Effect of microstructure on dynamic shear localisation in Alloy 718

The effect of microstructure on the strain localisation behaviour during dynamic shear deformation of Ni-Fe-base superalloy Alloy 718 was investigated by a combination of experiments and numerical simulations of Split-Hopkinson tests of specimens with top-hat geometry. The results show that strain localisation is promoted by small grain size and precipitation hardening, whereas large grains and solution annealing largely supressed the formation of shear bands. In addition, a smaller fillet radius facilitated the initiation of shear bands. Finite element simulations were able to reproduce the most important features of both global load-displacement histories, and presence of shear localisation. In particular, detailed simulations of the local deformation during localisation showed that temperatures exceeding 750°C (locally above 1000°C) and strain rates in the order of 2⋅105 s−1 were reached in the band.