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Report No.
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Mechanism of excellent mechanical properties in BCC refractory high-entropy alloys

Tsuru, Tomohito   ; Lobzenko, I.   

High-entropy alloys (HEAs) have received attention for their excellent mechanical and thermodynamic properties. Especially some body-centered cubic (BCC)-HEAs have an excellent balance between high strength and elongation. BCC-HEAs containing specific elements show unusual slip traces. It is essential to understand the atomic-level depiction of defect structures considering the effects of the constituent elements to elucidate the origin of excellent mechanical properties of HEA. The core structure and motion of dislocations should be the key to identifying the unique feature of the mechanical properties of HEAs. It is worthwhile considering the difference between the two BCC-HEAs, VNbMoTaW and TiZrNbHfTa. We believe that the origin of significant lattice distortion, unusual dislocation core structure, and slip trace is derived from the existence of the group IV elements such as Ti and Zr with a sufficient concentration. In the present study, we investigate the dislocation score of in BCC-HEAs using the first-principles calculations. We modeled randomly-distributed ternary- and quinary alloys with equiatomic fractions. We explored the effect of local lattice distortion and chemical composition on mechanical properties. As a result, the mean square displacement (MSAD) of TiZrNbHfTa was quite large, corresponding to over 6% of the Burgers vector. This extremely large lattice distortion must strongly influence the mechanical properties since the friction stress of dislocation motion definitely increases.

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