⟨10 0⟩ Dislocations in nickel-base superalloys:: Formation and role in creep deformation

a (10 0) Dislocations are observed in nickel-base superalloys after creep deformation at high temperatures and low stresses. They are formed in the gamma/gamma' interfaces by a three step mechanism. First, primary dislocations with Burgers vector a/2 < 101 > and 60 degrees character are left behind in the interfaces when dislocation loops glide through the gamma channels. The 60 degrees dislocations move into edge orientation and react forming secondary dislocations a/2 < 110 >. In the third step, new primary dislocations are knit into the already existing meshes of primary and secondary dislocations, which results in hexagonal misfit dislocation networks consisting of secondary dislocations a/2 < 110 > and tertiary dislocations a < 100 >, both of edge type. This self-organisation process is explained by dislocation theory and crystallography. Creep deformation accelerates when the a < 100 > interfacial dislocations enter the gamma' phase. During their climb towards the opposite interface, they attain a characteristic rectangular shape. This shape and the importance of the a < 100 > super dislocations for creep deformation are discussed. (c) 2005 Elsevier B.V. All rights reserved.