On the ductility of a surface severely plastically deformed nickel alloy

The tensile ductility of a Ni-base, single-phase, face-centered-cubic alloy decreases after surface severe plastic deformation (S2PD). The mechanism responsible for the reduced tensile ductility has been investigated via systematic experiments in conjunction with finite element modeling. The measured ductility parameters (i.e., the elongation, uniform true strain, and reduction of area), strain-hardening coefficient of the true stress–strain relation, and fracture surface observation have been elucidated based on the alternation of the microstructure and stress states induced by S2PD. It is found that the reduced ductility is not due to the increased surface roughness and the presence of macroscopic residual stresses. Instead, it is induced by the presence of the work-hardened surface region and the formation of a nanocrystalline surface layer in S2PD-processed samples.