Influence of rhenium on the microstructures and mechanical properties of amechanically alloyed oxide dispersion-strengthened nickel-base superalloy

The influence of a 3wt% Re addition on the creep strength and microstructur e of a mechanically alloyed and oxide dispersion-strengthened nickel-base s uperalloy was investigated. Two alloys, Ni-8Cr-6.5Al-6W-3Ta-1.5Mo-6Co-1Ti-3 Re-0.15Zr -0.05C-0.01B-0.9Y(2)O(3) (3Re alloy) and a non-rhenium containing (ORe) alloy were prepared for this study. The 3Re alloy showed two-fold im provement in creep life compared with that of 0Re alloy, presumably due to a change in the mode of the precipitate-dislocation interaction. For the 3R e alloy, finer, more cuboidal and aligned gamma' precipitates a re formed, which force the mobile dislocations at the gamma-gamma' interfaces to cut p recipitates in order to proceed. Shearing of precipitates is evinced by the existence of stacking faults and results in an increase of creep strength. In contrast, lower creep strength was observed for ORe alloy because a dis location looping mode is dominant with coarser and more irregularly shaped gamma' precipitates present in this alloy. Another possible explanation for an improved creep strength of 3Re alloy is related to the tangled dislocat ion structure formed by the interaction between glide dislocation and inter facial dislocation, which also acts as an effective barrier for further gli de dislocation motion. A 3wt% Re addition significantly retards gamma' coar sening kinetics. Rhenium acts as a rate-controlling species upon the volume diffusion-controlled coarsening process because it is a heavy element and also it almost solely partitions to the gamma matrix. X-ray diffraction exp eriments showed that the magnitude of the lattice mismatch between gamma an d gamma' increased with the 3wt% Re addition from 0% to -0.26% at room temp erature. Increased lattice mismatch for 3Re alloy causes the formation of m ore aligned and cuboidal gamma' precipitates rather than random and odd-sha ped gamma' precipitates for ORe alloy, and it also accelerates the coalesce nce between cuboidal gamma' precipitates. (C) 1998 Kluwer Academic Publishe rs.