The growth activation energy of sigma phase in nonequal molar CoCrFeNiV low entropy and high entropy alloys

Abstract

The present study investigates the as-cast state, as-homogenized state, and as-aged states with precipitation properties of CoxCrxFexNi60–2xV40-x alloys in low entropy alloy (x = 1, 2, and 5) and high entropy alloy (x = 10, 15, and 20). After solid solution treatment, the phase stability of six alloys are compared individually, and the formation of the σ phase has been comprehensively calculated and predicted by the parameters of valence electron concentration (VEC) and paired σ phase forming elements (PSFE), which results in a structure comprising both FCC and σ phases. As increasing the vanadium, exceeding the criteria for solid solution in high-entropy alloys, the as-homogenized state and as-aged states are precipitated with sigma phases. Using the Modified Johnson-Mehl-Avrami-Kolmogorov theory, the precipitation growth activation energy is estimated through hardness tests in low entropy and high entropy alloy. It was observed that for low entropy alloys, the activation energy increases with increasing configurational entropy. In contrast, for high entropy alloys, the influence of entropy diminishes, while the sluggish diffusion effect becomes more pronounced.