Micro-diffusion phase-field study on heterogeneous interface structure and precipitation mechanism of Ni59Al22V19 medium entropy alloy

Abstract

A micro-diffusion phase-field model based on the atom occupancy probability of single lattice point was presented to describe the phase transition process, the heterogeneous interface structure and composition evolution of Ni59Al22V19 medium entropy alloy during phase transformation at atomic scale. It is found that in the early stage of Ni59Al22V19 medium entropy alloy precipitation, L12 and a small amount of ordered phase of DO22 and L10 are precipitated. As the aging process goes on, the coexistence of L12 and DO22 is formed in the aging process and four kinds of heterogeneous interfacial structures are found. At the initial phase of phase transformation, interfacial structures of A play a dominant role. With the growth and decomposition of the ordered phase, the number of interfacial structures of A decreases while the number of interfacial structures of D increases; in the Ni59Al22V19 medium entropy alloy the ordered domain boundaries provide Al atoms for the growth of L12 during the precipitation process until the alloy reaches equilibrium. During the precipitation process, the precipitation mechanism of γ′ phase is compositional ordering and instable decomposition mechanism, and the precipitaion mechanism of phase θ is instable; the interaction potential between Ni-Al first neighbor atoms increases with the increase of the long program parameters and is proportional to the temperature, the incubation period of medium entropy alloy in Ni59Al22V19 becomes longer with the increase of temperature.

Keywords

• ni59al22v19 medium entropy alloy
• heterogeneous interface structure
• micro-diffusion phase field method
• ordered phase precipitation mechanism