Mechanical Behavior Of High Principal Element Hexagonal Close Packed Rare-earth High Entropy Alloys

Due to the excellent properties of high-entropy alloys(HEAs),HEAs in the center of the phase diagram have been extensively developed.The hexagonal close-packed(HCP)structure is one of the three most common structures in metals and alloys.In contrast,HCP HEAs are rarely found compared to the other two kinds with face-centered cubic(FCC)and body-centered cubic(BCC)structures.The good news is that many rare-earth HEAs with HCP structures are newly developed.As a result,the development and properties of these HCP HEAs have become a research hotspot in the materials community.However,the systematic studies on HCP HEAs are yet to be conducted,including mechanical properties at room temperature as well as deformation mechanisms during tensile deformation.Specially,the deformation behavior of HCP HEAs under high strain rates is evaluated since it is inevitable for materials under complex environments.It is of great significance to explore the tensile deformation behavior of HCP HEAs upon quasi-static and dynamic at room temperature.In the present work,the novel Sc YLa Gd Tb Dy Ho Er Lu(R1)and Sc YLa Nd Gd Tb Dy Ho Er Lu(R2)rare-earth HEAs that breaks through the current principal element limit were designed by the "likes dissolve each other" characteristics and empirical parameters of rare-earth elements.The microstructure and mechanical properties of the alloys under quasi-static and dynamic conditions were studied in detail.The following conclusions are reached:(1)The R1 and R2 rare-earth HEAs with HCP structures were prepared.The lattice constant,melting point,bulk elastic modulus,Young's modulus,and shear modulus of both alloys are in accordance with the “rule of mixture”.The hardness and compressive yielding strength of the R1 and R2 alloys are higher than the experimental values calculated by the rule of mixture,and there is obvious strengthening.(2)The main strengthening mechanism in rare-earth HEAs is solid solution strengthening upon room-temperature compression.The compressive yielding strength of the current HCP HEAs can be well predicted by the modified Labush equation.As the number of the composition element in the multicomponent alloy is increased,the solid solution strengthening becomes more obvious.The R1 and R2 rare-earth HEAs display the tensile ductility of 12.2% and 14.4% upon roomtemperature quasi-static compression tension,respectively.(3)Rare-earth HEAs exhibits significant positive strain-rate sensitivity upon dynamic compression and tension at room temperature.Unlike upon the quasistatic loading,the dislocation slip becomes the dominant mechanism accommodating plasticity under dynamic compression for the R2 rare-earth HEAs.