Effects of aging treatment on the evolution of precipitated phase in CoCrFeNiTi0.6 high entropy alloys

Abstract

In this study, the effect of aging time on the microstructure of precipitates in a face-centered cubic (FCC) CoCrFeNiTi0.6 high-entropy alloy (HEA) was investigated. The microstructure of precipitates was analyzed by SEM and TEM. The results showed that the CoCrFeNiTi0.6 alloy exhibited a typical dendritic structure, whose phase consisted of an ordered FCC solid-solution matrix (nanoscale L12-(Ni, Co)3Ti type particles) and intermetallic phases at 900 °C for different aging times. Meanwhile, the intermetallic compounds were composed of (Cr, Fe)-rich σ phases with a tetragonal structure and (Ni, Ti)-rich η phase with a long period stacking ordered (LPSO) structure. Additionally, the influence of aging time on the shape and structure of γ' precipitates was revealed. It was noticeable that the morphological transformation of nanoscale γ' precipitates evolved from an initially spheroidal to spheroidal-like shapes, following cuboidal-like shapes with flat edges, and finally, γ' precipitates with cuboidal shape were formed simultaneously with the appearance of the split with increasing aging time. Furthermore, the morphological evolution of γ' precipitates was quantitatively analyzed using a characteristic parameter's value of precipitates based on lattice misfit between the matrix and precipitates. This research would provide guidance for designing the precipitate structure in the L12-strengthened HEA and facilitate to establish the relationships between the microstructure of the precipitates and properties.