Inhibiting effect of tensile strain on the nucleation of M₆C at grain boundary

Electron microscope was utilized to detect the nucleation of grain boundary carbides in Haynes 282 Ni-based superalloy during creep. Besides, first-principles calculations were conducted to comprehensively explore the site preference of alloying elements during the nucleation as well as the effect of tensile strain on the site preference behaviors. Experiment indicates that Mo atoms will segregate to the M₂₃C₆/Ni interface, which promotes the nucleation of grain boundary M₆C at the interface, during creep. Therefore, the site preference of Mo at the M₂₃C₆/Ni interface was calculated. The results show that the segregated Mo atoms prefer to occupy the Cr sites rather than the Ni sites. Mo will occupy the two layers of Cr sites near the interface in an alternating way. Tensile strain as well as its directions can seriously influence the site preference of Mo at the interface, while the strains with directions of [001], [101] and [111] only affect the occupation sequence of Mo, the strains with directions of [110] and [100] will inhibit the segregation of Mo by increasing segregation energy. Therefore, in general, tensile strain inhibits the segregation of Mo to the M₂₃C₆/Ni interface and thus the nucleation of M₆C at the interface.