The influences of Re addition on the creep strength and microstructures of MA ODS nickel-base superalloy were investigated. Two different alloys, 8Cr-6.5Al-6W-3Ta-1.5Mo-5Co-1Ti-3Re-0.15Zr-0.01B-0.05C-1.$-1Y_2O_3$(3Re alloy) and non-Re containing(0Re alloy) were prepared for this study.
3Re alloy showed the two fold improvement in creep lives compared with those of 0Re alloy. This is due to the change in precipitate-dislocation interaction mode. For 3Re alloy finer, more cuboidal, and more aligned γ' precipitates are formed, so the mobile dislocations at γ/γ' interfaces must cut the precipitates in order to proceed. Shearing of precipitates accompanied with the formation of stacking faults results in an increase of creep strength. However, lower creep strength was observed for 0Re alloy because a dislocation looping mode was dominant with coarser and more odd-shaped γ' precipitates.
Re addition significantly retards γ' coarsening kinetics. The activation energy of 3Re alloy is increased by 18% compared to that of 0Re alloy. Re acts as a rate controlling species upon volume diffusion controlled coarsening process because Re is a heavy element and also it almost solely partitions to the γ matrix.
X-ray diffraction experiments showed that the magnitude of the lattice mismatch between γ and γ' increased from 0 to -0.26% at room temperature with 3 wt.% Re addition. This increased lattice mismatch for 3Re alloy causes the formation of more aligned and cuboidal γ' precipitates rather than random and odd-shaped γ' precipitates.
