〈1 0 0〉 Dislocations in nickel-base superalloys: Formation and role in creep deformation

Abstract

a〈1 0 0〉 Dislocations are observed in nickel-base superalloys after creep deformation at high temperatures and low stresses. They are formed in the γ/γ′ interfaces by a three step mechanism. First, primary dislocations with Burgers vector a/2〈1 0 1〉 and 60° character are left behind in the interfaces when dislocation loops glide through the γ channels. The 60° dislocations move into edge orientation and react forming secondary dislocations a/2〈1 1 0〉. 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〈1 1 0〉 and tertiary dislocations a〈1 0 0〉, both of edge type. This self-organisation process is explained by dislocation theory and crystallography. Creep deformation accelerates when the a〈1 0 0〉 interfacial dislocations enter the γ′ phase. During their climb towards the opposite interface, they attain a characteristic rectangular shape. This shape and the importance of the a〈1 0 0〉 super dislocations for creep deformation are discussed.