Dislocation microstructure in a single-crystal nickel-based superalloy after tensile testing at 823 K in the [001] direction

In the two phase Ni-based superalloy SRR 99, deformation mechanisms are analysed after tensile testing at 823 K in the [001] direction. Deformation starts by octahedral glide of screw dislocations in the matrix and creation of long 60° segments in the γ-γ interfaces. After 1% strain, γ' precipitates are cut by pairs of 60° dislocations which create long screw superdislocation dipoles. Dipole annihilation causes constant dislocation density in the γ' phase. Antiphase-boundary energies in the ordered phase are anisotropic. Concerning dislocation pair configurations the criterion for cross-slip developed by Paidar, Pope and Vitek and by Yoo is modified. The relations between microstructure and mechanical behaviour are discussed.