TEM observation and computer simulation of the interaction of superlattice dislocations with disordered γ-precipitates in L1 2-ordered γ′-(Ni,Co) 3(Al,Ti) intermetallics

Abstract

(Ni,Co) 3(Al,Ti)-based L1 2-long-range ordered γ′-intermetallics are strengthened by coherent precipitates of the disordered γ-phase because of the interaction between the superdislocations and the γ-precipitates. This interaction has been studied by transmission electron microscopy (TEM) during and after deformation of a Ni 69Co 9Al 18Ti 4 alloy at room temperature. Most superdislocations in the γ′-matrix are of screw character. They are dissociated dominantly into two unit 1/2〈110〉 dislocations separated by an antiphase boundary (APB), but also into two Shockley 1/3〈112〉 superpartials separated by a superlattice intrinsic stacking fault (SISF). The superdislocations with APBs are strongly attracted by the γ-precipitates. Their movement is jerky. On the other hand, the movement of the 〈110〉 superdislocations with SISF-ribbons depends on the configurations of the Shockley 1/3〈112〉 superpartials. The Shockley superpartials with sessile configurations are characterized by the straight SISF-ribbon edges parallel to 〈110〉 due to cross-slip from the SISF-ribbon planes onto cube planes, while the curved glissile Shockley superpartials move in the SISF-ribbon planes in a jerky way. The dislocation movement in the γ-strengthened γ′-matrix has been simulated in the computer.