Influence of rhenium on γ′-strengthened cobalt-base superalloys

The element Re is known to be a very potent strengthener concerning the creep properties of Ni-base superalloys. In this paper the influence of Re on the properties of new gamma'-strengthened Co-base superalloys is addressed. Atom probe tomography reveals that Re partitions preferentially to the gamma phase, but not as pronounced as in ni-base superalloys. Nanoindentation and micro-pillar compression tests of the gamma' phase indicate an increase of the hardness and the critical resolved shear stress caused by a considerable concentration of Re in the gamma' phase. Creep investigations show that the positive effect of Re is by far not as pronounced as in Ni-base superalloys. Several effects, which can contribute to this behavior, such as the lower Re concentration in gamma and hence a slightly reduced effective diffusion coefficient, a smaller diffusion barrier of Re in Cocompared to Ni, a slightly lower lattice misfit and gamma' volume fraction of the Re-containing alloy, are discussed.