Ultrafine-grained nanocluster-strengthened alloys with unusually high creep strength

The microstructure and mechanical properties of ultrafine-grained ferritic alloys containing nanoclusters (NCs) are investigated. The NCs (diameter ∼3 nm) as well as the grain size (∼200 nm) remain stable at 1000 oC. Substantial Hall–Petch strengthening occurs at room temperature. Surprisingly, the creep rate at 800 oC is up to a factor of 108 slower than that predicted for diffusional creep. Possible reasons are the high NC coverage as well as Cr and W enrichment at the grain boundaries, and inhibition of self-diffusion.