Because atoms in high-entropy alloys （HEAs） coordinate in very different and distorted local environ- ments in the lattice sites, even for the same type of constituent, their point defects could highly vary. Therefo...Because atoms in high-entropy alloys （HEAs） coordinate in very different and distorted local environ- ments in the lattice sites, even for the same type of constituent, their point defects could highly vary. Therefore, theoretical determination of the thermodynamic quantities （i.e., defect formation enthalpies） of various point defects is rather challenging because each corresponding thermodynamic quantity of all involve constituents is not unique. The knowledge of these thermodynamic quantities is prerequisite for designing novel HEAs and understanding the mechanical and physical behaviors of HEAs. However, to date there has not been a good method to theoretically derive the defect formation enthalpies of HEAs. Here, using first-principles calculations within the density functional theory （DFT） in combina- tion of special quasi-random structure models （SQSs）, we have developed a general method to derive corresponding formation enthalpies of point defects in HEAs, using vacancy formation enthalpies of a four-component equiatomic fcc-type FeCoCrNi HEA as prototypical and benchmark examples. In difference from traditional ordered alloys, the vacancy formation enthalpies of FeCoCrNi HEA vary in a highly wide range from 0.72 to 2.89 eV for Fe, 0.88-2.90 eV for Co, 0.78-3.09 eV for Cr, and 0.91-2.95 eV for Ni due to high-level site-to-site lattice distortions and compositional complexities. On average, the vacancy formation enthalpies of 1.58 eV for Fe, 1.61 eV for Cr, 1.70 eV for Co and 1.89 eV for Ni are all larger than that （1.41 eV） of pure fcc nickel. This fact implies that the vacancies are much more difficult to be created than in nickel, indicating a reasonable agreement with the recent experimental observation that FeCoCrNi exhibits two orders of amplitudes enhancement of radiation tolerance with the suppression of void formation at elevated temperatures than in pure nickel.展开更多
基金supported by the National Science Fund for Distinguished Young Scholars (No. 51725103)by the National Natural Science Foundation of China (Grant Nos. 51671193 and 51474202)+7 种基金by the Science Challenging (Project No. TZ2016004)by the “Hundred Talented Project” of the Chinese Academy of Sciencesfinancially supported by the National Natural Science Foundation of China (Nos. 51671018 and 51671021)111 Project (No. B07003)International S&T Cooperation Program of China (No. 2015DFG52600)the Program for Changjiang Scholars and Innovative Research Team in University of China (No. IRT 14R05)the Projects of SKL-AMM-USTB (Nos. 2016Z-04, 2016-09 and 2016Z-16)supported by the Hong Kong URC grant under the contract with City University of Hong Kong
文摘Because atoms in high-entropy alloys （HEAs） coordinate in very different and distorted local environ- ments in the lattice sites, even for the same type of constituent, their point defects could highly vary. Therefore, theoretical determination of the thermodynamic quantities （i.e., defect formation enthalpies） of various point defects is rather challenging because each corresponding thermodynamic quantity of all involve constituents is not unique. The knowledge of these thermodynamic quantities is prerequisite for designing novel HEAs and understanding the mechanical and physical behaviors of HEAs. However, to date there has not been a good method to theoretically derive the defect formation enthalpies of HEAs. Here, using first-principles calculations within the density functional theory （DFT） in combina- tion of special quasi-random structure models （SQSs）, we have developed a general method to derive corresponding formation enthalpies of point defects in HEAs, using vacancy formation enthalpies of a four-component equiatomic fcc-type FeCoCrNi HEA as prototypical and benchmark examples. In difference from traditional ordered alloys, the vacancy formation enthalpies of FeCoCrNi HEA vary in a highly wide range from 0.72 to 2.89 eV for Fe, 0.88-2.90 eV for Co, 0.78-3.09 eV for Cr, and 0.91-2.95 eV for Ni due to high-level site-to-site lattice distortions and compositional complexities. On average, the vacancy formation enthalpies of 1.58 eV for Fe, 1.61 eV for Cr, 1.70 eV for Co and 1.89 eV for Ni are all larger than that （1.41 eV） of pure fcc nickel. This fact implies that the vacancies are much more difficult to be created than in nickel, indicating a reasonable agreement with the recent experimental observation that FeCoCrNi exhibits two orders of amplitudes enhancement of radiation tolerance with the suppression of void formation at elevated temperatures than in pure nickel.
