Effects of severe plastic deformation on the microstructures, mechanical properties, and corrosion behavior of U-5.5Nb alloy

Equal-channel angular pressing (ECAP) and mechanical machining were employed to introduce large plastic shear strain into bulk and the surface layer of a U-5.5wt.%Nb (U-5.5Nb) alloy, respectively. Applying ECAP, the U-5.5Nb alloy exhibited a single yield feature on the stress-strain curve in comparison to the “double yield” feature in the water quenched (WQ) counterpart. The difference is attributed to the characteristics of severe plastic deformation (SPD) structures obtained by ECAP. Mechanical machining resulted in a further severe microstructure refinement of the SPD surface layer with nano-grains/subgrains, which is accompanied with a dramatic increase of both the hardness and the elastic modulus of the surface layer. It is further proposed that the suppression of the shape memory effect (SME) in the nanostructured U-5.5Nb alloy may be responsible for the enhanced elastic modulus. The results of corrosion rate and pitting susceptibility showed a microstructure dependency, where the ECAP sample exhibited a better pitting resistance than that of the WQ counterpart.