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

The creep properties of a Ni ₂Co ₁Fe ₁V _0.5Mo _0.2 medium-entropy alloy (MEA) in the temperature range 973–1073 K, and under the stresses 150–200 MPa, have been investigated in detail. The Ni ₂Co ₁Fe ₁V _0.5Mo _0.2 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 456.3 kJ · mo l − 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.