance of viscous dislocation glide mechanism in creep deformation. The activation energy for creep deformation was measured to be 456.3kJ·mol−1, which is comparable to the activation energy for self-diffusion of Mo, indicating a strong effect of Mo diffusion on viscous dislocation glide. Detailed transmission electron microscopy analysis reveals: (1) increased stress and strain can alter the dislocation configurations and promote dislocation climb, and thus to increase the creep rate; (2) increased temperature and strain can lead to active recovery and recrystallisation, and thus to cause grain refinement.