Precipitate phase heterostructures enabling the strength in Y-doped CoCrFeNi2Ti0.8 high-entropy alloys

Based on CoCrFeNi 2 Ti 0.8 high-entropy alloys (HEAs), this study systematically investigates the effect of Y content on compositions, microstructures and mechanical properties of (CoCrFeNi 2 Ti 0.8 ) 100- x Y x ( x = 0.1, 0.5, 1 and 2) HEAs from the perspectives of thermodynamic parameters, first-principles calculations and experiments, with particular emphasis on the underlying strengthening mechanisms. It has been confirmed that Y addition promotes the formation of a multiphase heterostructure consisting of a soft FCC matrix and hard intermetallic phases. And increasing the content of Y significantly enhances the volume fraction of hard phases and refines the grains. Hence the addition of Y can effectively improve the mechanical properties of (CoCrFeNi 2 Ti 0.8 ) 100- x Y x HEAs, but often at the expense of reduced ductility. Among them, Y1.0 alloys exhibit the highest yield strength (1380.3 MPa) without sacrificing too much strain (18.7%). It is attributed to the heterostructure of Y1.0, comprising a soft FCC matrix and hard phases ( η -Ni 3 Ti, σ and Ni-Y phases). This structure promotes synergistic back stress and forward stress interactions, enabling simultaneous strength improvement without severe ductility loss. Additionally, first-principles calculations reveal that Y atoms lead to an increasing number of Ni-Y phases, meaning that the proportion of ionic bonds gradually increases. Consequently, precipitation strengthening becomes the dominant mechanism in Y1.0 alloys, and the addition of Y simultaneously refines the grains, enhancing the grain boundary strengthening. As a result, a high strength and good plasticity is realized in Y1.0 HEAs.