TEM OBSERVATION AND COMPUTER-SIMULATION OF THE INTERACTION OF SUPERLATTICE DISLOCATIONS WITH DISORDERED GAMMA-PRECIPITATES IN L1(2)-ORDEREDGAMMA'-(NI,CO)(3)(AL,TI) INTERMETALLICS

(Ni,Co)(3)(Al,Ti)-based L1(2)-long-range ordered gamma'-intermetallics are strengthened by coherent precipitates of the disordered gamma-pha se because of the interaction between the superdislocations and the ga mma-precipitates. This interaction has been studied by transmission el ectron microscopy (TEM) during and after deformation of a Ni69Co9Al18T i4 alloy at room temperature. Most superdislocations in the gamma'-mat rix are of screw character. They are dissociated dominantly into two u nit 1/2[110] dislocations separated by an antiphase boundary (APE), bu t also into two Shockley 1/3[112] superpartials separated by a superla ttice intrinsic stacking fault (SISF). The superdislocations with APBs are strongly attracted by the gamma-precipitates. Their movement is j erky. On the other hand, the movement of the [110] superdislocations w ith SISF-ribbons depends on the configurations of the Shockley 1/3[112 ] superpartials. The Shockley superpartials with sessile configuration s are characterized by the straight SISF-ribbon edges parallel to [110 ] due to cross-slip from the SISF-ribbon planes onto cube planes, whil e the curved glissile Shockley superpartials move in the SISF-ribbon p lanes in a jerky way. The dislocation movement in the gamma-strengthen ed gamma'-matrix has been simulated in the computer. (C) 1997 Elsevier Science S.A.