Effect of Ti, Ta, Nb on structural transformation of Ni3Al in terms of stacking faults.

This study explored the structural stability, elastic properties, structural transformation, and critical concentration of Ni3Al and Ni3M (M = Ti, Ta, Nb) using L12, D024, and DO22 structures, along with three-dimensional supercells featuring stacking faults along [ 10 1 ¯ ] , [ 01 1 ¯ ] , [111] directions. First-principles calculations revealed that the most stable structures for Ni3Al, Ni3Ti, Ni3Ta, and Ni3Nb are L12, D024, DO22, and DO22, respectively. Notably, the bulk modulus, Young′s modulus, shear modulus, and isotropy of Ni3Ti, Ni3Ta, and Ni3Nb surpassed those of Ni3Al, with increased ductility, except for Ni3Ti. By substituting Al atoms with 0–8 Ti, Ta, and Nb atoms in a 32-atom Ni3Al structure, the critical concentration for the transformation from L12 to D024 or DO22 ranged between 18.75 at. % and 21.88 at. %, and between 15.63 at. % and 18.75 at. %, respectively. This critical concentration was influenced by the dynamic interplay among Ti, Ta, Nb, and Al atoms interacting with Ni atoms. The structural transformation from L12 to D024 or DO22 can be attributed to the reduction in the superlattice extrinsic stacking fault energies or the anti-phase boundary energies, respectively, a consequence of the redistribution of charge density between Ti, Ta, Nb atoms and Ni atoms. [ABSTRACT FROM AUTHOR]