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To clarify the different effects of alloying elements on the strength of Ni and Ni 3 Al, this study employs First-principles methods to investigate the effects of refractory elements Re, Ru, Ta, Mo and W on the generalized stacking fault energy and ideal strength of Ni and Ni 3 Al, respectively. The results reveal that the alloying elements Re, Ru, Ta, Mo, and W can help to improve the creep strength of Ni but reduce that of Ni 3 Al. Among these alloying elements, Re and Ru are more helpful for improving the strength of Ni, and for Ni 3 Al, Ru has the weakest enhancing effect on the strength of Ni 3 Al. Moreover, except for Ru, other alloying elements have more significant enhancing effects on the strength of Ni 3 Al. The electronic structure analysis shows that the d orbitals of alloying elements except Ru can form deep and wide pseudogap near the Fermi energy level, which causes the obvious enhancement of the strength of Ni 3 Al. Furthermore, the regular areas of charge distribution between atom Ru and its nearest neighbor atoms Ni are more vulnerable to be destroyed, resulting in Ni 3 Al–Ru owning a relatively lower ideal tensile strength and reaches its ideal tensile strength under a smaller strain. • Re, Ru, Ta, Mo and W can help to improve the creep strength of Ni, but reduce that of Ni 3 Al. • Re, W, Mo, and Ta have more significant enhancing effects on the mechanical strength of Ni 3 Al, compare with that of Ni. • The d orbitals of Ru cannot form deep and wide pseudogap near the Fermi energy level, as other elements do. [ABSTRACT FROM AUTHOR]